Crop breeding for conservation agriculture

Abstract

Cropping area under conservation agriculture (CA) has increased significantly worldwide with most located in South and North America and Australia. CA was initially introduced to control soil erosion but has become increasingly popular as the practice conserves soil moisture, reduces fossil fuel use, lowers cost and, once established, increases yield. In some countries, such as Australia, CA is practised on more than two thirds of the total cropped area. The new practice is more sustainable and environment friendly as microbial activity and soil organic matter increase, thus improving soil health and crop yields. Optimised crop rotations in CA help control weeds and improve nutrient availability, thus contributing to farming system sustainability. However, most crop cultivars currently grown under CA have been developed on conventional or full tillage and it is likely that valuable genetic variation for adaptation to CA has been lost. Some genetic studies found significant genotype × tillage practice interactions under CA; however, the trend has not been consistent over environments or across studies. The relatively weak genetic response to tillage practice is probably a function of selection under conventional tillage over thousands of years. Even early farmers tilled the soil and made seed selections for the next crop based on the best adapted and most vigorous plants. If a stronger response to CA is to be achieved, then germplasm resources that extend adaptive trait variability must be characterised and integrated with crop breeding. It is vital that crop improvement strategies are developed that incorporate CA as the interaction between improved crop genotype and an optimised farming system in order to produce the higher yields needed to keep pace with human population growth.