Guidelines for sustainable hazelnut irrigation

OUTGROWING PROJECT

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

This document is intended to be a user friendly operational guide addressed to the hazelnut growers.

Special thanks are due to Dr. Graziano Ghinassi (DAGRI, University of Florence) and Agristudio S.R.L. Florence, who made a professional contribution to the development of this Guideline.

This publication was made possible through support provided by the U.S. Agency for International Development, under the terms of Contract No. 72011219C00001.

The opinions expressed herein are those of the author and do not necessarily reflect the views of the U.S. Agency for International Development.

Ferrero Group waives any responsibility in respect to the completeness and accuracy of the content of this operational guide which in no case is to be considered as a binding document for the hazelnut growers.

Copyright Reserved - Disclosure of this document is not permitted unless expressly authorized by the Ferrero Group

IRRIGATION SYSTEMS FOR HAZELNUT ORCHARDS

INDEX CHARACTERISTICS OF WATER AND SOIL FOR HAZELNUT CULTIVATION 1.

Hazelnut and water

2. Introduction 2.1.

6 7

Sustainable irrigation in the era of climate change and increasing competition for the use of water resources

7

2.2.

Climate of Serbia

7

3.

Water for irrigation

9

3.1.

Availability of groundwater and surface water

9

3.2.

Physical and chemical characteristic

10

3.3.1

Physical

14

3.3.2

Chemical

14

4.

Soil types for hazelnut cultivation

14

4.1.

Soil hydraulics

16

4.1.1

Infiltration

19

4.2.

Soil hydrology

19

5.

Water needs for hazelnut cultivation

23

5.1. Evapotranspiration

23

5.1.1.

Data collection and analysis

23

5.1.2.

Calculation procedures (FAO methodology)

24

5.1.3.

Hazelnut water requirements along the season

26

5.2. Rainfall

27

5.2.1.

Gross precipitation

27

5.2.2.

Effective rainfall

28

5.2.3.

Irrigation water requirements

28

6.

Irrigation systems for hazelnut orchards

34

6.1.

Irrigation system design

34

6.2

Irrigation types

36

6.2.1.

Above ground drip system

36

6.2.2.

Subsurface Drip Irrigation (SDI)

38

6.2.3. Micro-sprinkler

41

6.3.

42

Components and equipment of the irrigation systems

6.3.1. Pipelines

43

6.3.2. Pumps

46

6.3.3. Filters

46

6.3.4. Laterals

52

6.3.5.

Emitters

57

6.3.6.

Valves

59

6.3.7. Accessories

60

7. Fertigation

62

7.1.

Fertigation principles

62

8.

Irrigation management and maintenance

64

8.1.

Irrigation system performance

64

8.2.

Water balance

65

8.3.

Sensors

66

8.5.

Maintenance

68

AUTOMATION OF HAZELNUT PLANTATION MONITORING 9.

Automation of hazelnut orchard monitoring

74

9.1.

The SCADA approach towards water economics

75

9.2. Overview

75

SCADA application to control irrigation and fertigation

75

Appendix 1

80

Appendix 2

81

CHARACTERISTICS OF WATER AND SOIL FOR HAZELNUT CULTIVATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

1. HAZELNUT AND WATER Most of hazel root system develops within the upper 50 cm of soil. Root expansion is facilitated by soil fertility and vigorous rootstocks. The exploitation of a large volume of soil guarantees greater availability of water and nutrients.

The water needs of hazel in the latitudes of Serbia are met when rainfall is about 700-800 mm, well distributed from March to October.

The critical period with respect to water is between June and August, during which both the growth of fruit and seed occur. Water shortages should be prevented in order to avoid damage to plant growth and commercial production. The irrigation system must be envisaged right from the planting of the hazel grove. Above ground and subsurface drip irrigation and, to a certain extent, micro-sprinkler irrigation, are the water application techniques for hazel grove mostly accepted worldwide. Whatever the preliminary choice made, it is important to consider all the aspects that characterize the environment where the hazel grove is located, in particular the soil and the climate, in order to select the most suitable irrigation equipment that will allow to correctly irrigate and fertilize the hazel grove along its economic lifetime.

2. INTRODUCTION

2.1.

Sustainable irrigation in the era of climate change and increasing competition for the use of water resources

The irrigation system to be designed for hazel grove must be able to provide sufficient water during the period of maximum water demand. The availability of water for irrigation depends on the overall availability and priorities for allocation of the resource to other users and production sectors. Domestic use usually has priority over others. Availability of water resource in quantity, quality, and duration over time, that is the economic lifetime of the hazel grove, must be well known in advance. Since the availability of water is linked to a number of factors which are difficult to predict in most cases, it is desirable to know expected future scenarios, i.e., forecast variations in precipitation and climate demand, taking into consideration other issues as given in Appendix 1.

2.2. Climate of Serbia According to the World Bank Group - Climate Change Global Portal, different climate scenarios, generated by different levels of greenhouse gas emissions ranging from low to high, are expected for Serbia in the period 2020-2039. In support of the calculations for the design of the systems and the management of irrigation, the following are the scenarios relating to the anomalies expected in the period 2020-2039 with medium-low emission levels regarding average monthly temperatures (fig. 1), minimum (fig. 2), maximum (fig. 3) and precipitation (fig. 4), compared with the average values recorded in the period 1986-2005 (Source: World Bank Group - Climate Change Global Portal, modified). The light blue band around the average of the predicted values represents the range of values produced by climate models.

6

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

3. WATER FOR IRRIGATION

3.1. Availability of groundwater and surface water The plantation of a hazel grove requires it to be equipped with an irrigation system. The decision must be made after checking the availability of water. The verification consists in the chemical-physical analysis and in the evaluation of the availability of the resource during the economic lifetime of the orchard.

It is therefore important to have a hydrogeological report if you want to access groundwater, as well as to collect information on possible other uses or divisions from surface water bodies for multiple use. This usually does not apply in the case of private reservoirs.

In general, deep aquifers (artesian) are preferred over the superficial ones (groundwater) for the higher and constant flow rate and for the best water quality.

Figure 1. Average daily temperature

Figure 2. Average minimum temperature

It is common for one or more to be drawn from the well to be associated with a reservoir in order to have greater and limited flow rates over time (for example in the peak period). The well flow rate measurements are made by those who dig the well and must be verified periodically to prevent the dynamic level from lowering more than expected. If the dynamic level drops a lot, it is easier for the water to contain soil particles (minerals) that can be harmful to the pump, causing clogging of filters and dispensers. The risk of the pump remaining dry is very low due to the presence of level sensors and safety devices.

The effects on the components of the production system derive from the characteristics of the water (Table 1).

Table 1. Effects of water quality on the irrigation environment.

System component

Crop

Water characteristics Salinity

Water stress

Na, Cl, B, N-NO3, heavy metals

Toxicity

Suspended solids Na, Ca, Mg, salts content, pH Soil Cl, heavy metals Figure 3. Average maximum temperature

Figure 4. Average precipitation

Farmer, consumer

The integration of the values recorded in the period 1986-2005 with the forecasts provided by the climate scenario with medium-low emissions, allows us to estimate the averages of climate demand (ETo) and precipitation on a monthly basis expected in the period 2020-2039. This is possible through the use of specific calculation procedures for potential evapotranspiration and effective precipitation.

Water bodies

Temperatures above 35 °C are to be considered limiting for the crop, especially if prolonged and in conditions of scarce rainfall.

Irrigation system

8

Risk type

Na, Ca, Mg, salts content, pH Pathogenic microorganisms Nitrogen and phosphorus compounds Heavy metals, pathogenic microorganisms, synthetic products Sand Suspended solids, bicarbonates, Fe, S, Mn

Effect Production reduction

Production reduction Spots and necrosis on leaves and fruits Residues on the aerial part Aesthetic depreciation Deterioration of soil structure, Alkalization Reduction of water infiltration rate Decreased productivity, Changes in microflora Sterilization Decreased productivity, Changes in microflora Sterilization Contamination Toxicity Contamination

Infectious diseases

Pollution

Toxic and infectious risk for humans and animals

Damage to pump impeller Poor distribution uniformity, high cost for water treatment

9

Abrasion Emitters clogging

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

3.2.

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Table 3. The relationship of EC to salinity, and the tolerances and symptoms of irrigated crops.

Physical and chemical characteristic

EC (dS/m) <0.5

Impurities carried in solution or in suspension determine water quality. Whether the water of a certain quality is acceptable for irrigation depends on climate, soils, crops grown, and depth of water applied.

Whatever the water quality constituent, its suitability for irrigation is assessed according to the specific water quality directives, and its tolerance classes for different crops. Directives indicate the degree of problem with the individual component, from none to serious. Tolerance groups crops from sensitive to tolerant. Based upon this approach, water suitability for irrigation is classified in four classes (Table 2).

Class 1 water is optimal (degree of problem: none), Class 2 is suitable for sensitive crops such as hazel, Class 3 is for semi-tolerant, mild-sensitive crops, Class 4 is for tolerant crops.

For all crops

0.5-0.75

Medium

Sensitive crops will be influenced.

Irrigation of soils cause few problems

0.75-3.0

High

Increasing number of crops shows a reduction in growth

Very high

Symptoms of excess salinity in crops under irrigation

Tolerant crops

Low to very low

>3.0

Table 2. Guidelines to assess water suitability for irrigation.

Salinity of irrigation water

Not suitable for irrigation, except tolerant crops that are cultivated in sandy soils with excellent drainage

Not applicable Leaf scorch on the edges of the leaves and leaf losses especially where leaves of crops are wetted Leaf scorch and eventually wilting of crops as EC rises Crop cultivation in most cases is not possible

Water Quality Constituent

Class 1

Class 2

Class 3

Class 4

Salinity (Electrical Conductivity – EC) (dS/m)

0-0.4

0.4-0.9

0.9-2.7

2.7-5.4

Salinity (Electrical Conductivity – EC) (dS/m)

0-1.5

1.5-3.0

3.0-5.0

5.0- 10.0

Sodicity (SAR)

0-0.2

0.2-0.9

0.9-1.5

1.5-3.0

Corrosive/aggressive irrigation water may reduce the life expectancy of irrigation pipelines and equipment, whilst water which is susceptible to sedimentation can reduce the flow rate due to full or partial blockage emitters. This in turn can lead to unequal water distribution, resulting in yield losses.

Boron (mg/l)

0-105

105-140

140-350

>350

A water analysis based on the appropriate water quality guidelines can be useful for early detection of problems such as blockage, corrosion, and sedimentation (Table 4).

Chloride (Cl) (mg/l)

0-70

70-115

115-160

160-200

Sodium (Na) (mg/l)

0-5

5-30

>30

Nitrogen (mg/l as N)

< 0.05

0.05-5

5-10

10-20

Manganese (Mn) (mg/l)

<0.05

0.05-0.2

0.2-5

5-10

The effect of water quality on irrigation equipment

pH (acceptable range)

Table 4. Physical, chemical, and biological factors that can cause dripper blockage.

6.5-8.4

The pH values between 6.5 and 8.4 are usually acceptable for crop cultivation. Different from that of soil, the pH of the irrigation water is not normally considered as critical because of the buffering capacity of the soil and the wide series of pH-values that crops can handle. However, where very high or low pH-values are recorded, possible causes other than that of the irrigation water must be investigated.

Whilst the EC reading gives an indication of how “salty” the water is, it does not show what ions are present at what concentration. The relationship of EC to the salinity of the irrigation water, the tolerance of crops to that salinity level, and the possible symptoms of excess salinity that occur in crops being irrigated with such water is shown in Table 3. Hazel is sensitive to salinity and irrigation water should not exceed 0.75 dS/m.

10

Physical

Chemical

Biological

Inorganic materials Sand (50-250μm) Silt (2-50 μm) Clay (<2 μm)

Alkaline heavy metals Cations calcium magnesium iron manganese Anions carbonates hydroxides silicates sulphides Fertilisers ammonia iron copper zinc manganese phosphate

Algae Bacteria filament slime Microbiological activities Iron manganese sulphates

Organic materials Water plants phytoplankton algae Water animals zooplankton snails Bacteria (0.4-2μm) Plastic pipe cuttings Oil

11

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Blockage of drippers is mainly caused by the following factors:

•

Physical: blockage is a result of suspended solids. Very fine particles tend to remain in suspension but may flocculate out in places where the water velocity is low, or the water turbulence drops (Figure 5);

The water quality guidelines for quantifying drip blockage hazard of the irrigation water (Bucks et al., 1979), are shown in Table 5.

Table 5. Water quality classification for drip irrigation clogging.

Hazard rating

Clogging factors

Figure 5. Blockage of the flow path due to aggregation of fine particles in drippers, a and b. Deposition of big particles in c. Deposition of particles at the labyrinth inlet and corner in d and e. Deposition due to emitter imperfections in f (From: Lavanholi et al., 2018, modif.).

