Influences of Land Use with Different Crops on Soil Fertility and Productivity in the Area Above the Three Gorges Reservoir of China

Groundwater level rising after the Three-Gorges-Dam built in China may create a potential impact on soil fertility, land productivity and the development of sustainable agriculture in the area above the Three-Gorges-Reservoir (TGR). A comprehensive survey was conducted in 2009 through 3 counties (Zigui, Xingshan, and Badong) to evaluate the soil fertility, land productivity and economic output from different land uses including cereal/vegetable crops, citrus, and tea crop at various altitudes in the agricultural area above the TGR. The results showed that the soil fertility in cereal/vegetable crop fields on average had soil organic matter (SOM) 15.32 g/kg, total nitrogen (TN) 1.11 g/kg, total phosphorus (TP) 0.62 g/kg and total potassium (TK) 17.10 g/kg, respectively; followed by citrus (SOM 12.97 g/kg, TN 1.02 g/kg, TP 0.60 g/kg and TK 19.21 g/kg), and tea crop (SOM 9.44 g/kg, TN 0.70 g/kg, TP 0.57 g/kg and TK 10.04 g/kg). Regarding the productivity, cereal/vegetable crops had a decrease after water filled up in the TGR, especially in Zigui county but citrus remained a stable increase in these three counties. However, the economic benefit of citrus industry was significantly greater than those of tea and other crops, which stimulated the citrus acreage and remained the economic output increase in all these three counties. The soil fertility was closely related to the elevation and land use. For instance, the land at altitude 600-700 m with citrus growing had SOM 25.47 g/kg, TN 1.42 g/kg, TP 0.50 g/kg and TK 16.4 g/kg; and the land at altitude 700-900 m with cereal/vegetable crops had SOM 15.73 g/kg, TN 1.04 g/kg, TP 0.70 g/kg, and TK 19.54 g/kg. A change from slope to terrace farming helped improve soil fertility including soil nitrogen and phosphorus, which might be resulted from the reduction of water runoff and soil erosion. A 10-year monitoring result (2005-2014) displayed that soil fertility was generally decreasing in this area, which has become a main constraint to the local agricultural production. The degradation in soil fertility without efficient approaches in soil and water reservation can also be a major concern for a sustainable development of agriculture in this area.