Effects of exogenous organic matter addition on agricultural soil microbial communities and relevant enzyme activities in southern China

Effects of foliar selenium, biochar, and pig manure on cadmium accumulation in rice grains and assessment of health risk

Addressing cadmium (Cd) contamination in agricultural lands is crucial, given its health implications and accumulation in crops. This study used pot experiments to evaluate the impact of foliar selenium spray (Se) (0.40 mM), corn straw biochar (1%), and pig manure (1%) on the growth of rice plants, the accumulation of Cd in rice grain, and to examine their influence on health risk indices associated with Cd exposure. The treatments were designated as follows: a control group without any amendment (CK), biochar (T1), pig manure (T2), Se (T3), Se and biochar (T4), Se and pig manure (T5), and Se along with biochar and pig manure (T6). Our results indicated that the treatments affected soil pH and redox potential and improved growth and the nitrogen and phosphorus content in rice plants. The soil-plant analysis development (SPAD) meter readings of leaves during the tillering stage indicated a 5.27%-15.86% increase in treatments T2 to T6 compared to CK. The flag leaves of T2 exhibited increases of 12.06%-38.94% for electrolyte leakage and an 82.61%-91.60% decline in SOD compared to treatments T3 to T6. Treatments T1 to T6 increased protein content; however, amylose content was significantly reduced in T6. Treatment T6 recorded the lowest Cd concentration in rice grains (0.018 mg/kg), while T2 recorded the highest (0.051 mg/kg). The CK treatment group showed a grain Cd content reduction of 29.30% compared to T2. The assessment of acceptable daily intake, hazard quotient, and carcinogenic risk revealed an ascending order as follows: T6 < T3 < T5 < T4 < T1 < CK < T2. In conclusion, the application of treatment T6 demonstrates the potential to lower oxidative stress, enhance production, reduce cancer risk, and ensure the safe cultivation of rice in environments affected by Cd contamination.

Effects of aftercrop tomato and maize on the soil microenvironment and microbial diversity in a long-term cotton continuous cropping field

Long-term continuous cropping affects the soil microecological community and leads to nutrient imbalances, which reduces crop yields, and crop rotation can increase soil productivity. To study the effects of the cultivation of tomato (Solanum lycopersicum) and corn (Zea mays) on the microbial community, physical and chemical factors and the structure of aggregates in cotton (Gossypium hirsutum) long-term continuous cropping soils were examined. Four cropping patterns were established, including one continuous cropping pattern and three crop rotation patterns, and the diversity of the soil microecological community was measured using high-throughput sequencing. The physical and chemical properties of different models of soil were measured, and the soil aggregate structure was determined by dry and wet sieving. Planting of aftercrop tomato and corn altered the bacterial community of the cotton continuous soil to a lesser extent and the fungal community to a greater extent. In addition, continuous cropping reduced the diversity and richness of the soil fungal community. Different aftercrop planting patterns showed that there were very high contents of soil organic carbon and organic matter in the cotton-maize rotation model, while the soil aggregate structure was the most stable in the corn-cotton rotation model. Planting tomato in continuous cropping cotton fields has a greater effect on the soil microbial community than planting maize. Therefore, according to the characteristics of different succeeding crop planting patterns, the damage of continuous cropping of cotton to the soil microenvironment can be alleviated directionally, which will enable the sustainable development of cotton production.

Straw Soil Conditioner Modulates Key Soil Microbes and Nutrient Dynamics across Different Maize Developmental Stages

Soil amendments may enhance crop yield and quality by increasing soil nutrient levels and improving nutrient absorption efficiency, potentially through beneficial microbial interactions. In this work, the effects of amending soil with straw-based carbon substrate (SCS), a novel biochar material, on soil nutrients, soil microbial communities, and maize yield were compared with those of soil amendment with conventional straw. The diversity and abundance of soil bacterial and fungal communities were significantly influenced by both the maize growth period and the treatment used. Regression analysis of microbial community variation indicated that Rhizobiales, Saccharimonadales, and Eurotiales were the bacterial and fungal taxa that exhibited a positive response to SCS amendment during the growth stages of maize. Members of these taxa break down organic matter to release nutrients that promote plant growth and yield. In the seedling and vegetative stages of maize growth, the abundance of Rhizobiales is positively correlated with the total nitrogen (TN) content in the soil. During the tasseling and physiological maturity stages of corn, the abundance of Saccharimonadales and Eurotiales is positively correlated with the content of total carbon (TC), total phosphorus (TP), and available phosphorus (AP) in the soil. The results suggest that specific beneficial microorganisms are recruited at different stages of maize growth to supply the nutrients required at each stage. This targeted recruitment strategy optimizes the availability of nutrients to plants and ultimately leads to higher yields. The identification of these key beneficial microorganisms may provide a theoretical basis for the targeted improvement of crop yield and soil quality. This study demonstrates that SCS amendment enhances soil nutrient content and crop yield compared with conventional straw incorporation and sheds light on the response of soil microorganisms to SCS amendment, providing valuable insights for the future implementation of this material.

Soil quality and microbial communities in subtropical slope lands under different agricultural management practices

Land degradation is a major threat to ecosystem. Long-term conventional farming practices can lead to severe soil degradation and a decline in crop productivity, which are challenging for both local and global communities. This study was conducted to clarify the responses on soil physicochemical properties and microbial communities to changes in farming practices. Slope land orchards under three agricultural management practices-conventional farming (CF), organic farming (OF), and ecofriendly farming (EFF)-were included in this study. We found that soil carbon stock increased by 3.6 and 5.1 times in surface soils (0-30 cm) under EFF and OF treatments, respectively. EFF and OF significantly increased the contents of total nitrogen by 0.33-0.46 g/kg, ammonia-N by 3.0-7.3 g/kg, and microbial biomass carbon by 0.56-1.04 g/kg but reduced those of pH by 0.6 units at least, and available phosphorous by 104-114 mg/kg. The application of phosphorous-containing herbicides and chemical fertilizers might increase the contents of phosphorous and nitrate in CF soil. High abundances of Acidobacteria and Actinobacteria were observed in EFF and OF soils, likely because of phosphorous deficiency in these soils. The abundance of fungi in OF soil indicated that plants' demand for available soil phosphorous induced the fungus-mediated mineralization of organic phosphorous. High abundances of Gammaproteobacteria, Planctomycetes, Firmicutes, and Nitrospirae were observed in CF soil, possibly because of the regular use of herbicides containing phosphorous and chemical fertilizers containing high total nitrogen contents.