Soil aggregation and aggregate-associated carbon, nitrogen, and phosphorus under different aged tea (Camellia sinensis L.) plantations in hilly region of southern Guangxi, China

Abstract

To have a comprehensive understanding towards the dynamics of soil carbon (C), nitrogen (N), and phosphorus (P) during tea planting, it requires to evaluate the distribution of these elements within soil aggregates at various sizes. In this study, soil organic C (OC), labile OC (LOC), total nitrogen (TN), alkali-hydrolyzable N (AN), total P (TP), and available P (AP) had been detected within soil aggregates obtained at the 0–20 cm depth from tea plantations of various ages (8-, 17-, 25-, and 43-yr.) in hilly region of southern Guangxi, China. Soil aggregates were divided into micro-aggregates (<0.25 mm), small (1-0.25 mm), medium (2-1 mm), and large (>2 mm) macro-aggregates through a dry-sieving procedure. As main carriers of soil C, N, and P, both large macro-aggregates and micro-aggregates had relatively high stores of these elements in all of tea plantations. Tea planting age significantly influences the dynamics of C, N, and P stores in whole-soil, except for total P. During the 35-yr. of tea planting (from 8- to 43-yr.), the accumulation rates of soil OC, TN, AN, and AP were 27.91 g OC m−2 yr.-1, 0.96 g TN m−2 yr.-1, 0.06 g AN m−2 yr.-1, and 0.04 g AP m−2 yr.-1, respectively. Notably, the accumulation rates of these elements in whole-soil differed with the stage of tea planting. For example, soil OC store was increased by 54.94 g OC m-2 yr.-1 at early (from 8- to 17-yr.) stage of tea planting, while by 25.82 and 15.31 g OC m-2 yr.-1 at middle (from 17- to 25-yr.) and late (from 25- to 43-yr.) stages, respectively. Also, similar trends were observed in the TN, AN, and AP in whole-soil. Differently, soil LOC store was first increased and then decreased, and the store was significantly higher in the 17-yr. tea plantations relative to other tea plantations. These results indicated that long-term tea planting brought various benefits, such as the accumulation of soil OC, TN, AN, and AP. However, their accumulation rates in whole-soil decreased with the increase of tea planting age. In addition, it is of critical importance to develop and implement an appropriate management scheme to maintain the soil as a LOC sink after 17-yr. of tea planting in hilly region of southern Guangxi, China.