Vadakattu V.S.R. Gupta
CSIRO Agriculture & Food, PMB 2, Glen Osmond, SA 5064, Email: [email protected]
Nitrogen mineralized from the soil organic matter (SOM) and crop residues makes a substantial contribution to crop N uptake. Soil N supply comes from soil organic matter and recent crop residues and the rate of supply is influenced by the soil biological capacity, i.e. microbial biomass (MB) and microbial turnover, and modulated by management and environmental factors. Soil type, crop rotation and management practices associated with tillage, stubble retention and fertilizer application can influence the diversity of microbial populations and the size of MB, and along with the environment they affect biological processes involved in N2 fixation, mineralization and availability and losses. The rate and timing of the availability of N from stubble to the following crops is determined by the rate of decomposition and immobilization by soil microorganisms (N in MB). The amount of MB-C & N vary with soil type, crop rotation, tillage and other management practices that can influence microbial populations. In southern Australian cropping regions, the effect of loss of N from stubble removal may not be greater than its temporary tie-up during decomposition.