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.

Brackish water has to be used to irrigate crops for harvest due to the scarcity of freshwater resources. However, brackish water irrigation may cause secondary soil salinization. Whether the combined utilization of different non-conventional water resources could relieve the risk of secondary soil salinization has not been reported. In order to explore the safe and rational utilization of brackish water in areas where freshwater resources are scarce, a pot experiment was conducted to study the risk of secondary soil mixed irrigation and rotational irrigation using brackish water and reclaimed water or freshwater. The results indicated that: (1) Short-term irrigation using reclaimed water did not cause secondary soil salinization, although increasing soil pH value, ESP, and SAR. The indices did not exceed the threshold of soil salinization. (2) Compared with mixed irrigation using brackish–freshwater, the contents of soil exchangeable Ca²⁺, K⁺, and Mg²⁺ increased, and the content of soil exchangeable Na⁺ decreased under rotational irrigation using brackish-reclaimed water. In addition, the contents of soil exchangeable Na⁺ and Mg²⁺ under mixed irrigation or rotational irrigation were significantly lower, and the exchangeable K⁺ content of the soil was higher compared with brackish water irrigation. The exchangeable Ca²⁺ content under rotational irrigation was higher than that of brackish water irrigation, while the reverse was seen under mixed irrigation. (3) For different combined utilization modes of brackish water and reclaimed water, the ESP and SAR were the lowest under rotational irrigation, followed by mixed irrigation and brackish water irrigation. The ESP under brackish water treatment exceeded 15%, indicating a certain risk of salinization, while ESPs under other treatments were below 15%. Under mixed irrigation or rational irrigation using reclaimed-brackish water, the higher the proportion or rotational times of reclaimed water, the lower the risk of secondary soil salinization. Therefore, short-term combined irrigation using brackish water and reclaimed water will not cause the risk of secondary soil salinization, but further experiments need to verify or cooperate with other agronomic measures in long-term utilization.

Not only is solving freshwater resource shortages effective but also an important measure for realizing the sustainable development of agriculture through the development and use of unconventional water resources. This pot experiment investigated the role of exogenous silicon in the risk of secondary soil salinization and the growth physiology of Lvxiu pakchoi cabbage under irrigation by using brackish water alone (BW), reclaimed water alone (RW), and compound irrigation with brackish water and reclaimed water at a ratio of 1:1, as well as the distribution of silicon in a soil–crop system. The results showed that with the extension of the spraying period of silicon fertilizer, the electrical conductivity (EC) decreased under 1:1 compound irrigation. The pH values in all treatments ranged from 7.95 to 8.10 without a potential risk of alkalization. Spraying silicon fertilizer had a positive effect on increasing the ratio of exchangeable potassium to sodium in soil. Spraying silicon fertilizer significantly reduced the percentage of exchangeable sodium (ESP) and the sodium adsorption ratio (SAR) in soils irrigated using BW, and increased the soil ESP and SAR under compound irrigation and RW irrigation, but these factors did not exceed the threshold of soil salinization. The proper application of silicon fertilizer had no significant effect on the total silicon content in the soil but increased the total silicon content in the plants to some extent. In addition, the yield was improved through proper silicon fertilizer application. In summary, exogenous silicon has positive effects on soil physical and chemical properties and crop growth, and relieves secondary salinization risk under compound irrigation via brackish water and reclaimed water.

Water resource shortage has become an important factor limiting agricultural sustainability in China. In addition, the development and utilization of unconventional water resources are greatly important for alleviating agricultural water resource deficit. The Pakchoi was cultivated by using the surface soil (0–20 cm) from the field in this pot experiment. The experiment lasted for approximately 1 month to study microbial community structure variation under brackish water and reclaimed water irrigation. The 16S rDNA high-throughput assays revealed that soil bacteria mainly consisted of Proteobacteria and Actinobacteria at the Phylum level, along with Arenimonas and Nocardioides at the Genus level under mixed irrigation with brackish water and reclaimed water. In summary, irrigation with pure reclaimed water promoted part of microbial communities and irrigation with pure brackish water inhibited the growth and activities of certain microbial communities. We found that mixed irrigation improved the microbial community structure diversity compared with that in response to pure brackish water irrigation, while decreased the community structure diversity compared with that in response to fresh water irrigation and pure reclaimed water irrigation.

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.

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.