Canopy development and grain yield of dryland wheat is modified by strategic nitrogen supply and stubble management

Yield in dryland wheat could be improved through a better understanding of crop responses to no-till (NT), stubble retention and nitrogen (N). Field experiments were established at Roseworthy and Karoonda in South Australia to evaluate wheat crop responses to contrasting tillage systems, different amounts of stubble and N timing. Canopy development regulated grain yield. No-till crops produced more biomass compared with conventional tillage while large amounts of stubble (5 t ha−1) reduced biomass at harvest compared with both moderate amounts of stubble (2.5 t ha−1) and bare ground. The application of N at sowing produced large vegetative biomass compared with delayed N supply. However, delayed N supply allowed more rapid accumulation of biomass between stem elongation and flowering, the critical period for yield determination in wheat. Crop growth rate during this period positively correlated with grain number (R = 0.44) but negatively with tiller numbers (R = 0.66). Grain yield declined with the retention of more than moderate amounts of stubble, irrespective of whether the stubble was applied as mulch or left standing; similarly, additional stubble did not improve water conservation benefits. Results demonstrate that the strategic supply of N under stubble retention can increase crop growth rate during the critical period between stem elongation and flowering.