Effect of summer fallow management on crop yield: Field experiment and simulation analysis

Potential yield of a crop is limited by the factor which most restricts its productivity. In dryland cropping systems this factor is often the available soil water. Nitrogen fertiliser is also a high cost input in crop production systems. Conservation of these resources is essential to increase agricultural productivity and profitability. A field experiment and computer simulation modelling were conducted for the dryland farming system of south eastern Australia to investigate the effect of summer fallow management on growth and yield of canola (Brassica napus L.). A factorial experiment with two residual nitrogen levels and three residual soil water conditions was conducted. Soil water content and crop growth were monitored. At harvest, canola grain yield and above-ground biomass were measured. The biophysical model APSIM was used to analyse the effect of seasonal variation on crop yield by simulating canola grain yield at different residual water and nitrogen levels. The field experiment and simulation modelling indicated that in seasons with high in-crop rainfall, high residual soil water does not increase crop yield. However, residual nitrogen increases crop yield if in-crop rainfall is high. Irrespective of the in-crop rainfall, controlling summer weeds increases crop yield due to residual mineral N and/or residual soil water.