Soil microbiological properties and enzyme activity in Ginkgo-tea agroforestry compared with monoculture

Agroforestry practice is believed to be an effective means of maintaining and improving soil fertility, and is widely used by farmers around the world. To gain better understanding of the effects of agroforestry practice on soil fertility, the organic carbon content, total nitrogen content, microbial biomass, basal respiration, and activity of soil enzymes at three soil depths (0-10, 10-20, and 20-30 cm) of Ginkgo (Ginkgo biloba L.)-tea (Camellia sinensis (L.) O. Kuntze) agroforestry systems were investigated. Study plots were established in Yushan Farm in Changshu, Jiangsu Province, China. These involved two densities of Ginkgo trees mixed with tea (G(1) and G(2)) and monoculture tea systems (G(0)). The results showed that C, N, microbial biomass, and enzyme activity were higher in surface soil than in soil from the middle and lower layers whereas pH and metabolic quotient increased with soil depth. pH, microbial biomass C, N, basal respiration, and catalase and invertase activity in the 0-10 cm layer were significantly lower for G(0) than for G(1) and G(2). Polyphenoloxidase activity in the 0-10 cm layer was significantly lower for G(2) than for G(0) and G(1). Metabolic quotient in the 20-30 cm layer was significantly higher for G(0) than for G(2). The activity of soil enzymes, including catalase, dehydrogenase, urease, protease, and invertase, significantly and positively correlated with soil organic carbon and total nitrogen. The results of this study suggest that growing tea with Ginkgo could be regarded as good agroforestry practice which could enhance accumulation of organic matter in soil, improve the activity of soil enzymes, and maintain soil productivity and sustainability.