•

Physical: Suspended solids (mg/l) Chemical: pH Bicarbonate (mg/l) Calcium (mg/l) Manganese (mg/l) Iron (mg/l) Total diluted solids (mg/l) Hydrogen sulphide Nitrates (mg/l) Biological: Bacteria (per ml)

chemical: blockages can occur as a result of a chemical reaction in the water, resulting in a deposit, usually due to the presence of either calcium and magnesium carbonates (Figure 6), iron and magnesium sulphides, or iron and manganese oxides;

Figure 6. Calcium carbonate deposit at the emitter orifice (From: Limestone coast, modif.).

•

biological: algae growth and microbiological activities may cause blockages. Fertiliser application through the irrigation system, especially where the laterals are exposed to the sun, will lead to an increase in the formation of bacterial slime. (ARC, 2010).

Blockage material is identified by the colour of the deposit in the blocked dripper. Salt deposits are white, iron oxides are a rusty colour, and blockage material resulting from microbiological activities is black.

Each type of blockage has a unique solution. A water analysis that indicates the exact nature of blockage is therefore essential.

12

13

Minor

Severe

<50

>100

<7.0 <100 <10 <0.1 <0.2 <500 <0.2

>8.0 >200 >50 >1.5 >1.5 >2 000 >2.0 >10

<10 000

>50 000

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

3.3.

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Table 7. Solutions selected to prevent possible clogging problems.

Water treatments

Problem

3.3.1. Physical Water treatment to prevent clogging can be physical (sedimentation and filtration) and chemical (acidification, chlorination). Filtration can be performed with different types of filters. The recommended treatment in relation to the type and characteristics of the water used is indicated in Table 6.

Solution

Carbonate deposit (whitish colour) HCO3 > 100 mg/l pH > 7.5

Continuous acid application – Maintain pH of 5 to 7.

Shock acid application at end of irrigation cycle.

Maintain pH of 4 for 30-60 minutes.

Aeration to oxide iron (especially suited to high iron concentration of 10 mg/l or more).

Acid application to promote iron deposits: - Injection rate of 1 mg/l chlorine per 0.7 mg/l iron.

- Application before filter, so that deposits are retained.

Lower pH to ≤ 4 by daily acid applications for 30-60 minutes to dissolve iron deposits.

Table 6. In farm water treatments according to different types of irrigation water.

Treatment

Characteristic

Water source

high concentration of suspended solids sedimentable inorganic

surface (canals, rivers)

presence of iron

well

Hydro-cyclone filter

with high concentration of sand

well and river

Mesh filter or disks

with solid in suspension inorganic

surface, well and wastewater

Sand or grit filter

with high concentration of solids suspended organic and inorganic

surface and waste

presence of bicarbonates and iron

well

development of microorganisms

surface and well

presence or possibility of development of microorganisms (ferro bacteria, sulfur bacteria, etc.)

surface, well and waste

Sedimentation tank

Chemical treatment of acidification Chemical treatment with chlorination

Both sedimentation and filtration are used to eliminate particles of a physical nature up to 0.074 mm in size (Capra and Scicolone, 2016). Therefore, single (non-aggregated) particles of very fine sand, silt and clay are not eliminated.

Iron deposits (reddish colour) Iron concentration > 0.2 mg/l

Manganese deposit (black colour) Manganese concentration > 0.1 mg/l

Application of 1 mg/l chlorine per 1.3 mg/l manganese, before filter.

Iron bacteria (reddish slime) Iron concentration > 0.1 mg/l

Application of 1 mg/l chlorine (free chlorine available) continuously or 10-20 mg/l for up to 60 minutes as required.

Sulphur bacteria (white cotton-like slime) Sulphide concentration > 0.1 mg/l

Continuous application of chlorine at 1 mg/l per 4-8 mg/l sulphur hydroxide.

Application of chlorine as required until 1 mg/l free chlorine is available for 30 to 60 minutes.

Algae, slime

Application of chlorine at a continuous rate of 0.5-1 mg/l or 20 mg/l for 20 minutes at the end of each irrigation cycle.

Iron sulphide (black, sandy material) Iron and sulphide concentration > 0.1 mg/l

Dissolving of iron by continuous acid application to reduce pH to between 5 and 7.

3.3.1. Chemical In addition to filtration, to protect the emitters from chemical (mainly due to bicarbonates and iron) and biological (due to bacteria that can develop inside pipes and emitters) occlusion, it may be necessary to conduct acidification (against chemical occlusion) and chlorination (against biological occlusion) (Table 7). For this purpose, specific devices are used for the injection of acids or chlorine into the system. Special attention and specific safety rules must be paid during chemical treatment of water.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

4. SOIL TYPES FOR 5. HAZELNUT CULTIVATION

4.

In this case, about soil suitability for hazel, the results are expressed in quantitative terms only. Figure 7 indicates the positioning of the suitable units. Classifications can refer to the actual suitability or consider the potential suitability, which is the suitability after major land improvements that could be implemented in the future. Land utilization types which we considered for the suitability are rainfed agriculture and irrigated agriculture.

Soil types for hazelnut cultivation and irrigation

Land Suitability Land Suitability is the fitness of a given type of land for a specified use, also taking into account its sustainability. Land suitability assessment methods always use quantitative inputs, but results can be expressed in qualitative as well as in quantitative forms. For each characteristic, a subdivision of the measures in different classes is obtained, each related with a degree of limitation which integrate the effects of a number of different characteristics on the quality. The existing scientific literature provides important information for this selection, as well as for the ranking to be assigned to the values obtained. Then the ranking values are summarized, giving for each land unit a class of suitability. The classes are S1 (highly suitable), S2 (moderately suitable), S3 (marginally suitable), N (not suitable) (Table 8).

Table 8. Land suitability definitions and classifications.

ORDER

Suitable

Not suitable

DEFINITION Land on which sustained use for the defined purpose in the defined manner is expected to yield benefits that justify required recurrent inputs without unacceptable risk to land resources on the site or in adjacent areas.

Land having characteristics which appear to preclude its sustained use for the defined purpose in the defined manner or which create production, upkeep and/or conservation problems requiring a level of recurrent inputs unacceptable at the time of the interpretation.

16

CLASS

S1: suitable S2: moderately suitable S3: marginally suitable

N: not suitable N1: actually unsuitable, but potentially suitable.

N2: actually and potentially unsuitable.

Figure 7. Characterization of soils. Suitability map for cultivation.

For each land utilization type, it is necessary to establish the land‐use requirements, which are the conditions which are fully satisfactory, acceptable, or unsatisfactory for its management. At the same time, it is necessary to assess the properties of the land units in terms of land characteristics and land qualities. The matching of land‐use requirements with land qualities and land characteristics determines the suitability of a particular land unit for a particular land utilization type (Table 9).

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Table 9. FAO Land Suitability classification (modified).

4.1.

Rating table for Halzenut suitability (Control section = 80 cm) Suitability class Rating

S1 100

85

S2

S3

N1

N2

65

45

25

0

Weight

300-500 800-1000

<300 >1000

<300 >1000

1

Soil hydraulics

The type of soil affects the movement of water, both when it infiltrates and when it is inside.

Climate (c) 600-700

500-600 700-800

1-2

3-5

5-10

10-15

>15

1

Medium daily temperature during flowering C°

14-15

12-13

5-12

0-5

<0

2

Rainfall mm in MayJune

200-250

250-350

350-500

>500

>500

2

Rainfall mm/year Frosty days in AprilMay (during flowering)

Landscape (t) Slope % Elevation m slm Aspect

<5

5-10

10-15

15-25

>25

1

300-500

500-700 200-300

700-900 100-200

>900 <100

>900 <100

1

Flat SE-SO

S - NE - E

SO - O

N - NO

N

1

Stoniness (%)

<1

1-3

3-15

15-35

>35

1

Rockiness (%)

<2

2-5

5-10

10-50

>50

1

Well drained

Moderately well drained Somewhat Poorly drained

Somewhat excessively drained Poorly drained

Excessively drained, very Poorly drained

No drainage, Excessively drained

1

Soil (s) Internal drainage Rooting depth (cm)

4.1.1. Infiltration Infiltration refers to the entry of water into the soil. The rate at which water enters is called the infiltration rate. Permeability refers to the percolation of infiltrated water through the soil. An infiltration rate that is less than 3 mm/hour is considered low, while a rate above 12 mm/hour is relatively high. This can be affected by factors such as water quality, physical characteristics of the soil, such as soil texture and type of clay minerals, and chemical characteristics including exchangeable cations. The infiltration rate generally increases with increasing salinity and decreases with either decreasing salinity or increasing sodium content relative to calcium and magnesium, the SAR (sodium adsorption ratio). Therefore, salinity and SAR must be considered together for a proper evaluation of the ultimate effect on water infiltration rate. When the ground slope is >10%, grassing of the inter row is strongly recommended in order to facilitate water infiltration and reduce runoff and erosion, since the infiltration rate reduces as the slope increases. Indicative values are in Table 10.

Table 10. Reduction of infiltration rate according to topography Slope (%)

Decrease of Vi (%)

0-5

0

6-8

20

9-12

40

13-20

60

>20

75

As a rule, recommendation for grassing the inter row does not apply when total precipitation during spring is <500 mm and the soil texture is from clay to sandy loam clay.

>100

70-100

50-70

50-35

<35

2

L, SLC, SiL

CL, SL, SC

Si, FLA, AL

C<60%, LS

S, C>60%

1

<5

5-10

10-25

25-35

>35

1

Moderately high 3.6-36

Moderately low 0.36-3.6

Low 0.036-0.36 High 36-360

Very low <0.036 Very high >360

Very low <0.036 Very high >360

1

Wetted diameter

AWC mm (available water capacity)

>200

150-200

100-150

50-100

<50

2

Both the infiltration rate and the distribution of water within the soil depend primarily on the texture (Figure 8).

Water table (cm from surface)

>100

80-100

100-50

25-50

<25

1

These characteristics can be reliably established through experimental observation and calculation, according to the following guidelines:

5.5-7.2

5.0-5.5 7.2-8.0

4.5-5.0 8.0-8.5

<4.5 8.5-9.0

<4.5 >9.0

1

<3

3-5

5-9

9-12 ESP 8-15%

>12 ESP>15%

1

Texture Coarse fragments (%) Ksat (permeability mm/h)

•

Fertility (f) pH Salinity ds/m Alcalinity (ESP %)

<6

6-10

10-15

>15

>15

1

CEC (meg/100gr)

>18

12-18

10-12

5-10

<5

1

Calcium carbonate %

<8%

8-15%

15-25%

25-35%

>35%

2

<2.5%

2.5-5%

5-8%

>8%

>8%

2

Active calcium carbonate %

18

4.2. Soil hydrology

• • • •

lay-out dripper lines (preferably 20 m to 30 m long), on the soil that is to be irrigated, with different inter-dripper spacing; connect the lines to a water source which will provide a continuous and stable supply; switch on the system at the required operating pressure and irrigate for about 12 hours on heavier clay soils, and for about six hours on lighter sandy soils; allow the water to penetrate the soil for a further 24 and 12 hours respectively, without any interference, in order to allow the wet zone to reach its maximum dimensions; dig longitudinal and cross profile furrows and make the necessary observations and measurements to establish whether the proposed system will satisfy all requirements according to established norms (ARC, 2010).

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Available water, AW, is the amount of water the soil retains from 0.1-0.3 bar (the so-called field capacity condition, FC, the gravitational water being drained) to 15 bar (the so-called permanent wilting point, PWP, the plant being no longer able to extract water from the soil).

The fraction of AW the crop is able to extract without any stress, p, is the readily available water, RAW (RAW= pxAW). AW is expressed in mm of water per meter of soil depth. For hazel, that is sensitive to water stress especially from June to August, p should not be more than 0.4, that amount corresponding to calculated maximum net irrigation requirement, NIR. The values of AW can be found either in the bibliography or obtained from field measurements. In the first case they are average values per textural class, as shown in figure 10, in the second case they come from measurements made on representative profiles and refer to homogeneous soil layers explored by the crop active root system (Figure 10). For each profile, the water retention curve is being built, this assessment being particularly important for soil types affected by great hydrological variability, in spite of the same classification. This is the case of silty loam soils, typical of Vojvodina, whose water retention capacity varies from about 140 mm/m to 220 mm/m.

Figure 8. Typical water distribution patterns under drip irrigation in different soils.

Due to the lower emitter discharge of drippers, the standing time is usually longer, and the farmer’s operating system should be able to accommodate the choice.

The size of wetted soil volume will influence the selection of both emitter spacing and dripline position from hazel stems. This applies to surface and subsurface drip lines.

In permeable soils, emitter spacing along the lateral should be 0.3-0.5 m, in loamy textures spacing increases to 0.5-0.7 m, in silty to clay up to 0.7-1.0 m.

Water holding capacity The water retention capacity depends on soil characteristics. Indicative values for different soil types are shown in Figure 9.

Figure 10. Retention curves of upper layer 0-0.60 m. The one on left refers to homogeneous layer 0-0.60 m, the two on right to homogeneous 0-0.25 m (curve 1) and 0.25-0.60 m (curve 2) layers.

