Irrigation of meat processing wastewater onto land

This study examined the effects of application with primary-treated and nitrogen-reduced-treated animal processing effluents on plant production, drainage water composition and soil properties. Multiple lysimeters containing undisturbed soil cores were installed in an outdoor facility. Two soil types were investigated: Horotiu silt loam (Allophanic Soil) and Manawatu silt loam (Recent Soil). Effluents were applied onto the lysimeters fortnightly for 2 years at a nitrogen loading rate of about 600 kg N ha−1 per year, giving different hydraulic loading rates for the two effluents. Equivalent volumes of water were applied to control lysimeters. Plant production in all the lysimeters to which effluents were applied increased considerably, and the increases were similar on both soils. Plant materials “cut and carried” accounted for the removal of large amounts of the nutrients applied in the effluents. Nitrogen and phosphorus concentrations in the drainage water from both the control and the effluent-treated lysimeters were low (<1 g NO3−-N m−3 and <1 g P m−3). Measurements of total soil nitrogen did not show any increase in nitrogen content. There was an indication of phosphorus accumulation in the Horotiu surface soil with the application of the N-reduced effluent. Application of both effluents increased the leaching losses of cations (Na+, K+, Ca2+ and Mg2+). The N-reduced effluent had a more profound effect on the concentrations of cations in the drainage water than the primary-treated effluent. This was due to the higher total loading of cations in the N-reduced effluent. After the application of both effluents, total amounts of cations in the drainage water were generally in the order: Ca2+>Na+>Mg2+>K+ for both soils, while the amounts of cations in the effluents applied were in the order: Na+>K+>Ca2+>Mg2+. For the effluent-treated lysimeters, Ca2+ loss in the drainage water was up to twice that applied in the effluent, whereas <40% of the total Na+ applied in the effluent was recovered in the drainage water. After the application of the effluents, soil exchangeable Na+ and K+ in both soils increased significantly. However, there was a decreasing trend in soil exchangeable Ca2+ and Mg2+. It is concluded that application of meat processing effluents can increase plant production due to increased nutrient loadings. In the long term, however, the changes in soil exchangeable cations may affect soil quality and the sustainability of plant production, and could be a problem for sustainability of effluent application.