Soil C and Aggregate Stability Were Promoted by Bio-fertilizer on the North China Plain

Soil fertility can be potentially improved and degradation can be retarded by replacing some of the chemical fertilizer with bio-fertilizer (BF). To optimize such change, BF was applied at substitution ratios of 0% (BF0), 30% (BF30), 50% (BF50), 70% (BF70), and 100% (BF100) in a field experiment in 2018 and 2019. Soil organic carbon (C) contents, stability, and organic C contents of aggregate fractions were determined in 0–20 cm layer. Soil organic C (SOC) increased with the increase in BF application rates, and the increases reached to 71.2% and 68.2% in 2018 and 2019 in BF100 treatment. Water-soluble organic C (WSOC) was highest in BF50 both years. Microbial biomass C (MBC) and KMnO4-oxidizable C contents were significantly increased by BF application. The decrease of basal respiration in BF100 was largest and reached to 26.06% in 2018 and 26.09% in 2019. Significant increases of mean weight diameter (3.16 mm in 2018 and 3.39 mm in 2019) were observed in BF50 compared with BF0. Organic C contents in aggregate fractions were highest in BF50 and more organic C accumulated in 0.053–0.25 mm aggregates in BF-amended soils. Bio-fertilizer combined with chemical fertilizer had stronger effects on stability and organic C content of aggregates in both years in comparison with control and bio-fertilizer treatments alone. This study provided insights into appropriate application of bio-fertilizer; BF50 was better for increasing soil C and improving soil aggregate stability in the given soil.