Enhanced soil aggregation and soil organic carbon in fluvo-aquic soil through continuous application of biochar and straws.

[Objective] Amending soil with biochar and crop straw is an effective technique to improve soil quality and agricultural productivity. This paper investigates the long-term impact of continuous application of straw and biochar on soil aggregation and soil organic carbon (SOC) content in fluvo-aquic soil. [Method] A four-year (2019--2023) experiment was conducted in a winter wheat and summer maize rotation system in the western Shandong Plain. Biochar and maize straw were applied annually at the start of the winter wheat season. Straw was applied at rates of 3.80 (S0.5), 7.60 (S1.0), 11.40 (S1.5), and 15.20 t/hm2 (S2.0), while biochar was applied at rates of 1.14 (B0.5), 2.28 (B1.0), 3.42 (B1.5), and 4.56 t/hm2 (B2.0). The control treatment (CK) involved no soil amendment. After four years, we measured the changes in soil bulk density, aggregate stability, and SOC content in the 0-10 cm and 10-20 cm soil layers. [Result] Both straw and biochar applications reduced soil bulk density. The soil bulk density in the 0-10 cm soil layer under B2.0 treatment and in the 10-20 cm soil layer under B1.5 treatment decreased the most compared with the corresponding soil layers of CK, with significant reductions of 9.08% and 7.97%, respectively. Both of the two straw returning methods promoted the increase of soil aggregate to a certain extent, and the improvement effect was best for >5 mm soil aggregate, and worst for 1-2 mm soil aggregate. Compared with CK, the aggregate volume of >5 mm granular soil treated with B1.0 in 0-10 cm soil layer increased the most significantly by 107.35%, and that of >5 mm granular soil treated with S1.5 in 10-20 cm soil layer increased the most significantly by 106.63%.Except for SOC content in aggregates < 0.25 mm in the 0-10 cm soil layer under S15.5 and aggregates of 1-2 mm in the 10-20 cm soil layer under B0.5, where SOC content decreased, biochar and straw application significantly increased SOC content in all other aggregate fractions and treatments. SOC content increased with the increase in biochar and straw application. [Conclusion] Annual applications of maize straw and biochar during the winter wheat season effectively improved soil quality by reducing bulk density, enhancing water-stable aggregates, and increasing SOC content in fluvo-aquic soil. For all treatments we compared, our results showed that applying 3.42-4.56 t/hm² of biochar is most effective for improving soil quality in the studied region. [ABSTRACT FROM AUTHOR]