John Angus is a researcher with the CSIRO and a mixed enterprise farmer in southern NSW. At the 2016 GRDC research updates John reported on a three stage process to make strategic decisions about Nitrogen (N) nutrition through the season for dryland farmers.
Stage 1 – Prior to sowing
Prepare a Nitrogen budget using a conservative yield potential to predict crop-N demand
e.g. N budget (kg N/ha) = target yield (t/ha) x target protein (%) x 2.34
Estimate the soil supply of available N – an Autumn soil test to 60cm is the best measure – and calculate the required amount fertiliser N. This should be the basis of the starter N rate applied.
e.g. N fertiliser (kg N/ha) = N budget – soil supply of N x 2
Both predicted crop-N demand (your N budget) and estimated soil-N supply are imprecise, so the actual fertiliser-N rate recommended might range 20-50kg N/ha from the calculation.
Stage 2 – At stem elongation
Re-calculate your N budget based on a revised target yield. Revise N availability in the paddock based on counts of the number of shoots at crop stage DC30-31:
- More than 700 shoots per m2 – don’t apply N, N is likely to be sufficient.
- Less than 500 shoots per m2 – do apply N as growth is likely to be N limited.
Topdressing N at this stage is most effective just prior to rain.
Stage 3 – Approaching booting
There may be another opportunity to topdress nitrogen as the crop approaches booting (DC40-45). In the rare circumstance that the soil moisture profile is full, and there is the prospect of more rain, topdressing N can be a profitable tactic to increase both yield and protein.
2016 GRDC update paper from John Angus: Budgeting crop nitrogen supply: better estimation, better decisions
John Angus, CSIRO, Tim Weaver, NSW DPI, Graeme Sandral, NSW DPI.