Linking root functional traits and soil enzymatic dynamics to productivity in wheat under conventional and nano-urea fertilization

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Efficient wheat production relies on a well-developed root system synchronized with shoot growth and adequate nitrogen (N) availability. Although nano-urea (NU) has shown potential to enhance crop productivity and nutrient use efficiency, its influence on root architecture and soil microbial activity is not fully understood. In this study, the application of 75% recommended dose of nitrogen (RDN) along with two foliar sprays of NU markedly improved root traits and biological activity. Root length density (RLD) was significantly higher under the 75% RDN + NU treatment (1.68 cm cm⁻³; 2-year mean) compared with the control (0% NU) (1.05 cm cm⁻³) and 50% RDN + NU (1.49 cm cm⁻³). However, it remained statistically at par with 100% RDN (1.59 cm cm⁻³) at 0-15 cm soil depth at 90 days after sowing (DAS). Similarly, root surface areas density (RSAD) was significantly enhanced under 75% RDN + NU (16.9 × 10⁻² cm² cm⁻³; 2-year mean) over the control (11.6 × 10⁻² cm² cm⁻³) and was statistically comparable to 100% RDN (15.9 × 10⁻² cm² cm⁻³). The root volume density (RVD) also followed a similar trend, with significantly higher values under 75% RDN + NU (2.00 × 10⁻² cm³ cm⁻³; 2-year mean) compared with control (1.29 × 10⁻² cm³ cm⁻³) and 100% RDN (1.71 × 10⁻² cm³ cm⁻³). Dehydrogenase activity (DHA) peaked under 75% RDN + NU, being approximately 80% higher than the control, indicating enhanced microbial activity in the rhizosphere. Irrespective of the basal dose there was a higher activity of root traits was observed in NU applied plot. However, root cation exchange capacity and urease activities were higher at 125% RDN, reflecting stronger ion adsorption under higher N level. These findings suggest that moderate nitrogen doses (75% RDN), especially in conjunction with nano-based foliar sprays, can enhance root growth and improve belowground nutrient use efficiency.