Is soil an appropriate dumping ground for our wastes?

Abstract

New Zealand and Australia generate large quantities of agricultural, industrial, and municipal wastes. As authorities move to protect the environment by regulating waste disposal practices, environmentally sound methods of waste disposal are being sought. In particular, land application of wastes as a means of disposal, nutrient re-cycling, and water conservation is becoming increasingly popular. This paper provides an overview of the types, quantities, and characteristics of wastes generated in New Zealand and Australia, and highlights the problems with current waste disposal practices, including landfilling, incineration, and discharging into waters. This is followed by a detailed review of the beneficial effects and adverse impacts of land application of wastes on plant production and soil and environmental quality, and possible hazards to human health. The management of waste application on land is a challenging task and requires rigorous scientific input. Sludges and euents contain significant concentrations of plant nutrients, particularly nitrogen, phosphorus, and organic matter. Their application on land has been shown, in many cases, to result in significant increases in plant yields and improvements in soil physical conditions and chemical fertility. The constraints with some wastes, particularly those of industrial and municipal origin, are that they contain undesirable constituents, e.g. heavy metals, toxic organics, pathogens, and salts, or have extremely high or low pH. High concentrations of nitrate and phosphate derived from wastes are also of concern for ground and surface water contamination. The processes that control the fate of wastes in the soil are complex and many of them are poorly understood, e.g. rate of release of nutrients and other chemicals; leaching of nutrients, metals, and organics through macropores and as suspended solids; emission of greenhouse gases; impact of solvents, surfactants, and sludge organic matter on the sorption, degradation, and leaching of hydrophobic organics; and the long-term bioavailability and fate of metals and organics fixed by soil organic matter. More research is urgently required to develop a sound understanding of waste characteristics and the processes affecting their fate in the soil in order to ensure that land application of wastes is safe.

Environmental implications of low nitrogen use efficiency in excessively fertilized hot pepper (Capsicum frutescens L.) cropping systems

“…Even higher total N inputs are often used for greenhouse vegetable crops by mixing poultry manure into the soil for each crop and growing annually two or more crops. Nitrogen fertilizers are important in vegetable production systems but there is concern about the potential for nitrate leaching and groundwater contamination (Rossi et al, 1991;Barraclough et al, 1992;Cameron et al, 1997;Li et al, 2001;Zhu et al, 2004). Leaching of NO 3 À -N occurs in many vegetable production areas because N application rates often exceed crop demand (Biernbaum, 1992;Jackson et al, 1994;McNeal et al, 1995).…”

Land application of farm dairy effluent: Results from a case study, Wairarapa, New Zealand

“…Land application of effluent, as opposed to direct discharge to waterways, is becoming widespread in New Zealand as regulatory authorities move to protect and enhance water quality and meet Maori spiritual and cultural values (Cameron et al 1997; Ministry for the Environment 1999; Wellington Regional Council 1999a). This method has been used to treat effluent from townships, meatworks, dairy factories, and dairy farms (Schipper et al 1996;Selvarajah 1996;Cameron et al 1997;Tomer et al 1997;Sparling et al 2001).…”

“…This method has been used to treat effluent from townships, meatworks, dairy factories, and dairy farms (Schipper et al 1996;Selvarajah 1996;Cameron et al 1997;Tomer et al 1997;Sparling et al 2001). A major concern in New Zealand at present is the potential impact of farm dairy effluent (FDE) on the environment (Environment Waikato 1998;Wellington Regional Council 1999b).…”

“…The objective of land-based effluent application is to utilise the chemical, physical, and biological properties of the soil/plant system to assimilate the waste components without adversely affecting soil quality or releasing potential contaminants to water bodies (including the groundwater) or the atmosphere; hence, the area of land, and the soil physical, chemical, and biological conditions are important in order to achieve this objective (Cameron et al 1997;Bond 1998;Sparling et al 2001). The management of nitrogen and phosphorus to prevent possible groundwater or surface water contamination is a key issue for the long-term sustainable use of effluent-irrigated land (Falkiner & Polglase 1997).…”

A lysimeter study of the fate of15N‐labelled nitrogen in cow urine with or without farm dairy effluent in a grazed dairy pasture soil under flood irrigation

“…Nitrate (NO3 -) leaching from agricultural land and the subsequent contamination of water resources is a major environmental issue that could undermine the long-term sustainability of intensive agricultural production systems (Spalding & Exner 1993;Jarvis et al 1995;Addiscott 1996;Cameron et al 1997;Di & Cameron 2002a). High concentrations of NO3 -in drinking water are deemed to be detrimental to human health; world and national health organisations have established drinking water guidelines limiting NO3 --N concentration to a maximum of 10-11.3 mg NO3 --N l -1 .…”