A MISMATCH between soil water supply and available soil nitrogen is likely to drive growers from across NSW to topdress nitrogen early this season in winter cereals and canola.
All year, Jim Laycock, Cowra-based agronomist with Incitec Pivot Fertilisers, has been seeing soil test results with low to very low soil nitrogen levels.
“It’s the only negative in what has been an excellent start to the season for many growers, with good rainfall in March and above average soil moisture profiles,” he said.
“Unfortunately, deep N soil test results continue to show that in many cases, the nitrogen tank is running on empty.”
The Nutrient Advantage laboratory has analysed more than 700 deep N soil tests from NSW between the start of January and the end of April this year.
“An alarming 43 per cent of these tests are showing less than 30 kilograms to the hectare of plant-available nitrogen in the main root zone, and 75pc are showing less than 60kg/ha of nitrogen,” he said.
With less than 30kg/ha of nitrogen in the soil, Mr Laycock estimated that crop yields would be capped at about 1.6 tonnes to the hectare of APW grade wheat without any nitrogen fertiliser, assuming a 40kg/ha contribution from mineralisation in crop.
“Crops are going to need more nitrogen to achieve their yield potentials where there is adequate or above adequate soil moisture,” he said. He said growers were likely to want to topdress crops soon, because early applications usually produced the greatest yield responses.
However, current Bureau of Meteorology forecasts predict below average rainfall prospects for May, June and July. He said growers should start topdressing as soon as the airseeder was put away.
