Evaluation of NEXEN™ stabilized nitrogen applied to overhead irrigated cotton (Gossypium hirsutum L.)

This study was conducted to determine the agronomic feasibility of using NEXENTM (urea treated with the urease inhibitor N-(N-butyl) thiophosphoric triamide) for surface of nitrogen (N) fertilizer in irrigated cotton, particularly, for in-crop season N applications. Field experiments were established on a cotton farm in southern Queensland (Australia) during the 2015-2016 season. Fertilizers were applied at N rates equivalent to 0 (control), and 140, 200 (farm practice) and 260 kg ha-1, respectively, to provide a ±30% range of the standard rate used for the commercial crop. The fertilizer was applied on the surface, incorporated or a combination of both pre-plant incorporation and surface application in-crop. Results showed that there was no fertilizer type or nitrogen rate effect above an application rate of 140 kg ha-1 N. This was consistent with analyses of cottonseed N from fertilizer-treated crop, which suggested that the crop was over-supplied with N above that rate. Given these results, the use of NEXENTM appears to be a promising alternative for (overhead) irrigated cotton, for both pre-plant and in-crop season application of N. Although commonly used in the Australian cotton industry, techniques such as ‘water-run‘ urea are considered as low efficiency because of the associated environmental losses of N. Surface application of nBTPT-treated urea with conventional twin discs fertilizer spreaders may enable for improved field operating efficiency and reduced cost of fertilizer application compared with other methods or fertilizer types that require soil incorporation. Our estimates indicated that operating costs may be reduced from approximately AUD16 per ha to AUD5 per ha (AUD1 ≈ USD0.75) when fertilizer is surface-applied compared with soil incorporation, because of lower energy requirements (draft) and labor (operating width, forward speed), with further savings achieved through improved timeliness. This alternative requires investigation to determine the potential risk of N losses through gaseous evolution (volatilization, N2/N2O), particularly in furrow irrigated systems