Effects of Nitrogen Fertilizer Types and Planting Density on the Yield and Nitrogen Use Efficiency of Salt-Tolerant Rice Under Salt Stress Conditions

Soil salinization poses a serious threat to global food security, as high Na⁺ contents in soils hinder nitrogen use efficiency (NUE), affecting the growth and yield of crop plants. The present study aims to explore the effects of different nitrogen fertilizer types viz., NO₃^- (N1) and NH₄⁺ (N2) and planting densities, viz., D1: 30 × 10 cm, D2: 20 × 20 cm, and D3: 30 × 20 cm, on growth and development, nitrogen absorption and utilization, and yield formation. The salt-tolerant rice variety 'Jingliangyou 3261' was exposed to 0.3% salt irrigation water. Results revealed that N2 substantially improved the rice yield by increasing the number of effective panicles and the rate of grain-setting compared to N1. In addition, the N2 also increased leaf chlorophyll content, dry matter accumulation, antioxidant enzyme activity such as superoxide dismutase, peroxidase, and catalase activity and reduced the content of malondialdehyde. In comparison with N1, the N2 treatment resulted in an increase of 12.21%, 31.89%, and 37.53% in total nitrogen accumulation, nitrogen recovery efficiency (NRE), and nitrogen agronomic efficiency (NAE), respectively. This increase can be attributed to enhanced leaf nitrogen metabolic enzyme activity, including nitrate reductase and glutamine synthetase, and a more robust root system. Under N1 and N2 conditions, compared to D3, D1 resulted in an increase in the number of tillers but decreased the percentage of productive tillers, the grains per panicle, the grain-filling rate, and the thousand-grain weight, thereby reducing yield. Additionally, the D3 treatment also significantly improved NRE and NAE compared to the D1 treatment. Therefore, the rational selection of nitrogen fertilizer type (N2) and planting density (D3) is crucial for improving the yield and nitrogen use efficiency of salt-tolerant rice. This would broaden the scope of agricultural solutions for saline soils, potentially improving food security in regions where soil salinization is a widespread issue.