Figure 9. Average partition of water in different soils. Figures are indicative of soil texture only.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

The curve on the left of Figure 11, represents a homogeneous silty loam layer of 0.60 m made as follows:

• • • •

texture is 39% sand, 5% clay, 56% loam; volumetric water content at FC (0.3 bar) is 29.8%; volumetric content at PWP (15 bar) is 13.6%.

AW= FC-PWP= 29.8-13.6= 16.2%= 162 mm/m.

Along the active rootzone: AW= 162x0.60= 97 mm; Allowed depletion (the max net irrigation depth): NIR= 97x0.40= 39 mm.

The curves on the right of Figure 11 also refer to silty loam soils. Characteristics are: Curve 1 (layer 1, 0.25 m):

• • • •

texture is 41% sand, 8% clay, 51% loam; volumetric water content at FC (0.3 bar) is 30.7%; volumetric content at PWP (15 bar) is 13.5%.

AW= FC-PWP= 30.7-13.5= 17.2%= 172 mm/m.

5. WATER NEEDS FOR HAZELNUT CULTIVATION

5.1. Evapotranspiration 5.1.1. Data collection and analysis The amount of crop evapotranspiration (ETc) is defined as the maximum amount of water that the crop would require under ideal circumstances (i.e., when there are no other limiting factors). Significant amounts of rainfall available to plant roots should be subtracted from the ETc to determine the net irrigation requirement (NIR) measured in mm. Water from precipitation and irrigation refills the rootzone profile, the excess can recharge groundwater or be lost as surface runoff. The water needs of irrigated hazel orchards can be assessed through a simplified water balance at the soil surface, illustrated in Figure 11.

Along the active rootzone 1: AW= 172x0.25= 43 mm; Allowed depletion (the max net irrigation depth): NIR1= 43x0.40= 17 mm.

Curve 2 (layer 2, 0.35 m):

• • • •

texture is 26% sand, 1% clay, 73% loam; volumetric water content at FC (0.3 bar) is 33.3%; volumetric content at PWP (15 bar) is 15.3%.

AW= FC-PWP= 33.3-15.3= 18.0%= 180 mm/m.

Along the active rootzone 2: AW= 180x0.35= 63 mm; Allowed depletion (the max net irrigation depth): NIR2= 63x0.40= 25 mm.

The total allowed depletion along the hazel rootzone profile is: NIR= NIR1+NIR2= 17+25= 42 mm.

Curves such as those in Figure 11 are useful for irrigation management through soil moisture monitoring.

Depending on the sensor chosen, they allow to know the amount of soil water corresponding to measured tension (e.g., through tensiometers) or the tension corresponding to the measured water content (e.g., through capacitive probes). Attention must be paid to the use of tensiometer, since measurement begins to fail when soil water tension approaches 0.7-0.8 bar.

As for the above procedure, measurements of water content at field capacity and wilting point are sufficient for the assessment of AW.

Figure 11. Simplified water balance at the soil surface (From: Allen et al., 1998, modif.).

Calculation of ETc according to FAO procedure requires to assess the climatic demand, ETo, and the use of crop coefficients, Kc. Values of climatic parameters, namely temperature, radiation, relative humidity, and wind, can be taken from different sources, such as from private on farm agrometeorological stations or from the Regional meteorological network. The station network of Serbia is indicated in Figure 12.

Assessment of ETc is the basis for both system design and irrigation management.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

The mean daily temperature should be calculated taking into account the actual evolution of air temperature, monitored at defined time scans. In the absence of data calculated in this way, the mean between minimum and maximum measured value is normally used.

System design The procedure applies both to new installations and to modernization of existing irrigation systems. Peak period requirement is determined using historical series of climatic parameter values, the number of which varies according to the chosen procedure.

Precipitation and temperature are always used for the scope. Influence of climate change on future irrigation scenarios must be considered at the planning stage.

The value Ra*0.408 indicates the extra-terrestrial radiation in mm/day.

The average daily values of extra-terrestrial radiation, Ra, referring to the latitudes of Serbia for the period April-September, are reported in Table 11.

Table 11. Average daily values of Ra, in mm/d, at the latitudes of Serbia in the spring-summer period

Month

Irrigation management With reference to a period of time (e.g., irrigation interval, in days), the water consumed as ETc is determined and effective precipitation of the period, Pe, is subtracted to calculate the net irrigation requirement. Under management solely based upon agrometeorological inputs, calculation of NIR is simply: NIR = ETc-Pe. Figure 12. Meteorological stations network in Serbia (From: Anđelković et al., 2018, modif.).

5.1.2. Calculation procedures (FAO methodology) According to the standardized FAO methodology, ETc= ETo x Kc.

The simplest procedure that guarantees temporal continuity of the data on a daily basis is that of Hargreaves, which requires only the measured temperature, that information provided by a commercial maximum and minimum thermometer. A rain gauge will help to calculate the water balance to manage irrigation (Figure 13).

The Hargreaves formula is as follows:

Figure 13. Maximum and minimum thermometer (left). For calculating the irrigation dose, it is useful to have a totalizing rain gauge to measure rainfall.

Where:

• • • • • • 24

-ETo = reference evapotranspiration (mm/g); -t mean = mean temperature (°C); -t max = maximum temperature (°C); -t min = minimum temperature (°C); -Ra = extra-terrestrial radiation (MJ/m2g) depending on the latitude and the day of the year; -0.408 = conversion coefficient to mm/d.

42°

43°

44°

45°

46°

April

13.8

13.6

13.5

13.4

13.3

May

16.0

15.9

15.9

15.8

15.8

June

16.9

16.9

16.9

16.9

16.9

July

16.4

16.4

16.4

16.3

16.3

August

14.6

14.5

14.4

14.3

14.2

September

11.8

11.6

11.5

11.3

11.1

Example of daily application of the Hargreaves formula in Aleksa Santic (Figure 14):

• • • • • • •

Among the models proposed by the FAO to calculate ETo, the Penman-Monteith equation is recognized as the most accurate, with the drawback consisting of a set of required data currently unavailable by most meteorological stations.

When available, these data cover short time series in most cases.

Latitude

t max = 30°C; t min = 16°C; mean t = (t max + t min)/2= 46/2 = 23°C; t max-t min = 30-16 = 14°C; Latitude: 45°58’08 N; Month: June; Ra*0.408= 16.9.

ETo = 0.0023*(23+17.8)*

30-16 * Ra*0.408

ETo = 0.0023*40.8* 14*16.9 ETo = 0.0023*40.8*3.74*16.9 = 5.9mm

In the subhumid climates of Serbia, the Hargreaves formula tends to overestimate the ETo value by around 10% (Alexandris et al., 2008).

The minimum and maximum daily temperature values can be found online or measured directly on site using a minimum and maximum thermometer.

25

Figure 14. Latitude and longitude of Serbia

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

5.2. Rainfall

5.1.3. Hazelnut water requirements along the season For hazel, the critical period for the availability of water is from April to September, with the peak climatic demand in July. Table 11 shows the monthly average values of ETo calculated with the adjusted Hargreaves formula for Palic and Sombor, located in northern Serbia (see Figure 12) at a straight distance of about 60 km, using the temperature values of the period 1981-2010.

5.2.1. Gross precipitation The distribution of rainfall in Serbia, as an average for the period 1961-2010, is shown in Figure 16.

Table 12. Average monthly values of ETo, in mm, in Palic and Sombor for the period 1981-2010.

Month

Total

Meteorological Station

J

F

M

A

M

J

J

A

S

O

N

D

Year

AprSep

Palić (PA)

9

18

43

77

119

135

145

125

76

42

16

8

811

676

Sombor (SO)

10

19

46

82

125

141

153

132

81

44

17

9

858

713

Indicative monthly mean Kc values for hazel at the higher latitudes of Serbia are reported in Figure 15.

Figure 16. Rainfall distribution pattern in Serbia from 1961 to 2010 (From: Anđelković et al., 2018, modif.).

Annual precipitation less than 800 mm characterizes large areas of central and northern Serbia. Table 13 shows the monthly average values of rainfall measured by the meteorological stations of Palic and Sombor, located in the north of the Country. It is evident that natural precipitations from April to September are insufficient for the cultivation of hazel unless irrigation is considered.

Table 13. Average monthly values of rainfall, in mm, measured in Palic and Sombor from 1981 to 2010.

Month

Meteorological Station

Figure 15. Average monthly values of Kc for hazel in the north of Serbia (ungrassed inter row).

In the north of Serbia, the net water requirement, e.g., the monthly ETc, increases from April to July. In August remains higher than in June.

26

Total

J

F

M

A

M

J

J

A

S

O

N

D

Year

AprSep

Palic (PA)

33

30

34

44

56

81

57

52

50

40

48

47

571

339

Sombor (SO)

37

30

36

45

60

82

66

53

54

47

54

47

612

360

The graphs in Figure 5 show that rainfall is maximum in June and that the projection for 2020-2039 indicates a reduction on a national scale in July, August, and September.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Example of simplified water balance at the soil surface to support irrigation scheduling is given in Table 15.

5.2.2. Effective rainfall Effective rainfall, Pe, is the fraction of the gross precipitation, Gp, that can be retained by the soil in the active root zone and therefore absorbed by the plant for transpiration. It depends on the type of soil, the slope, the plant, and the characteristics of the precipitation.

Table 15. Water balance at the soil surface as a basis for irrigation scheduling.

Day

t max (°C)

t min (°C)

t mean (°C)

Ra (mm/d)

ETo (mm/d)

Kc

ETc (mm/d)

Pe (mm)

NIR (mm)

GIR (mm)

the slope decreases;

25-May

27.1

13.9

20.5

15.8

5.1

0.6

3.1

-

3.1

3.3

the water retention capacity of the soil increases;

26- May

25.1

13.1

19.1

15.8

4.7

0.6

2.8

-

2.8

3.0

27- May

23.5

11.8

17.7

15.8

4.4

0.6

2.6

-

2.6

2.7

28- May

25.7

9.6

17.7

15.8

5.2

0.6

3.1

-

3.1

3.3

29- May

18.7

11.8

15.3

15.8

3.2

0.6

1.9

8

-6.1

-

30- May

23.2

13.3

18.3

15.8

4.1

0.6

2.5

-

-3.6

-

31- May

23.6

11.4

17.5

15.8

4.5

0.6

2.7

-

-0.9

-

01-June

25.7

11.4

18.6

16.9

5.3

0.65

3.5

-

2.6

2.7

The value of Pe increases when:

• • • •

the intensity and duration of the precipitation decreases; the root depth increases.

For practical applications, the following values in Table 14 of Pe as a fraction of Gp in different soils, can be used (Morari et al., 2004).

Table 14. Indicative values of the effective fraction of Gp for different soil types.

Gp (mm)

Pe (%Gp) Sandy

Loam

Clay

02- June

28.6

12.4

20.5

16.9

6.0

0.65

3.9

-

3.9

4.1

55%

70%

68%

03- June

25.9

16.5

21.2

16.9

4.6

0.65

3.0

-

3.0

3.2

04- June

22.3

15.9

19.1

16.9

3.6

0.65

2.3

2

0.3

0.4

05- June

25.1

16.4

20.8

16.9

4.4

0.65

2.9

-

2.9

3.1

06- June

25.8

14.7

20.3

16.9

4.9

0.65

3.2

-

3.2

3.4

07- June

25.0

15.4

20.2

16.9

4.6

0.65

3.0

-

3.0

3.2

15-40

5.2.3. Irrigation water requirements The net irrigation requirement, NIR, corresponds to the difference between the water requirement, ETc, and the effective rainfall, Pe. The gross irrigation requirement, GIR, is the actual depth to be applied by the irrigation system, to be determined as:

GIR= NIR/Eff where Eff = irrigation efficiency (<1).

Average (mm/d)

Below, an example of hazel irrigation calculation according to water balance at the soil surface is given: Period: last week of May-first week of June;

• • • •

ETo calculation procedure: Hargreaves formula, using on farm measured temperatures;

Place: Aleksa Santic; Latitude: 45°58’08 N; Last irrigation or sufficient precipitation: May 24;

•

Irrigation efficiency with the subsurface drip irrigation system: 95% (default value. For other irrigation systems, see Reinders, 2011); Soil type: silty loam (Figure 11, left); Maximum NIR along the root zone: 39 mm; Farmer irrigation strategy (e.g., daily irrigation); 28

2.9

3.1

Some necessary clarifications:

•

• • • • •

4.6

• •

When micro irrigation is used, the actual infiltration (or wetted) area must be considered, in order to avoid deep percolation or other water losses. Assuming water is applied through the area corresponding to the projection of the canopy (e.g., 2 m diameter), when row spacing is 5 m the wetted area is 40%. As a rule, the 39 mm must be applied through that limited area. The total volume is therefore 40% of that resulting from calculated GIR (e.g., 39 mm to be applied to 40% of the field correspond to 390m3/hax0.40ha= 156 m3).

The farmer irrigates according to specific management strategies, i.e., given threshold of soil moisture content or tension, given interval. Taking into account the objective of hazel cultivation, depletion of maximum NIR is not practised in most cases. However, the possibility to delay irrigation (e.g., jumped because of technical problems) represents an important buffer opportunity for the grower.

The complexity of water management at the field level requires specific investigations to check whether preliminary choices are suitable or not, such as the selection of dripline.

