Combined slag and biochar amendments to subtropical paddy soils lead to a short-term change of bacteria community structure and rise of soil organic carbon.

Applying industrial waste amendments, such as steel slag and biochar, to soils is an increasingly common practice to improve soil fertility, crop yield, and soil carbon (C) pool storage and stability. However, the effects of separate and combined applications of slag and biochar on total and active soil organic C (SOC) pools and the associated relationships between soil microorganisms and C cycling are unclear. Therefore, this study examined the effects of steel slag, rice straw biochar, and slag+biochar amendments to subtropical early and late rice paddy soils on total and active SOC concentrations and microbial abundance and diversity. The results showed that slag+biochar increased SOC content in early and late rice, with increases in dissolved organic C of 28.7 and 52.6 % in the early and late rice jointing stages, respectively. Soil organic C was positively correlated with soil C:N ratios in the two crop seasons. Applications of slag and biochar alone increased the diversity of soil bacteria in early rice but decreased in late rice. Meanwhile, the combined application of slag and biochar decreased diversity of soil bacterial community diversity and increased the relative abundance of some beneficial bacterial taxa, such as Pseudomonas, Bacillus, Flavisolibacter , and Ferruginibacte which are related to SOC cycling and sequestration. The results highlight that the combined slag and biochar amendments can improve soil specific properties, such as pH and SOC stocks, which elicit alterations in soil bacterial composition, especially of some keystone genera, altogether resulting in enhanced soil C sequestration and C pool stability. [Display omitted] • Combined slag and biochar amendment increased soil pH and SOC concentrations. • Combined amendment altered soil bacterial community composition. • Combined slag and biochar amendment can maintain the stability of soil C pool. • Soil properties and bacterial community influenced soil C sequestration. [ABSTRACT FROM AUTHOR]