Assessing the scope for nano-urea to reduce nitrogen inputs while maintaining rice yields in India

Excessive nitrogen (N) fertilizer use in rice (Oryza sativa L.) cultivation results in significant nutrient losses and environmental degradation. Nano fertilizers offer a promising solution to enhance nutrient use efficiency, reduce losses, and mitigate environmental impacts in rice-based systems. This study aims to evaluate the effects of nano-urea application on rice yield, economic returns, and N use efficiency in India. Field experiments (2022–2024) were conducted at Varanasi and Guwahati, assessing nine treatments in 2022 and seven treatments in 2023 and 2024 in a Randomized block design (RBD) replicated thrice. Treatments included conventional soil-applied N at 75, 66, and 50% of the recommended dose (RDN) and was tested with foliar applications of nano-urea, applied once at panicle initiation (PI) or twice at maximum tillering (MT) and PI. These were compared with control and state fertilizer N rate. Application of 66–75% RDN with nano-urea applied twice (MT and PI) produced yields comparable to 100% RDN. However, applying nano-urea with 50% RDN resulted in a yield penalty of 17% (0.88 t ha−1) in Guwahati (2023–2024) and 16–19% (0.95–1.2 t ha−1) in Varanasi (2022–2023). Our findings indicate that 27–40 kg N ha−1 can be saved in Varanasi and 15–20 kg N ha−1 in Guwahati without yield loss using RDN 66–75% with nano-urea. N66–N75% with nano urea sprays achieved economic returns comparable to RDN100, with reduced N inputs. Based on these findings, the application of urea at 66–75% RDN is recommended, supplemented with two foliar applications of nano-urea at MT and PI stages to sustain yield while reducing overall N input.