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.

The present study aimed to investigate the effects of different soil amendments coupled with nitrogen fertilizer on the morpho-physiological characteristics and yield of salt-tolerant rice under saline conditions. The soil amendments, i.e., S1: zeolite amendment, S2: coconut coir amendment, S3: humic acid amendment, and S0: no amendment, and fertilizer treatments, i.e., N1: urea, N2: slow-release urea, and N0: no N fertilizer, were kept in main plots and sub-plots, respectively, in a split-plot design. The salt-tolerant variety ‘Shuangliangyou 138’ was exposed to 0.3% salt irrigation water. The results showed that during the entire growth period, compared to S0, the S1 and S3 treatments increased the SPAD values by an average of 6.3%and 5.5%, respectively, the leaf area index by an average of 24.5% and 19.8%, the canopy interception rate by an average of 11.5% and 4.1%, and the aboveground biomass by an average of 36.8% and 13.9%, respectively. Moreover, under S1 and S3 conditions, the tiller number per square meter, leaf water potential, leaf water content, and chlorophyll contents were also improved under the slow-release urea than urea. Moreover, slow-release urea promoted root vitality and nutrient absorption as well as enhanced the activity of antioxidant and nitrogen metabolism enzymes than urea under the S1 and S3 conditions. In sum, the rational application of soil amendments and slow-release urea could improve the rice productivity on saline-alkali land.

The rising temperatures and changes in precipitation due to climate change have significantly impacted agricultural production. Evaluating the effects of climate change on rice production is crucial for improving rice cultivation techniques and ensuring food security. It is essential to comprehensively examine the climatic, spatial, and temporal variations during the duration of crop production. Previous research has mainly focused on different rice planting areas, rice types, and various growth stages of rice. However, more research is needed on the climatic changes during the crop-growing season in specific regions. Therefore, this study compiled complete daily meteorological data from 37 meteorological stations in Hunan Province from 1961 to 2020. The period from 1961 to 2020 was divided into three segments: 1961–1980 (a), 1981–2000 (b), and 2001–2020 (c), to analyze the characteristics of agricultural climate resource changes during different growth stages of early-season rice in Hunan Province. Results show that the heat resources were significantly increased (accumulated temperature growth rate of 43.36 °C/10a), the sunshine resources were decreased by −14.60 h/10a, and the precipitation resources were slightly increased by 6.85 mm/10a. The increase in heat resources mainly occurs during the vegetative growth stage of early-season rice. Additionally, the high-value regions of heat resources and precipitation in period c are 97.8% and 34.2% higher than the average values of periods a and b, respectively. In contrast, the regions with high sunshine hours significantly decreased in period c compared to periods a and b. In summary, the heat, sunshine, and water resources in the central and eastern regions of Hunan Province increase simultaneously, and appropriate cultivation measures should be adopted in the future to improve the yield and resource utilization efficiency of early-season rice in a double-cropping system.

Soil salinization negatively affects rice growth and yield; however, how different sludge sources regulate rice growth and yield under salt stress was rarely investigated. This study evaluated the performance of two salt-tolerant rice cultivars, Chaoyou 1000 and Longliangyou 506, grown in two sediment sources, pond sediment (PS) and river sludge (RS), under salt stress (56 ds m⁻¹ brine irrigation) with conventional soil (CS) used as the control. The results showed that the rice yield under the PS and RS treatments was enhanced by 51.0% and 43.6% as compared with CS, respectively, owing to an improvement in spikelet per panicle, 1000-grain weight, dry matter accumulation, and the chlorophyll content in both rice cultivars. Compared with CS, the total nitrogen accumulation, nitrogen grain production efficiency, nitrogen harvest index, and nitrogen partial productivity under the PS and RS treatments were increased by 18.9–28.9%, 17.0–20.6%, 7.2–16.6%, and 43.8–50.9%, respectively. Moreover, rice grown in PS and RS showed higher activities of nitrogen metabolism-related enzymes (nitrate reductase, glutamine synthetase, and glutamate synthetase) at the heading stage and higher K⁺ and K⁺/Na⁺ contents in the leaves. Overall, a balanced utilization of sediment resources (especially pond sediment) can effectively alleviate salt stress and improve the yield and nitrogen use efficiency in rice.