Contribution of Locally Manufactured Organic Fertilizers to Soil Environment
1. Introduction In the past few decades, chemical fertilizers have come into widespread use throughout the Asian and Pacific region. This strong focus on chemical fertilizer use has meant that the soil has tended to be regarded as an inert medium for plant roots, rather than as a living biosphere in which the crop is only one of hundreds or thousands of interacting species. However, it is now realized that in fields under intensive monoculture which receive heavy applications of chemical fertilizers alone, there is a slow decline in productivity. This decline occurs even in irrigated crop fields. In the light of these problems, we are beginning to see agriculture in a new perspective. Modern agriculture is seen, not just as a series of a technical problem for human beings to solve, but as a process which has a long-term effect on the environment. This effect must be a beneficial one if agriculture is to be sustainable in the long term. The use of organic fertilizers and microbial materials is an important part of this new attempt to make agriculture a viable part of a healthy ecosystem. Continued depletion of plant nutrients and organic matter in the soil and inadequate availability of soil moisture for crop growth, especially under dryland conditions, are major problems affecting sustainable crop production in many countries. The use of organic fertilizers and water-retaining products, if economically viable, may contribute to overcome these constraints and improve land productivity. In the present work two locally manufactured organic fertilizers were tested for their contribution towards plant growth and soil properties as well.
2. Organic Fertilizer The use of organic manures was widely practiced in Asia in irrigated rice in the past, but the interest declined with the increase in cropping intensity and ready availability of chemical fertilizers in the last few decades. With energy shortages, increased fertilizer cost, deterioration in soil health and environmental concerns, the use of organic manures has again become important. Over a longer period of time, applications of organic materials such as
livestock manure and crop residues have been found to bring about a gradual improvement in soil productivity and crop performance (Allison, 1978). Materials of plant and animal origin that are applied to the soil for increasing the yields of crops are called organic fertilizers. These are generally voluminous substances used in the raw or processed condition. An organic fertilizer is derived from natural sources and guarantees the minimum percentages of nitrogen, phosphate, and potash (BARC, 1997). Other definitions are available, but they do not specify minimum nutrient content. â€˘ â€˘
Carbonaceous material mainly of vegetable and/or animal origin added to the soil specifically for the nutrition of plants [The International Organization for Standardization (ISO), 1980]. By product from the processing of animals or vegetable substances that contains sufficient plant nutrients to be of value as fertilizers [The Soil Science Society of America (SSSA), 1984]. (web1)
Naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed, sewage , and guano. Naturally occurring minerals such as mine rock phosphate, sulfate of potash and limestone are also considered organic fertilizers. Manufactured organic fertilizers include compost, bloodmeal, bone meal and seaweed extracts. Other examples are natural enzyme digested proteins, fish meal, and feather meal (FAO, 2006).
3. Types of Organic Fertilizers All organic fertilizers are not alike. Some feature one product source, such as greensand, while others are a blend of organic materials. However, most fit into one of the basic categories -- plant, animal, mineral, or compost.
3.1. Plant Substances These fertilizers (e.g., alfalfa meal, cottonseed meal, corn gluten meal) are often rich in
Alfalfa Cotton seed
Corn gluten meal Specific nutrients, such as nitrogen. They can be considered renewable resources, but we should take into account the resources that are used to grow as well as process or transport them. Some, such as cottonseed meal, are by-products of other industries. 3.1.1 Green Manures
Green manures are derived from plants, either as ground-up plant products, whole plants, or as cover crops. Green manures have a higher carbon to nitrogen ratio than most animal manures (except manures with a lot of bedding material), and thus are excellent for improving soil structure. Additions of the more woody materials, such as wheat straw, sawdust, wood shavings, and composted yard waste, should be accompanied by addition of more nitrogenous materials, such as animal manures or leguminous crops. Plants that have deep root system, grow more quickly with little care and produce large quantities of biomass are desirable as green manure. Spices that are commonly used in Bangladesh include Dhaincha (Sesbania aculeata, Sesbania rostata), Sunhemp (Crotalaria juncea) and Cowpea (Vigna unguilata).The kharif season in Bangladesh is more favourable than the rabi seasons for growing green manure crops (BARC, 1997). Some of the wild plants used as green manure are presented in Table 1.