Monitoring of the soil moisture status is fundamental for irrigation management, and it is allowed by the correct number and positioning of soil moisture sensors. At this stage, adjustments are still possible.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

IRRIGATION SYSTEMS FOR HAZELNUT ORCHARDS 33

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

6. IRRIGATION SYSTEMS FOR HAZELNUT ORCHARDS Soil, plant, and climate are evolving members of the same dynamic context to which the irrigation system must guarantee the performance for which it was designed and built, that is to say, guarantee the availability of water to plants in appropriate way, time, and amount, and respond effectively and efficiently to the changing needs of the system.

Two steps are required in succession:

A. Information collection on agroclimatology The list includes the following application of science and technology:

• •

Agronomy (crop type and characteristics, planting layout);

• •

Hydrogeology (groundwater location and availability);

Pedology (preliminary evaluation of soil suitability, characteristics and pattern of the active root system, assessment of hydraulic and hydrologic soil water relationships and parameters); Climate (available agrometeorological data, investigation of evapotranspiration and rainfall trend with respect to depth and temporal distribution); Geomorphology (elevations, slopes, gradients); Water and energy availability (position of the water source, water quality and discharge, available power).

B. Technical choices and data analysis Collected agricultural, soil and climate information address the design choices. Equipment selection based on functionality and size will result in cost optimization both at the initial (installation) and operating (working) stage. The following choices are crucial (Ghinassi, 2008):

• • • • •

Whatever the irrigation system selected, it must be able to match the performance set at design by the grower along the expected economic lifetime of the orchard. Attention must be paid to quality.

Hydraulic design The capacity of a system to supply water to hazel grove must be chosen considering the available discharge, the agroclimatic conditions and the cropping strategies, taking into account economic evaluations.

The irrigation system can be divided into sectors if one or more of the following conditions occur:

6.1. Irrigation system design

• •

Choice of equipment

Irrigation type and equipment quality (e.g., above ground drip system, Subsurface Drip Irrigation, microsprinklers, flow rate coefficient of variation); Definition of irrigation parameters (net and gross irrigation application, irrigation time, minimum irrigation interval); Calculation of the system flow rate (discharge to deliver during the peak period); Hydraulic design (pipeline positioning and diameters, total head calculation and choice of lifting devices); System characteristics (length and diameter of laterals, discharge per emitter or linear meter, design efficiency, application rate, filter types, fertigation, automation, and controls).

34

• • • •

soils with different hydrological characteristics (retention capacity, hydraulic conductivity); position (flat and sloping); microclimatic zones (climatic demand differentiated from exposure); available flow.

Available discharge is the factor that most frequently determines the division into sectors:

• •

The available flow rate is insufficient to supply the entire system at the same time;

•

Power required for the lifting system is not sufficient.

The available flow rate is sufficient, but large equipment is required (diameters of pipes, fittings, valves, filters);

Splitting the system into sectors has some advantages:

• • •

better control of irrigation; water applications are not stopped in case of breakdowns or during maintenance operations; water application is more precise.

Among the disadvantages:

• • •

greater quantity of equipment for water distribution is requested; increasing the number of sectors results in higher costs in most cases; there is the need to assess the size of the different irrigation units. About this, it should be pointed out that:

• •

sectors of the same dimensions simplify calculations and require the same equipment;

•

the optimal size of the irrigation sector is basically the result of the compromise between immediate costs and expected revenue. Whatever the choice, a certain degree of resource losses must be computed;

•

monitoring of the soil moisture content through probes is simpler and more effective in small sectors;

working conditions of the pump take advantage from similar flow rates, especially if it is not equipped with an inverter.

As a guideline, the modular approach allowed by sectorization should result in economic and environmental benefits.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

6.2. Irrigation types

The drip line must be kept in horizontal position by a steel wire to prevent improper water application (Figure 18). The lateral is not in contact with the ground and therefore there is neither the risk solid particles enter the emitter orifice during system emptying, nor obstacle to mechanized operations.

Compared to other fruit tree crops, hazel irrigation is a quite recent practice.

The dripping line lying on the ground (Figure 19) is not affected by the wind, but can suck up the soil particles due to depression during the emptying of drip lines not equipped with anti-siphon emitters. Moreover, drip lines positioned in this way can be obstacle to mechanized cultivation and damaged during operations, resulting in higher cultivation cost. These are the main reasons why drip lines lying on the ground are not commonly used.

Currently, the types of irrigation used on the hazel grove are all variants of localized irrigation and fall within the so-called fixed systems:

• • •

above ground drip irrigation (suspended or placed on the ground); subsurface drip irrigation (SDI); micro sprinkler.

Each type has its own characteristics and relative advantages and disadvantages.

6.2.1. Above ground drip system The drip line, single or double, should be suspended at a height compatible with that of the plant and with the need not to be influenced by the wind (Figure 17).

Figure 18. Suspended drip line held horizontally by a steel wire.

Figure 19. Drip line lying on the ground.

Above ground drip system A. Arguments for: Simple to:

• • • • • •

place; control; repair; remove; replace; change.

B. Arguments against:

• Figure 17. Schematic representation of a suspended drip line. Pipe is kept horizontal, so this condition is facilitating proper infiltration and movement of water in the soil. A regular wetted strip should appear on the soil surface.

36

• •

incomplete wetting of the root system when one lateral per row is in use (insufficient water uptake can occur during high ET demand); incomplete use of water storage capacity along the root zone; some evaporation loss from the soil surface.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Along one side of the row.

6.2.2. Subsurface Drip Irrigation (SDI) Subsurface drip irrigation is widely used in hazel irrigation, despite the lack of a robust scientific bibliography to provide reliable information about the application on hazel grove. The installation of SDI laterals should preferably take place in homogeneous soils, or at least in fields where the laterals can be installed at a constant depth and constant sub-surface slope. This is to eliminate the problem of specific laterals being installed with high and low points along their length. Installing laterals with varying longitudinal profiles (e.g., undulating topography) can lead to airlocks and thereby the formation of vacuums and the suction of soil particles into the emitter apertures. The testing of the system after installation is important to detect and fix any leaks and thereby prevent the possible entry of soil, etc. It is important that laterals should be flushed thoroughly before the first irrigation starts. Installation should be made in the year of planting (Figure 20). Average installation depth of the lateral, usually between 0.1 m to 0.3 m, depends on the root system and the lateral water distribution capacity of the soil.

Ways to position the dripline:

The dripping line is buried at a depth of 30-35 cm. It is considered that the uptake of water occurs mainly from the roots that are within the projection of the canopy, for which a diameter of 2.0-2.2 m is expected as normal (Figure 22). The distance of the drip line from the stem is variable between 0.3 and 1.1 m.

Figure 20. Positioning of HDPE manifold and sub surface laterals.

Along the centre line of the inter-row.

This solution starts from the assumption that the entire surface of the hazel grove is being explored by the root systems of the crop. The water moves towards the row if the horizontal component of the flow is high enough and the flow rate of the emitter is sufficient. In the example of Figure 21, with a distance between the rows of 5 meters, a quite high flow rate per emitter, q, is recommended (e.g., q> 2.0 l/h), higher than that required with a shorter row spacing. For example, for an inter-row of 4.5 m, q between 1.6 and 2.0 l/h may be sufficient.

Figure 22. Representation of an underground drip line. The dimensions indicate an emitter spacing along the lateral of 0.70 m and canopies with a diameter of 2.2 m.

The evidence of moisture at the soil surface depends on the hydraulic conductivity of the soil, the burial depth of the drip line, the flow rate and spacing of the emitters (flow rate per emitter or per linear meter). (Figure 23).

Figure 24 shows in projection the distribution of soil moisture according to the strip wetting principle, applicable to both the above ground and subsurface lines. It is noted that the plant is reached by water since the planting time, with the risk of root concentration towards the wet side during the crop development.

Figure 23. Surface moisture in a sub-irrigation system with one line on each side

Figure 24. Representation of the continuity of the wetted zone in a lateral line, buried or above ground, positioned 50 cm apart from the stem.

Figure 21. Drip line buried in the middle of the inter-row. Lateral expansion of water depends on soil type and emitter discharge.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Along both sides of the row.

To avoid improper root development and to increase both the volume of wetted soil and the flow rate that can be absorbed by the crop, a second line is placed on the other side (Figure 25).

Whatever the system in use, it is commonly said that when the seasonal depth of irrigation is from 50 to 200 mm, the irrigation system should have the capacity to apply about 45 litres per tree per day. According to results from studies carried out from 2003 to date, the optimal solution is the installation of a two-line subsurface drip irrigation, to be positioned from the first year of planting.

Subsurface Drip Irrigation (SDI) A. Arguments for:

• • •

potential high irrigation efficiency (low evaporation from the soil surface); better application of nutrients; no obstacles to cultivation operations.

B. Arguments against:

•

Figure 25. Double drip line, equidistant from the stem. In this way, a more balanced development of the root system is guaranteed, and the irrigation time is reduced.

The development of the root system in width and depth can be increased with vigorous rootstocks.

Deepening up to 0.8 m and lateral expansion beyond 2.2 m in diameter can be expected. This leads to a greater volume of soil explored (> 30%) and possible increase of the irrigation interval. Among the strategies to stimulate root development, the placement of the two drip lines at different distances from the stem and at different times can be suggested. The first at about 0.5 m, at planting, the second at 80 cm and more when the root system is in active development (Figure 26).

• • • • • •

incomplete wetting of the root system when one lateral per row is in use (insufficient water uptake during high ET demand); high investment cost; clogging due to soil particles and root intrusion; limitations in control and repair operations; limitations in modifications and transformation after installation; limited beneficial use of rain; soil dependent.

6.2.3. Micro-sprinkler It is the type of localized irrigation that, from the agronomic and management point of view, can be considered as the overall best solution for the irrigation of perennial crops. It is a sprinkler irrigation that applies water over a fraction (40-60%) of the cultivated area by means of micro sprinklers (Figure 27) characterized by different operating pressures, flows and throws (Figure 28).

Figure 26. Parallel drip lines at different distances from the stem to better exploit the root zone volume stimulated by vigorous rootstock.

Figure 27. Mini sprinkler positioned on the sideline.

40

Figure 28. Mini sprinkler in operation on a young orchard

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Among the recognized advantages of micro-sprinkler, the good root development, and the support of inter row grassing (useful for shell fruit harvesting) should be pointed out. However, some aspects penalize its large-scale diffusion.

6.3.1. Pipelines For the typical sizes and classes of pipes used for irrigation mainlines, there are various plastic pipe solutions that offer the most appropriate solutions in terms of economy, durability, and handling.

Micro-sprinkler

U-PVC pipes

A. Arguments for:

Most on-farm conveyance pipelines are buried, in which case PVC (polyvinylchloride) are the best to use.

U-PVC pipes are available in rigid bars of different lengths. Compared to Polyethylene, the wall thickness is thinner given the same outer diameter and the nominal working pressure. This results in larger inner diameter which allows significant minor friction losses to deliver the same discharge. PVC pipes and fittings should conform to UNI EN ISO specifications.

• • • • •

up to total wetting of the root system (max water uptake allowed very high ET periods); better uptake of nutrients; rapid irrigation applications (short irrigation times); minimal risk of clogging;

PVC bars can be coupled by means of the bell-shaped end equipped with an elastomeric gasket (Figure 30), or by means of sleeves to be welded.

easy to control and repair.

B. Arguments against (compared to drip):

• • • • •

higher discharge; larger pipe diameters; higher working pressure; more expensive; higher evaporation losses.

Figure 30. Cross section of a PVC pipe and the bell-shaped pipe-end with elastomeric seal (from: System Group, modif.).

6.3.

Components and equipment of the irrigation systems

A typical micro irrigation system can be represented as in Figure 29.

Figure 29. Schematic representation of a micro irrigation system.

42

Laying U-PVC pipes Ensure that the pipe is laid in accordance with the manufacturer’s recommendations. Pipes must be backfilled immediately after laying, leaving the joints exposed for testing (Figure 31).

Figure 31. Positioning of PVC pipe serving as manifold. Pavement is smooth. The trench is filled in soil layers 30 cm each.

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GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

GUIDELINES FOR SUSTAINABLE HAZELNUT IRRIGATION

Trenches

PE pipes

Depth of trench

High density polyethylene (HDPE) pipes are more suitable to stand on the ground surface, due to their UV resistance properties. HDPE pipes are more expensive than PVC pipes and should therefore only be used if the installation conditions require it. Pipes should conform to standard specifications.

Depth of trench is normally determined by a specialist after extensive investigation. Consideration should also be given to pipe deflection under buried conditions before the pipe is installed.

Excavation The width of the trench at the crown of the pipe should be as narrow as practicable but not less than the outside diameter of the pipe plus 300 mm to allow proper compaction of the side fill. Above the crown of the pipe, the trench may be any convenient width. The trench should not be opened up too far in advance of pipe laying.

Width of trench and depth of cover

Development of new materials have led to improvement in strength properties with new grades of HDPE. Small diameters of HDPE pipes (e.g., <180 mm outer diameter hoses) are available in rolls.

