Nutrient shortfall contributing to yield gap in high rainfall zone

GRAIN growers in the southern cropping region’s high rainfall zone could be limiting their yields and profits by not applying enough fertiliser to their crops according to Agriculture Victoria.

A Grains Research and Development Corporation (GRDC) research investment has found that under-fertilising in the high rainfall zone (HRZ) appears to be a major cause of yield gaps – the difference between the actual yield achieved by a grower and the water-limited yield potential.

Research led by Dr Malcolm McCaskill, a soil scientist with Agriculture Victoria, has established that by providing sufficient nutrients, wheat and canola yields could be equal to or even exceed the water-limited potential, except in cases of severe waterlogging or drought.

“Commercial wheat and canola yields are well below their water-limited potential in the HRZ,” Dr McCaskill said.

“The potential is defined as the maximum possible yield able to be grown with the optimal sowing date, current varieties and non-limiting nutrients, and with minimal detrimental effect from pests, diseases and weeds.”

Under-fertilising in the HRZ could be linked to the use of soil test interpretation guidelines developed for low and medium rainfall areas. Dr McCaskill said these guidelines may not be appropriate for the HRZ, given its higher yield potential.

To assist HRZ growers in achieving higher yields, Dr McCaskill and his research team have produced three Excel-based decision-support tools to determine the economic optimum application rate of nitrogen, phosphorus, potassium and sulphur under a range of conditions.

Dr McCaskill’s GRDC Grains Research Update paper, “filling the yield gap – optimising yield andeconomic  potential of high input cropping systems In the HRZ”, can be found at goo.gl/qBsBky.