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. N 66 –N 75% with nano urea sprays achieved economic returns comparable to RDN 100 , 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.