Soil organic carbon and nutrients associated with aggregate fractions in a chronosequence of tea plantations

Abstract

Research on the changes of soil aggregate-associated organic carbon (C) and nutrients in different aged tea (Camellia sinensis L.) plantations is essential for improving our understanding of soil organic C mitigation and nutrient restitution during tea cultivation. However, the short- and long-term implications of the conversion of abandoned land to tea plantations on these elements associated with aggregate fractions remain poorly understood. In this study, soil organic C, total nitrogen (N), available phosphorus (P), as well as exchangeable cations, namely potassium (K+), sodium (Na+), calcium (Ca2+), and magnesium (Mg2+), were analyzed in different size fractions of soil aggregates that were collected from 0 to 20 cm depth in four tea plantations with the same cultivar (Sichuan tea) of various ages (16-, 23-, 31-, and 53-years) in the hilly area of western Sichuan in China. Soil aggregates were classified into six fractions by a wet-sieving procedure, namely >5, 5–2, 2–1, 1–0.5, 0.5–0.25, and <0.25 mm. As main carriers of soil organic C and nutrients, both >5 and <0.25 mm fractions had relatively high stocks of these elements in all the tea plantations. During the 37-years of tea cultivation (from 16- to 53-years), the accumulation rates of soil organic C, total N, and available P were 40.32 g C m−2 year−1, 1.43 g N m−2 year−1, and 0.03 g P m−2 year−1, respectively, while the loss rates of soil total exchangeable bases (TEB) were 3.54 cmol TEB m−2 year−1. Notably, the change rates of these element stocks in the whole-soil differed with the stage of tea cultivation. For example, using the stock of soil organic C in the 16-year-old tea plantation as a reference point, an average increase in soil organic C stock of 96.09 g C m−2 year−1 occurred in the early (from 16- to 23-years) stage, while the increase was 51.70 g C m−2 year−1 in the middle (from 23- to 31-years) and 18.43 g C m−2 year−1 in the later (from 31- to 53-years) stages. Similar trends were observed in the soil total N and available P. Furthermore, an average decrease in soil TEB stocks of 2.83 cmol TEB m−2 year−1 occurred in the early stage, while the decrease was 12.67 cmol TEB m−2 year−1 in the middle and 0.80 cmol TEB m−2 year−1 in the later stages. These results indicated that long-term tea cultivation brought various benefits, such as the accumulation of soil organic C, total N, and available P. However, their accumulation rates in the whole-soil decreased with the increase of tea plantation age. In addition, it is important to establish sustainable management practices to minimize soil exchangeable cations loss during the tea planting process, especially after 23-years, in the hilly area of western Sichuan in China.