Applying Organic Amendments to Agricultural Land - Essay Example

? The Benefits and Environmental Implications of Applying Composts and other Organic Amendments to Agricultural Land By ID Number Module Title and Number Name of Professor/ Tutor Date of Submission The Benefits and Environmental Implications of Applying Composts and other Organic Amendments to Agricultural Land INTRODUCTION The main aim of employing organic amendments such as composts or recycled organic wastes is to help “restore soil organic matter (SOM) content and soil organic matter fertility functions in soils intensively-cropped and organic-depleted” (Senesi, Miano & Brunetti, 1996, p.533). Composts and other organic amendments also raise the organic content levels in soils intrinsically poor in organic matter. Further, the recycling of waste materials in the form of organic soil amendments helps to resolve several problems related to practical, resource-recovery, environmental and economic issues arising from the disposal of large amounts of organic wastes. These include sewage sludges, municipal solid wastes, urban yard refuses, food industry residues, wood processing wastes, and agricultural crop residues; these are produced in considerable quantities by the human community, particularly in urban, highly populated areas, state Senesi et al (1996). Besides their application to agricultural land after appropriate treatment, other alternatives for their disposal are incineration, land filling, and discharge to water bodies. However, the most environmentally safe and economically satisfactory solution is the application of composts and other organic amendments to agricultural land. “This choice also provides advantages which may result in soil fertility and agricultural production benefits” (Senesi et al, 1996, p.533). Organic wastes and residues of any nature require appropriate treatment before soil application. These treatments serve to eliminate or reduce various adverse effects on soil properties, and at the same time to optimize their fertility effects on the soil. Thesis Statement: The purpose of this paper is to investigate the implications of applying composts and other organic amendments to agricultural land. Soil benefits pertaining to its physical, chemical and biological aspects, the economic benefits to agriculture, the measures to prevent adverse environmental outcomes, alternative options, and whether benefits outweigh negative effects will be examined. BENEFITS OF APPLYING COMPOSTS AND OTHER ORGANIC AMENDMENTS TO AGRICULTURAL LANDS The application of compost benefits the biological, chemical and physical properties of soil. Biologically, compost promotes the development of fauna and microflora, reduces plants’ susceptibility to attack by parasites, and supports the faster root development of plants. Chemically, compost has beneficial outcomes on soil in several ways. It “increases nutrient content, turns mineral substances in soil into forms available to plants, and regulates the addition of minerals to soil, particularly nitrogenous compounds” (EPA, 1994, p.87). Additionally, compost serves as a buffer in making minerals available to plants, and provides a source of micronutrients. Moreover, compost improves numerous physical characteristics of the soil including the soil’s “texture, water retention capacity, infiltration, resistance to wind and water erosion, aeration capacity, and structural and temperature stability” (EPA, 1994, p.87). In Tigray Region of Ethiopia, the Bureau of Agriculture and Rural Development undertook since 1998 the production of compost as a part of its extension package. By 2007, at least 25% of the farmers were making and using compost. The success of this approach is emphasized by the doubling in the quantity of grain yield between 2003 and 2006, from 714 to 1,354 thousand tonnes. At the same time, since 1998, there has also been a steady decrease in the use of chemical fertiliser from 13.7 to 8.2 thousand tonnes (Asmelash, Araya, Egziabher et al, 2007, p.19). Other regions of Ethiopia are also promoting the production and incorporation of compost in agricultural soil. This is particularly undertaken by the Ministry of Agriculture’s ‘Community-Based Participatory Watershed Development’ project, and the Environment Protection Authority’s Land Rehabilitation project, and has been supported “through three successive phases of the Country Cooperation Programme of the United Nations Development Programme (UNDP)” (Asmelash et al, 2007, p.20). Further, it is considered necessary to integrate the work of plant breeders and farmers towards participatory plant breeding. The objective is to investigate and develop the potential of the farmers’ varieties to give consistent high yields under an organic agriculture system whereby compost is made and applied to agricultural lands by the farmers. The extensive data collected by the end of the twentieth century on the use of sewage sludge in agriculture, has resulted in strict governmental regulations such as the 86/278 EEC in Europe. Its purpose is to safely