Plant-available nitrogen in the soil profile is lower across the western grainbelt this year compared with the previous four years. Grain growers across the Western region are urged to monitor crops for nitrogen deficiency.
Last season’s high grain yields and the dry summer have combined to reduce soil nitrogen. For mineralisation, the number of days that the topsoil is wet is more important than the amount of rain that falls.
The biggest change was found in the Central Agricultural Region, where the WA No Till Farming Association’s Northam and Cunderdin sites had 50kg N/ha, which had been above 100kg for the previous four years due to an accumulation of surplus nitrogen (about 45kg N/ha is required to produce 1t/ha of wheat). This data is from the Farm Focus Paddock project (DAFWA and GRDC). Concerns about low soil nitrogen were also reinforced by monitoring undertaken by the Facey Group in the Upper Great Southern, as well as by a University of Western Australia trial with the Liebe Group in the Midwest.
Several tools are available to assist growers to make informed decisions about their nitrogen regime for the rest of the season:
- Tissue testing is an effective way to assess whether the soil supply of nitrogen and other nutrients is keeping up with crop demand, though the weather conditions prior to taking the tissue sample needs to be taken into account. Deficiencies of other nutrients will limit the response to N applications
- Commercial and online crop nutrition models – most fertiliser companies have their own recommendation models, and growers can also access valuable information from local Yield Prophet® sites, which is supported by DAFWA, and an app called N-Broadacre, based on DAFWA’s Select Your Nitrogen model.
“Yield Prophet® is probably the best model we have for dealing with unusual seasons, because it uses daily rainfall and temperatures to model wheat growth for different nitrogen scenarios” said Dr Craig Scanlan, DAFWA.
For more information about nitrogen deficiency visit DAFWA’s website and watch for more local information in local AgTactics and AGMEMO newsletters.
Prepared by Stephanie Alt with technical input from Liam Ryan, DAFWA and James Easton, CSBP.
Photo courtesy of the GRDC.