In-depth analysis of soil nitrogen reserves in the Mallee and Riverina Plains has revealed that last year’s bumper winter crop has severely depleted nitrogen levels for the coming season.
Testing was undertaken by Incitec Pivot Fertilisers agronomist Lee Menhenett, who sampled barley, wheat and canola crops across the region and tested the soil, grain and tissue and site specific yield and protein results.
Mr Menhenett said studying protein levels would indicate whether yields could have been increased if more nitrogen had been applied.
‘‘Protein values below 10.5 to 11.5 per cent for wheat and 10 per cent for barley indicate that the crop ran out of nitrogen before it ran out of moisture and yields may have been compromised,’’ he said.
In some cases the inability to apply additional nitrogen fertiliser as a result of paddocks that had become too wet only escalated the nutrient losses that occurred as a result of the high yields.
One paddock in the Mallee which was soil tested revealed that after the grain was harvested, only 9kg/ha of nitrogen remained, which Mr Menhenett said was negligible for stubbles.
‘‘A sound strategy for this paddock could be to increase nitrogen rates at sowing, as long as it is within safe seed rates, or opt for a very early nitrogen top-dress,’’ he said.
‘‘Another option would be to grow a legume crop.’’
While burning may be considered necessary to avoid sowing into a large stubble, Mr Menhenett said it was important to consider all options, pointing to the potential financial cost of burning a field with 80kg/ha of nitrogen.
‘‘If we value the nitrogen in the stubble at $1/kg, burning it could cost the grower up to $64/ha in lost nitrogen alone, with up to 80 per cent of nitrogen lost in hot burns,’’ he said.
‘‘Another option could be cycling some nitrogen through sheep to keep some of the nitrogen in the system.’’