recycle sewage sludge, and to ensure the improvement of its characteristics. However, there is persistent controversy over the efficacy of the imposed limits, especially in relation to potentially toxic elements (PTEs) such as heavy metals. There is a requirement for long-term research on sludge use on agricultural land, the slow evolution and difficulty in prediction of the possible build-up of toxic elements in soil, state Gaskin, Brobst, Miller et al (2003). Further, sludge benefits to farmers should be assessed on a crop rotation basis, taking residual impacts on subsequent crops into consideration. These may be considerable even in the case of mobile elements such as Nitrogen, assert Binder, Dobermann, Sander et al (2002). The characteristics and performance of sludge can be markedly changed through treatments converting it into biosolids. Therefore, spreading techniques as well as their application rates have to be optimised for the different materials. The various features related to biosolid use should be taken into consideration. It is most essential to ensure whether these materials can economically substitute inorganic fertilisation in crop producion, particularly with regard to Nitrogen supply. Similarly, Mantovi, Baldoni and Toderi (2005) assert that it is important to ascertain the ways in which they modify soil characteristics to prevent environmental pollution and crop product contamination. Physical Benefits to Soil: Composts and other Organic Amendments The physical benefits of compost to soil include reduced bulk density, increased porosity, aggregation of sandy soil reducing erosion and increasing water holding capacity, suppression of plant pathogens, weeds, and others, and remediation of contaminated soil. Compost enhances the organic matter, tilth, and fertility of agricultural soils. Compost also increases the aeration and drainage of dense soils, improves the water infiltration rate due to aggregation of sandy soils, and raises the soil’s capacity for cation exchange. Additionally, compost increases soil porosity, strengthens resistance to erosion, raises the level of nutrient storage and release, and reinforces disease suppression. The almost neutral pH of compost is also beneficial for growing most agricultural crops. Further, it forms an efficient amendment to eroded soils (EPA, 1994). These desirable outcomes are reiterated by Bulluck, Brosius, Evanylo et al (2002) who add that the application of organic soil amendments results in the fostering of beneficial microorganisms, pH stabilization, and lowering of bulk density of the soil. Epstein, Taylor and Chancy (1976) studied the effects of different application rates of sewage sludge and sludge compost (0, 40, 80, 120, and 240 metric tons/ ha) on soil physical and chemical properties, at two different pH levels. A cloddy seedbed was produced by sludge application rates of over 120 metric tons/ ha which were difficult to apply. However, the same rate of compost was applied easily and resulted in a friable seedbed. Sludge and compost caused a rise in the water content and water retention of a silt loam soil. Both the sludge and the compost raised the salinity and chloride levels of the soil to a level which may be detrimental to salt-sensitive plants. Ramos and Martinez-Casasnovas (2006) investigated erosion rates and nutrient losses resulting from the application of composted cattle manure in vineyard lands of North East Spain. The Mediterranean region is highly vulnerable to erosion, with its frequent, heavy rainfalls, and yearly unpredictable rainfall fluctuations. The types of crops and management practices also contribute to soil erosion. Vineyards undergo the highest runoff and soil losses across Spain, Italy, France and other countries. To improve soil conditions, the application of organic waste has been generalized in the study area in N.E. Spain, before plantation and every 3 to 4 years at rates of 30-50 Mg ha_1 mixed in the upper 30 cm of soil. These organic wastes recycled through application to agricultural land, result in enhanced physical properties of soil, such as porosity, structure and water holding capacity (Ouedraogo, Mando & Zombre, 2001). Hence, the application of organic waste or compost is considered as beneficial for soil conservation, particularly in degraded soils and those predisposed to risk of erosion. Chemical Benefits to Soil: Composts and other Organic Amendments Some of the chemical benefits of composts and other organic amendments to agricultural land include an increased capacity for cation exchange, nutrient availability and uptake, reduced need for nitrogen fertilizer, and carbon sequestration. In the research conducted by Epstein et al (1976), the application of sludge and compost led to a threefold increase in the soil’s cation exchange capacity. The levels of nitrates and nitrogen were highest at the 15-20 cm soil depth, but declined rapidly below this level. Phosphorus availability was at high levels during the 2-year research study, and exceeded that required for a good crop growth (Epstein et al, 1976). A field experiment pertaining to a winter wheat-maize-sugar beet rotation on a silty-loam soil in the eastern Po Valley (Italy) conducted over twelve years, compared the effects of repeated sewage sludge applications to mineral fertilisers. Municipal-industrial wastewater sludge anaerobically digested, belt-filtered and dewatered, and composted with wheat staw, was applied at 5 and 10 MgDM ha_1yr_1. Mantovi et al (2005) found that biosolids helped to produce crop yields similar to the effects of introducing the highest mineral fertiliser. At the same time, it was evident that with the higher rate of liquid and dewatered sludge, excessive supply of Nitrogen was harmful, “leading to wheat lodging and poor quality of sugar beet and wheat crops” (Mantovi et al, 2005, p.289). From this perspective, compost use was found to be safer. Organic soil amendments such as biosolids increased organic matter, total Nitrogen, and available Phosphorus in the soil, and lessened soil alkalinity. These outcomes were more pronounced at the highest rate of incorporation of biosolids. The application of compost led to the most prominent organic matter topsoil accumulation. Mantovi et al (2005) observe that in amended topsoil, considerable accumulations of total Zinc and Copper were detected, but no other heavy metals such as Cadmium, Chromium, Nickel or Lead were found, their total concentrations remaining well below the hazard limits. According to McBride and Spiers (2001), there are significantly high levels of Zinc and Cadmium at higher sludge rates, but Cadmium content was similarly high in mineral fertilised plots, probably due to its marked presence in superphosphate. Biosolid applications markedly raised the content of Nitrogen, Phosphorus, Zinc and Copper in wheat grain, Nitrogen and Copper in sugar beet roots, and only Copper in maize grain. Significant benefits to soil fertility by the incorporation of biosolids were alongside possible adverse outcomes on water quality due to increased content of Phosphorus, and on soil ecology because of Zinc accumulation (Mantovi et al, 2005). The significant increase in Phosphorus is not only because of high loading with sludge, but also due to an increased availability in amended soils, state Shober & Sims (2003). According to Karboulewsky, Dupouyet and Bonin (2002), although Phosphorus is beneficial to crops, an excessive content of mobile Phosphorus is detrimental to the environment. Penn and Sims (2002) support this view, adding that excessive Phosphorus may pose a risk in water eutrophication. Another adverse outcome of biosolid use is the raised electrical conductivity of soils. The increase in electrical conductivity is only minor after twelve years; however it is considered as a likely contributor to the observed poor quality of sugar beet (Mantovi et al, 2005). Biological Benefits to Soil: Composts and other Organic Amendments The Environmental Projects Agency (EPA) Ltd.. promotes the Greenleaf Project on agricultural use of compost and development of on-farm composting techniques, The EPA (2006) carried out tests to measure biological activity in agricultural land, prior to the application of compost, and following the first year of application. At this stage, no effects were found from the incorporation of compost. The biological activity of the soil was determined by two methods developed by the University of Reading. Measurement of respiration rate on samples of soil under controlled conditions, was on the basis of uptake of oxygen (O2) and the production of carbon dioxide (CO2). Additionally, a pioneering technique using soil enzyme activity was also employed. According to EPA (2006), the indicators of considerable biological activity include high oxygen uptake, high carbon dioxide production, and high enzyme activity. Similar to other methods, an immediate effect was not obtained after the application of compost. Effects could be determined only after repeated application of the compost and its assimilation into the soil, and microbiological populations had sufficient time to increase according to the improved availability of food and moisture. After six months of application of compost to the soil under study, and no application of compost to the control sample, no clear trends were identified at this early stage. Similarly, “no clear trends were found in the analysis of biological activity in the second year” (EPA, 2006, p.50). The researchers decided that it would take a long time for the effect of compost to become evident; therefore they channelised the limited resources to measures that would more directly reveal the benefits of compost. Thus, trials which are undertaken for longer than the four years of the Greenleaf Project are required for investigating the increased biological activity resulting from the application of compost. According to Wallace (2005), research trials on a sandy loam soil with 1% organic matter content at the beginning, recorded greater biological activity on plots that had been treated with compost at a rate of 50 