Improving Irrigation Water productivity Ahmed Hachum, Professor Irrigation Eng. & Water Management October 9, 2011 – Mosul, IRAQ
Water is Life Our daily per capita domestic water needs ranges from few liters (in some African countries) to as high as 550 liters (in the USA), with a worldwide mean of 30 to 50 liters (including all house activities: drinking, cocking, cleaning, washing, bathing, etc‌). However, it takes 2000 - 5000 liters of water to produce a person's daily food. In other words, it takes roughly 70 to100 times more water to produce food than people need for domestic purposes. That is why agriculture is consuming almost 70 percent of all world water withdrawals, and up to 95 percent in developing countries. Currently in WANA region, agriculture accounts for more than 80% of all available fresh water of the region.
What is the problem???!!! The world’s population is growing by about 80 million people a year, implying increased freshwater demand of about 64 billion cubic meters a year. An estimated 90% of the 3 billion people who are expected to be added to the population by 2050 will be in developing countries. This is one of the main reason for the crisis of water scarcity or shortage. The other main reasons include: *The amount of water of the globe is finite and fixed, but the distribution varies with space and time. *Improved life style and eating habits *Increased demand for water from industry, domestic, and environment put great pressure on water for agriculture and food production. *Climate change/warming exerts more pressure on water for agriculture. * Deterioration of water quality of available fresh water.
Annual renewable water share
18000
Latin America and Canada: 120 000 m3/capita/year 16000
Per capita annual m3
16000 14000 12000 10000 8000
7000
6000
5000
4000 2000
2000 0
170 Jordan
WANA
Europe
World North America
Declining agricultural water Share % Agriculture share of total Total available water per capita Agriculture share of water per capita
85
1000
100
80
90
70
80 70
800
53
600
60 50 40
400
30 20
200
10 0
0 1990
2000
2025
2050
% of total water resources
Cubic m eter per capita
1200
Typical furrow irrigation system
Sprinkler irrigation One can under irrigate No DP / 100% application Eff 50% storage Eff.
One can over irrigate 100% storage efficiency 50 % application efficiency
Trickle irrigation • Under irrigation – Application eff. 100% – Storage eff. 50%
• Over irrigation – Application eff. 50% – Storage eff. 100%
Water stored (mm) Application Efficiency =---------------------------x100% Water applied (mm)
Ignores recoverable losses Nothing to do with return to water %
Water stored (mm) Storage efficiency = -----------------------------100% Water needed (mm)
Reflects how full is the root zone Ignores deep percolation Nothing to do with return to water %
Water productivity: the new concept
Return WP = --------------------------------Unit of water consumed
What water ?? Quality (EC) Location (GW depth) Time available
What return ?? Biomass, grain, meat, milk (kg) Income ($) Environmental benefits (C) Social benefits (employment) Energy (Cal) Nutrition (protein, carbohydrates, fat) Consumed (depleted) Evaporation Transpiration Quality deterioration
Field water balance Transpiration Precipitation
Runoff recoverable
Evaporation Losses
Irrigation
Storage Drainage Partially recoverable Quality losses
Seepage recoverable Deep percolation
To ground water recoverable
Standardizing water quality Equivalence of one cubic meter of fresh water
EC (dS/m) 1.0
Wheat
Barley
Tomato
Beans
1
1
1
1
2.0
1
1
1
1.25
4.0
1
1
1.25
3.2
8.0
1.2
1
3.2
10
12.0
1.72
1.25
10
??????
Potential WP improvements China Loess Plateau Mediterranean Basin 6 North American Great Plains n = 691 Source: The Comprehensive Assessment of Water Management SE Australia 22 x (water use - 60) Breeding: improve 5 1.2
Yield (t/ha)
1
4
fundamental processes
Biomass/T
0.8
Increase harvest index
Yield/T
Vapor shift from E to T
3 0.6 Yield/ET (“Lower YRB”)
0.4
2
0.2 Yield/ET (“Sahel”)
0
1
.-25
0
Now
Biomass/T
0
100
Yield/T
200
300
.+ 25
.+ 50
Yield/ET (high)
400
Water use (mm)
500
Yield/ET (low)
600 Sadras and Angus
Irrigation systems • Does not guarantee high WUE • Surface irrigation can be as efficient as other systems • Helps if management is appropriate • Saving should be in real losses (E, EC) • More contribution to water productivity
Case Study (4 ha farm) Farmer's practice
100% irrigation
Rainfed
50% irrigation
16.6 12.5
10.8
P
d
W ax
M
M
ax
yi
rm Fa
in fe
el
er
7.2
d
18 16 14 12 10 8 6 4 2 0
Ra
• Limited water supply 50% of full irrigation requirements • 33% higher farm production by maximizing WP over maximizing yield
4-ha farm total production (ton)
4-ha farm - wheat grain
Yield
WUE= Yield/Water
Y= a + bw + c w2
Max Yield Max WUE
W of Max WUE =SQRT (- a/ c)
W of Max Yield = - b/2c
Water
WUE
Example: Y = -9500 + 58 w – 0.054 w2 Depth of seasonal irrigation water that maximizes yield per unit area (kg/ha) = - b / 2c = - 58/ (2 * 0.054) = 537 mm Max Y = -9500 + 58* 537 – 0.054* (537)2 = 6074 kg/ha. Depth of seasonal water that maximizes WUE (WP) = (a/ c) ½ = (-9500/- 0.054) ½ = 420 mm Yield at maximum WUE = Y = -9500 + 58 w – 0.054 w2 = -9500 + 58 * 420 – 0.054 (420) 2= 5334 kg/ha But: 5334 * (537/420) = 6827 kg > 6074 kg from the same amount of irrigation water.
Calculate WP for each case and compare: WP when we maximize Yield per unit area= Yield per hectare /(Volume of water applied/ha) = 6074/(537 * 10) = 1.13 kg of wheat grain/m3 water WP when we maximize Yield per unit water (1 m3) = 5334/(420 * 10) = 1.27 kg of wheat grain/m3 water
Basic Performance Indices of Farm Irrigation Systems Uniformity of water distribution
Adequacy of irrigation Farm Water Management
Efficiency of Irrigation
Y= a + bw + c w2 This is for 100% uniformity For non-unifrom irrigation, total yield (Production) is: Y = a + bw + c w2 – c v2 Where v= standard deviation of the depths of irrigation water applied to different points in the field
Y/ W = S / P Y= a + bw + c w2 Y/ W = b + 2c W = S/P >>>>>> = 0 Therefore the amount of seasonal irrigation water that maximizes the net economical return = [(-b + (S/P)]/2c = - [b – (S/P)]/2c Note that since c is always negative, the W for maximum net economic return is always is less than the W that maximizes the yield per unit area. Meantime, this W value is greater than W that maximizes WP. Therefore, it is in between.
Effect of Field Irrigation uniformity on crop yield and Consequently on Field WP
Y = a + bw + c w2 – c v2 Y= -9500 + 58 w – 0.054 w2 – 0.054 v2 If you know the irrigation uniformity (UC), then v = 1.25 (mean W) (1 – UC) If UC= 80% = 0.8 Mean w (mm)
v (mm)
Yield (UC = 100%)
Yield (UC = 80%) (Kg/ha)
WP Kg/m3
420
105
5334
5334 – 595 =4739
1.13
491
123
5960
5960 – 817 =5143
1.04
537
134
6074
6074 – 970 =5104
0.95