Australian wheat-growing areas are dry. Historically, tillage was used to remove weeds, but tillage further dried out the soil. Herbicides have made it possible for Australian wheat farmers to stop tilling entirely. As a result, soil moisture retention has increased and wheat yields have doubled.
“An analysis of the yield trends of wheat production in Australia showed that yields have increased by an average of 12-13 kg ha-1 year-1 over the past six decades, despite rainfall not changing and irrigated wheat contributing only a very small proportion to total production. A more recent analysis of wheat yield trends in Australia and the various states of Australia has shown that since the early 1980s there has been a more rapid increase in yield of over 30 kg ha-1 year-1. In Western Australia, where wheat is not irrigated and rainfall has probably declined over the last 25 years, the increases… arise solely from increases in rainfall-use efficiency.
However, the major impact of agronomic management on rainfall-use efficiency has not arisen from increasing total water use by the crop in evapotranspiration, but from increasing water use by the crop itself in transpiration at the expense of water loss by weeds or from the soil by soil evaporation, deep drainage, surface runoff, or lateral throughflow.
The use of minimum tillage or conservation tillage, whereby residues from the previous crop are left on the surface, weeds are controlled by herbicides rather than tillage, and the seed is sown with minimum disturbance of the soil surface by the use of narrow tines, has led to reduced losses of water by soil evaporation and increased yields. Further, minimum tillage systems allow earlier planting as delays resulting from using tillage to remove weeds are reduced.”
Author: Turner, N. C.
Affiliation: CSIRO Plant Industry.
Title: Agronomic options for improving rainfall-use efficiency of crops in dryland farming systems.
Source: Journal of Experimental Botany. 2004. 407:2413-2425.