Profitability of grazing crop stubbles may be overestimated by using the metabolisable energy intake from the stubble
D. T. Thomas A E , J. Finlayson B , A. D. Moore C and M. J. Robertson DA CSIRO Livestock Industries, Private Bag 5, Wembley, WA 6913, Australia.
B School of Agricultural and Resource Economics and Future Farm Industries CRC, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
C CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2061, Australia.
D CSIRO Sustainable Ecosystems, Private Bag 5, Wembley, WA 6913, Australia.
E Corresponding author. Email: dean.thomas@csiro.au
Animal Production Science 50(7) 699-704 https://doi.org/10.1071/AN09213
Submitted: 17 December 2009 Accepted: 4 May 2010 Published: 30 July 2010
Abstract
Grazing crop stubbles affects soil structure, groundcover, and the productivity of subsequent crops, but the cost of this practice is highly variable and not easily compared against the value of feed provided to livestock. To compare with and without grazing stubbles in terms of whole-farm profit and water-use efficiency we created a mixed enterprise farm model using the Agricultural Production Systems Simulator and GRAZPLAN biophysical simulation submodels, and the Model of Integrated Dryland Agricultural System linear programming model. We hypothesised that grazing crop stubbles would increase farm profit by an amount equivalent to the value of the metabolisable energy (ME) consumed by sheep when they grazed the crop stubbles. Representative mixed farms where sheep were or were not allowed to graze crop stubbles were compared for two locations in the wheatbelt of Western Australia (Cunderdin and Geraldton) at two stocking rates. Across locations and stocking rates, the estimated value of the ME intake from crop stubbles was 2.2 times the increase in farm gross margin when stubble grazing was allowed. Contributing to this difference was that stubble grazing provided a less flexible feed source than supplementary feeding and in the absence of adjustments in stocking rates sheep tended to utilise more of the annual and permanent pastures when stubble grazing was not permitted. Therefore, the value of grazing crop stubbles to the profitability of the farm enterprise was overestimated by the ME value of the intake. Owing to reduced consumption of supplementary feed by livestock, whole-farm water-use efficiency of protein production was increased by 15% when grazing of crop stubbles was permitted. This simulation study shows that the value of grazing crop stubbles cannot be predicted well using energy intake from stubble grazing or reduced supplementary feeding costs.
Acknowledgements
This work was supported by the Grains Research and Development Corporation through the pre-experimental modelling for the Grain & Graze 2 project. We thank Julianne Lilley, James Hunt, Lindsay Bell, John Kirkegaard, Phil Barrett-Lennard and David Masters for their contribution to the design of the farm simulations, and Dean Revell for comments on the manuscript. Dean Thomas was the recipient of a CSIRO J. M. Rendel Fellowship.
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