Integrated evaluation of soil fertility in Ginkgo (Ginkgo biloba L.) agroforestry systems in Jiangsu, China

Abstract

Ginkgo (Ginkgo biloba L.) is a traditional economic tree species in China, and often cultivated in agroforestry systems. The objective of the study was to examine the effects of different Ginkgo and crop species combinations on soil fertility. We established two Ginkgo and crop species systems: Ginkgo + wheat + soybean (G+W+S), Ginkgo + rape + soybean (G+R+S), and one Ginkgo + mulberry (G+M) system, one pure mulberry plantation (M), and one crop systems of rape + soybean (R+S) in the field. Soil chemical properties and enzymes activities were measured 4 years after planting. These soil chemical properties and enzyme activities were used as soil fertility indicators (FI). Soil fertility of the five planting systems was finally evaluated by using improved Analytic Hierarchy Process (AHP). The result showed that soil chemical properties (including pH, organic matter, total N, hydrolysable N, available P and K, total K) and soil enzyme activities (including catalase, sucrase, urease, dehydrogenase, phosphatase, polyphenol oxidase and protease) in the five planting systems were significantly different from each other (P = 0.0237). The above parameters were also different at different soil depths. The concentration of total N, P, organic matter, available P and K of soil decreased significantly with soil depth (P = 0.0146), however, pH increased. The concentrations of organic matter, total N, hydrolysable N, available P and K of soil under rape + soybean (R+S) was lowest among the five planting systems. The activities of sucrase, urease, dehydrogenase, phosphatase and protease decreased with soil depth, however, the activity of catalase and polyphenol oxidase increased. Except for catalase, the activities of these enzymes in the R+S system were the lowest among the five planting systems. The integrated evaluation of soil fertility showed that soil fertility indicators (FI) were significantly different, and the FI values for the five systems followed order: G+M (0.847) > G+W+S (0.446) > M (0.399) > G+R+S (0.343) > R+S (0.211). These results indicated that adoption of a Ginkgo-crop combination could lead to increased long-term sustainability of soil fertility by improving levels of soil organic matter, pH, available nutrient and soil enzyme activity.