Modelling Nitrogen Losses from Sheep Grazing Systems with Different Spatial Distributions of Excreta

Matthew J. Bell, Brendan R. Cullen, Ian R. Johnson and Richard J. Eckard
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Matthew J. Bell: Melbourne School of Land and Environment, University of Melbourne, Vic. 3010, Australia
Brendan R. Cullen: Melbourne School of Land and Environment, University of Melbourne, Vic. 3010, Australia
Ian R. Johnson: Melbourne School of Land and Environment, University of Melbourne, Vic. 3010, Australia
Richard J. Eckard: Melbourne School of Land and Environment, University of Melbourne, Vic. 3010, Australia

Agriculture, 2012, vol. 2, issue 4, 1-13

Abstract: The aim of this study was to assess the effect that the randomised versus even distribution of excreta (dung and urine) may have on modelling nitrogen (N) losses by leaching, volatilisation and denitrification from a grazing system. A range of stock densities (from 200 to 2000 sheep/ha, equivalent to an annual stocking rate of 3 to 33 dry sheep equivalent (DSE)/ha respectively) were simulated to represent an increasing application of N excreta to a grazed 1 hectare area either distributed randomly or uniformly. This study found that the proportion of annual N inputs lost by denitrification were significantly lower and leaching N losses were higher at high stocking densities compared to if excreta was distributed uniformly. The results of this study indicate that N losses from a sheep grazing system could be adequately modelled assuming uniform distribution of excreta at stocking densities up to 1200 sheep/ha (equivalent to an annual stocking rate of 20 DSE/ha). But at higher stock densities, when N loads are high, the spatial distribution of excreta is important and models need to explicitly deal with the distribution of dung and urine N returns.

Keywords: distribution; excreta; grazing system; modelling; nitrogen losses (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2012
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