The Effects of Manure Application on Soil - Coursework Example

THE EFFECTS OF MANURE APPLICATION ON SOIL THE EFFECTS OF MANURE APPLICATION ON SOIL Introduction Soil is the most important and essential resource base for agricultural activities. In addition to being a medium for crop growth, soil also functions to sustain crop productivity, maintain environmental quality and support the health of plant, animal and human beings. Hence, it can be considered as one of the most important natural resource on earth. Manure is organic matter used to increase the fertility of the agricultural soil. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen. These nutrients are further trapped by bacteria in the soil. These fungi and bacteria are in turn consumed by other organisms and there by creating a soil food web (Wikipedia, 2007). Manure application can have both positive as well as negative impact on soil. The main objective of this paper is to discuss the impact of manure application on soil. The paper begins with the introductory section on manure, then the positive and negative impact of manures are discussed giving examples from different studies and the final section is the conclusion. Manures are organic fertilizers applied to the farm land. It is an excellent source of major plant nutrients such as nitrogen, phosphorus and potassium and the secondary nutrients that plants require. Its application is comparatively less costly than the inorganic fertilizers. It is very essential to take enough care to apply the right quantity of manure to the soil as over application can result in serious environmental problems. Types of manure Manures can be classified into two classes- green manures and animal manures. A green manure is a type of cover crop that is grown basically to add nutrients and organic matter to the soil. A green manure crop is grown for a specific period, and then these are plowed under and incorporated into the soil. By this process, the soil fertility is increased through the nutrients and organic matter (Wikipedia, 2007). Soil health is measured by the presents of soil organic content. The organic content of the soil increases by growing crops that produce large amounts of high residue and those that have fine roots such as corn, small grains, grasses. The increased organic content automatically improves the water retention, aeration, and other soil characteristics. Leguminous green manures such as clover contain nitrogen-fixing symbiotic bacteria in root nodules that fix atmospheric nitrogen in a form that plants can use. In addition the cover crops also prevent soil erosion. The second type of manure is animal manure. Animal manure is often a mixture of animals feces and bedding straw. Excrement include "droppings" or "crap" etc of plant-eating or herbivorous mammals and poultry — or plant material (often straw) which has been used as bedding for animals and thus is heavily contaminated with their feces and urine. Liquid manure from pig/hog operations is generally injected directly into the soil to reduce the unpleasant odors. Though poultry droppings are considered harmful to plants when fresh, after a period of composting these are valuable fertilizers (Wikipedia, 2007). Positive impact of manure on soil Manure application is not only employed as an amendment for nitrogen and other nutrients in cropping systems, but also as a disposal method for large amounts of bio-degradable organic waste. Besides being a good source of organic matter to the soil, manure also brings in structural stability, water holding and cation exchange capacity (Gallet et al. 2003). Manure nutrients help the gradual build up and further maintenance of soil fertility. Manure can also improve soil tilth, reduces wind and water erosion, improves soil aeration, increase water-holding capacity and promotes the growth of beneficial organisms. Plant nutrients in commercial fertilizers are mostly water soluble and are readily available for plant uptake, whereas the nutrients in manure are less available. As a result of this plants take up these nutrients based on its requirement at a slower rate which contributes to improved plant utilization and decreased nutrient losses to surface and groundwater. There are several studies that have established that crop yields are much higher with manures when compared to those attainable with inorganic fertilizers. Besides it is also seen in few studies that crop quality has also been improved by manure additions. These improved responses are usually attributed to manure-supplied nutrients or improved soil conditions that are not generally provided by inorganic fertilizer. Manure, particularly poultry litter, can neutralize soil acidity and raise soil pH which is again very helpful to plants and increase the value of manure. The addition of manure to the soil also brings about significant impact on the chemical, physical and biological properties of the soil. These have been proven in many researches conducted around