t/ ha for five years. Bailey and Lazarovits (2003) examine the application of organic amendments, manures and composts rich in nitrogen, for reducing soil-borne diseases. This occurs by the release of allelochemicals generated during storage of the organic products, or by subsequent microbial decomposition. Disease suppression to prevent plants getting affected includes the development of disease suppressive soils. This is undertaken by introducing organic amendments and crop residue management, which are long-term interventions. However, “the benefits accumulate across successive years improving soil health and structure” (Bailey & Lazarovits, 2003, p.169). ENVIRONMENTAL IMPLICATIONS The environmental implications of applying composts and other organic amendments to agricultural land include carbon sequestration, reduced need for Nitrogen fertiliser, greater potential for leaching heavy metals, bioaerosol emissions, improved efficiency for water use, the potential to remediate polluted soil, and reduced need for inorganic pest controls. “Erosion processes are accelerated by changes in land use and in cropping patterns for field mechanisation” (Ramos & Martinez-Casasnovas, 2006, p.178), which render most conventional soil conservation measures inapplicable. Field mechanisation to reduce slope gradients may be executed without preserving the topsoil. Sometimes the more fertile surface is mixed into the poorer materials deep in the soil profile. These interventions have considerable environmental implications, resulting in alterations to the landscape form, and soil degradation with poorer structure and decline in organic matter content. These lower the soil’s water-retention capability, and increase runoff and erosion. “The Anoia-Penede’s area, located in NE Spain, is a clear example of this situation” (Ramos & Martinez-Casasnovas, 2006, p.178). Organic wastes are important sources of nutrients such as Nitrogen and Phosphorus and other elements, which could further reduce costs of fertilisation. It is noteworthy that it has become common practice to intensify agricultural systems and employ organic waste to improve soil physical conditions. These enhance soil Phosphorus and Nitrogen levels in particular areas to unprecedented levels. This leads to potentially greater “Phosphorus and Nitrogen losses from these areas, and an environmental risk of surface water pollution associated with runoff from fields to which organic waste has been applied”, state Ramos and Martinez-Casasnovas (2006, p.178). Additionally, based on the high susceptibility to sealing of these soils, erosion rates are comparatively high; hence a greater nutrient concentration in the soil surface increases non-point pollution due to runoff. The research study conducted by Ramos and Martinez-Casasnovas (2006), assessed the impact of a single application of composted cattle manure at a rate of 40 Mg ha_1 on vineyard soil from the Alt Penedes-Anoia region, NE Spain. The focus of the study was on the alterations in runoff and soil losses, and on nutrients transported by runoff at laboratory and field scale. The researchers found that composted cattle manure applied to soils led to positive outcomes, “improving infiltration and decreasing runoff volumes by up to 20%” (Ramos & Martinez-Casasnovas, 2006, p.184). This has beneficial effects for soils that are highly degraded due to land levelling works and a lowered cost of fertilization. However, the evidence indicates that the Nitrogen and Phosphorus concentrations in runoff generated in treated soils were nearly double those in untreated soils, for the rainfall recorded in the study area. The authors identify a requirement for alternative waste or products to improve soil properties in order to avoid the presence of high surface nutrient concentrations resulting in water pollution. The problems of soil and water pollution caused by heavy metals contained in composts and other organic amendments applied in agricultural lands, “can be overcome by composting only organic raw materials with a low level of potential contaminants” (Pinamonti, Stringari, Gasperi, et al, 1997, p.30). Evidence from the 14 trials conducted by Pinamonti et al (1997) reveals that Municipal Sewage Waste (MSW) compost when applied over a period of six years increased the concentrations of heavy metals such as Zinc, Copper, Nickel, Lead, Cadmium, and Chromium. “However, no symptoms of phytotoxicity were noticed in the trials” (Pinamonti et al, 1997, p.140). Structurally Bound (SB) compost used over a six year duration, containing far less quantities of heavy metals than MSW compost, caused only a significant increase of Zinc in the soil. There was no difference in the concentrations of the other heavy metals tested. It is clear that Structurally Bound (SB) compost can be used as a valid alternative to conventional commercial manures, because when of a high quality “it safeguards both the environment and healthy crops” (Pinamonti et al, 1997, p.140). Freibauer, Rounsevell, Smith et al (2004) analysed the technical and economically