Sheep grazing on crop residues do not reduce crop yields in no-till, controlled traffic farming systems in an equi-seasonal rainfall environment

Abstract

In southern Australia, the majority of farms combine a sheep enterprise with a cropping enterprise to form a mixed farming business. Crops are grown in sequence with pastures, and sheep graze vegetative juvenile crops and crop stubble residues after harvest. Recently, growers practicing no-till, controlled traffic cropping became concerned that grazing livestock would damage soil and reduce soil water capture, crop yield and profitability. Sheep grazing on stubbles remove residue cover and compact surface soil, but there is little published research on potential impacts on subsequent crop performance. Two experiments were conducted in high (Temora) and low (Condobolin) rainfall environments from 2009 to 2013 to determine whether sheep grazing crops during the vegetative phase and/or stubbles after harvest damaged soil, reduced soil water capture and storage or affected the performance of subsequent crops. Sheep grazing on stubbles did not reduce crop yields provided summer weeds were controlled with herbicides and at least 70% stubble cover (2–3 t/ha cereal stubble) was maintained on the soil surface. Sheep grazing on stubble increased soil strength and bulk density and reduced water infiltration rates, but rarely to levels that were detrimental to soil water capture, crop growth or grain yield. Where reduced infiltration rates did reduce soil water capture, it was due to removal of cover by grazing rather than compaction. Grazing of vegetative crops in winter when soils were generally wet further increased soil strength compared to grazing stubbles alone, but not to an extent that was detrimental to plant growth. Yield effects from grazing crops in winter were not due to soil physical effects, but to differences in plant growth in response to defoliation. Grazing of both stubbles and crops increased the availability of soil mineral N to subsequent crops which increased grain yield and protein in some seasons. The results from these experiments provide strong evidence that livestock can be retained within modern conservation cropping systems without compromising crop performance, and continue to provide the production and business risk benefits for which they have been historically valued.