the world. The increase in soil organic matter is the most significant contribution of manure application. The ability of manure to support formation of water-stable aggregates in the soil has an intense effect on soil structure and its physical characteristics. Water-stable aggregates increase infiltration, porosity and water holding capacity of the soil and decrease soil compaction and erosion (Risse, et al N.D.). Soil management that improves soil tilth will help increase water infiltration. Soil tillage creates an immediate increase in infiltration, but as the growing season progresses, the infiltration rate decreases. In no-till soil, infiltration rates are determined by macropores such as old root channels and earthworm burrows, while the residue cover protects the soil from sealing up under the impact of raindrops. The earthworms flourishes well in soils treated with manure. The acidifying inorganic fertilizers, such as ammonium sulfate or urea, can have a negative impact on earthworms. The quantity and quality of food available to earthworms often determines their density per acre. Often, crop residue contains too little nitrogen to be digested by earthworms. Hence manure applications, have been found to favor earthworm populations because they help make the crop residue more palatable (Tiwari, 1993). In yet another study it was noted that soils that had been treated with cattle manure for over a century, and inorganic fertilizers such as P, NP, NPK, or NPK plus lime for over 70 years were analyzed. The results showed that cattle manure application promoted the growth of bacteria, and not of fungi, when compared with the control soil. Application of chemical fertilizers enriched the K-strategist bacterial community, while application of manure enriched both r- and K-strategists. In this study DNA recovered was most abundant in the manure-treated soil. Effects on bacterial species richness and evenness following long-term soil treatments were also demonstrated by analyzing bacterial community DNA using amplified ribosomal DNA restriction analysis and repetitive extragenic palindromic-polymerase chain reaction fingerprinting. The richness and evenness of the bacterial community were enhanced by manure treatment and treatments that included N and P, which were positively correlated with soil productivity (Parham, et al 2003). In general, it can be said that soil health is determined mainly by the content of organic matter in the soil. Soil organic matter is known to affect many of the soil chemical properties, such as the cation exchange capacity and the soil buffering capacity that enable manure-treated soils to retain nutrients and other chemicals much more longer period of time. In addition to these activities, soil organic matter is known to affect activity, degradation and persistence of pesticides, and several studies have shown reduced pesticide losses from manure-treated fields. Through improvement in soil physical properties, manure application also reduces the energy required for tillage and the impedance to seedling emergence and root penetration. Application of manure to the soil has an added advantage of reducing soil erosion and surface water runoff. Several studies on manure amended soils indicate runoff and erosion rates are influenced by manure characteristics, loading rates, incorporation and the time between application and the first rainfall. Application of manure is also said to have an impact on the global climate which is of great concern today. Animal manures can help tone down potential negative consequences of rising atmospheric CO2 on the global climate by contributing to greater sequestration of carbon in soil. In other words, soil organic carbon sequestration on an area basis appears to be greater with an increased rate of manure application. Global warming is another important problem faced by the global community. The utilization of manure can bring about the decrease in methane which is also a significant contributor to global warming. Animal agriculture is a significant contributor of methane emissions globally. Soil application of manure can considerably decrease the net quantity of methane emitted to the atmosphere compared with stockpiling or storage of manure (Risse, et al N.D.). Negative impact of manure on soil The benefits of utilizing manure through land application are obvious. However, there are also several problems that discourage greater use of manure in cropping systems. These include potential water quality problems associated with runoff, uncertainty linked with the nutrient availability, high transportation and handling charges that discourage transport and greater utilization, and above all public perception regarding odor issues. The main concern in livestock wastes are organic materials, nutrients and pathogenic microorganisms that may have deleterious effect. Surface water is mainly affected through soluble contaminants in runoff or insoluble pollutants carried on soil particles