Dr Ben Jones1, Mr Nick Poole1, Mr Darcy Warren1, Mr Maxwell Bloomfield1, Mr Aaron Vague1
1Field Applied Research (FAR) Australia Ltd, Bannockburn, Australia
Biography:
The nitrogen response in wheat is an unintentionally recurring theme in Ben's career. It began with targeting the narrow protein range for white salted noodle wheat in the medium rainfall Wimmera. Then followed GPS-driven side-dressed wide-row wheat, soil-specific economic optimum rates in the low rainfall Mallee, schemes for satellite-driven rate recommendations anywhere, and teaching nitrogen agronomy to agriculture students. Ben currently works with FAR Australia on a GRDC project using Hyper Yielding Crops and other past experimental data to try to improve APSIM NextGen wheat yield predictions in high yielding environments. The nitrogen response is also part of that.
Abstract:
Inadequate nitrogen nutrition is regarded as a key reason that Australian rain-fed crops do not achieve their water-limited potential yield. There is a belief that overall nitrogen nutrition could be increased without penalty ('nitrogen bank' concept). Newer varieties are less likely to experience 'haying-off', and excess nitrogen should be recovered in grain protein or at least have minimal yield effect. Results from 34 nutrition experiments in southern Australia (part of the "Hyper Yielding Crops" program) challenge these ideas.
Enough nitrogen was applied that yield maxima were observed in 22 experiments (mostly winter wheat, range 3.6 to 11.4 t/ha dry basis). Grain recovery of additional nitrogen only exceeded 18 kg N/ha in one experiment where a large nitrogen increment likely straddled the optimum (maximum 45 kg/ha N). The yield loss with additional nitrogen for winter wheat ranged up to 1.2 t/ha and fitted a frontier of about 15 kg grain/kg N applied. This was three times the ‘haying off’ rate previously observed in spring wheat, and implied assimilate being used in protein storage, possibly when grains were being set.
In the wider experimental program, no more than 340 kg/ha N was recovered in grain from crops yielding up to 15.4 t/ha. Grain proteins for high yielding crops appear to converge on a narrow range between 11.5-13%. This implies that world record crops of 15.5 t/ha (dry basis) would not recover more than 350 kg/ha N in grain. Growers targeting high wheat yields need to also be cautious about over-application of nitrogen.