Plastic pipes that are manufactured from virgin material will last longer and have a smoother finish (reducing friction losses and therefore energy requirements) than pipes made from recycled material.

Irrigation designers and irrigator should use pipes from reputable manufacturers.

Selection of pipe diameter is driven by economic criteria related to initial and running cost.

Initial cost increases with the diameter, the cost during system use increases as the diameter reduces.

Objective for the designer is to find the most economical solution, that is the diameter which minimizes the sum of fix and variable costs. The graph in Figure 32 represents the approach.

For most purposes, a trench 300 mm wider than the diameter of the pipe allows enough room for jointing.

Depth of cover should be at least one meter from top of pipe to ground surface.

Normal subsoil On normal subsoil, replace more than 100 mm thickness of the excavated ground with suitably sifted sand to be used as bedding. River sand should be used if the excavated sand is not suitable.

Backfilling around the pipe Backfill soil should be free of stones and rocks and filled into both sides of the pipe evenly to prevent displacement of the pipe. The soil should be filled and tamped using hand tampers to firmly compact the soil around the pipe. This operation should be continued until the backfill has reached a height of 300 mm above the crown of the pipe.

Backfilling to the ground level The remainder of the trench (but not the pipe joints) should be filled (in layers of encompassed thickness of approximately 300 mm) over the full width of the trench with the excavated trench material, each layer being individually firmly tamped. If the excavated material is such that subsequent subsidence may occur selected material may be required (e.g., in cases where pipelines are laid under roads).

Flushing Following the installation of all system components, the system can be filled with water under supervision of the designer or engineer. The first water available to the system should be used to flush all pipelines to remove any possible soil or other impurities that could have entered the system during installation.

Pressure control Once the system is under full pressure, any control valves that require adjustments should be set to provide the correct pressures at the various locations on the system. Pressures should be checked and compared with the design values.

44

Figure 32. Economic pipe design approach. For fixed flow rate, the most economical solution minimizes the sum of capital (production) and running (use) cost, taking into account interest rate, pumping hours per year and energy cost.

The following values for allowable pipe friction in mainline are proposed as norms and applies for pipelines with a diameter of 200 mm or smaller:

• •

rising pipeline: maximum 1.5% (m/100 m) friction; gravity pipeline: maximum allowable flow velocity of 3.0 m/s

If the above figures are exceeded, the designer must show that the chosen pipe diameter’s total cost (capital and annual running cost) has been optimised and is the best of the available options.

For pipelines of larger diameter, the effect of water hammer is critical and must be investigated and optimised.

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6.3.2. Pumps The capacity of the pump should be sufficient to supply flow and pressure according to system requirements and to cater for lateral and manifold flushing.

Compared to the duty point (pressure and flow) of calculated system capacity, design margins can be changed by adding the following accepted values:

• •

discharge: 10% pressure: 5%

Where an irrigation pump is also used for the mixing and application of fertilisers, then an additional 20% pump capacity must be provided (Van Niekerk et al., 2008).

6.3.3. Filters The filter is the heart of any drip system. Filtration of irrigation water for application through drip systems is essential to prevent substances from blocking the emitters.

Because dripper blockages are difficult to see, and can only be repaired by replacement, drip irrigation in general requires a high degree of filtration.

Appropriate maintenance and management of the filtration system is important for optimum performance of the irrigation system.

The type of filter to be used, and the level of filtration, which is to be handled by the filter medium, are closely related to both the type of system which is to be served and the amount and type of dirt in the water, strictly related to the source.

Both filter type and filtration degree can be suggested by manufacturers of drip irrigation equipment.

Filters can be categorized according to the position in the filtration sequence.

Primary filters are cyclone and sand filters, selected according to the source of water. They must remove most of the impurities conveyed in suspension. They are positioned at the beginning of the filtering bank.

Secondary or security or control filters are mesh (screen) and disc filters. At least one security filter must be positioned downstream from the primary filter, especially when drip irrigation is practiced.

Figure 33. Sand separator. At the bottom, the collection container with quick drain valve.

Separation of particles occurs through the acceleration caused by the rotational movement of water which enters tangentially with respect to the body of the cyclone. Mineral particles drop to the tank, while clean water flows out from the upper central part of the body. Maintenance is limited to emptying the tank where particles are trapped.

The operation lasts until water is clean, and this happens in a few seconds. When water is rich in suspended particles, the capacity of the tank must be considered. In addition, a secondary filter must be placed downstream from the sand separator (Figure 34). Pressure drop should be <9 m, and measure is made at the inlet and outlet of the filter.

Primary filters Sand separator (cyclone) Water from boreholes, ponds or rivers can be rich in suspended solids. Cyclone filter, also called sand separator or tangential filter, is a primary filter used to remove heavy solid particles, in particular sand and gravel (Figure 33). It is the first in a complete filter bank.

Figure 34. Filter bank made of sand separators and disc filters to treat water from borehole

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Sand filters

Secondary filters

Like disc filters, sand filters also offer a three-dimensional filtering action. They offer a large medium area; thus, the total capacity of a sand filter is much higher than that of other filter types. It also has a finer filter action, making it a very popular choice. Most manufacturers specify a sand filter with a wide spectrum of granular sizes capable of removing particles down to 80 microns from the water.

Mesh filters

The medium area is the determining factor for calculating the filter capacity. The theoretical maximum filter capacity of a 0.8 mm sand is 50 m3/h per square metre of sand surface. There are two main reasons why it is not advisable to use sand filters maximally:

The filtering qualities are determined by the size of the mesh openings, the total mesh area, and the facility for cleaning the mesh during regular maintenance operations. Mesh filters are suitable for filtering good quality water in which sand and silt occurs. Algae can however block the openings of a mesh filter. Filtration ratings are given in Table 16.

• •

the lower the flow rate during filtration, the better the result; at the same time, backwashing intervals increase in inverse proportion to the decline in utilisation.

Sand filters require little maintenance. However, it is important that the filters are backwashed regularly to prevent excessive accumulation of dirt which could screen off the sand surface, and consequently be forced through the sand due to the increased pressure difference resulting in a process known as funnelling. It has been determined in practice that the best backwashing rates of sand filters should be identical to or slightly lower than the maximum filtration rate. It is also recommended that the sand is replaced on a regular basis, at least once a year.

Sand filters are always operated in conjunction with secondary disc or mesh filters. There are two reasons for this:

• •

under normal circumstances, the secondary filter serves as a check on the performance of the sand filter. During incidental funnelling, the material will move through the sand and will be intercepted by the secondary filter. This condition warns the operator that the sand filter needs to be serviced;

Mesh filters consist of a permeable membrane which is usually located inside a supporting, cylindrical core (Figure 36). The mesh is usually manufactured of stainless steel or a nylon compound.

Figure 36. Mesh filters (From: Arkal)

Table 16. Filtration fineness ratings

Standard filter ratings Micron

300

250

200

130

100

80

mm

0.3

0.25

0.2

0.13

0.1

0.08

Mesh

50

60

75

120

155

200

if the sand filter is damaged internally, the filter sand is intercepted by the secondary filter, preventing it from entering the emitters.

The shape and function of a typical sand filter is illustrated in Figure 35.

Filter openings must be smaller than 1/5th of the emitter orifice diameter (Table 17). The appropriate micro emitter manufacturer’s recommendations must be used for flow path openings of ≤ 1 mm.

Table 17. Filtration degree suggested for different flow path diameters

Figure 35. Filtration and backwash in sand filter

Mesh

20

40

80

100

120

150

180

200

Filter openings (mm)

0.711

0.420

0.180

0.152

0.125

0.105

0.089

0.074

Orifice diameter (mm

5

3

1.2

1.0

0.9

0.7

0.6

0.5

The standard filtration degree is 120 mesh.

Sand filters fitted with secondary filters are recommended for drip irrigation with ‘normal’ stored or running water. Because mesh filters are basically not back-washable, disc filters are recommended for this purpose.

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Disc filters

Cleaning cycle

Disc filters offer a three-dimensional filter action, and therefore have a much higher capacity compared to

Filter management includes periodic cleaning of the filtering elements (screen, disc, sand).

mesh filters of the same basic dimensions. The filter consists of a number of grooved circular plastic discs which are tightly stacked cylindrically. Water flows from the outside of the cylinder through the discs to the inside. All foreign matter larger than the permeable openings of the specific grooves is retained by the discs. Dirt is removed from the discs by flushing with filtered water in the opposite direction through the discs (backwashing). In some filters, the discs can also be loosened from one another and even rotated during backwashing, resulting in cleaner discs.

Cleaning can be either manual or automatic.

The frequency of cleaning interventions depends on the characteristics of the irrigation water, the emitter used and the filter type. It can be done at fixed time intervals or when the pressure drop reaches a given threshold (difference between the pressure reading at the inlet and outlet of the filter).

During the filtration process there is an increase in the total pressure loss over the filter due to blockage. The pressure loss over a typical filter is illustrated in Figure 39.

The flow pattern of a typical disc filter during filtration and backwashing is illustrated in Figure 37.

Disc filters are usually adequate in cases where clean water (e.g., most borehole water) is used for irrigation.

The filtration level will be fine enough, and the only limitation will be the length of the backwash cycle.

The following norms are suggested:

• Figure 37. Filtration and backwash in disk filter (from: Arkal).

Selection of filter size or filter capacity The size and/or the number of filters required for a system depends on:

• • •

Figure 39. Filter clogging increases with the amount of filtered water.

maximum allowable pressure drop over disc and screen filters:

- over a clean filter is ≤ 10 kPa;

- over clean filter bank is ≤ 30 kPa;

- over a filter bank before backwashing is ≤ 70 kPa.

•

maximum allowable pressure drop over the sand filter:

- over a clean filter is ≤ 10 kPa;

The total flow in the system and the maximum recommended flow through each filter

- over a clean filter including secondary filter is ≤ 40 kPa;

The amount of dirt present in the water

- over the filter bank before backwashing is ≤ 60 kPa.

The minimum back-wash or cleaning cycle

•

Maximum flow rate

• •

The higher the flow rate through a filter, the higher the pressure loss over the filter (Figure 38).

•

The finer the grade of filtration, the higher the pressure loss through the filter at the same flow rate.

• • •

Pressure loss information are provided by the manufacturer.

Figure 38. Friction loss over the filter increases with discharge. Allowed pressure interval is from 10 to 50 kPa

Pressure losses should be limited for both physical and economic reasons. The total pressure loss over a clean filter at the maximum allowable flow rate should not exceed 10 kPa.

when using a sand filter, a control (secondary) screen or disk filter must be placed on the downstream side of the sand filter to catch escaped impurities. the drip manufacturer’s recommendations must be followed when using a disk or screen filter. maximum allowable flow rate through a clean sand filter matching a pressure drop ≤ 10 kPa is ≤ 50 m3/h per m2. for sand filters backwash, a minimum of 50% of the maximum filtration rate (50 m3/h per m2 sand surface) is required. the maximum backwash rate must not exceed 1.2 times the filtration rate. a minimum of 6 m inlet pressure is required during sand filter backwashing. the backwash time of sand filters can be between 90-180 seconds.

As the cleaning process starts, the raw water is above the sand bed, and at first appears to be clean.

Thereafter the dirty water, which was trapped in the sand bed, is then expelled. During the flushing process, the water will gradually appear cleaner. Thus, it is so important to provide sufficient time during the backwash operation to ensure all impurities are removed from the filter.

This guideline, however, is not rigid, but can be adapted according to relevant system factors. Excessive pressure losses may adversely affect the filtration efficiency and may even damage the medium.

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Available products A huge variety of filtration equipment is available on the market. Only filters from reputable irrigation companies where good quality control and testing are in place must be used.

The method of placing irrigation water on top of the soil, as well as the distribution of water in the soil (especially lateral distribution), should correlate well with the nature, shape and extent of the root system, and any limitations affecting these. The unknown factor is the ability of the soil to distribute irrigation water laterally.

Three basic, interactive factors are responsible for this characteristic:

• • •

6.3.4. Laterals Type of laterals Emitters can be mounted onto dripper lines (laterals) in various ways. It can be:

• • • •

Inline Internal

the percentage of fine fraction in the sand; the presence of organic material in the soil.

Although these factors are individually quantifiable, their combined effect on the lateral water distribution capacity of the soil cannot be calculated theoretically. Further, it is generally assumed that soil with a high clay content gives better horizontal distribution than soils with a high sand fraction (ARC, 2010).

Integral

Agronomic suitability of the lateral

External

The use of laterals is based upon the conventional strip wetting principle. The aim of the general conventional approach is to create a continuous wet zone in the soil, whether the lateral is placed above ground or underground (SDI). The maximum use of the lateral water distribution capacity of the soil requires adequate overlapping of wetted zones (see 4.2). Emitter spacing should therefore be selected carefully. A pre-assembled dripper line is normally manufactured according to standard manufacturing processes with a wide range of dripper spacing options, ranging normally from about 0.3 to 1.0 m and more. This allows to satisfy the minimum system requirements to determine the potential lateral water distribution capacity of the specific soil.

