Super absorbent polymers (SAPs) have been applied as soil conditioners to reduce soil water loss, but there are few studies about how SAPs affect structures of soil bacterial community, and these associated chemical residues are uncertain. Treatments under different soil moisture conditions by application of sodium polyacrylate in repacked soil columns were used to investigate their effects on the soil bacterial community structures by Illumina MiSeq sequencing. Alpha diversity analysis showed that adding SAPs had an impact on bacterial diversity. On phylum level, adding SAPs significantly reduced the amount of Actinobacteria (1.9–2.4-fold), Bacteroidetes (1.1–2.1-fold) while increased the amount of Firmicutes (1.9–4.6-fold). At genus level, effects of SAPs on the soil bacterial community structures varied with the soil moisture conditions. Under water deficit, SAPs reduced the soil pH, which promoted the proliferation of Lactobacillus (9.9–29.1-fold), and acid production by these bacteria might further promote the reduction of pH, potentially inhibiting growth of Acidobacteria (1.3–1.8-fold) and Chloroflexi (1.6–2.3-fold). The pyrolysis analysis showed that some substances such as methanesulfonyl chloride, long-chain amides and esters, were only derived from water-saturated soil treated with SAPs, which might subsequently have negative impacts on the environment and associated agriculture.

This study was carried out to investigate effects of subsoiling on the diversity and composition of the bacterial community in a wheat–maize rotation field in the Guanzhong area of Shaanxi Province, China. After the wheat harvest, surface soil samples were collected under two tillage methods (single rotary tillage (RT) and subsoiling + rotary tillage (ST)) to perform high-throughput sequencing and bioinformatics analysis. Soil properties and root length density (RLD) of winter wheat at booting and flowering stages were also studied. Results showed that ST treatment significantly raised the water storage, organic carbon and total nitrogen contents of deep soil (>40 cm), and notably increased the total soil pH, ammonium nitrogen content and RLD in the tillage layer from 0–70 cm at booting stage and 0~100 cm at flowering stage, but the residual nitrate nitrogen significantly decreased by 17.74%. Compared with RT, soil bacterial richness and diversity in the 10~20 cm layer of ST treatment showed a significantly decreased trend. The relative abundances of GAL15, Actinobacteria, Nitrospirae, Rhizobiales, Burkholderiales, Pseudomonas and Serratia in the 10–20 cm layer were remarkably increased in ST. Principal Component Analysis (PCA) and Redundancy Analysis (RDA) results showed that surface soil pH, ammonium nitrogen and nitrate nitrogen contents have the strongest effect on the bacterial structure. In addition, there were positive correlations between the RLD and the relative abundances of Rhizobiales, Burkholderiales, Pseudomonas and the ammonium nitrogen content. In conclusion, although subsoiling was not conducive to improving soil bacterial community richness and diversity, it significantly increased soil beneficial bacteria (biological nitrogen-fixing bacteria, ammonifying bacteria, nitrobacteria) abundances, reduced the nitrogen loss caused by denitrifying bacteria, promoted earlier root development and improved the plant utilization ratio of soil nutrients.

This study was carried out to evaluate the effects of the combined application of water-retaining agents and nitrogen fertilizers on soil physicochemical properties, bacterial communities, and root growth under winter wheat planting mode in the Guanzhong area of Shaanxi Province. Based on the positioning experiment of dry farming in the loessal soil area of Shaanxi Province, four treatments were set up by using the tillage method of subsoiling + rotary tillage and straw returning: only fertilization (U), only water retention agent sodium polyacrylate (C₃H₃NaO₂)n (S), combined use of water-retaining agent sodium polyacrylate (C₃H₃NaO₂)n and fertilizer (US), and control group CK (no treatment). The ultra-high-throughput sequencing of 16S rRNA genes of soil bacteria was performed by the Illumina Hiseq platform, and the effects of different tillage measures on soil bacterial diversity and community structure were analyzed. In addition, the effects of these tillage measures on soil physicochemical properties and winter wheat root length density at booting and flowering stages were evaluated. The results indicated that the combination of the water-retaining agent and fertilizer markedly enhanced the contents of ammonium nitrogen, available phosphorus, and available potassium in the 0~20 cm soil layer, significantly increased the soil moisture content, and promoted the deep growth of roots. The root length density was 4.70 times higher than that of the control group at the booting stage. In addition, the combined application alleviated the decrease in soil microbial diversity caused by individual fertilization, especially significantly increasing the abundance of Gemmatimonadetes, Acidobacteria, and Planctomycetes in the 0~10 cm soil layer. This study reveals the potential of the combined use of water retention agents and fertilizers to optimize the soil environment and enhance winter wheat yield, which provides a scientific basis for improving local agricultural practices.

Mixing saline and fresh water can help to increase the agricultural water utilization rate and solve the water shortage situation, but its role on rhizosphere microbes is unknown. This study revealed the effects of mixed saline and freshwater sprinkler irrigation at different proportions on the rhizosphere soil microbial community of summer maize. Compared to freshwater sprinkler irrigation, sprinkler irrigation with 2 g·L⁻¹ of mixed saline and fresh water significantly increased the bacterial α-diversity and significantly affected the structure and composition of bacterial communities, increasing the number of OTUs, the ACE index, and the Shannon index in the rhizosphere soils, whereas sprinkler irrigation with 3 g·L⁻¹ did not lead to significant changes. In addition, there was a significant difference in β-diversity between the mixed saline and freshwater sprinkler irrigation and the freshwater sprinkler irrigation. Principal coordinate analysis revealed that the 2 g·L⁻¹ and 3 g·L⁻¹ sprinkler irrigation treatments were closer to each other, but both were at a greater distance from the freshwater sprinkler irrigation, indicating that mixed saline and freshwater irrigation significantly affected the structure of rhizosphere soil bacterial communities. Ammonium nitrogen, alkaline dissolved nitrogen, and total nitrogen all affected the soil bacterial community structure by more than 10%, with ammonium nitrogen being the most influential environmental factor. The relative abundance of most microbes in the mixed saline and freshwater sprinkler treatments was positively correlated with ammonium nitrogen, especially in the 2 g·L⁻¹ treatment, while that of most microbes in the freshwater sprinkler treatment was negatively correlated with ammonium nitrogen. In conclusion, selecting a sprinkler irrigation model with a mineralization level of mixed saline and freshwater not exceeding 2 g·L⁻¹ could enhance the rhizosphere soil microbial community while conserving water resources.

Drip irrigation burial depth is a critical management factor for saline-alkali agriculture, yet its mechanisms of influencing crop productivity through soil–microbe–plant interactions remain poorly understood. To explore the regulatory effects of drip irrigation burial depth on the growth and rhizosphere microenvironment of dryland wheat in saline-alkali soil, three treatments (no irrigation control, CK; 5 cm shallow-buried drip irrigation, T5; 25 cm deep-buried drip irrigation, T25) were set up, with soil physicochemical properties, microbial community characteristics, and crop yield analyzed. The results showed that drip irrigation significantly improved soil environment and yield, and T25 exhibited superior comprehensive benefits: soil electrical conductivity was reduced by 63%, organic matter content increased by 44%, and water-salt status was significantly optimized; meanwhile, microbial community structure was altered and root nutrient uptake capacity was enhanced, ultimately achieving a yield of 5347.1 kg ha⁻¹, 55.0% higher than CK. In conclusion, 25 cm deep-buried drip irrigation may provide advantages for wheat cultivation primarily through improved water distribution, desalination, and soil structure enhancement.