Influence of sheep rxcreta on pasture uptake and leaching losses of sulfur, nitrogen and potassium from grazed pastures

Abstract

In situ mini-lysimeters with ion exchange resin traps were used to measure the effect of dung and urine return on pasture growth and pasture uptake and leaching losses of sulfur (S), nitrogen (N) and potassium (K) in hill pastures grazed by sheep.Single dung or urine events in winter boosted pasture production by 37% and pasture uptake of S, N and K by up to 35%, 55% and 57%, respectively, during the following year. Whereas the late summer single superphosphate application increased late spring and mid summer pasture growth of the following year only, dung or urine return increased pasture growth in every season of the following year. Despite the addition of 11.5, 4.7 and 376 kg of readily available S, N and K ha-1 in a single dung event and 14.5, 28.5 and 146 kg of S, N and K ha-1 in a urine event, accelerated leaching of S, N and K did not occur from dung or urine affected soil. Less than 3 kg S, 0.5 kg N and 2 kg K ha-1 were lost by leaching from dung or urine affected soil. The majority of S, N and K from excreta remained in the soil, either immobilized in soil organic matter and/or adsorbed on to soil sesquioxide surfaces and cation exchange sites with the equivalent of only 1.6% of S, 4.4% of N and 9.0% of K from dung and 29% of S, 18.7% of N and 31% of K from urine being recovered in increased pasture uptake over a period of one year. Under the climatic conditions that prevailed after the winter deposition of excreta, immediate loss of excreta-derived nutrients was negligible but urine deposition markedly accelerated the leaching losses of native soil calcium and magnesium (8 kg Ca and 2.9 kg Mg ha-1 from urine and 6.4 kg Ca and 2.4 kg Mg from dung, respectively). Quantitative information of this kind is important for determining the long-term sustainability of soil fertility in grazed pastures before a comprehensive understanding of pasture nutrient cycles is complete.