Agronomic responses of grain sorghum to DMPP-treated urea on contrasting soil types in north-eastern Australia

Grain sorghum grown in north-eastern Australia's cropping region increasingly requires nitrogen (N) fertiliser to supplement the soil available N supply. The rates of N required can be high when fallows between crop seasons are short (higher cropping intensities) and when yield potentials are high. Fertiliser N is typically applied before or at crop sowing and is vulnerable to environmental loss in the period between application and significant crop N demand due to potentially intense rainfall events in the summer-dominant rainfall environment. Nitrification inhibitors added to urea can reduce certain gaseous loss pathways but the agronomic efficacy of these products has not been explored. Urea and urea coated with the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) were compared in sorghum crops grown at five research sites over consecutive summer sorghum growing seasons in south-east Queensland. Products were compared in terms of crop responses in dry matter, N uptake and grain yield, with DMPP found to produce only subtle increases on grain yield. There was no effect on dry matter or N uptake. Outcomes suggest any advantages from use of DMPP in this region are most significant in situations where higher fertiliser application rates (>80 kg N/ha) are required.