viable potentials for carbon sequestration in the agricultural soils of Europe from 2008 to 2012. They provide a quantitative estimation of “the carbon absorption potential per hectare and the surface of agricultural land that is available and suitable for the implementation of these measures, their environmental impacts as well as the effects on farm income” (Freibauer et al, 2004, p.1). The researchers identified some measures as most promising: the application of organic amendments on arable land instead of grassland, the introduction of perennials such as trees and grasses on arable land set aside for conservation or biofuel purposes; to promote organic farming, to raise the water table in farmed peatland, and within limits zero tillage or conservation tillage. Most of the measures have environmental benefits, but may increase the emissions of N2O. “For most measures it is impossible to determine the overall impact on farm profitability” (Freibauer et al, 2004, p.1). Efficient carbon sequestration on agricultural soils requires a permanent change in the management and implementation concepts adjusted to local soil, climate and management features, to permit the selection of areas with high carbon sequestering potential. ECONOMIC BENEFITS: COMPOSTS AND ORGANIC AMENDMENTS To the farmer, the economic value of organic wastes such as sludge compost used for improving and maintaining the productivity of agricultural lands, “is the value of the increase in crop production derived from its application, less any application costs” (DOA, 1982). The economic value depends on the crop to be grown, the crop revenue expected, the type of soil and its level of productivity, climatic factors, and other variables that impact crop response to sludge compost application. Determining the value of a crop production input such as a sludge compost, requires the development of a yield response function that associates crop yield to the particular compost or other organic amendment used, and its substitutes. The increase in crop yield is greater at low rates of compost than at higher rates. The economic value per unit of compost to the farmer is correspondingly higher at low rates of application of compost than at higher rates. The price of chemical fertilizers is required to be used as the reference point, in analysing agricultural revenues affected by the use of composts or other organic amendments to the soil. “The cumulative discounted economic value of organic wastes applied to some agricultural soils could as much as five times greater than the value realized during the application year” (DOA, 1982, p.92). This is because of the time release of plant nutrients in the compost. alternativeCONCLUSION This paper has studied the application of composts and other organic amendments to agricultural land. The benefits to soil in relation to physical, chemical and biological characteristics, the environmental effects, the economic benefits to agriculture, and the measures to produce optimal results and prevent adverse environmental outcomes have been examined. The results from various studies demonstrate that organic amendments enhance the soil’s biological, chemical and physical attributes, and improve agricultural yield. Negative effects include pollution of water and soil, and crop product contamination caused by their excessive leaching of heavy metal in soil. The evidence indicates that the benefits of using composts and other organic amendments far outweigh their negative effects. The adverse outcomes can be prevented by the use of appropriate organic raw materials to help lower the amount of heavy metals added to the soil, for example, by the use of Structurally Bound (SB) composts instead of Municipal Sewage Waste (MSW) composts. Similarly, soil-borne diseases affecting crops and subsequently humans, are suppressed with residue management and organic amendments. It is clear that yields are higher in fields with long-term organic amendments, which consequently provide greater revenue for the farmer. Further, there were few statistically significant differences in yields between agricultural lands amended with alternative organic composts and soils amended with synthetic fertilizers, irrespective of production system. Therefore, it is concluded that the use of composts and other organic amendments is equal in productive value to chemical fertilizers in the short term, and of greater economic value in the long term, when their nutrients are released. It is essential for future research to focus on preventing the accumulation of organic contaminants in soil, for optimizing the beneficial effects of organic amendments. BIBLIOGRAPHY Bailey, K.L. and Lazarovits, G. 2003. Suppressing soil-borne diseases with residue management and organic amendments. Soil & Tillage Research, 72, 169-180. Binder, D.L., Dobermann, A., Sander, D.H. and Cassman, K.G. 2002. Biosolids as Nitrogen source for irrigated maize and rainfed sorghum. Soil Science Society of America Journal, 66, 531-542. 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