Interaction of soil pH, organic matter, exchangeable acidity, and cation exchange capacity in a managed tea farm

The Yangai tea farm was established in 1952, with a long history of cultivating tea plants. The tea plant can activate Al³⁺ of the soil and affect soil physicochemical properties. Understanding soil physicochemical properties is crucial for studying soil fertility, nutrient retention, and long-term agricultural sustainability. Therefore, we investigated the distribution characteristics of soil pH, exchangeable acid, soil organic matter (SOM), and cation exchange capacity (CEC) in the surface soil and soil profile to assess their interaction in the managed tea garden.

We collected surface soil and soil profile samples from the managed tea garden and three land-use types (i.e., managed tea garden, unmanaged tea garden, and Pinus massoniana forest), respectively. We measure soil pH value with a laboratory pH meter. We measured the SOM, soil exchangeable acid, and CEC content, respectively, with potassium dichromate heating, potassium chloride leaching, and spectrophotometric methods.

The average soil pH value, exchangeable Al³⁺ content, and exchangeable H⁺ content were 4.50 (ranging from 3.95 to 5.88), 6.11 (0.04 to 9.32) cmol kg^-1, and 0.30 (0.03 to 0.62) cmol kg^-1, respectively. The surface soil acidification is severe, and the exchangeable acids in the tea garden were mainly exchangeable Al³⁺. The surface soil of the Yangai tea farm had a high ability to keep and supply fertilizer due to its enriching SOM content (average 55.94g kg^-1) and soil CEC (24.06 cmol(+) kg^-1). Surface soil exchangeable acid and CEC contents were higher after spring tea picking than before spring tea picking in the Yangai tea farm, while their SOM content was just the opposite. Therefore, it was recommended to supplement organic fertilizers after tea-picking because the surface SOM of the Yangai tea farm would decompose and be consumed more during the spring, summer, and autumn tea-picking periods than in winter. In addition, the SOM contents and soil pH values decreased and then increased with the increasing soil depth of the soil profile in three land-use types. The soil acidification rate of the managed tea garden was faster than that of the unmanaged tea garden and Pinus massoniana forest, and the difference in the acidification rate between the unmanaged tea garden and Pinus massoniana forest was slight. Therefore, there should be attention to preventing excessive soil acidification in the later tea garden management.