Dr Ismail Garba1, Ms Heidi Horan1, Dr Lindsay Bell2
1CSIRO Agriculture & Food, St Lucia, Australia, 2CSIRO Agriculture & Food, Toowoomba, Australia
Biography:
Ismail Garba is a cropping systems scientist with CSIRO. His work focussed on system-oriented approach to managing agroecosystem for improved farming system productivity and resilience through participatory research, field experimentation, and modelling with the aim of improving analytic-driven on-farm decision making for enhanced resource use efficiency, precision and farm enterprise risk management.
Abstract:
In dryland grain cropping systems of Australia, nitrogen (N) deficiency account for ~ 40% of the wheat yield gaps. Nitrogen banking strategies that match soil N supply to crop N demand have the potential to reduce these yield gaps and potentially reverse declines in soil organic carbon (SOC) and soil N stocks. Here, we identify optimal N banking strategies at national level that minimise trade-offs between productivity (grain yield and crop gross margin) and negative environmental outcomes (N2O and GHG emissions). We simulated ten N banking scenarios across nine soil types, different SOC fractions and crop-fallow rotations were compared to national average N fertilizer specific to each soil type and production region. N banking scenarios were simulated by balancing soil mineral N at sowing with fertiliser N to meet different levels of annual N supply or N bank levels. The optimal N bank averaged 150±12, 180±9 and 207±4 kg N ha–1 in low, medium and high rainfall environments with large variability across initial SOC content and soil types. On average this equates to 38 – 92 kg N ha–1of fertilizer needed to maintain soil mineral N stocks and productivity. The optimal N bank target was predicted to reach long-term N balance when inputs and outputs were approximately equal, even though soil C was still predicted to be declining irrespective of the production environments. Thus, this study demonstrated that optimized N banking strategies that take cognisance of soil, and seasonal climatic boundaries have the potential to mitigate yield gaps while balancing productivity- sustainability trade-offs in dryland cropping systems.