Effect of nano-urea and fertilizer deep placement on nutrient uptake and nitrogen use efficiency in wet direct seeded rice (Oryza sativa L.)

Efficient nitrogen management is essential for improving nutrient uptake and nitrogen use efficiency in rice cultivation, particularly under wet cultivation systems where nutrient losses are high. A field experiment was conducted during the kharif seasons of 2022 and 2023 at the Instructional-cum-Research Farm, Assam Agricultural University, Jorhat, to evaluate the effect of different nitrogen management practices on nutrient uptake (N, P and K) and nitrogen use efficiency indices in rice. The experiment was laid out in a randomized block design with three replications and thirteen treatments, comprising different levels of recommended dose of nitrogen (RDN), nano-urea application and fertilizer deep placement (FDP). Grain and straw samples collected at harvest were analyzed for nitrogen, phosphorus and potassium content, and nutrient uptake was calculated. Partial factor productivity of nitrogen (PFPN) and agronomic efficiency of nitrogen (AE) were computed to assess nitrogen use efficiency. Nutrient uptake showed numerical variation among treatments. The highest total nitrogen uptake (68.57 kg ha⁻¹) was recorded under 125% RDN + nano-urea, followed by 100% RDN as FDP (63.70 kg ha⁻¹), whereas the lowest uptake (22.09 kg ha⁻¹) was observed under the control. Similarly, total phosphorus uptake ranged from 6.12 kg ha⁻¹ in the control to 16.89 kg ha⁻¹ under 100% RDN as FDP, while total potassium uptake varied from 27.53 to 61.79 kg ha⁻¹ across treatments. Nitrogen use efficiency indices responded distinctly to nitrogen management practices. Higher PFPN was observed under reduced nitrogen doses combined with nano-urea, with a maximum PFPN of 181.42 kg grain kg⁻¹ N under 50% RDN + nano-urea. Agronomic efficiency was highest under 125% RDN + nano-urea, recording 75.20 kg grain kg⁻¹ N, indicating better yield response to applied nitrogen. Overall, the results suggest that nano-urea application and fertilizer deep placement improved nutrient uptake and nitrogen use efficiency compared to conventional surface application. The study highlights that optimizing nitrogen application methods and timing is more effective than increasing nitrogen dose for achieving sustainable rice production.