during soil erosion events from the manure applied land. Groundwater can also be contaminated with excessive pollutants from percolation, seepage and direct infiltration. Some of the plus points that were mentioned about the application of manure may also turn out to be negative. For instance, though nutrients are important, excessive nutrients are the most common pollutant associated with animal waste. Researches have acknowledged the fact that watersheds with predominantly animal agriculture tend to have higher nutrient levels in their drainage systems. Over-application of manure to crops can result in leaching of nitrate to groundwater or high levels of nitrogen in surface waters, resulting in eutrophication and low dissolved oxygen levels. This may result in the death of fishes and other organism in the water body. The death and decomposition process will further deplete the oxygen content in the water. Studies have also shown that the concentration of phosphorus in runoff increases as the phosphorus concentration in the topsoil increases. Here is again another problem due to manure application. Since the nitrogen-to-phosphorus ratio in manures is lower than that needed by crops the excess phosphorus builds up to environmentally harmful levels in fields that receive repeated applications of manure (Risse, et al N.D.). Manure increases the solubility of P in soils, whether applied once or repeatedly. Long-term application of manure often results in the build-up of soil P to the point that a critical degree of soil P saturation is reached. Although this is good in terms of crop yield potential, the risk of P transfer from soil to water bodies may increase. Areas characterized by a high density of confined livestock operations are more at risk than others (Simard, et al. 2001). Though manure can be considered as a soil conditioner, cases of surface and groundwater contamination by nutrients and bacteria have been a major problem (Epstein, et al 1976). Manure is also a source of numerous plant metabolites, including soluble (phenolic acids) and insoluble (lignin) phenolic compounds that are very stable compounds and only partially degraded in the bovine stomach. Although some of them are deleterious to soil fertility and animal health, their fate in manure has been very rarely studied (Gallet et al. 2003). Conclusion Manure is an important part of farming. However the optimum quantity of manure required for a particular type of soil need to be determined before the application. Manure management is a decision making process that combine profitable agricultural production with minimum nutrient losses from manure, for the present and in the future. Good management of manure will not only minimize the negative effects but also stimulate the positive effects on the environment. Methane gas emission and leaching of nutrients, organic matter and odor from the manure have undesirable effects on the environment. The role of manure to the improvement of plant nutrition and build up of soil organic matter is the most important aspect of manure application. Negative and positive aspects of manure are closely interrelated because emissions at an early stage unavoidably have repercussions on positive effects on the soil and on crops at a later stage. There are several hidden facts about manure application that calls for further research in this area. Manure application cannot be uniform on all types of soil. Hence the farming community needs to be supported by the scientific community in order to find out the optimum amounts and the timing of application of manure. This will not only aid to reduce the negative impact on the environment but also increase the benefits of manure application. References Epstein E., Taylor J.M. and Chaney R.L., 1976. Effects of sewage sludge and sludge compost applied to soil on some soil physical and chemical properties. J. Environ. Qual. 5: 422–426. Gallet, C., Boissier, J.M. and Berlandis, M. 2003. Short-term effects of manure application on soil leachates in a mountain catchment. Agronomie 23: 335–344. Risse, L.M. et al (N.D.) Land Application of Manure For Beneficial Reuse. White Paper Summaries. [Online] Available: http://www.cals.ncsu.edu/waste_mgt/natlcenter/whitepapersummaries/landapplication.pdf [15 March 2007] Parham, J.A. et al 2003. Long-term cattle manure application in soil. II. Effect on soil microbial populations and community structure. Biology and Fertility of Soils. Vol 38, No 4, August, 2003: 209-215. Simard, R.R., S. Beauchemin, I. Royer and G. M. Barnett. 2001. Manure impact on phosphorus transfer from soils to surface waters. Pages 21-33 in Proc. 38th ann. Meet. Alberta Soil Science workshop, February 20-22, Lethbridge, AB, Tiwari, S.C. 1993. Effects of organic manure and NPK fertilization on earthworm activity in an Oxisol. Biology and Fertility of Soils. Vol 16, No 4. October,1993: 293-295. Wikipedia, 2007. Manure [Online] Available: http://en.wikipedia.org/wiki/Manure [15 March 2007] Read More