Mitigation of nitrous oxide emissions from furrow-irrigated Vertosols by 3,4-dimethyl pyrazole tetra-methylene sulfone, an alternative nitrification inhibitor to nitrapyrin for direct injection with anhydrous ammonia

Abstract

Nitrogen (N) fertiliser inputs for irrigated cotton production are rapidly increasing to support ever-increasing yields, but much of the applied N may be lost as N gases, including nitrous oxide (N2O), via denitrification in medium–heavy clay soils. The addition of a nitrification inhibitor can reduce overall N loss and N2O emissions. Currently, nitrapyrin (2-chloro-6-trichloro methyl pyridine) is the only inhibitor used with anhydrous ammonia (AA), whereas 3,4-dimethyl pyrazole phosphate (DMPP) has potentially greater stability and longevity in soil, but is not compatible with AA. A newly-developed formulation based on DMPP, 3,4-dimethyl pyrazole tetra-methylene sulfone (DMPS), can be direct-injected with AA. We compared N2O emissions from DMPS- and nitrapyrin-treated AA from two Vertosols used for irrigated cotton. At Emerald (Queensland), both inhibitors reduced N2O emitted by 77% over 2 months. At Gunnedah (New South Wales), DMPS was active in the soil for 3 months, reducing N2O by 86%, whereas nitrapyrin activity lasted for 2 months and reduced N2O by 65%. Realising the potential for improved environmental benefits from directly injecting DMPS with AA requires an agronomic benefit justifying its additional cost to the farmer. Future research needs to investigate the potential for reduced N rates when using these inhibitors – without compromising high yields.