Table 1: Wild Plants Used for Green Manuring and Their Nutrient Content (Maskey and Bhattarai, 1984) Plants Titepati (Artemisia vulgaris) Asuro (Adhatoda vasica) Taramandal (Helianthus annus) Banmara (Eupatorium Adenophorum)
Nutrient Content (%) N2 2.40 4.30 4.90 2.35
P2O5 0.42 0.88 0.87 0.71
K2O 4.90 4.49 5.23 -
3.1.2. Cover Crops
Plants (crops) seeded, grown, and then plowed into the garden soil to provide green manure is called cover crops. By cover cropping, we can provide all of the benefits of adding organic matter, plus help recover/recycle nutrients from past seasons. And, by planting a legume as cover crop, we can actually supply additional nitrogen. Legumes form nodules on their roots; inside the nodules, bacteria convert atmospheric nitrogen to forms of nitrogen that the plant can use. To be most beneficial to the garden, the cover crop must be plowed down (or added to a compost pile) so that this "captured" nitrogen can be released by the process of nitrification. 3.1.3. Living Mulches
One old organic practice is the use of living mulch. The idea is to first sow a green manure crop (leguminous preferred) on the plot, followed by the setting of vegetable plants throughout the plot and into the established living mulch. Experience with living mulches (vetch and ryegrass combined) has shown a negative effect on the growing crop unless sufficient organic fertilizer is also applied at planting time.
3.2. Animal-Derived Products It includes the excreta (dung & urine) of the domestic animals. Stubbles used as bedding of animals also become part of the manure. In Bangladesh, cow dung is the most important animal manure, although a big portion of the cow dung produced in the country used as fuel. Fresh animal manure should not be applied to standing crops, because the heat generated during the vigorous decomposition that follows immediately after application is harmful for the young roots (BARC, 1997).
Animal manures vary greatly in their content of fertilizing nutrients, depending on type, age, and condition of animal; kind of feed used; age and decomposition of manure; moisture content; and the litter accompanying the manure (Parr, et al., 1986). A variety of organic fertilizers are applied to the soil in different countries, but the following are the most important everywhere. The N, P, K contents of different organic materials is shown below (Table 2). Table 2: Organic manure & their nutrient composition (%) (BARC, 1997) Name of the organic manure Cow dung Poultry manure Farmyard manure Compost(general) Compost(Town) Compost(Water hyacinth) Dried Blood Bone Meal Fish Meal Mustard Oil Cake Groundnut Cake SeasameOil Cake Dhaincha Sunhemp
0.5-1.5 1.6 0.5-1.5 0.4-0.8 1-2 2-3
0.4-0.8 1.5 0.4-0.8 0.3-0.6 1 1-2
0.5-1.9 0.85 0.5-1.9 0.7-1.0 1.5 3-4
10-12 4 4-10 5.1-5.2 7-7.2 6.2-6.3 0.62 0.75
1.0-1.5 9 3-4 1.8-1.9 1.4-1.6 2.0-2.1 0.02 0.12
0.6-0.8 0.5-1.5 1.1-1.3 1.3-1.4 1.2-1.3 0.3 0.51
Cowpea Blackgram Mungbean Rice Straw Wheat Straw Weeds Ash
0.71 0.85 0.72 0.52 0.63 0.8 -
0.15 0.18 0.18 0.52 0.46 0.30 -
0.58 0.53 0.53 1.61 0.86 0.20 2.3-12
3.2.1. Other Animal-Based Products Other animal-based products are: Blood meal and animal tank age products derived from slaughter or meat processing plants.
Leather meal products derived from leather tanning and may contain chromates (unsuitable for gardens).
Fish meal / emulsions.
Crab waste crab remnants generally composted.
Mushroom compost waste product from the mushroom industry; contains 20% chicken litter. Raw meat can cause sanitation problems by drawing flies or scavengers, and causing odors (unsuitable for gardens).
