Foliar efficacy of phosphorous formulations for rainfed cotton with graded levels

Soil amendment with phosphatic fertilizers (50 or 100%) as basal is susceptible to fixation losses, leading to low phosphorus use efficiency (PUE). Consequently, foliar spraying of di-ammonium phosphate (DAP) up to 2% is preferred for rainfed cotton. In addition, it has been reported that nano-fertilizers facilitate a steady release of nutrients, enhance nutrient uptake, and boost nutrient use efficiency, ultimately resulting in increased crop yields and profitability. Therefore, this study aimed to investigate the foliar efficacy of DAP formulations to increase the growth, yield and nutrient uptake in rainfed cotton grown in black calcareous soils with graded levels. The field experiment consists of 13 treatment combinations with 3 replications, which were laid out via randomized complete block design (RCBD) during the kharif seasons of 2023 and 2024. These include varying levels (100, 75, 50%) of recommended dose of fertilizer (RDF) with foliar spray (FS) of nano DAP one time at 45 DAS, two-times at 45 and 60 DAS, foliar spraying of DAP one time at 45 DAS, two-times at 60 DAS and a water spray (control 0% RDF). Nano-DAP (2% N, 5% P₂O₅) and DAP (18% N, 46% P₂O₅) were sprayed in both the years. In 2023 and 2024, the treatment T₄ (nano-DAP FS two times + 100% RDF), increased seed cotton (SC) and seed cotton yield (SCY) by (19.7, 15.7%) and (13.3, 12.9%), respectively, compared to T₁ (DAP FS one time + 100% RDF). Similarly, root length (10.9, 9.8%), boll weight (10.8, 13.8%) and seeds boll^- 1 (9.8, 10.0%) in T₄ were increased compared to T₁ in 2023 and 2024. Reducing the RDF by 25%, i.e., T₈ (nano-DAP FS two times + 75% RDF), increased both the SC and SCY by 16.2, 3.8% and by 4.7, 10.0%, respectively, in both consecutive years compared to T₁. However, seed index and fibre quality were not significantly influenced by foliar spraying of the DAP formulations. Economic analysis revealed significantly higher gross monetary returns of US$ 2490, US$ 2696 and net monetary returns of US$ 1422, US$ 1660 and benefit-cost ratio of 1.45, 1.63 were recorded in T₄ during 2023 and 2024, respectively. Among all the treatments, T₄ treatment also resulted in significantly higher profitability (ha^- 1 day^- 1) of US$ 9.82 and US$ 11.06. Foliar spraying of DAP formulations combined with varying RDF levels improved the growth, yield, nutrient uptake and use efficiency, economic viability of rainfed cotton. Nevertheless, these parameters were statistically comparable to those observed in T₁. However, T₄ achieved the highest NMR and benefit-cost ratio compared to T₁ over both the years of experimentation. However, T₄ (nano-DAP FS two times + 100% RDF) resulted in the highest benefit-cost ratio and per day profitability compared to other treatments.