Soil aggregation and aggregate-related exchangeable base cations under different aged tea (Camellia sinensis L.) plantations in the hilly regions of southern Guangxi, China

Abstract

ABSTRACT As the secondary nutrients in soils, exchangeable base cations can form cationic bridges with clay particles and organic matters to promote the formation of soil aggregates, and to protect soil organic carbon (Corg) and nutrients from loss. To have a comprehensive understanding toward the dynamics of soil exchangeable base cations in the tea planting process, it requires to evaluate these cations’ distribution in soil aggregates at various sizes. In this study, soil samples (0–20 cm) from the tea plantations at various ages (8, 17, 25, and 43 yr.) in the hilly regions of southern Guangxi, China were divided into >2, 1–2, 0.25–1, and <0.25 mm aggregate fractions through a dry-sieving procedure. Then, the cation exchange capacity (CEC), total exchangeable bases (TEB), and different individual cations, such as exchangeable potassium (K+), sodium (Na+), calcium (Ca2+), and magnesium (Mg2+), in soil aggregates were detected. Our results suggested that the mean weight diameter (MWD), that is an indicator evaluating the stability of soil aggregates, in the 17-yr. tea plantations appeared to be the highest among all the tea plantations, indicating that more stable soil aggregates could be formed in the 17-yr. tea plantations in comparison with the rest plantations. During tea planting of 35 yr. (from 8 to 43 yr.), the increasing rate of soil CEC stock was 33.42 cmol m−2 yr.−1, while the loss rates of soil exchangeable K+, Na+, Ca2+, Mg2+, and TEB were 0.89, 0.52, 3.86, 1.23, and 6.51 cmol m−2 yr.−1, respectively. Interestingly, the loss rates of soil exchangeable base cations in the middle phase (from 17 to 25 yr.) were greater than those in other phases. Therefore, it is of critical importance to implement a sustainable management scheme to maintain soil aggregate stability and to minimize the loss of soil exchangeable base cations in the tea planting process, especially after 17 yr., in the hilly regions of southern Guangxi, China.