Composting is a biochemical process converting various components in organic wastes into relatively stable humus-like substances that can be used as a soil amendment or organic fertilizer (Jeong and Kim, 2001). It helps improve the physical and chemical properties of the waste and reduce its phytotoxicity (Marchain et al., 1991). Composting is also considered one of the most suitable ways of disposing of unpleasant wastes and of increasing the amount of organic matter that can be used to restore and preserve the environment. The finished compost was rated as "stable" with minimum impact on soil C and N dynamics. Good compost should be tolerated readily by growing crops and should not interfere with root growth and development in the way which fresh manure can do. Composted organic materials, therefore, can act as slow-release sources of plant-available N (Stentiford, 1987).
The preparation with living or latent specific microbial strains that are associated with the cycling of N, P, C assisting the supply of plant nutrients are popularly known as biofertilizers. Blue Green Algae, Rhizobium, Azotobacter, Azospirillum, Vesicular Arbuscular Mycorrhizal Fungi (VAM) and Phosphobacter are the commonly known as of biofertilizer (Sarkar, et al., 1973).
3.5 Mineral-based fertilizers
Naturally occurring mineral fertilizers are considered organic only in the sense that they were not extensively processed. Among them are nitrate of soda, rock phosphate, greensand and iron sulfate.
4. Characteristics of Organic Fertilizer Organic nutrient sources are highly heterogeneous and vary in quality and quantity. The quality aspect is important in determining the nutrient release potential of the organic fertilizer. Microorganisms that decompose organic fertilizers use the carbon in such materials as an energy source for growth. Required in even bigger quantities by microorganisms for growth and reproduction is nitrogen (N). Commonly available materials are often particularly low in N content. For organic fertilizers with low N contents (such as cereal straw and most smallholder farmyard manures), microorganisms themselves will consume much of the available N for their own growth (Robertson and Morgan, 1995). Consequently, insignificant amounts of N will be released for the crop. Thus, on their own, poor quality materials have limited potential to enhance productivity. The effectiveness of such materials can be improved by combining them with mineral N fertilizers such as ammonium nitrate or urea.
Mineral fertilizers may be used more efficiently by crops growing on soils with adequate amounts of soil organic matter supplied by organic fertilizers. Nutrient contents can vary widely according to manure type (Titiloye et al., 1985) or compost materials. Organic matters added to soils contain a wide range of C compounds that vary in rates of decomposition. The biological breakdown of the added organic matter depends on the rate of degradation on each of the C-containing materials present in the sample (Reddy et al., 1980). Ajwa and Tabataba (1994) showed that the amount of CO 2-C releases increased rapidly initially, but the pattern differed among the organic materials used. Gilbertson et al. (1979) showed that the annual mineralization rate of organic N in animal manure was positively correlated with the N content of waste. Variation in environmental factors, however, may cause a change in the decomposition rates of organic materials in soils. Of these factors, moisture content, temperature, soil pH, aeration and soil structure and texture, agricultural practices (e.g., cultivation), substrate specificity, and available minerals have been reported to be most important (Broadbent et al., 1964). Most of the N found in a composting mixture is organic, principally as part of the structure of proteins and simple peptides. The proportion of added organic matter that is mineralized after compost application ranks from several up to a hundred percent, depending on experimental conditions and compost types. Hadas and Pornoy (1994) reported that the mineralization constant for composted manure was commonly 5% to 10% per year. They also found that an average of 66% of the organic N in poultry manure was mineralized in the first year. Cabrera et al. (1994) confirmed this rapid mineralization from poultry manure, estimating that 35% to 50% of organic N could be mineralized within 14 days of incorporation into soil. Griffin and Honeycutt (2000) reported that the amount of N in manure mineralized in a cropping season varied with the different manures: cattle manure, 25%; dairy manure, 35%; poultry manure, 60%; and swine manure, 50%. Chicken manure is one of the most economically efficient types of manure. This efficiency is due to its high pH, low organic C, high inorganic N, and low C: N ratio compared with the other types of manure. In practice, in order to increase soil fertility on the basis of crop N requirement, organic materials of low C: N ratios such as seed cake, or poultry manure are the better choice. The optimum C: N ratio for finished compost is about 15:1. On the other hand, when the significant organic C accumulation is more important, the organic manure of higher C: N ratio such as bark compost, compost with a higher proportion of woody materials, or cattle manure would be better (Stentiford, 1987).
