Nitrogen rates, crop rotation and root health are proving to be the biggest factors affecting crop yield for southern region farmers, according to interim results from the GRDC's National Paddock Survey.
The national study of 250 leading grain farms has revealed the size, variation and cause of yield gaps across Australia, and highlighted two options to ensure crops reach their full potential. These are more targeted nitrogen (N) management and crop rotation.
Lead researcher Dr Roger Lawes, of CSIRO Agriculture and Food, says there is potential to reduce the size of the yield gap through more targeted N management and crop rotation, but multiple interacting factors can influence the final outcome.
The survey sought to determine the gap between actual and potential yield across Australia to identify the main yield constraints and help close the gap.
The yield gap is the difference between actual yield and water limited yield potential, the maximum possible yield with the optimal sowing date, current varieties and nutrients, and limited effect from pests, diseases and weeds.
While a small yield gap indicates management is near optimum, the survey showed priorities for growers to improve yield and profit differ in each region.
In the southern region, the amount of applied N, the previous crop and root health score were the most important variables. Weeds and growing season rainfall were secondary drivers.
Results suggest larger yield gaps occur in the high rainfall zone, possibly because the yields are harder to achieve.
Nitrogen does appear to limit the ability of growers to capture higher yield potentials, while crop rotation plays a role, according to the survey findings.
The average amount of N fertiliser applied to wheat was 26 kilograms of N per hectare in the northern region, 43kg N/ha in the southern region and 32kg N/ha in the western region. But this varied greatly among paddocks in each region.
Previous research using shire-level data showed current growers across Australia are yielding about half of what is potentially possible.
In the northern region, 43 per cent of paddocks fell within 80 to 100 per cent of yield potential. In the southern region, 38 per cent fell within the range. In the western Region, 46 per cent achieved 80 to 100 per cent of yield potential.
Average dry wheat yields were higher in the northern and southern regions and lower in the western region.
More information: Dr Roger Lawes, CSIRO, 08 9333 6455, firstname.lastname@example.org