Increase in soil nutrients in intensively managed cash-crop agricultural ecosystems in the Guanting Reservoir catchment, Beijing, China

Since the late 1970s, transitions in socioeconomic status and new governmental policies have led to drastic changes in agricultural land use types and farm management practices across rural China, such as an increase in the area of land cultivated for cash–crops (e.g. vegetables and orchards) and intensive fertilization and irrigation of this land. How this more intensive management and land use for the more profitable cash crops affects soil nutrients is of great concern for carbon, soil and water quality management. In this paper, we attempted to assess the influence of cash crop ecosystems on soil nutrients in the catchment upstream of the Guanting Reservoir, in the Beijing municipality, North China plain. Soil nutrients in cash crop (orchard and vegetable) ecosystems with between 8 and 20 years of intensive management history were compared with traditional agro-ecosystem management patterns (corn and soybean). Results showed that soil organic carbon (SOC) had improved, and total nitrogen (N), and available phosphorus (P) concentrations had marginally increased under intensive management practices in the vegetable and orchard ecosystems in the last 25 years. The increases in SOC and total P densities at the 100 cm soil depth in orchard, vegetable and irrigated corn systems were greater than those in the rain fed corn and soybean systems. Soil available P and electrical conductivity (EC) were highest in the vegetable lands. However, no significant changes were found between the soil physical properties (i.e. bulk density, clay content and water stable aggregate content) of the traditional and cash-cropping systems. Multi regression analysis showed that manure and mineral fertilizer contributed significantly to the increase in soil nutrients. Intensively managed orchards are a better option for improving soil quality and SOC sequestration. However, the risks of nonpoint source pollution from, and soil salinization in, the land used for vegetable cultivation should be considered in the future.

► Soil physical properties were not different between the agro-ecosystems.
► Soil organic carbon and nutrient contents have increased in the last 25 years.
► The orchard ecosystems were better for soil carbon sequestration.
► The risk of water eutrophication with the vegetable ecosystems was high.
► Soil nutrients under irrigated corn were higher than under rain fed corn and soybean.