Fate of 15N-labelled urea under cotton and maize as affected by urease and nitrification inhibitors, and application method

Context The use of urease and nitrification inhibitors is an important mitigation strategy to reduce fertilizer-N loss from croplands. However, limited information exists on the performance of urease and nitrification inhibitors in alkaline calcareous soils under warm climate in the Indo-Gangetic plains. Aims The study aimed at elucidating the effects of urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and nitrification inhibitor 4-amino-1,2,4-triazole (ATC) on the fate of 15N-urea applied to cotton and maize grown in an alkaline calcareous soil under greenhouse conditions. Methods Four fertilizer treatments (15N-urea, 15N-urea + NBPT, 15N-urea + ATC, and 15N-urea + NBPT + ATC) were applied either by the conventional method (granules surface broadcast in splits followed by incorporation/irrigation) or in subsurface bands (granules or liquid; all applied at sowing). Cotton plants were grown to maturity (197 days) whereas maize was harvested at the tasseling stage (61 days). Soil and different plant components were analyzed for total N and 15N contents. Key results With the conventional application method, NBPT reduced urea-N loss under cotton, whereas ATC increased the loss both under cotton and maize. The lowest N loss was recorded with urea + NBPT applied as liquid in subsurface bands. Conclusions In alkaline calcareous soils, ATC may not be effective in reducing urea-N loss under crops exposed to high summer temperatures (average, 33.7–35.7°C), whereas high urea-N loss under these crops can be substantially reduced by subsurface banding of urea along with NBPT. Implications The results warrant further studies to explore appropriate fertilizer-N management practises to reduce fertilizer-N loss under agro-climatic conditions in the Indo-Gangetic plains.