5. Fundamentals of Organic Fertilizer Application Just like chemical fertilizers, adequate organic fertilization programs supply the amount of plant nutrients needed to maximize crop production and net return. Essentially, fertilization management makes certain that soil fertility is not a limiting factor in crop production. The major factors that affect the selection of the kind, rate, and placement of organic fertilizers are fertilizer characteristics, crop characteristics, soil characteristics and management, fertilizer placement, and carryover effects. Manure application in excess of crop needs can cause a significant buildup of P, N, other ions, and salts in the soil. Cabrera et al. (1994) showed that cattle feedlot manure application for 20 years resulted in a significant increase in soil P levels (from9 mg/kg to 1,200 mg/kg).
The research work of Hao et al. (2003) showed that the high application rate of manure resulted in considerable nitrate N accumulation, reaching 80-100 mg/kg. General application rates for compost or other organic soil amendments are based on the salt content of the materials and soil and on the depth to which it is cultivated into the soil. Ideally, the soil amendment is cultivated into the top six to eight inches of the soil. On compacted/clayey soils, anything less can lead to a shallow rooting system with reduced plant growth, lower vigor, and lower stress tolerance. In Table 3, given below, are presented recommendations for organic fertilizers. Table 3: Organic Fertilizer Recommendations (Stentiford, 1987) Recommendations Nitrogen 1 Needed for for 5 lbs. of 5-10-15 Inorganic From Organic Source Fertilizers
Phosphorus Needed for 5 lbs. of 5-10-15 From Organic Source
5 lbs. 5-10-15 2.0 lbs. blood meal (using component 8.3 lbs. alfalfa meal fertilizers) 4.2 lbs. cotton seed meal 2.0 lbs. feather meal 2.5 lbs. fish meal 2.0 lbs. hoof meal 8.0 lbs. of cricket manure 4.0 lbs soybean meal
4.5 lbs. bone meal 3.1 lbs. Sul-Po-Mag 1.4 lbs. colloidal 15.0 lbs. greensand phosphate 15.0 lbs. granite dust 25.0 lbs. kelp
Nitrogen Needed for 5 lbs. of 6-12-12 5 lbs 6-12-12 2.0 lbs. blood meal (using component 10.0 lbs. alfalfa meal fertilizers) 5.0 lbs. cotton seed meal 2.0 lbs. feather meal 2.5 lbs. fish meal 2.5 lbs. hoof meal 10.0 lbs. of cricket manure 3.7 lbs soybean meal
Phosphorus Needed for 5 lbs. of 6-12-12
Potassium Needed for 5 lbs. of 5-10-15 From Organic Source
Potassium Needed for 5 lbs. of 6-12-12
5.5 lbs. bone meal 2.7 lbs Sul-Po-Mag 3.0 lbs. colloidal 12.0 lbs. greensand phosphate 12.0 lbs. granite dust 20.0 lbs. kelp
Nitrogen, Phosphorus and Potassium Needed for 5 lbs. of 10-10-10 5 lbs. 10-10-10 33.3 lbs. of compost (1.5-1-1.5) (for even analysis 33.0 lbs. of 30% poultry manure (3-2.5-1.5) fertilizers) 50 lbs of Fertrell 1-1-1 Nitrogen Needed for 5 lbs. of 10-10-10 Phosphorus Needed for 5 lbs. of 10-10-10 5 lbs. 10-10-10 4.2 lbs. blood meal (using component 17.0 lbs. alfalfa meal fertilizers) 8.3 lbs. cotton seed meal 3.3 lbs. feather meal 5.0 lbs. fish meal 4.2 lbs. hoof meal
Potassium Needed for 5 lbs. of 10-10-10
4.5 lbs. bone meal 2.3 lbs. Sul-Po-Mag 2.8 lbs. colloidal 10 lbs. greensand phosphate 16.6 lbs. of kelp
16.7 lbs. of cricket manure 7.5 lbs soybean meal 1
Use only one of these amounts of fertilizer materials to equal 5 lbs. of nitrogen or use one-half of 2 different materials to make up the 5 lbs. of nitrogen required. The same process can be used for any other nutrient in the chart.
