[Responses of soil aggregate-associated organic carbon and nutrients to tea cultivation age in southern Guangxi, China].

Understanding the response mechanism of soil aggregate-associated organic carbon (OC) and nutrients to tea cultivation age can lay a theoretical foundation for improving soil fertility, ensuring soil health, and promoting sustainable utilization of soil resources in the tea plantations. In this study, concentrations of soil OC and nutrient were analyzed in >2, 2-1, 1-0.25, and <0.25 mm fractions (split by a dry-sieving procedure) at the 0-20 cm soil layer in four tea plantations with Baimao tea of different ages (8, 17, 25, and 43 a) in southern Guangxi, China. The distribution of soil aggregates showed that the dominant aggregates were >2 mm fractions with a mean value of 63.8%, followed by <0.25 mm fractions, while 2-1 and 1-0.25 mm fractions with mean values of 9.9% and 7.8%, respectively. As an indicator of soil aggregate stability, the mean weight diameter (MWD) in the tea plantations showed an order of 17 a >8 a >25 a >43 a. Regardless of tea cultivation age, soil aggregate-associated OC and total nitrogen (TN) concentrations increased with increasing aggregate size. Soil OC and TN concentrations in >2 and 2-1 mm fractions were significantly higher than those in other fractions. The mean values of soil OC and TN concentrations were 18.76 and 0.84 g·kg in the >2 mm fractions, and were 18.65 and 0.80 g·kg in the 2-1 mm fraction. Soil aggregate-associated available nitrogen (AN), available phosphorus (AP), and availa-ble potassium (AK) concentrations were highest in the <0.25 mm fractions with mean values of 50.43, 23.06, and 68.04 mg·kg, respectively. Long-term tea cultivation was favorable to the accumulation of soil OC, TN, AN, and AP, whereas the accumulation rates of these element stocks in the whole soil decreased with increasing tea cultivation age. In contrast, soil AK was susceptible to leaching in tea cultivation, with the loss rate of this element stock in the middle stage (from 17 to 25 a) being higher than those in the other stages. To ensure soil quality and promote the sustainable utilization of soil resources, more attention should be paid to the problems such as the decrease of soil aggregate stability and the aggravation of AK loss after 17 a of tea cultivation.