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Soil aggregate is important to soil quality. Straw return is beneficial for soil amendment, but the effects of straw and straw-derived biochar on aggregate formation and stability in paddy soil are unclear. This study carried out a field experiment for 2 years in Northeast China with four treatments: conventional fertilization (CF), straw (ST, 7.5 t ha−1 year−1), biochar (BC, 2.5 t ha−1 year−1), and biochar-based fertilizer (BCF, 0.75 t ha−1 year−1). Compared with the CF and BCF, BC and ST improved the macroaggregates and significantly increased soil total carbon and aggregate organic carbon, indicating a sustained positive role in promoting the formation and stability of aggregates. BC significantly improved aggregate stability. Correlation analysis showed that macroaggregates (2–0.25 mm) can be increased by increasing the heavy fraction organic carbon (HFOC), BC and ST significantly increased the HFOC, and BC had a greater effect. Scanning electron microscopy (SEM) showed that the combination of biochar and soil particles can be captured with strong water scouring. BCF showed an increasing trend in the formation and stability of soil aggregates. In comparison, biochar had a greater effect on promoting the formation of macroaggregates and the stability of soil aggregates with a significant sustainable effect. [ABSTRACT FROM AUTHOR]

Continuous cropping obstacles limit soybean production. Biochar is beneficial for soybean growth, but it is unclear whether biochar performs a sustainable role in continuous cropping. To further explore the effects of biochar on soil properties and soybean growth, a ceramic Wagner pot-simulated field experiment was conducted with biochar at different doses (12, 24, and 48 t·ha−1) over a period of 3 years, no fertilizer, no biochar (CK) and fertilizer (F)treatments were used for comparison. The results showed that biochar significantly reduced soil bulk and improved the rhizosphere soil pH, available nutrients (N, K), and total nutrients (C, N, P, and K) compared with CK and F. Moreover, the soybean root length, surface area, volume, and exudates increased with biochar amendment. In particular, biochar significantly increased the nodule number, dry weight, and nitrogenase activity of soybean. Furthermore, biochar promoted soybean growth and increased soybean yield. In general, we found that the soybean yield increased with biochar and that biochar had a positive, sustainable effect on soil properties and soybean root growth, providing a new cultivation measure for soil health and soybean production in continuous cropping, which is very important for increasing soybean productivity to break the limitations of soybean traditional continuous cultivation. [ABSTRACT FROM AUTHOR]