6. Nutrient Release Rates from Compost and Manure An ideal agricultural soil can contain as much as 5% organic matter by weight. However, an increase in soil organic matter content increases the risks of nutrient losses to the environment. Organic matter losses can be as great as 1.5% annually. Insufficient knowledge of specific fertilizer values and inadequate application rates can result in under or over use (Reddy et al., 1980). The ultimate purpose of applying organic fertilizer is to establish the suitable soil organic matter content. High initial applications to build up the organic pool and cut back in subsequent years would be appropriate (Titiloye et al., 1985). The typical nitrogen release rates from manure is only 30% to 50% the first year (fresh manure), 15% to 25% the second year, 7% to 12% the third year, 3% to 6% the fourth year, and so on. With compost and composted manure, the release rate is even slower, 5% to 25% the first year, 3% to 12% the second year and 1% to 6% the third year. Since the nitrogen percentage of compost and manure products is typically only 2% to 4%, the amount of actual nitrogen release to support crop growth is very small. For soil with 4% to 5% organic matter, the mineralization (release) of nitrogen from soil organic matter will likely be sufficient for crop growth. For soils with 2% to 3% organic matter, the mineralization of nitrogen from soil organic matter will not likely be sufficient for heavy feeding vegetable crops. Some locally manufactured organic fertilizers of Bangladesh are presented in Table 4. Table 4: Some Common locally manufactured organic fertilizers in Bangladesh (Ministry of Agriculture, 2006) Organic fertilizer E-2001 Microsoil (Biofertilizer) BINA Zibanusar Chook Chook Chuk-Chuk Northern Organic fertilizer Northern Shakti Sar Megna Organic fertilizer
Crops Wheat, Tomato, Potato & Rabi crops Rabi crop Pulse, Lentil, Pea-nut, Gram, Soybean Tomato Banana Tea For all vegetables, Cotton, Jute, Tea Lentil, Cholla, Soybean, Vegetables
7. Effect of organic fertilizer on soil
Most important use of organic fertilizer is itâ€™s application to soil. This can take several forms: it can be used as fertilizer, as a soil conditioner, as mulch and can be used as a means of land reclamation. It may be added to soil for many purposes: Urban agriculture, horticulture, home gardening, vegetable gardening, viticulture, landscaping, landfills, forestry or commercial farming. (Polprasert, 1989).The role of organic matter in crop production is well known. Soil rich in organic matter are generally more productive, than those poor in organic matter. The restorative ability of various amendments was assessed by Francis and Janzen (1996) by using plant dry matter. They found that the beneficial effects of manure in restoring soil productivity were much larger than those from inorganic fertilizer.
7.1 Effect of organic fertilizer on soil physical conditions Organic fertilizer has positive effect on soil physical conditions. The benefit of adding manures and composts to soils have been documented extensively in the literature (Bishop et al., 1964). They observed that a greater than additive effect occurs when organic matter and fertilizer are added together. It improves the soil structure, aeration system and increases the availability of nutrient elements (Stevenson, 1986).The productivity of agricultural land can often be increases by application of sewage sludges, when provide essential macro and micronutrients for plant growth and improve the soil physical properties (Epstein et al., 1976). The addition of plant residues may change the decomposition rate of soil organic matter. This change was reffered to as priming effect. The priming effect usually resulted in an accelerated decomposition when decomposition takes place, many gelatinous like substances are released, improve soil structure, aeration, porosity as well as soil productivity. But some reports indicated negative or decreased decomposition (Broadbent, et al.,1964).Compost has a nutritional function in that it serves as a reservoir of N, P and S for plant growth, a physical function in that it promotes good soil structure and biological function in that it serves as a source of energy of micro-organisms (Stevenson,1986). Organic fertilizer plays a role in soil physical properties. It maintain the humus balance in the soil, which improves the structure of the soil, helps to bind nutrients, ensures the proper circulation of air and water and is thus indispensable for the growth of healthy crops. When organic fertilizer is applies around the plant, it has a mulching effect which includes moisture holding capacity, prevention of weeds and reduction of soil erosion. The greatest improvement in soil physical properties occurs in sandy and clay soils (Polprasert, 1989). Recommended rate of application of a compost for various soil conditions are shown below (Table 5)
Table 5: Recommended rate of application of a compost for various soil conditions (Gaur, 1975)
