Foliar efficacy of urea formulations in Bt cotton for enhancing yield and nitrogen use efficiency under rainfed black calcareous soils

Inadvertent use of nitrogenous (N) fertilisers has resulted in low N use efficiency and cotton productivity in high yielding Bt cotton hybrids. Apparently, soil application of prilled urea is associated with substantial N losses posing serious threats to the ecosystem and environment. Consequently, foliar spray of N fertilisers is being practiced in rainfed cotton. However, literature on foliar efficacy of nano urea (12 %) in cotton remains limited. Therefore, a field experiment was conducted with 13 treatment combinations with urea and nano urea as foliar spray one-time at 35 days after sowing (DAS) and two-times at 35 and 55 DAS along with three recommended doses of nitrogen (100 %, 75 %, 50 % recommended dose of nitrogen (RDN)) and compared with foliar spray of urea once at 100 % RDN. The study results revealed few significant (p < 0.05) differences with foliar spray of urea formulations in growth and yield attributes over other treatments. Notably, nano urea two times spray + 100 % RDN significantly increased seed cotton (SC g plant-1) and seed cotton yield (SCY kg ha-1) by 9 % and 6 % respectively, compared to urea spray + 100 % RDN. Similarly, nano urea two times spray + 100 % RDN has significantly increased N concentration and uptake by 7 %, 12 % respectively compared to urea one time spray + 100 % RDN. In contrast, seed index and fiber quality were not significantly influenced by foliar spray of urea formulations. Economic calculations postulated that nano urea two times spray + 100 % RDN recorded the highest benefit to cost (BC), marginal cost benefit ratio (MCBR), with an additional net return of ₹4093 compared to other treatments. Overall, the study highlights the potential of urea formulations as foliar spray at 35 and 55 DAS with 100 % RDN in improving rainfed cotton production under black calcareous soil.