For both surface and subsurface drip irrigation of perennials (e.g., hazel), emitters are internal to the dripper line. The dripper is fixed to the inner wall of the unique dripper pipe by thermal fusing (also known as bond on), during the manufacturing process. Standard polyethylene (PE) pipes are therefore out of the question in this case. Two kinds of drippers are mainly used:

• •

the clay percentage in the soil;

Cylindrical drippers.

Elongated drippers.

These drippers have long flow path type, where friction and turbulence in the flow path decrease the lateral pressure until the design discharge is reached. The cross-section area of the flow path is usually about 1 mm². The flow is regarded as turbulent because of the continuous changes in direction experienced along the labyrinth.

Lateral and soil The lateral water spreading capacity of the soil is a determining factor in the decision-making process. The shape and size of the wetted profile in the soil are important because it should be able to store at least enough water in an area accessible to the feeding roots of the crop. The distribution of the water in the soil occurs along the hydraulic gradient between the wet and the dry soil: laterally by means of capillary action, and vertically due to gravitation. With point application, this wetting and distribution pattern, more or less, takes the shape of an onion, as shown in Figure 40.

Intrusion of roots and soil particles Root penetration is a potentially serious problem (Figure 41). Drippers that close automatically under low pressure conditions are more resistant to penetration.

Potential soil penetration of the drippers due to vacuum conditions is a common problem, especially when the system is switched off. Anti-vacuum valves should be installed at all high points and downstream of all shut-off valves.

Figure 40. Water distribution in soil on surface (a) and subsurface (b) drip irrigation (From Reinders et al., modif.).

Figure 41. Emitter pathway and orifice invaded by plant roots.

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Lateral selection according to hydraulic adequacy

Within-field manifold location

Continuous wetted zone in the soil requires emitter discharge remains close to the design flow. Allowed pressure variation along pressure sensitive lateral should not exceed a given threshold, e.g., 20% the working pressure, in order to keep discharge variation of the emitters within 10% of the design flow rate.

Economical solutions to cover long distance and keeping pressure variations within acceptable values, can be found by placing the manifold within the field and feeding the laterals from the opposite sides. The intermediate position of the manifold depends on the field ground slope, e.g., flat and inclined.

Pressure variation occurs due to friction loss and difference in elevation due to morphology.

Friction loss increases:

• • •

Flat ground

as the flow rate increases;

On flat ground, the manifold is placed in the middle, this way halving both drip line length and discharge flowing at the inlet of each segment (Figure 42). Diameter of the manifold does not change since the discharge at the manifold inlet is the same.

as internal diameter of the pipe decreases; as the lateral length increases.

The same dripline model can be available in variants that differ in:

• • • • •

emitter spacing, m (most common: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0); emitter discharge, l/h (0.6, 1.0, 1.2, 1.6, 2.0, 2.4, 2.8, 3.0, 3.8); working pressure, bar (1 to 3.5); pressure sensitive (PS) or pressure compensated (PC); diameter, mm (PC: 16, 20, 22).

Performance of the dripline, working within the suggested pressure range, is provided by the manufacturer.

Given the design spacing, e.g., 0.8 m, and discharge, e.g., 1.6 l/h, the maximal length of the drip line is affected by pipe diameter and pressure at the inlet. Indicative values are as follows (Table 18): Table 18. Indicative values of maximal lengths for PC and PS drip lines on flat ground.

Pressure (bar) Diameter (mm)

PC

Figure 42. Schematic representation of bilateral supply in SDI. The hydraulics applies to all conditions.

PS

1

3,5

1

16

190

360

152

20

284

536

210

22

390

690

300

Inclined ground The length of each segment of the lateral is affected by the field slope. As the field slope increases, the length of the uphill segment, Lu, reduces, while the length of the downhill lateral, Ld, increases. Manifold position within the field, L, should guarantee the minimum head at the closed end of both uphill and downhill segment of the lateral (figure 43).

Selection of the lateral should therefore take into account:

• • • •

the field length; to need to avoid excess of pressure variation; the cost for equipment (increases with diameter and PC device); the cost for energy (decreases with diameter).

Compared to the 16 mm PC, the 20 mm PS dripline is about 20% cheaper.

Figure 43. Schematic representation of the manifold position within inclined field.

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Lateral spacing and wetted area

Available products

Soil wetted pattern is designed by lateral spacing and emitter spacing along the lateral and depends on soil type and soil texture.

A huge variety of laterals are available on the market. Data from the most prominent suppliers can be found in the technical sheets. Furthermore, individual suppliers can be contacted for information and specifications. Only laterals from reputable irrigation manufacturers, where good quality control and testing are in place, must be used.

Preliminary selection of emitter spacing should consider the theoretical diameter of wetted soil (see the field test in 4.2). This is function of emitter discharge and soil type (Figure 44).

6.3.5. Emitters A huge variety of emitters are available on the market. Data on drippers from the most prominent suppliers can be captured from the technical catalogues provided on the net. Normally, the individual suppliers can also be contacted for information and specifications. Only emitters from reputable irrigation companies where good quality control and testing are in place must be used.

Emitter characteristics Figure 44. Schematic representation of the influence of soil type and emitter discharge on the wetted diameter

There is a wide variety of drip emitters commercially available. Distinctions between types can be made on the basis of operating principle (pressure sensitive or pressure compensating), positioning relative to the lateral (internal, external, etc.), and construction (flow path length, etc.).

Table 19 illustrates the relationship between discharge rate, soil texture, emitter spacing and lateral spacing for practical application. Although this table is for surface drip irrigation, similar relationships exist for subsurface drip irrigation.

Regardless of the type of emitter selected for use, it is always important to select good quality, tested components when designing and installing drip irrigation. The use of cheap but inferior materials and novel components which have yet to prove their worth should be avoided.

Table 19. Percentage of wetted area, Wa, under emitters with different delivery rates, spacing and soil textures.

Emitter delivery rate Soil texture Wetted diameter under emitter (m) Max emitter spacing on lateral (m) Drip line spacing (m)

2 l/h Coarse Medium

4 l/h Fine

Coarse Medium

Dripper types

8 l/h Fine

Coarse Medium

Fine

0.39

0.78

1.24

0.78

1.24

1.26

1.24

1.62

2.10

0.30

0.60

1.00

0.60

1.00

1.30

1.00

1.30

1.70

0,8

50

100

100

100

100

100

100

100

100

1,0

40

80

100

80

100

100

100

100

100

1,2

33

67

100

67

100

100

100

100

100

1,5

26

53

80

53

80

100

100

100

100

2,0

20

40

60

40

60

80

60

80

100

2,5

16

32

48

32

48

64

48

64

80

3,0

13

26

40

26

40

53

40

53

67

3,5

11

23

34

23

34

46

34

46

57

4,0

10

20

30

20

30

40

30

40

50

4,5

9

18

26

18

26

36

26

36

44

5,0

8

17

24

17

24

32

24

32

40

6,0

7

14

20

14

20

27

20

27

34

Percentage wetted area (% Wa)

56

The purpose of a drip emitter is to apply water at a specific flow rate (determined during the planning process and called the design emitter discharge) over a specific area of soil in the field. Emitter discharge is determined by the pressure of the water at the emitter; the design discharge is delivered at a specific pressure called the design operating pressure. At pressures higher than the design operating pressure, the emitter will discharge more than the design discharge, and at pressures lower than the design operating pressure, the emitter will discharge less than the design discharge. The discharge pressure relationship is characterised by the equation:

q=Khx Where: q = emitter discharge (l/h); K = discharge coefficient (include qe); h = operating pressure (m); x = discharge exponent.

This relationship is presented graphically in Figure 45 and Figure 46.

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•

advanced design techniques such as complicated equations and graphic aids, or even computer programmes, are not required for the designing process. Sensible application of basic pipe hydraulics is all that is required for this purpose.

Disadvantages usually associated with pressure compensating emitters:

• • Figure 45. Representation of the discharge pattern of pressure sensitive emitters. Discharge increases with pressure.

Figure 46. Representation of the discharge pattern of PC emitters. Discharge is constant within the working pressure interval, commonly varying from 5 to 35 m.

complicated composition involves more components, resulting in increased vulnerability and difficulty to maintain low CV values; higher emitter costs.

6.3.6. Valves Valves are expensive items on the schedule of quantities of any irrigation system, but correct placement can improve the ease of operation of a system and reduce maintenance costs dramatically.

There are various valves available to control flow and/or pressure at block or system inlets.

Pressure sensitive emitters The discharge of pressure sensitive emitters (Figure 45) is a function of the operating pressure inside the lateral. It is therefore essential to ensure that system pressure inside the side-lines and laterals is kept within the required tolerances during the designing process, in order to maintain uniformity of emitter discharge within the specified ranges. In pressure sensitive emitters x is between 0.3 and 0.8.

Mechanical valves such as butterfly, gate or ball valves are mostly operated manually although they could be fitted with a gearbox for automatic or remote operation (Figure 47 and Figure 48).

Disadvantages of pressure sensitive emitters:

• • • •

• lateral length and therefore discharge is influenced by topography, directly influencing the operating pressure; • larger pipe diameters are normally used along flatter gradients to limit friction losses; • it is often necessary to maintain downhill flow directions in both laterals and side-lines. Costs will rise in case a more extensive supply system is required; • relatively complicated design processes (normally requiring the use of advanced equations, graphic aids, and even computer programmes) are inevitable, and complicate the design process.

Pressure compensated emitters In a pressure compensated emitter (Figure 46), where x value should be 0, the regulating mechanism affects the discharge/pressure relationship, with discharge remaining constant over a specified pressure range.

Usually, the only limitation is that a minimum required pressure (e.g., 2.5 m) should be maintained to perform the compensating function. Pressure compensated emitters are available for all types of pressurised systems but are more expensive than non-compensating emitters.

Advantages of pressure compensating emitters:

• • • •

longer laterals of the same diameter pipe can be used, because emitter discharge remains constant and is not influenced by pressure variations due to friction or topography; similarly, smaller diameter pipes can generally be used in side-lines and laterals, and in some cases even in the distribution network; in most cases it is advantageous to maintain a flow direction opposite to that of the soil gradient in the side-lines and emitter lines; the CV of the emitters constitutes the total discharge variation of a system. Low CV values of welldesigned and well-manufactured emitters therefore ensure even distribution of water and plant nutrients, often safely within the normal allowable tolerances; 58

Figure 47. Butterfly valve operated manually on a main line

Figure 48. Gate valves at system inlet.

Control valves are needed at the irrigation block and system inlets, as well as at the water supply (usually the pump station) of the whole system.

Hydraulic valves are more suited to automated systems, and this should be kept in mind when planning a new system.

Control valves at the water supply are often forgotten or left out due to cost considerations but can save large volumes of water if pipes or even dams have to be drained for repairs or maintenance, because there is no valve in place to isolate the section to be repaired.

Manufacturers’ recommendations regarding installation should always be followed, especially in the case of mechanical valves as incorrect installation practices can lead to valves not being able to open or close.

The correct size of valve should be selected on the basis of the flow rate that the valve must be able to handle. Selecting a valve that is too small, will result in excessive friction losses, while selecting a valve that is too big, especially hydraulic valves, will result inaccurate operation, especially at low flows.

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Control valves must be chosen correctly for the flow and/or pressure conditions in the system and require a minimum pressure to function correctly. It varies between the different manufacturers. If the pressure is too low, the valve cannot open enough or close tightly. The design and installation of large diameter pipelines is a specialist field and knowledgeable designers should be consulted.

depending on the need for energy to be transferred to the water. The initial cost is higher, but over the life cycle it can be lower than that of a pump that does not provide the benefits of better energy management.

In most cases, life cycle energy consumption represents the most significant cost of a pumping system, particularly when pumps run more than 2000 hours per year (Grundfos, 2004).

Air valves (Figure 49) are also an absolute necessity on mainlines, as it protects the pipeline from damage due to air. Air valves can be designed to let air out (air release, when filling an empty pipeline), or to meet air in (air & vacuum, to prevent negative pressures when a pipe is drained, or a pipe burst occurs).

Variable speed pumps have the characteristic of keeping the set pressure constant as the flow rate varies within the operating range of the pump motor system, while maintaining high efficiency. Each variation of the required flow rate, measured by a flow sensor, corresponds to a certain frequency of the electrical supply and therefore a different rotation speed of the impeller (Figure 50).

Air valves are installed at high points where air would naturally rise due to water during system filling and where negative pressure occurs during water drainage.

Figure 49. Air release valve (red) regulated by a ball valve (dark grey lever) positioned downstream the control valve (right) of an irrigation block (sector). Other PVC ball valves (blue levers) in the installation allow different options such as repair and maintenance operations, as well as halve the sector.

Air & vacuum, and air pressure release orifices are both open during filling. During filling, incoming water compresses the air in the pipe until the pressure difference across the air valve allows the air discharge at the same volumetric rate of the water entering the pipe. After all the air has been eliminated, water enters the valve and lifts the floats until both orifices are closed.

Figure 50. Operation of a pump equipped with inverter. Within the working range, pressure is kept constant while the flow rate varies (From: Pedrollo, modif.).

