Accumulation of heavy metals in agricultural soils tends to increase crop uptake of heavy metals, and can adversely impact human health through food chains. This study assessed the heavy metal pollution status and the potential ecological risk of tea plantation soils in southern Shaanxi Province, China. A total of 330 topsoil samples were collected to analyze the concentrations of seven heavy metals (Pb, Zn, Cu, Cr, Hg, As and Cd) and the pH level. The Hakanson potential ecological risk index was used based on the background levels of soil heavy metals in Shaanxi. Results showed that the averaged concentrations of soil Pb, Zn, Cu, Cr, Hg, As, and Cd were 10.0, 87.6, 16.4, 12.4, 0.2, 6.9 and 0.1 mg/kg, respectively. Cd and Hg concentrations exceeded level II of China's Soil Environment Quality Standard (GB 15618-2009) in 9.3% and 7.0% of the total samples, respectively. The coefficient of variation ranged from 29.2% to 52.2% for different elements, and was 49.3% for Cd and 48.6% for Hg. The averaged comprehensive potential ecological risk index was 95.4, and the overall potential ecological risk was low, with 82.4% of the total samples at a low level of potential ecological risk. Cd and Hg contributed most to the potential ecological risk (35.5% and 46.5%, respectively), and the risks associated with other elements were relatively minor. This study suggested that soil Cd and Hg pollution should be controlled to ensure the safe production of tea in the study area.

Optimization of water and fertilizer coupling management approaches could not only increase apple yield and quality, but also reduce the potential negative impacts of such management activities on the environment. The aim of the present study was to determine the optimal water-nitrogen (WN) coupling management strategy in an apple orchard in the Weibei Dryland, Shaanxi Province, China, under limited irrigation. A randomized complete block design was adopted to test the effects of three drip irrigation levels (W1, 300 m 3 /hm 2 ; W2, 600 m 3 /hm 2 ; W3, 900 m 3 /hm 2 ) and four N application levels (N0, 0 kg/hm 2 ; N1, 200 kg/hm 2 ; N2, 400 kg/hm 2 ; and N3, 600 kg/hm 2 ) on N distribution in the 0-100 cm soil profile. Apple yield and economic benefits under different treatments were also evaluated over a three-year period (2012)(2013)(2014). Compared with the N0W1 treatment, soil N contents were higher and exhibited distinct trends in the soil profile under other treatments. Overall, total N contents exhibited a downward trend from the surface to the subsurface layers (0.11-2.34 g/kg); however, the total N contents of the lower soil layer increased with an increase in irrigation amount. NO 3 -N contents were the lowest in the 40-60 cm soil layer and then increased with an increase in soil depth. The highest NO 3 -N contents of different soil layers were observed under the N3W3 treatment, ranging from 124.7 mg/kg (0-20 cm) to 90.9 mg/kg (80-100 cm). NH 4 + -N contents were low (<10 mg/kg), mainly accumulating in the surface layer and decreasing toward the deeper layers>20 cm. Different water-N coupling treatments also increased apple yield by 7.30%-41.62% when compared with the N0W1 treatment. The highest apple yield (three-year mean: 41.01 t/hm 2 ) was observed under the N2W2 treatment, with an output value of 237 900 RMB yuan/hm 2 and a net income of 232 000 RMB yuan/hm 2 . Considering fruit yield, partial productivity of N fertilizer, and economic and environmental benefits, the N2W2 treatment is the optimal water-N fertilizer coupling drip irrigation scheme for apple production in the study area and other similar dryland areas.

Accumulation of heavy metals in agricultural soils tends to increase crop uptake of heavy metals, and can adversely impact human health through food chains. This study assessed the heavy metal pollution status and the potential ecological risk of tea plantation soils in southern Shaanxi Province, China. A total of 330 topsoil samples were collected to analyze the concentrations of seven heavy metals (Pb, Zn, Cu, Cr, Hg, As and Cd) and the pH level. The Hakanson potential ecological risk index was used based on the background levels of soil heavy metals in Shaanxi. Results showed that the averaged concentrations of soil Pb, Zn, Cu, Cr, Hg, As, and Cd were 10.0, 87.6, 16.4, 12.4, 0.2, 6.9 and 0.1 mg/kg, respectively. Cd and Hg concentrations exceeded level II of China's Soil Environment Quality Standard (GB 15618-2009) in 9.3% and 7.0% of the total samples, respectively. The coefficient of variation ranged from 29.2% to 52.2% for different elements, and was 49.3% for Cd and 48.6% for Hg. The averaged comprehensive potential ecological risk index was 95.4, and the overall potential ecological risk was low, with 82.4% of the total samples at a low level of potential ecological risk. Cd and Hg contributed most to the potential ecological risk (35.5% and 46.5%, respectively), and the risks associated with other elements were relatively minor. This study suggested that soil Cd and Hg pollution should be controlled to ensure the safe production of tea in the study area.