Tea plantation age effects on soil aggregate-associated carbon and nitrogen in the hilly region of western Sichuan, China

Abstract

Research on the variations of organic carbon (C) and total nitrogen (N) in soil aggregate fractions is important for better understanding C and N dynamics in agricultural soils. However, the effect of continuous planting of tea (Camellia sinensis L.) after the conversion of abandoned land to tea plantation on C and N dynamics has not been studied in detail. This study aimed to investigate the shifts in C and N concentrations in soil aggregate fractions after the conversion of abandoned land into tea plantation that were grown for varying periods of time (16, 23, 31, and 53 years) near Zhongfeng in the Mingshan district in the hilly region of western Sichuan, China. Soil samples were collected from the 0–20 and 20–40 cm depth intervals. Six aggregate fractions (>5, 5–2, 2–1, 1–0.5, 0.5–0.25, and <0.25 mm) were obtained by shaking and wet-sieving. In all studied tea plantations, the soil aggregates were dominated by the >5 and <0.25 mm fractions, which were the main pools of C and N. The mean weight diameter (MWD) of soil aggregates in the 23-year-old tea plantation was the greatest, indicating that aggregates in the 23-year-old tea plantation were more stable than in the other plantations. Aggregate stability was more strongly correlated with labile C than with organic C concentrations. Soil aggregates with different particle sizes had considerable variations in their organic C and total N concentrations in all tea plantations. The fractions that were most important to the retention of organic C and total N were the coarse aggregate fractions (>2 mm). The greater C/N ratio of the coarse aggregate fractions implied that their organic C was younger and more labile than that in the fine aggregate fractions (<0.5 mm). Long-term tea cultivation was favorable to the sequestration of soil C and N, especially in the <0.25 mm fraction. However, the rates of C and N sequestration in the whole soil decreased with tea plantation age. It can be concluded that the development and implementation of a suitable management protocol is critically important to the maintenance of soil C and N sinks after 53 years of tea cultivation.