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

Abstract

Abstract. 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.

Comparison of grain yields and N2O emissions on Oxisol and Vertisol soils in response to fertiliser N applied as urea or urea coated with the nitrification inhibitor 3,4-dimethylpyrazole phosphate

“…3b) there was a suggestion of a lower critical N rate for the DMPP (100 kg N ha -1 ) compared with the urea (125 kg N ha -1 ) in order to achieve Y 90% . The consistency of these trends across a broader range of sites and seasons is reported in Lester et al (2016), with this study also suggesting only small agronomic benefits from use of DMPP in summer sorghum cropping.…”

“…As concluded by Lester et al (2016), DMPP might have a greater scope to increase AE of urea in higher rainfall or irrigated production regions, or when high rates of N fertiliser are required to meet seasonal yield potential under highintensity cropping situations. Examples of the latter would include double cropping from a winter cereal to summer sorghum in a high rainfall year, where systems are characterised by high amounts of crop residues and low levels of soil Nconditions that require high fertiliser N rates to prevent severe crop N deficiency.…”

“…Nitrification inhibitor-coated urea has been reported in several studies to substantially decrease N 2 O emissions and increase crop yields in humid, high rainfall environments (Prasad and Power 1995;Linzmeier et al 2001a;Pasda et al 2001;Hatch et al 2005), which are the prevalent environmental conditions during subtropical summers. Among nitrification inhibitors, DMPP (3,4-dimethylpyrazole phosphate) has been reported by many authors as the most efficient in slowing nitrification and reducing N 2 O losses (Weiske et al 2001b;Liu et al 2013;Lester et al 2016). While DMPP was shown to efficiently reduce N 2 O emissions on Oxisol soils in subtropical cropping systems in north-east Australia (De Antoni Migliorati et al 2014), it is still uncertain whether it has the same effectiveness in Vertisols -the dominant cropping soils in the region.…”

“…Plots at the Vertisol and Oxisol sites each measured 6 m  12 m and 5.4 m  13 m, with buffer areas of 1-2 m between plots. Further information on the experimental details is outlined in full in Lester et al (2016).…”

Effect of enhanced efficiency fertilisers on nitrous oxide emissions in a sub-tropical cereal cropping system

“…There was surplus N to meet crop demands in all treatments and hence there was no significant scope for the EEF products to increase NUE or increase crop yield. As shown by Lester et al (2016), DMPP might have the greatest scope to increase NUE under high-intensity cropping when high rates of N fertiliser are necessary to meet crop demand. Future EEF studies should involve a range of N rates to identify if decreased N rates can be used with EEF products to achieve the target yield.…”