Influence of nitrification inhibitors, placement technique and irrigation sequence on utilization of labelled urea-N by wheat (Triticum aestivum L.)

To investigate the fate of fertilizer nitrogen applied in combination with dicyandiamide (DCD) and neem cake (NC) to wheat, we conducted a field experiment on Mehrauli loam soil (Typic Haplustept). The ¹⁵N-labelled urea was applied to wheat in different splits, either alone or in combination with DCD and NC. The results indicated that application of urea-N either alone or in combination with DCD and NC significantly increased both grain as well as straw yields of wheat. Magnitude of N response varied from 0.96 to 1.28 and 0.09 to 2.05 t ha⁻¹ in grain and straw, respectively. Highest grain and straw yields were found when urea amended with DCD was applied in two splits of 60+60 kg, with topdress-N applied just before irrigation. Highest N use efficiency was observed in DCD-amended urea. Neem cake blended urea was at par with urea+DCD, when applied in two splits, with topdressing done just before irrigation. This showed that 30 kg nitrogen could be saved without significantly sacrificing on the grain production of wheat, when urea was blended with either DCD or neem cake. The ¹⁵N analysis of wheat grain samples showed that only 40 to 71% nitrogen was derived from the fertilizer source. The highest percent of nitrogen derived from fertilizer (%Ndff) was observed in case of three split applications of urea alone applied @ 120 kg N ha⁻¹ (30+45+45 kg) before irrigation. Total fertilizer nitrogen uptake varied from 40.3 to 76.3 kg ha⁻¹ with dose of N varying from 90 to 120 kg of urea-amended with DCD.