Soil Sand or gravel Sand or gravel Clay, clay loam Silty-clay loam Disturbed soils
Surface or ground water condition Shallow depth to ground water (less than 120 cm)with no intervening soil Deep ground water(over 180cm)heavier material intervening Shallow ground water Deep ground water Deep ground water
Plant or crop Grass or shrubs Grass, shrubs, cereals, cotton
Compost Rate t/ha/year 50-100 50-100
Grass 50-100 Grass ,turf 50-200 Parks, highway 100-3000 tilled construction into upper 10 cm sites Generally beef cattle feedlot manure contains 15% C that can be used to improve soil physical and chemical properties. Carbon in manure is likely to have far greater value than the nutrients it contains if applied to a low organic matter or eroded soil. Many studies have been done on the relation between organic matter and soil structure. Organic matter content has been found to be a reliable index of crop productively in semiarid regions, because it positively affects soil water holding capacity (Mc Daniel and Munn, 1985).
7.2 Effect of organic fertilizer on soil chemical composition Organic fertilizer has positive effects on soil chemical compositions. Some relevant findings of various scientists are given below: Many chemical properties of soil may be changed due to application of compost. The properties change due to several properties of compost and its composition. From 20-70% of the exchange capacity of the soil is due to colloidal humic substances (Stevenson, 1986).The addition of Municipal solid waste compost to soil to increase cation exchange capacity (Paino et al., 1996).Humus exhibits buffering over a wide pH range. The following properties of soil change due to application of organic fertilizer. 7.2.1 Soil reaction change At favorable soil environmental condition, decomposition of organic fertilizer may take place. As a result many organic acids are produced and are responsible for pH change. Moreover, during decomposition of organic fertilizer, CO2 is produced. When this CO2 comes in direct contact with water, carbonic acid is formed and changes the soil pH OM+O2â†’H2O+CO2â†’H3CO3 As organic matter decomposes, both organic and inorganic acids are formed. The simplest and perhaps the most widely found is carbonic acid, a product of the reaction of carbon dioxide and water. The slow but persistent solvent action of carbonic acid on the mineral constituents of the soil is responsible for the removal of large quantities of base-forming cations (e.g., Ca2+ and Mg2+) by dissolution and leaching. Much stronger organic acids, from the very simple to more complexes, are products of microbial decay. Inorganic acids such as sulfuric acid (H2SO4) and nitric acid (HNO3) are potent suppliers of hydrogen ions in the soil. In fact, these acids, along with strong organic acids, encourage the
development of moderately and strongly acidic conditions. Sulfuric and nitric acids are formed not only by the organic decay processes, but also from the microbial action on certain inorganic sulfur and nitrogen containing materials such as elemental sulfur, ammonium nitrate and ammonium sulfate (Brady,1999). Maynard (1995) carried out an experiment and found that pH of the soil increased after addition of Municipal solid waste compost. Soil pH has a strong effect on both dissolution and fixation of inorganic P. Sludge addition and subsequent transformation of N and other constituents may strongly affect the soil pH. 7.2.2 Change in the concentration of N and P in soil Organic fertilizer has effects on the availability of nutrient elements in soil. The availability changes due to mineralization or immobilization of organic matter. Compost contains huge amount of N, P, K, S and other essential trace elements in organic forms. Conversion of these organic forms to available mineral forms (NH 4+, NO3-, PO4, etc.) occurs through the activity of micro-organisms. This process is reffered to as mineralization and is nearly always accompanied by conversion of mineral forms of nutrients to organic forms or immobilization (Stevenson, 1986). The amounts of N released from different organic sources have been related to both their total N content and C/N ratios. In a study, the average restoration percentage (1992-94) of nine amendment materials showed a significant linear relationship with the total N content of the amendments. The higher the total N contents of the amendment, the greater its restorative ability. It has been found that application of Municipal solid waste compost may lead to the immobilization of the soil mineral nitrogen and can cause N deficiencies in plants and depress crop yield (Frankenberger and Abdelmagid, 1985). Nuruzzaman et al., (1998) found that tannery waste and effluent contain high level of N, P, S and high organic matter content. The concentration of these elements was hazardous level. Francis and Janzen (1996) found cattle manure containing wood shavings was not as effective in restoring soil productivity as the other types cattle manure. This was probably due to its lower N content and higher C/N ratio. They also found that Municipal solid waste compost could enhance soil organic matter and crop nutrient supply. A large amount of P is recycled annually through aboveground and below ground plant residues. The P contained in crop residues or in a legume green manure incorporated into soil, can increase available soil P. Manure application in excess of crop needs can cause a significant build up of N, P and other ions, and salt in soils. Cattle feedlot manure application for 20 years resulted in significant increases in soil P level (Frankenberger and Abdelmagid, 1985). 