Western Australian grain growers may need to consider adjusting 2014 nitrogen fertiliser strategies due to the influence of high stubble loads and a dry summer and autumn on plant available nitrogen in the soil.
This is the message from Department of Agriculture and Food (DAFWA) development officer Liam Ryan, whose work is partly supported by the Grains Research and Development Corporation (GRDC).
He said some growers had reported low soil test results for nitrogen in the lead up to this year’s cropping season and wanted to know if extra fertiliser was needed at seeding time.
Mr Ryan suggested growers use these results and assess stubble loads to determine if additional fertiliser was required, and consider adjusting their nitrogen application method at seeding time or using split (separate) nitrogen applications which could decrease any risk of low nitrogen availability.
“Knowing your current soil nitrogen status; stubble density; stubble quality (including the amount of nitrogen relative to carbon); and soil moisture content can help you manage fertiliser applications and rates to ensure that adequate nitrogen is supplied to the crop,” he said.
“On paddocks where high stubble loads are retained, there is a high likelihood that nitrogen fertiliser applied at sowing or early in the season may be temporarily unavailable to young crop plants.
“A higher than usual proportion of applied nitrogen may be immobilised, or ‘locked up’ by soil microbes due to such a large input of carbon in the form of heavy stubble loads.
“Recent rainfall events will have triggered microbial activity and associated decomposition of crop residues.”
Mr Ryan said banding nitrogen fertiliser at seeding time could potentially decrease nitrogen immobilisation by physically separating the nitrogen from carbon residues.
“This will ensure that most of the applied nitrogen is available to emerging crop plants,” he said.
More information about soil nitrogen immobilisation is available at www.agric.wa.gov.au/soil-carbon/immobilisation-soil-nitrogen-heavy-stubble-loads.
The DAFWA-led work is supported by the Australian Government and the GRDC, including through its More Profit from Crop Nutrition (MPCN) initiative.
Information about the GRDC MPCN initiative is available in a GRDC Ground Cover supplement available at www.grdc.com.au/GCS108.
Caption: Nitrogen deficiency in the previous year’s harvester windrows caused by accumulation of carbon from residues which led to the immobilisation of nitrogen by microbes.
Liam Ryan, DAFWA
08 9690 2081
GRDC Project Code