The role and value of crop residues in dryland agriculture

The major reasons advanced for the retention of crop residues in rainfed systems include increased water infil- tration, reduced evaporation from the soil surface, increased soil organic carbon, reduced soil erosion and ulti- mately the yield of following crops. The residues of crops are valued in various ways in the cropping systems of the dryland regions of the world, including feed for livestock, protection against soil erosion and for maintenance of soil organic matter. Minor uses include building materials, bio-energy production and fuel. Retention of crop resi- dues forms a major part of the system of conservation agriculture along with zero tillage and diverse crop rotation, but retention of crop residues has not been as widely adopted as the other components. This review discusses some of the reasons that crop residues are valued in various agro-ecological environments. It reveals some gaps in knowledge about the short and longer term effects of retaining or removing crop residues and the need to clearly separate the contributions of the components of conservation agriculture. There may be a trade-off be- tween the value of crop residues for livestock feed and the value for soil protection and fertility maintenance. It is suggested that the relative values for different purposes and in a variety of situations requires further elucidation of the impact of residue retention on soil water storage, organic matter content, grain yield increases, and reduction of soil erosion in relation to the potential gains from animal production and survival.