Optimizing nitrogen fertilizer efficacy under narrow irrigation limit range: a synergistic approach to okra nutrient management

Optimizing water and nitrogen (N) management is critical for enhancing crop productivity under water scarcity. This study aimed to determine if a high irrigation upper limit can compensate for a low lower limit and whether optimal N application can mitigate the impacts of a wide irrigation range in okra. A pot experiment was conducted with three irrigation ranges (defined by the lower and upper limits of soil field capacity, FC) and two N rates: W1 (45-55% FC), W2 (35-65% FC), W3 (25-75% FC) and N1 (110 kg ha⁻1), N2 (220 kg ha⁻1). Results demonstrated that a high upper limit could not compensate for the adverse effects of a low lower limit. The narrow irrigation range (W1) consistently outperformed wider ranges, increasing yield by up to 42.3% compared to the wide irrigation range (W3). Moderate N application (N1) effectively alleviated the impacts associated with W3, boosting its yield by 24.9%, whereas excessive N (N2) was often detrimental. The optimal W1N1 combination synergistically enhanced system performance, achieving the highest yield (56.7% greater than the poorest N2W3 treatment), improving fruit quality (e.g., 11.5% higher soluble sugar), and increasing soil urease activity by 25.9%. Conversely, N2 led to soil acidification and nutrient imbalance. These results demonstrate that coupling a narrow irrigation limit range with moderate N is an optimal strategy for enhancing okra productivity and soil health, providing a viable guide for sustainable cultivation.