Long-term saline water irrigation has the potential to balance greenhouse gas emissions and cotton yield in North China plain.

Saline water has proven to be one of the alternative sources of freshwater for agricultural irrigation in water-scarce areas. However, the changes in farmland ecology caused by saline water irrigation remain unclear. In this study, six irrigation water salinities (CK: 1.3 dS m-1, S1: 3.4 dS m-1, S2: 7.1 dS m-1, S3: 10.6 dS m-1, S4: 14.1 dS m-1, S5: 17.7 dS m-1) were set in a three-year (2019, 2021-2022) experiment to investigate their effects on soil environment and greenhouse gas emissions in cotton fields under long-term saline water irrigation. Results show that soil salinity in the same layer increased as increasing water salinity. Soil moisture of S3-S5 increased significantly by 4.99-12.94%. There was no significant difference in soil organic matter content between CK and S1. Saline water irrigation increased soil ammonium nitrogen content by 0.57-49.26%, while decreasing nitrate nitrogen content by 1.43-32.03%. Soil CO2 and N2O emissions and CH4 uptake were lower in S1-S5 than in CK at different cotton growth stages. In addition, saline water irrigation reduced the global warming potential by 6.93-53.86%. A structural equation model was developed to show that soil salinity, moisture, and ammonium nitrogen content were negatively correlated with global warming potential, while organic matter and nitrate nitrogen had positive effects on global warming potential. Considering the comprehensive perspectives of gas emissions and cotton yield, irrigation water with salinity less than 10.6 dS m-1 could effectively reduce greenhouse gas emissions from cotton fields while maintaining stable cotton yields in the experimental area and similar region.

Long-term saline water irrigation affected soil carbon and nitrogen cycling functional profiles in the cotton field.

Saline water irrigation (SWI) plays an important role in alleviating water resource shortages. At the same time, the salt input of irrigation water affects soil microorganisms which participate in various ecological processes of terrestrial ecosystems. However, the responses of soil microbial functional potential to long-term SWI remains unclear. Therefore, Metagenomics method was utilized in cotton fields under long-term SWI to reveal the microbial functional profiles associated with soil carbon and nitrogen cycles. Results indicated that SWI impacted the microbial functional profiles of soil carbon and nitrogen cycles in the cotton fields significantly. Especially, irrigation water salinity inhibited the relative abundances of sacC and vanB, which are soil carbon degradation genes. SWI also affected the functional gene abundance of nitrogen degradation, dissimilatory nitrate reduction, and nitrification. Moreover, SWI significantly increased the abundance of Candidatus_Cloacimonetes in both carbon and nitrogen cycles. In the discussion, we used person analysis found that soil salinity, pH, and ammonium nitrogen were important factors affecting the abundance of functional genes and microbial taxa. Overall, this study indicated that long-term SWI significantly influenced specific microbial functional genes and taxa abundance, which may lead to predictable outcomes for soil carbon and nitrogen cycling, and is of great importance in exploring the impact of SWI on soil environments.

[Effects of brackish water irrigation on grain quality characteristics and yield of winter wheat]. / 咸水灌溉对冬小麦籽粒品质特性和产量的影响.

Brackish water resource is widely distributed in the North China Plain, which has not been effectively utilized. Using brackish water for irrigation can alleviate water resource conflict in the well-irrigated area and solve the problem of groundwater over-exploitation of the North China Plain. A long-term experiment (since 2006) was conducted to investigate the effects of brackish water irrigation on the quality and yield of winter wheat in the North China Plain. There were five salinity degrees of irrigation water, i.e. 1, 2, 4, 6, and 8 g·L-1, respectively. The results showed that higher salinity degree of irrigation water (4-8 g·L-1) significantly increased water absorption, development time, sedimentation, wet gluten content, and protein content, but decreased the stabilization time, flour yield, and gluten index. There was no significant difference between the treatments of 1 g·L-1 and 2 g·L-1 on grain yield and yield components, but the treatment of 2 g·L-1 significantly improved grain quality, including water absorption, development time, sedimentation, wet gluten, and protein content. Higher salinity degree of irrigation water (4-8 g·L-1) treatments significantly decreased spike number (44.0%-60.7%) and grain yield (35.6%-64.7%), compared with 1 g·L-1 treatment. Results of principal component analysis showed that 2 g·L-1 treatment had the best overall effect with no significant decrease in grain yield and quality of grain. This study could provide theoretical basis and technical support for use of brackish water in the North China Plain.

[Effects of saline-water furrow irrigation on the stability of soil water-stable aggregates in cotton field]. / 咸水沟灌对棉田土壤水稳性团聚体稳定性的影响.

It is of great importance to explore the effects of saline-water furrow irrigation on soil water-stable aggregates for safe and efficient utilization of saline water resources. We conducted a long-term cotton experiment with six levels of saline-water furrow irrigation (1, 2, 4, 6, 8, 10 g·L-1) since 2006 and analyzed the variations of soil salinity and water-stable aggregates in the 10th and 15th years under saline irrigation. The results showed that soil salinity in the 0-30 cm layer at the ditch increased with increasing salinity level of irrigation water. There were significant differences between the 6, 8, 10 g·L-1 and 1 g·L-1 treatments. Soil salinity in each treatment increased gradually with increasing soil depth. Saline-water furrow irrigation tended to reduce the stability of soil water-stable aggregates. When the salinity level of the irrigation water was ≥6 g·L-1, the mass fraction of macroaggregates (>0.25 mm), the mean weight diameter and geometric mean diameter of water-stable aggregates significantly decreased. In contrast, the fractal dimension and mean weight specific surface area increased significantly. The stability of soil water-stable aggregates decreased with soil depth in all treatments. Under the condition of saline-water furrow irrigation for several years, there was no accumulation of soil salinity and instability of water-stable aggregates in the 0-30 cm soil layer at the ditch with each passing year. With the irrigation scheduling of this study, saline-water furrow irrigation with salinity ≤4 g·L-1 did not affect soil salinity and water-stable aggregate stability of cotton field in this area.