Nano-fertilizer integration enhances soil nitrogen fractions and nitrogen uptake in wheat (Triticum aestivum L.)

Nitrogen use efficiency (NUE) is a key economic and ecological consideration in wheat production systems that must be addressed through innovative approaches such as nano-fertilizers. Wheat ( Triticum aestivum L.) is central to global food security, yet productivity in the sub-tropical plains of Jammu (India) remains below the national average, largely because of inefficient nitrogen management. The present study was undertaken to quantify the effect of nano-NPK foliar fertilization, integrated with the recommended dose of nutrients (RDN), on soil nitrogen fractions and plant nitrogen uptake in wheat. A two-year field experiment (rabi 2021–22 and 2022–23) was conducted at SKUAST-Jammu, Chatha, using a randomized block design with twelve treatments and three replications. Treatments combined three RDN levels (100%, 75% and 50%) with two or three foliar sprays of a commercial nano-NPK formulation (guaranteed 8% N, applied at 4 mL L −1 ) at the tillering, jointing and booting stages, using wheat variety RSP-561. Post-harvest soil (0–15 cm) was analysed for available N, ammoniacal-N, nitrate-N, total N and organic N and nitrogen uptake was determined in grain, straw and roots. Treatment means were separated by Fisher’s protected LSD ( p = 0.05) and are reported with grouping letters and standard error (± SEm). The treatment receiving 100% RDN with three foliar sprays of nano-NPK (T8) recorded the highest available nitrogen (274 kg ha −1 in 2022–23; a 46% increase over the unfertilized control), the highest ammoniacal-N (115 kg ha −1 ), nitrate-N (93 kg ha −1 ) and grain nitrogen uptake (64.05 kg ha −1 ; 59% above control). Apparent nitrogen recovery efficiency, calculated from total plant N uptake, rose from 37% at 100% RDN alone (T2) to 54% under T8 and was highest (59%) under 75% RDN with three sprays (T9), quantifying the improvement in NUE. Available N, nitrate-N and ammoniacal-N were strongly correlated with grain N uptake (r = 0.84, 0.89 and 0.84, respectively) and straw N uptake (r = 0.82, 0.89 and 0.85), whereas organic and total N showed weaker associations. Notably, T9 was statistically at par with the full dose (shared LSD grouping) in the second season, indicating scope for a 25% reduction in conventional fertilizer without a penalty in nitrogen uptake, subject to yield and economic validation. Integrating nano-fertilizers with RDN therefore enhances soil nitrogen availability and uptake and improves apparent nitrogen recovery, supporting more efficient nutrient management in wheat-based systems.