Organic residues & soil mixing alter plant available nitrogen

Experimental field research considering the effect of different crop residues and level of soil incorporation on the timing and amount of nitrogen that is supplied through a growing season in the subsequent year.


  • Nitrogen supply was more strongly associated with wet-dry cycles than residue management
  • The rate of nitrogen supply increased with increasing intensity of soil disturbance and great soil-residue contact
  • Microbial biomass was increased under legume crop residues compared to cereals
  • Despite differences in the magnitude of N release, neither crop type nor incorporation method significantly altered the timing or pattern of N release
  • Residues with a narrow carbon to nitrogen ratio released surplus nitrogen to the crop.


Despite our understanding of plant nitrogen (N) uptake and soil N dynamics in arable systems, the supply and demand of N are infrequently matched as a result of variable seasonal and soil conditions. Consequently, inefficient N use often leads to constrained production and can contribute to potential environmental impacts. This study aimed to examine the influence of plant residue quality (C/N ratio) and extent of residue incorporation into soil on temporal changes in microbial biomass, soil mineral N and the associated plant N uptake by wheat in the semi-arid agricultural production zone of Western Australia.


Project funded by the GRDC in collaboration with the Department of Agriculture and Food WA


Frances Hoyle
The University of Western Australia