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Soil aggregates provide microhabitats for microorganisms. However, the bacterial communities within various aggregate size fractions under organic amendments have rarely been evaluated especially in sandy soils. A field experiment involving addition of biogas residue (BR), pig manure (PM), biochar (BC), and straw (ST) of a sandy soil was performed to determine the structure of the bacterial community in aggregate size fractions by using high‐throughput sequencing. We found that organic amendments change soil aggregate fractions and nutrient content, alter bacterial diversity and composition, and contribute to the predicted bacterial functions. The BR increased bacterial α‐diversity in <0.25‐mm aggregates. The Nitrospirae was abundant in almost all aggregate sizes, whereas the abundance of Actinobacteria decreased in most of aggregates following BR addition. The PM amendment primarily facilitated the growth of Bacteroidetes and inhibited the growth of Acidobacteria and Chloroflexi in 0.25‐ to 2‐mm aggregates, whereas bacterial α‐diversity was decreased in the >0.25‐mm aggregates. The BC treatment decreased the bacterial α‐diversity in the <0.25‐mm aggregates and the Gemmatimonadetes abundance in all <2‐mm aggregates, but the Actinobacteria abundance was significantly increased in the >0.053‐mm aggregates. Collectively, the effects of organic amendments on the bacterial community varied greatly depending on type of amendments and aggregate size. The BR supported highly diverse bacterial taxa in the <0.25‐mm aggregates, whereas it proliferated N cycling‐related bacteria in all aggregates. Our results highlight the links between bacterial community and aggregate size fractions in sandy soils depending on organic amendments. [ABSTRACT FROM AUTHOR]

To address the low productivity of sandy farmlands, our study aimed to conduct a comparative study on the effects of different organic amendment (OA) inputs for the potential improvement of crop yield and soil quality in sandy alkaline farmlands through the selection of a suitable OA. This study set up straw (ST) returning as control and chemical fertilizer (CF) treatment as a side control, and chose three OAs returning as treatments, including pig manure (PM), biogas residue (BR), and straw biochar (BC), for improving soil fertility, with all amendments having matched doses of nitrogen (N). The experiment was conducted at the Wuqiao Experimental Station (37°41 N, 116°37 E) of China Agricultural University in Hebei Province, China, from October 2012 to September 2016. The cropping rotation was the winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation system. Through a consecutive four-year field experiment, the principal results showed that three types of OA application significantly increased soil organic carbon from 1.46 g kg−1 to 8.24 g kg−1, soil total N from 0.21 g kg−1 to 0.64 g kg−1, soil available potassium from 55.85 mg kg−1 to 288.76 mg kg−1, and soil available phosphate from 4.86 mg kg−1 to 65.00 mg kg−1 in the 0–20 cm soil layer. The BR was the most effective in improving soil nutrients as compared with the ST. The PM and BR treatments were more conducive to promoting crop yield by 6–20% than ST, and the BC treatment significantly reduced the yield of winter wheat by 19% and summer maize by 8%. As the BR and PM treatments improved the soil nutrient content and significantly increased crop yield, these were the top choices for transforming the low-yield sandy farmlands. [ABSTRACT FROM AUTHOR]

Abstract Organic amendment has proven to reduce resource waste and environmental pollution, in addition to increasing soil quality. However, the effect of different organic amendment methods on water-stable aggregates and soil organic carbon (SOC) accumulation is unknown, especially in barren sandy soil. A field experiment with four organic amendment methods, straw (ST, local practice), biogas residue (BR), manure (PM), and biochar (BC), was designed with the equal amount of nitrogen (N) input in the North China Plain. Soil aggregate distribution, stability, and aggregate-associated C at two depths (0–10 cm and 10–20 cm) were analyzed after a treatment was applied to evaluate soil quality improvement. The main results were as follows: compared to ST treatment, BC treatment enhanced SOC in the 0–10 cm and 10–20 cm layers by 143.8% and 156.5%, respectively (P < 0.05). The mean weight diameter (MWD) of soil aggregates in BR, PM, and BC treatments decreased by 16.2%–31.8%, 10.0%–24.7% (except the 2015 0–10 cm layer), and 18.9%–43.2% compared with ST treatment from 2014 to 2016. BC treatment increased C concentrations in all aggregate fractions compared to ST treatment in 2015–2016 (P < 0.05). The correlations between soil microbial biomass C and MWD (R = 0.7185, P < 0.001) and dissolved organic C and MWD (R = 0.5600, P < 0.001) indicated that soil aggregation is mainly affected by labile organic C in barren sandy soil. All four types of organic amendments increased SOC content; additionally, ST amendment had the highest capacity for aggregate formation. The results indicated that ST amendment is more appropriate for barren sandy soil than BR, PM or BC amendments, and improves soil quality for sustainable soil management. [ABSTRACT FROM AUTHOR]