Municipal sludge as source of nitrogen and phosphorus in perennial pasture Eragrostis curvula production: Agronomic benefits and environmental impacts

Abstract

Land application of sludge has been shown to improve soil properties and aid crop growth, but the possibility of constituent nutrients such as nitrogen and phosphorus reaching environmentally toxic levels has caused governing authorities to set limits to how much sludge can be applied to agronomic land. The high nitrogen utilisation potential of pasture grasses suggests that more sludge can be used in this cropping system without the risk of excess nitrates. This study investigates the effect of exceeding the South African sludge application limit on hay yield, soil nitrates and phosphorus. Field plots were arranged in a complete block design comprising 4 replications of 4 treatments planted to Eragrostis curvula . The treatments consisted of 0, 4, 8 and 16 Mg∙ha-1 anaerobically digested sludge. Soil samples were collected before treatment application and at the end of each growing season for N, P, NO 3-, NH4+, and Bray-1P analyses. Plant samples were collected at flowering stage for hay yield and N and P uptake determination.

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