Agricultural waste can be defined as the residues from the growing and first processing of raw agricultural products such as fruits, vegetables, meat, poultry, dairy products, and crops. Although agricultural waste is a general term used to describe waste that is produced on a farm through various farming activities, these activities can include other activities such as seed
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growing, nursery plots, and even woodlands that are used as ancillary to the use of the land for other agricultural purposes. Agricultural wastes can be in the form of solid, liquid or slurries, depending on the nature of agricultural activities in a farm or agricultural field, and can be both natural (organic) and non-natural wastes.
Although the quantity of wastes produced by the agricultural sector is significantly low compared with wastes generated by various industries, the pollution potential of agricultural wastes is high on a long-term basis. For example, the land spreading of manures and slurries can cause nutrient and organic pollution of soils and waters. Given animal excreta also contains a plethora of organic chemicals, and pathogens, the risk of surface and groundwater contamination as a result of waste being applied onto the soil can be high. Agricultural waste encompasses a broad class of biodegradable and non-biodegradable components, and the major components of agricultural solid wastes (Table 1) are biodegradable organics. These are unlikely to result in hazardous conditions except when there are inadequate oxygen resources to assimilate the wastes. When this occurs in streams, inadequate dissolved oxygen and high concentrations of ammonia can cause fish kills.
Throughout many developed and developing countries, large quantities of food and crop processing, forestry, and animal solid and liquid wastes are generated each year. Although the majority of these wastes are readily biodegradable, they also contain significant quantities of nutrients (e.g., nitrogen, phosphorous), human and animal pathogens, and various medicinal products and feed additives used in livestock operation. Excretion by grazing livestock and application of effluent onto land as a supplement to fertiliser can cause damage to the receiving environment through surface run-off and/or leaching of many of these pollutants associated with agricultural waste.
Given the broad connotations associated with the term 'agricultural waste', the focus in this chapter is placed mainly on those agricultural wastes derived through animal farming practices and on the environmental implications of applying the waste onto land. In addition, utilization of agricultural waste to obtain environmental and economic benefits is also briefly discussed.
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