Among the advantages of using the inverter:

• • • • •

better regulation of flow rates on the whole system or sectors;

While the large orifice remains closed, the small orifice reopens to release air that has been collected in the valve after it has closed. When the internal pressure falls below atmospheric pressure, both orifices open to allow air to enter the system at the same volumetric rate at which water is draining. In this way critical vacuum and damage to the pipe are avoided. Due to the fact that the sub-surface emitters are covered with soil, vacuums created in the laterals can promote the entry of soil particles into the orifices. It is therefore recommended that a vacuum breaker or air inlet valve be installed at each irrigation block. If a situation exists where the slope of the lateral is not constant, and a high point is created, an additional vacuum breaker should be installed at the highest point on the lateral.

Among the disadvantages:

In fields where water is pumped uphill in a lateral, a vacuum breaker should be installed at the highest point.

If a flushing manifold is installed, the vacuum breaker should be installed at the highest point of the block.

• •

The topography of the main line will determine if an additional vacuum breaker is necessary (Burger et al., 2003).

6.3.7. Accessories

reduced energy consumption; less heavy use of the pump which extends its useful life; progressive start-up and shutdown; reduced risk of water hammer.

the cost is even higher than traditional pumps; when systems that only allow pressure setting are in use, a flow meter is required to check system malfunction, such as leaks or occlusions.

Flow meter

Inverter About 20% of the world’s electricity is consumed by pumping systems. Those equipped with a frequency variation device of an alternating current, the inverter, allow giving a variable rotation speed to the impeller 60

It is recommended that a flow meter be installed in every drip system. It can provide valuable information on whether the system is operating correctly by comparing the measured flow rate into the system with the design flow rate, providing early warning of possible dripper clogging or leaks. It is also a useful scheduling tool through which the amounts water applied can be verified if meter readings are collected regularly and is required to operate fertiliser injection systems. Installing the meter behind the filter in the system will protect it from possible breakdowns due to physical impurities in the water.

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Pressure gauge Monitoring data, particularly the amount of irrigation water applied, is fundamental to irrigation scheduling and is needed to assess the effectiveness of an irrigation strategy and to make improvements if necessary.

At the inlet to the irrigation system, block (sector) or lateral, the pressure in the system should be monitored and compared against the design inlet pressure provided in the design report. A system operating at the correct pressure will supply the correct amount of water, and it is easier to measure pressure than flow at an inlet.

Deviation from the design inlet pressure will provide the operator with an early warning of leakages or pipe bursts (low pressure), blocked emitters (high pressure) and other in-field problems. Pressure in pipes can be measured with a pressure gauge (manometer), either permanently installed or portable, which is read manually at the point of measurement. Piezo-electric pressure gauges can also be used, and the electronic readings are conveyed to a central point via telemetry. This may require electricity to be available at the point of measurement. Selection of measurement point (e.g., the outlet of the farthest drip line) is crucial to support reliable diagnosis of system operation.

Figure 51. Fertilizer injection based on pressure differential between inlet and outlet. Fertilizer tank made of anti-corrosive material

Flow can also be measured at system, block, or lateral inlets, but this is more expensive than pressure measurement.

Figure 52. Venturi injector working principle

7. FERTIGATION Application of fertilisers Fertiliser application through a drip irrigation system must be done with great care, and according to the guidelines of the fertiliser supplier.

Issues and guidelines associated with applying fertilisers:

• •

In all cases, farmers must be supplied with clear guidelines and recommendations on the type of fertilisers to use, the application rate, and the time of application.

Several options are available for fertiliser application. These form part of the range of options considered standard in drip irrigation, e.g., the use of a Venturi apparatus, a fertiliser tank, hydraulic injectors, electrical injectors, and the mixing of fertilisers in a storage tank at the water source or a purpose made fertiliser injection.

7.1.

Fertigation principles

Traditional (injection using energy of the water flow, not expensive, low precision):

• •

pressure differential (Figure 51); Venturi (Figure 52).

Figure 53. Fertilizer injection calibrated by a dosing pump under the command of the fertigation control unit.

Additional features allowed (Figure 54):

• • • • • • •

monitoring irrigation pH and EC through probes positioned along the fertigation net at inflow and outflow; dosage and mix of different fertilizers through control valves; application of different fertigation programs; mixed solutions to be applied (injected) to a large number of control valves (irrigation block or sector); remote monitoring (e.g., via GSM); control of pump and filters; alert communication.

Computerized (additional energy required, high precision applications, Figure 53).

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Figure 54. Highly automated fertigation bank (From: Agricolplast website).

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8. IRRIGATION MANAGEMENT AND MAINTENANCE 8.1. Irrigation system performance Distribution Uniformity (DU) of a system is a performance indicator that is calculated for an already installed system, following an irrigation system evaluation. It is calculated by using emitter discharges measured from a representative sample of at least 16 emitters precisely located within the block as in Figure 55.

Uniformity of applied water is affected by factors such as pressure variation along the laterals and manifold, manufacturing coefficient of variation (CV, which indicates the variability in the flow rate of a random sample of a given emitter model), emitter clogging, damages (e.g., due to insects, worms or during field operations).

Assessment is made as:

DUlq=

hlq havg

Where: DUlq= Distribution Uniformity of the low quarter (25% least values);

hlq= average value of the 25% least values;

havg= average value of all measured values.

The DUlq values can be interpreted according to the following scale: >90%: excellent distribution uniformity 75-90%: good uniformity

Figure 55. Representative samples for DU assessment.

8.2. Water balance When considering the performance of irrigation systems, it is helpful to think in terms of the components of the water balance, or the fates of applied water. Ideally, the bulk of the applied water should contribute to the objective of irrigating: i.e., to preventing undesirable crop water stress. This relates to keeping stomata open, so that photosynthesis is not unduly inhibited.

In Figure 56 there are indicated the various fractions of applied water which are involved in defining irrigation performance at the field level.

The various components of the water balance (fates of applied water) are:

60-75%: acceptable <60%: unacceptable.

The emitter design, materials used in production, and manufacturing precision determine the variation of any particular emitter type. The standard ranking of variability, given by the CV, is as follows (ARC, 2010): CV <0.05: excellent 0.05-0.07: average 0.07-0.11: marginal 0.11-0.15: poor >0.15: unacceptable 64

• • • •

deep percolation;

•

transpiration.

surface runoff; evaporation from the exposed soil surface; spray evaporation, wind drift and plant interception; Figure 56. Various fates of water in the soil-plant-atmosphere system (From: Allen et al., 1998. Modif.).

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8.3. Sensors

The neutron probe makes use of radioactive materials: a strict safety programme is necessary regarding the operation, transport, and storage of the equipment.

Soil water In the irrigation sector, soil water status may be measured in terms of soil water content or soil water potential.

Soil water content can be divided into gravimetric or volumetric soil water content.

Gravimetric soil water content is a description of the weight of water for a given weight of soil. Gravimetric methods of measuring soil water content involve removing and oven drying a soil sample, which can be impractical for irrigation management applications.

Volumetric soil water content is a description of how much water is present in the given volume or depth of soil, typically expressed in mm water per m soil.

Soil water potential is a measure of the suction energy required by the crop to extract water.

Soil water potential (in soil physics terms) describes the forces that drive water movement. The phrase soil water tension is also often used. Tension refers to the strength with which the soil particles cling on to water.

Assuming the soil water tension relationships in hazel cultivation as reference criteria, an appropriate soil water monitoring tool is selected taking into account the following characteristics:

• • • • • • •

ease of use; cost; accuracy; robustness, as the suitability of the monitoring system to the agricultural environment; a potential user should be particularly aware of: calibration of the sensor; sensitivity of sensor performance to incorrect/correct installation procedures.

TDR instruments send an electromagnetic signal down steel probes buried in the soil. The signal reaches the end of the probes and is reflected back to the TDR control unit. The time taken for the signal to return varies with the soil dielectric. TDR can be calibrated to provide very accurate methods of monitoring soil water status and require specialised knowledge, both to record measurements and to interpret the data.

Capacitance probes, otherwise known as frequency domain reflectometers, are relatively inexpensive compared to TDR instruments, and are becoming increasingly popular. As shown schematically in Figure 58, the capacitance probe typically consists of a plastic tube which houses concentric parallel electrodes.

For most practical management purposes, careful analysis of trends in the sensor readings is normally adequate to determine when the soil water is below the stress point or above the drained upper limit.

Soil water potential sensors Tensiometers and porous type instruments such as Watermark sensors can be used to monitor soil water potential. Tensiometers (Figure 59) are one of the oldest and most widely used instruments for irrigation scheduling. They act allowing the soil moisture to interact with the instrument through the ceramic tip. Soil water tension outside of the instrument tries to remove the water from it and creates a measurable tension inside the column.

At least two tensiometers at varying depths are required for deep-rooted crops. The shallower tensiometer will indicate when irrigation should be started, while the deeper tensiometer indicates whether irrigation is done correctly. For shallow-rooted crops, only one tensiometer is necessary.

This tension is read with either a mechanical gauge or a transducer attached to the instrument. While this is the most accurate and proven method available, there is some maintenance required periodically to keep them full of water, and they must be removed from the field during the winter months to avoid freezing.

Tensiometers are limited to soil water potentials above -85 kPa. If the soil dries out to water potentials below -85 kPa, air enters the device, breaking the vacuum with which the tensiometer operates. For this reason, tensiometers can be a high maintenance apparatus. The installation of tensiometers also requires considerable knowledge and attention.

Available tools and current trends Soil water content measure

• • •

Neutron probe; Time domain reflectometers, TDR, (Figure 57); Capacitance type sensors (Figure 58).

Figure 57. TDR probes.

Figure 58. Operation of a capacitance probe.

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Figure 59. Example of tensiometers.

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Other soil water potential sensors include the Watermark (Figure 60), a granular matrix sensor. It consists of two concentric electrodes embedded in a porous reference matrix material, which is surrounded by a synthetic membrane for protection against deterioration. Movement of water between the soil and the sensor results in changes in electrical resistance between the electrodes in the sensor. The electrical resistance can then be converted to soil water potential through a calibration equation. The Watermark sensor can be used to determine soil water potential down to approximately -200 kPa.

A list of minimum maintenance schedule requirements for drip irrigation systems is provided in Table 20.

Table 20. Indicative maintenance operations for drip systems Monitor

Every cycle

Inspect system for leaks and calcium carbonate precipitation Check pressure difference across filters and system operating pressure Adjust filter back flush cycle Flush laterals (depending on water quality) Clean filters thoroughly Monitor pressure at lateral outlets Monitor air valves and pressure control valves Figure 60. Watermark soil moisture sensor.

Monitor system flow (main flow meter)

8.4. Maintenance

Check hydraulic and electrical connectors

Regular maintenance (routine or emergency) will reduce operating costs and water losses. Maintenance includes all sections of the system, from the water source to the root zone.

Replace sand in sand filters

On-farm conveyance

Take water samples at end of the laterals and evaluate changes in water quality

Check hydraulic valves and filters to inspect moving parts

Timely fixing of leaks, checking of valves (especially hydraulic ones) and filters and maintenance of pumps and motors will ensure that water is supplied to the intended destination in the most energy (and therefore cost) efficient manner. Complete guidelines for different system components are available from the manufacturers and should be adhered to.

Chlorine treatment (depending on water quality and application method)

In field application The maintenance of a drip system is of paramount importance for the effective operation. Regular maintenance of the filters system, vacuum valves, the prompt fixing of leaks, the prevention of damage to equipment, the scheduled application of lateral cleaning chemicals are important maintenance aspects, especially in the case of SDI systems. It is important to inspect the irrigation block after each irrigation cycle to identify possible clogging problems (dry patches or under-performing plants) at an early stage. If leaks occur, they must be repaired as soon as possible.

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9. AUTOMATION OF HAZELNUT ORCHARD MONITORING Automation of farming activities is increasing at a high rate due to the advantages potentially allowed, and the spreading of information technology at accessible costs.

The choice to automate the on farm irrigation must take into account:

• • • •

Proper management of the variables that characterize a modern irrigation system takes advantage from the SCADA (Supervisory Control and Data Acquisition) approach.

9.2. Overview SCADA is a computer system designed to monitor and supervise all the components of a physical infrastructure, such as irrigation and fertigation systems, from the water source (e.g., the well) to the distribution system (e.g., the drip line). The system can interface with a wide range of sensors and actuators installed to monitor and control the irrigation and fertigation operations. The user can operate through a graphical interface.

availability of data and information necessary to the proper working of the irrigation system; in farm availability of adequate skills for data management; if the use of data takes advantage from the use of software and hardware; if actual performance of machinery and equipment used for irrigation are optimal.

SCADA application to control irrigation and fertigation Depending on the water source and irrigation type, SCADA will monitor and control different elements, whose number should not be so high for the following reasons:

• •

Therefore, the farmer needs to consider whether:

• • •

9.1.

The SCADA approach towards water economics

he can manage information and data; data can be transformed into knowledge and then into actions; the investment is convenient, that is, if the benefits outweigh the costs.