7.2.3 Reduction in the Concentration of Heavy Metals in Soil Heavy metals and their salts occur naturally in the environment. Heavy metals are nondegradable, persist in the nature for long periods and are toxic to living organism at fairly low concentration. The concentration of heavy metals in soil may be changed due to application of compost. Compost can effectively be used on contaminated soils. The addition of organic matter such as well-aged compost, by at least 25% by volume, plus keeping the soil pH level above 6.5-7.0, prevents the uptake of heavy metals by plant roots (Aina and Egolum, 1980).
Among the soil environmental factors, soil temperature and organic matter are known to affect the trace metals transfer between soil phases. Organic substances are essentially a mixture of compounds with different molecular weights. However, at higher soil pH levels, dissolved organics can increase the solubility of metal ions by formation of soluble organometallic complexes, which compete with the solid phases for metal ions (Wade, 1986b). 7.2.4 Increase in the Concentration of Heavy Metals in Soils The concentration of heavy metals in soil increases due to application of compost, containing high concentration of heavy metals. When the concentration is excessive, it shows toxic effect. The concentration of trace metals in sewage sludge is potential hazard in many of the disposal methods currently being employed. A suggested method for sewage sludge disposal is application to agricultural land. Sludge amendments substitute for or supplement N and P fertilization and have beneficial effect on soil physical condition. It is inherent in the nature of most sewage sludges, however to have elevated levels of potentially phytotoxic trace elements. Land application of sewage sludge compost can be restricted, however by pathogen considerations and by excessively high heavy metal levels which lead to undesirable metal accumulations in plants (Mc Daniel and Munn, 1985).
7.3 Effect of organic fertilizer on Soil Biological Conditions Organic fertilizer serves as a source of energy for both macro and micro-organisms. The number of bacteria, actinomycetes and fungi in the soil are related in a general way to compost (humus) content; macro faunal organisms are similarly affected (Stevenson, 1986).When microbial activity is optimum the growth of plant is also optimum. The role played by the soil fauna has not been completely elaborated, but the functions they perform are multiple and varied. For instance, earthworms may be important agents in producing good soil structure. They construct extensive channels through the soil that serve not only to loosen the soil but also to improve drainage and aeration. Earthworms can flourish only in soils that are well provided with organic matter. The addition of Municipal solid waste compost can increase soil microbia and enzymatic activities in the soil (Frankenberger and Abdelmagid, 1985).
7.4. Effect of organic fertilizer on plant growth Addition of composts and manures to soil has often resulted in increase plant yields. Beef cattle feedlot manure or compost manure can be effectively used for crop production. It was found that application of beef feedlot manure and composted feedlot manure resulted in corn silage yield similar to yield from commercial fertilizer application (Stevenson, 1986). Composts contain macronutrients such as P that may contribute to greater yield. Sandy soil occasionally responded to amendments of organic material and produced better yields especially under droughty conditions (Epstein et al., 1976). Nuruzzaman et al., (1998) demonstrated that compost addition to soils provided protection of lettuee (Lactuca sativa L) from leaf wilt through the addition of competing microbial populations. Some compost adds lime, which resulted in greater yields in acid soils.Due to addition of organic matter in soil, decomposition rate may change; it may be decreased or increased. Increased decomposition
of soil organic matter could cause increased yields and N uptake by plants grown in soils amended with composts. Table 6 provides information on the recommended compost application rates to lawns, cereals, pastures and tree nurseries. The amount of compost need for agronomic crops depends on the nitrogen requirement of the crops as well as nitrogen content of the soils.
