Optimizing irrigation and nitrogen levels for improved soil nitrogen dynamics and use efficiency in temperate ecology...

The present study aimed to evaluate nitrogen dynamics and use efficiency of transplanted rice under variable irrigation regimes and nitrogen levels. Two field experiments were conducted during the 2021 and 2022 rice-growing seasons using a split-plot design with four irrigation treatments in the main plots and four nitrogen levels in the sub-plots, each replicated thrice. Results indicated that nitrogen concentration and uptake by grain and straw were significantly influenced by both irrigation scheduling and nitrogen application. Among irrigation treatments, recommended scheduling and irrigation at field capacity produced the highest nitrogen concentration and uptake, whereas 10 and 20% depletion from field capacity resulted in lower values. For nitrogen levels, 125% of the recommended dose (RDN) recorded the highest grain nitrogen content and uptake, but values were statistically similar to 100% RDN. Flooded rice cultivation led to the greatest nitrogen removal from soil, followed by field capacity and deficit irrigation treatments. The highest nitrogen use efficiency was observed under deficit irrigation, followed by field capacity, while flooded irrigation was the least efficient. Adequate irrigation (I₁/I₂) resulted in the highest nitrogen uptake and grain yield, while deficit irrigation (I₄) saved water but led to lower yield and nitrogen use efficiency, with greater amounts of residual nitrogen remaining in the soil. Overall, applying irrigation at field capacity combined with 100% RDN was found optimal for maximizing nutrient uptake and nitrogen use efficiency in transplanted rice, suggesting a sustainable approach to improve resource use without over-application of water or fertilizer.