As a rule, uncertainty on whether automation is suitable or not for operation and control of irrigation reduces as the farm size and complexity increases (Figure 61).

ensure effective control of the system as a whole; a huge number of sensors and actuators would lead to manage too much information (data) which in turn can weaken the system and make it difficult to manage.

In the case of well supply and irrigation through a drip system, the basic elements the system will have to implement are: Well: Measurement of the water level, both static and dynamic; Pump: Flow rate and energy absorption, outlet pressure, on/off control; Inverter: frequency regulation, variable according to requested flow rates or pressure, set for the operation of individual sectors; Filters: Inlet and outlet pressure, outlet flow to the backwash, opening and closing of the backwash valves; Dripping lines: Pressure at the end of some sample laterals by pressure switch; Microelements dispenser for fertigation: Monitoring of pH and electrical conductivity of irrigation water; Soil: Measurement of soil moisture; Weather forecast: Probability of rainfall.

User interface

19th century

The user interface is the heart of all SCADA systems. Through the user interface it is possible to have access to all the monitoring and control elements of the irrigation and fertigation system.

A typical module of this interface will consist of a graphic scheme like the one shown in Figure 62.

Figure 61. The convenience to automate a production process basically depends on the resulting economic benefit (From: https://media.innovarurale.it, modif.)

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Report All data from both sensors and recordings during the operation of SCADA will be organized in appropriate reports that allow the operation of the system to be verified when requested. The reporting relating to the flow delivered to the sectors will be fundamental, also in relation to the information provided by the soil moisture sensors.

Alarms There are various levels of automatisms aimed at protecting the system from malfunctions and ensuring an efficient use of energy, water, and fertilizer. For this purpose, there are a number of alarms that have the effect of interrupting the irrigation service in order to preserve vulnerable and expensive elements of the system.

For example, excessive lowering of the water table can compromise the safety of the pump. An excessive number of filter backwashes is indicative of non-optimal operation and suggests that therefore it is necessary to intervene in order to maintain the proper functioning of the system.

Figure 62. Example of SCADA interface.

Other alarms detect simple inefficiencies, such as the failure to open a sector due to insufficient flow rate detected by the specific sensor in charge. This information is read by the system so as not to interrupt programming and go to the next sector. Particular attention must be paid to setting the alarms regarding the pressure switch data. It should be remembered that the operating pressure of the irrigation system is a design datum and that therefore the deviation of the operating conditions from this value, if it exceeds a certain threshold, represents an alarm. The detection of the anomaly indicates that it is necessary to intervene. The positioning of pressure switches in strategic positions allows complete control of the system. When design pressure is available in the most disadvantaged part of the system, then all the components, e.g., pump, filters, pipes, valves, emitters, are working as required by the project specifications.

From the interface the user can monitor the entire system and access, by simply clicking on the tabs, the control and command modules of the individual subsystems, e.g., fertigation, filters, irrigation sectors identified by block valves.

From each element of the system, it is possible to access the related settings. For example, for flow meters it will be possible to adjust the flow rate corresponding to each pulse launched according to the type of flow meter used. Each SCADA system designed for irrigation must have the following interfaces:

• • •

Scheduling Report Alarms

Scheduling From this interface it is possible to calendar the irrigations. Each irrigation can be planned in terms of duration according to the flow rate delivered to each sector. It will also be possible to foresee, from the operating logic of the SCADA, a certain degree of automatism on the basis of sensor inputs, such as rain gauges or soil moisture sensors. It is also possible to connect to weather forecasts, in order to adapt the irrigation scheduling according to both actual soil water and expected natural precipitations. The degree of automation must be planned during the SCADA settings.

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REFERENCES

Lavanholi, R., Oliveira, F.C., de Camargo, A.P., Frizzone, J.A., Molle, B. (2018) Methodology to evaluate dripper sensitivity to clogging due to solid particles: an assessment [Metodologija za procenu podložnosti kapaljki začepljenju zbog čvrstih čestica: procena]. The Scientific World Journal.

Limestone Coast Grape & Wine Council Inc., https://limestonecoastwine.com.au

Agricoplast website: https://www.agricolplast.it Alexandris, S., Stricevic, R., Petkovic, S. (2008) Comparative analysis of reference evapotranspiration from the surface of rainfed grass in central Serbia, calculated by six empirical methods against the Penman-Monteith formula [Komparativna analiza referentne evapotranspiracije sa površine nenavodnjavanje trave u centralnoj Srbiji, sračunate pomoću šest empirijskih metoda u odnosu na Penman-Montitovu formulu], European Water 21-22: 17-28, E.W. Publications.

Allen, R.G., Pereira, L.S., Raes, D., Smith, M. (1998): Crop evapotranspiration-Guidelines for computing crop water requirements. [Evapotranspiracija useva – Smernice za proračunavanje vodnih potreba useva.] FAO Irrigation and Drainage Paper n.56, FAO Editions, Rome.

Anđelković, G., Jovanović, S., Manojlović, S., Samardžić, I., Živković, L., Šabić, D., Gatarić, D., Džinović, M. (2018): Extreme Precipitation Events in Serbia: Defining the Threshold Criteria for Emergency Preparedness.

[Pojava ekstremnih padavina u Srbiji: Definisanje graničnih kriterijuma za pripravnost u vanrednim situacijama] Atmosphere, 9, 188.

ARC-Institute for Agricultural Engineering (2010): Standards and Guidelines for Improved Efficiency of Irrigation Water Use from Dam Wall Release to Root Zone Application [Standardi i smernice za poboljšanu efikasnost upotrebe vode za navodnjavanje od izlaska iz zida brane do primene u korenskoj zoni], GUIDELINES-Report to the Water Research Commission, WRC REPORT NO. TT 466/10, WRC Project No K5/1482/4).

Morari, F., Camarotto, C., Giardini L. (2004): Un impianto a misura d’acqua, Acer n. 3/04, pp. 57-61, ed. Il Verde Editoriale, Milano.

Reinders, F.B. (2011): Irrigation methods for efficient water application: 40 years of South African research excellence, in: WRC 40 Year Celebration Special Edition, Vol. 37 N. 5, pp. 765-770, ISSN 1816-7950, Water SA. Reinders, F.B., Grové, B., Benadé, N., Van Der Stoep, I., Van Niekerk, A. (2012): Technical aspects and cost estimating procedures of surface and subsurface drip irrigation systems-A manual for irrigation designers [Tehnički aspekti i postupci procene troškova za površinske i podzemne sisteme navodnjavanja kapanjem – Priručnik za projektante sistema navodnjavanja]. WRC report no. TT 525/12, ISBN 978-1-4312-0274-4.

System Group website: https://tubi.net/aziende/centraltubi/ Tecnoresine website: https://www.tecnoresine.net Van Niekerk, A.S., Koegelenberg, F.H., Reinders, F.B., Ascough, G.W. (2006): Guidelines for the selection and use of various micro-irrigation filters with regards to filtering and backwashing efficiency [Smernice za odabir i upotrebu različitih filtera za mikro navodnjavanje sa osvrtom na filtriranje i ispiranje]. Water Research Commission, ISBN 1-77005-468-5.

Bucks, D.A., Nakayama, F.S., Gilbert, R.G. (1979): Trickle irrigation water quality and preventive maintenance [Kvalitet vode za navodnjavanje kapanjem i

World Bank Group https://climateknowledgeportal.worldbank.org/

preventivno održavanje]. USA: Agric. Water Management.

Burger, J.H., Heyns, P.J., Hoffman, E., Kleynhans, E.P.J., Koegelenberg, F.H., Lategan, M.T., Mulder, D.J., Smal, H.S., Stimie, C.M., Uys, W.J., Van der Merwe, F.P.J., Van der Stoep, I., Viljoen, P. (2003): Irrigation Design Manual [Priručnik za projektovanje navodnjavanja]. Agricultural Research Council – Institute for Agricultural Engineering. RSA. Charlesworth, P. (2000): Soil Water Monitoring. Irrigation Insights.[Osmatranje vode u tlu. Uvid u navodnjavanje.]

Paper No. 1. Canberra, Australia: CSIRO Land and Water.

Ghinassi G. (2008): Manual for performance evaluation of sprinkler and drip irrigation systems [Priručnik za ocenu učinka sistema navodnjavanja sprinklerima i kapanjem]. ISBN: 81-89610-11-2, ICID publication no.94, New Delhi.

Grundfos (2004): Pump handbook [Priručnik za pumpu]. Grundfos Management A/S. Bjerringbro, Denmark.

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APPENDIX 1

APPENDIX 2

Summary of issues and guidelines for system planning; water, soil, and farm size.

Planning and design procedures for drip irrigation.

PLANNING

Issue

Guideline

Soil and water quality

Assess the quality of water and soil according to standard guidelines and procedures. This evaluation should influence design parameter decisions

Project scale

• • • • • • • •

Water supply

• • • •

Water supply management

Energy for pumping

• • • • •

Security considerations

• • •

Learning phase

•

1

Determine irrigation requirement from reliable source of information

2

Calculate the cycle length, gross irrigation requirement per cycle, standing time and emitter discharge for the peak irrigation period

Determine the legalities of water use.

3

Select a suitable emitter from a manufacturer’s catalogue based on required emitter discharge

Use expected minimum supply, as determined by seasonal or other variations, as a design parameter.

4

Calculate the system discharge, number of groups/blocks and the group/block size

5

Undertake a preliminary block lay-out

6

Decide on required EU for the design according to the relevant norms to calculate the allowable emitter discharge variation

7

Calculate the allowable pressure variation in a block and divide between laterals and branch line (Manifold: 0.5 m; Lateral: remaining part of Δp, this division be used as starting point)

8

Determine optimum lateral position along the length of the manifold

9

Determine the lateral pipe size taking topographic slope into account

Base the choice of system on the total volume of water required during the various stages of growth of the crops to be grown, the flow rate and the pressure available.

10

Calculate the required lateral inlet pressures and actual Δp (compare with allowable)

11

If the actual pressure variation is too big, choose larger diameter pipes or change block dimensions

Subdivide irrigation blocks into smaller sub-units when pressure or flow rates are subject to considerable variations.

12

Repeat steps 8 to 11 for each block

Small units will allow acceptable irrigation practice in each of the sub-units separately, even when pressure or flow rate is inadequate for the entire irrigation block.

13

Use remaining allowable pressure to determine suitable pipe sizes, taking topographic slope into account

Design safety measures into the system when the water supply is unreliable. This can include the building of a small water storage facility.

14

Check maximum discharge variation against allowable variation calculated in point 7

15

Calculate the required inlet pressure and discharge to each block

Pursue the option of having the water supply managed by a capable and experienced operator.

16

Select a suitable control valve (and secondary filter if applicable) for each block

Determine the supply of water, considering uses other than irrigation from the identified source.

Allow for a safety margin of at least 30% less than the minimum amount of water available at all times when determining the maximum area to be irrigated from the available source of water.

Use this safety margin to determine the size of the project for implementation at the initial stage. However, allow for expansion by designing for the full area that can be irrigated from the available supply.

Assess the reliability of the water supply. Determine the cause where unreliable.

Take the reliability of the water supply into account especially in climates characterised by high evaporative demand, or when soils have a low water holding capacity.

Avoid using drip irrigation when the reliability of the water supply is not ensured, when dealing with soils with low water holding capacity, or in areas where evaporative demand is high.

Ensure a well-functioning support system when a capable and experienced operator to manage the supply system is not available.

Use electricity driven motors where possible.

Ensure adequate hands-on training for operators of pump systems to perform routine maintenance and simple repairs Discourage theft by using components made of materials that have no inherent resale value wherever possible.

Design for the locking away of expensive system components.

HYDRAULIC DESIGN

LATERAL DESIGN

MANIFOLD DESIGN

17 18

Calculate most economic diameter for main line

19

Select available pipe sizes, calculate the hydraulic gradient, and select correct pipe classes

20

Determine maximum pressure and discharge required at the source (pump duty point) NON-CRITICAL PATH MAIN LINE DESIGN

21

Plan for sub-surface installation of immobile system components whilst avoiding measures which compromise system flexibility.

Plan for the planting of crops which are relatively insensitive to suboptimal water supply during the initial phases of implementation, allowing farmers to develop confidence to later try highvalue crops which are more sensitive to water stress.

Take the financial risk to farmers into account should the first planting fail and evaluate the effect of such an event on the survival of the enterprise as a whole. When this risk is unacceptably high, introduce intermediate steps (small introduction plots) or when this is not feasible, reconsider the desirability of drip irrigation.

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Repeat for all blocks MAIN LINE DESIGN (ON CRITICAL PATH FROM PUMP TO HYDRAULICALLY MOST REMOTE BLOCK INLET)

Use up available pressure difference from critical path take-off point to point of application to size the sub-mainlines to the block inlets WATER SUPPLY SYSTEM AND ACCESSORIES

22

Select, position and size suitable air valves for the whole system

23

Select a suitable primary filter or filter bank

24

Select suitable control and automation accessories for the pump station

25

Determine a suitable suction pipe size

26

Choose pump and motor to satisfy the peak system requirement

27

Calculate maximum static suction head for installation

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NOTES

NOTES

NOTES