The relationship between soil aggregate-associated potassium and soil organic carbon with glucose addition in an Acrisol following long-term fertilization

Abstract

Subtropical Acrisols have low soil organic carbon (SOC) and potassium (K) availability. However, the relationship between K distribution of aggregates and SOC levels is unclear. Five soil samples were collected from a long-term fertilization experiment in an Acrisol. Different K fertilization treatments included CK (without any fertilizer), ZK (zero rate of chemical K fertilizer), KF (conventional rate of chemical K fertilizer added to ZK treatment), KM (KF treatment including the application of fresh pig manure, and KS (KF treatment with half of crop straw returned to the field). Then, an incubation experiment was conducted in which different rates of glucose were added to attain 5 increased levels in SOC with 0, 10%, 20%, 50%, and 100% in the CK, ZK, KF, KM, and KS treatments. Compared with no glucose addition, glucose addition improved these > 2 mm aggregates by 9.16%− 104.19% among all soils. With increased SOC percentage, the > 2 mm aggregate increased. A non-linear equation indicated that there were significant correlations between > 2 mm aggregates and SOC content in KF, KM, and KS soils. The exchangeable K (EK) and non-exchangeable K (NEK) contents of > 2 mm aggregates were highest in KM soil, followed by KS and KF soils, while CK and ZK soils were the lowest. The linear equations indicated that the EK and NEK stock of > 2 mm aggregates could be increased by 8.41–9.10 kg ha−1 and 15.73–20.65 kg ha-, respectively, in all K fertilized soils, when SOC was increased by 1 g kg−1. The slopes of linear equations also showed that the growth rate for NEK stock of > 2 mm aggregates in KM soil (20.65 kg ha−1) was higher than those of KS and KF soils (15.73 and 17.59 kg ha−1). Additionally, the slopes of linear equations indicated that the growth rate for proportions of EK and NEK stock of > 2 mm aggregates in KM soil (1.14% and 1.64%) were lower than those in KS soil (2.22% and 2.28%). Combined with CK, ZK, KF, KM, and KS soils, the proportion of EK and NEK stock of > 2 mm aggregates increased by 1.62% and 2.32% along with increased SOC by 1 g kg−1. Therefore, the EK and NEK stock of > 2 mm aggregates increased through glucose addition in the Acrisol. However, these increases varied by fertilization treatments, which caused different SOC and K levels.