Soil fertility indices of citrus orchard land along topographic gradients in the three gorges area of China

In the Three Gorges Area of China, soil erosion and the resultant non-point source pollution and ecological degradation have endangered agricultural ecosystems and fresh water reservoirs. Although efforts have been undertaken to reduce soil and water losses from slope land used for citrus production, information on the effects of management practices on soil fertility indices is either limited or nonexistent. This study was conducted to compare the effects of 10 years of various management practices, citrus intercropped with white clover (WC), citrus mulched with straw (SM), citrus intercropped with contour hedgerows (CH), citrus orchard land with impermeable membrane (IM), and citrus intercropped with wheat (Triticum aestivum) and peanut (Arachris hypogaea) (WP), as treatments on soil fertility indices with that of the conventional citrus management (CM). Results showed that the soil organic carbon, total and available nitrogen, available potassium, and water-stable aggregate (> 0.25 mm) contents at the 0-5 cm depth were higher for the WC and SM treatments than the CM treatment. There was also spatial variation in soil fertility along slopes of the WC and SM treatments. The soil total and available nitrogen, phosphorus, and potassium, and water-stable aggregate (> 0.25 mm) contents at both the 0-5 and 5-20 cm depths were higher for the CH and IM treatments than the CM treatment. The average soil available nitrogen and available potassium contents were higher for the WP treatment than the CM treatment, but the WP treatment had little effect on the soil organic carbon, total nitrogen, and water-stable aggregate (> 0.25 mm) contents. These suggested that white clover intercropping and straw mulching were the most effective approaches to improve soil fertility in citrus orchard land of the Three Gorges area.