The use of unconventional water resources is an effective way to alleviate the scarcity of freshwater resources, especially in areas where freshwater is scarce, but reclaimed water is abundant. To explore the reasonable utilization of brackish water and reclaimed water, a pot experiment was carried out to study the risk of secondary soil salinization. The experiment set two salinity levels of brackish water, four mixed irrigation ratios of brackish water and reclaimed water, and freshwater irrigation as the control. The results showed that: (1) Soil moisture content, salt content, pH, ESP, and SAR decreased with the increase in the proportion of reclaimed water in the mixture. (2) Soil exchangeable Ca²⁺ content under mixed irrigation was higher than that of brackish water irrigation and reclaimed water irrigation. The content was especially significantly higher under the 1:2 mixed irrigation with brackish-reclaimed water. With the increase of the proportion of reclaimed water in the mixture, soil exchangeable Na⁺ content decreased, and a significant difference was found between treatments. The soil exchangeable K⁺ decreased at first and then increased, while the soil exchangeable Ca²⁺ increased at first and then decreased. The trend of the change of soil exchangeable Mg²⁺ content was similar to that of soil exchangeable Ca²⁺ content. (3) Based on the soil pH value, there was no risk of soil alkalization in all treatments. Based on ESP, ESP was less than 15% under freshwater irrigation, brackish (3 g/L)-reclaimed water 1:2 mixed irrigation, and reclaimed water irrigation, indicating no risk of alkalization. However, other treatments may cause soil alkalization. (4) At 3 g/L of brackish water, there was a salinization risk when the proportion of reclaimed water in the mixture was less than 1/2, but there was no salinization risk when the proportion was greater than 1/2. At 5 g/L of brackish water, there was a salinization risk under mixed irrigation. Therefore, the mixed irrigation of brackish water and reclaimed water had the risk of secondary soil salinization, and the appropriate salinity and mixing ratio should be selected.

Farmland ammonia (NH₃) volatilization is an important source of NH₃, and the application of chemical fertilizer nitrogen (N) is the main factor affecting NH₃ volatilization. The optimal substitution of chemical fertilizer with organic manure and straw reportedly reduces NH₃ volatilization, while reducing irrigation increases NH₃ volatilization. However, the combined effect of nitrogen fertilizer substitution and reducing irrigation on NH₃ volatilization and the role of microorganisms in this process remains unclear. In a soil column experiment, NH₃ volatilization and microbial composition were measured under both multiple N sources and different irrigation levels by the vented-chamber method and metagenomic sequencing. The results revealed that multiple N sources application reduced cumulative NH₃ volatilization by 16.5–75.4% compared to single chemical fertilizer application, and the decreasing trend of NH₃ volatilization under reduced irrigation conditions was greater. Microorganisms had a more important effect on NH₃ volatilization of reduced irrigation than conventional irrigation. The abundance of nirA, arcC, E3.5.1.49, and E3.5.5.1 (ammonia-producing) genes varied significantly at the two irrigation levels. Overall, multiple N sources could inhibit NH₃ volatilization increasing under reducing irrigation compared to a single chemical fertilizer. Our findings contribute valuable insights into the combined effect of reduced irrigation and multiple N sources on NH₃ volatilization.

The deep migration of soil nitrogen (N) poses a significant risk of N leaching, contributing to non-point-source pollution. This study examines the influence of microbial networks on the deep migration of chemical fertilizer N under varying irrigation management and multiple N fertilizer sources. A soil column experiment with eight treatments was conducted, utilizing ¹⁵N isotope labeling and metagenomic sequencing technology. The findings revealed that reduced irrigation significantly curbs the deep migration of chemical fertilizer N, and straw returning also mitigates this migration under conventional irrigation. Microbial network complexity and stability were markedly higher under reduced irrigation compared to conventional practices. Notably, network node count, average degree, and modularity exhibited significant negative correlations with the deep migration of chemical fertilizer N. The network topology indices, including node count, average clustering coefficient, average degree, modularity, and edge count, were found to be relatively more important for the deep migration of chemical fertilizer N. In conclusion, microbial networks play an important role in reducing the deep migration of chemical fertilizer N.

Heavy metal pollution impacts on soil microorganisms are of growing concern. This study employed high-throughput sequencing and qPCR to investigate rhizosphere microbial communities and functional genes responses in ryegrass (Lolium perenne L.) under cadmium (Cd) stress. Results showed dose-dependent shifts in microbial diversity, metabolic pathways and functional gene abundance. The relative abundances of bacterial classes Alphaproteobacteria and Bacteroidia and genera Cellvibrio and Algoriphagus increased with Cd levels, suggesting roles in Cd adaptation. The classes Actinobacteria, Saccharimonadia, and Acidimicrobiia and the genera Rheinheimera, Pseudomonas, and Sphingomonas decreased. The fungal genera Acremonium, unclassified Hypocreales, Cladosporium and Paramyrothecium increased under high Cd, while Albifimbria, Fusarium, and Ramichloridium decreased. Differential adaptive strategies to Cd toxicity were observed between bacterial and fungal phyla. Redundancy analysis identified pH, EC, TN, and Cd as key determinants of microbial variation. FAPROTAX prediction revealed significant changes in dominant functional groups involved in nutrient cycling, and FunGuild analysis indicated increased saprophytic fungi with elevating Cd levels, potentially enhancing detoxification. Functional genes related to nitrogen and carbon cycling also varied with Cd gradients. This study systematically elucidated the response of rhizosphere soil microbial communities and functional gene abundance to Cd stress, providing mechanistic insights for developing ryegrass tolerance strategies.