Uneven rainfall, in the context of global warming, can cause soil moisture fluctuations (SMFs) that harm crop growth, and it is not yet known whether nitrogen (N) can mitigate the harm caused by a strong SMF. This paper uses okra as a test subject and sets three SMFs of 45–55% FC (W₁), 35–65% FC (W₂), and 25–75% FC (W₃) and three N applications of 0 kg hm⁻² (N₀), 110 kg hm⁻² (N₁), and 330 kg hm⁻² (N₂) to investigate the effects of SMF and N application on the physiological and biochemical aspects of okra. The results demonstrated that okra exhibited the highest values in stem diameter, number of leaves, photosynthesis characteristics, antioxidant enzyme activity, and yield under the N₁ treatment. The average yield in the N₁ treatment was 149.8 g, significantly surpassing the average yields of the N₀ (129.8 g) and N₃ (84.0 g) treatments. Stomatal density, antioxidant enzyme activity, malondialdehyde content, and proline content in okra leaves were highest in the W₃ treatment, indicating that plants experienced stress in the W₃ treatment. However, the agronomic traits and yields of okra in the N₁ treatment were higher than those in the N₀ and N₁ treatments, indicating that the crop damage caused by W₃ could be mitigated by an appropriate amount of N application. The N₁W₁ treatment emerged as the most suitable combination for okra growth in this study, exhibiting the highest stem diameter, leaf count, photosynthetic characteristics, and yield (201.3 g). Notably, this yield was 67.8% higher than the lowest treatment (N2W3), signifying a significant improvement.

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.