Table 6: Recommended rates of application of compost for different crops (Gaur, 1975) Plant or crop Sod, turf, new lawns
Compost rate t/ha/year 100-200
Established lawns Cereals, cotton and agronomy crops Tree nurseries pasture
50-75 As required by the specific crop.eg.corn-50 50-100 50-100 depending on species
Method of application Till into surface layer preior to seedling Apply to surface Till into soil prior to planting Till into soil before planting Till into soil before planting or on to surface
8. Precautions When Using Organic Fertilizer and Manure Manure, compost made from manure, and bio-solids may be high in salts that will interfere with crop growth. It is usually recommended not to add more than one inch per season without conducting a soil test to evaluate potential salt build-up. Due to a health issue (E coli contamination), fresh manure additions should be made at least four months prior to the harvest of any edible crops. Fresh manure or unfinished compost products may be high in ammonia. It is better to avoid application of products with an ammonia smell; they could burn roots and leaves. Manure and compost may be source of weed seeds. Compost need to be thoroughly mixed into the upper six to eight inches of the soil profile. Compost should not be left in chunks, as this will interfere with root growth and soil water movement. As the soil organic content builds in a garden soil, the application rate should be reduced to prevent ground water contamination issues. A soil test is suggested every four to six years to establish a base line on soil organic matter content. In the vegetable garden, it is recommended not to plow in woody materials such as bark or wood chips. They may interfere with seedbed preparation and may result in soil nitrogen depletion.
9. Constraints on Popularity of Bio and Organic Fertilizers a. Though the usefulness of bio and organic fertilizers has been demonstrated, beyond doubly, the farmer's acceptance of this practice has been far from satisfactory in spite of low cost of these inputs. Being biological materials, they are subject to various environmental stress once introduces into the soil. b. Moisture regime level of available nitrogen, phosphorus and molybdenum salinity and alkalinity. These influence the response of legumes to bio-fertilizers. c. Non-availability of quality inoculants is another constraint in the culture with low shelf life and commonly are often being marketed.
d. Lack of suitable transport and storage facilities, optimum temperatures and humidity conditions are often not maintained. e. Farmers are not aware of advantage of non-traditional organic manures such as poultry manures, urban wastes etc. The use of bio-fertilizers and organic manures can be improved substantially. (Web 2)
10. Conclusion The contribution of organic fertilizer in agricultural lands is positive from the perspective of a recycling economy. Application of organic matter to soils directly maintains an adequate level of soil organic matter, a critical component of soil fertility and productivity. Especially in our country, because of intense cropping, plowing and continuous same crop cultivation, soil organic matter is declining at a tremendous rate. To overcome such problems, organic farming receives the top priority in sustainable agriculture. There is a considerable scope for supplementing of renewable resources such as locally manufactured organic fertilizer and organic wastes for improving crop productivity and crop health. Efficient plant nutrition management should ensure both enhanced and sustainable agricultural production and safeguard the environment. Organic fertilizer has its advantages in terms of nutrient supply, soil quality and crop growth. Developing a suitable nutrient management system the use of locally manufactured organic fertilizers may be a challenge to reach the goal of sustainable agriculture; however much research is still needed. There is urgent need to involve more and more scientists to identify the quality of locally manufactured organic fertilizer for the development of eco-friendly production technology.
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In the past few decades, chemical fertilizers have come into widespread use throughout the Asian and Pacific region. This strong focus on ch...
Published on Jun 20, 2013
In the past few decades, chemical fertilizers have come into widespread use throughout the Asian and Pacific region. This strong focus on ch...