Planting soybeans (Glycine max (L.) Merr.) in tea gardens decreased soil pH in theory but increased it in practice. This controversy was addressed in this study by treating the tea garden soil consecutively with different parts of a soybean cover crop: aboveground soybean (ASB) parts, underground soybean (USB) root residues, and the whole soybean (WSB) plants. In comparison with the control, the soil pH increased significantly after the third ASB and WSB treatments, but there was no significant change in the soil pH in the USB treatment. Concordantly, the soil exchangeable acidity decreased significantly and the soil exchangeable bases increased significantly in the ASB and WSB treatments. The exchangeable acidity increased in the USB treatment, but the amount of the increased acidity was less than that of the increased bases in the ASB treatment, resulting in a net increase in the exchangeable bases in the WSB treatment. Soybean planting and covering also increased the microbial richness and abundance significantly, which led to significantly more soil organic matters. Exchangeable K+ and Mg2+, and soil organic matters played significantly positive roles and exchangeable Al3+ played negative roles in improving soil pH. Our data suggest that consecutive plantings of soybean cover crop increase the pH of the acidified tea garden soil.
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