Status of salinity, pH and nutrients in soils in main vegetable production regions in China

This study was conducted to determine status of salinity, pH and nutrient fertility (OM, NO3--N, and available P and K) of 1201 representative plow layer soil samples from main vegetable production regions in China. The results showed that serious secondary salinization was found in the vegetable soils of greenhouse with wall and without wall in main vegetable production regions in China, with 28.1% and 29.3% of respective total soil samples from greenhouse with wall and without wall for soil electrical conductivity beyond the critical value (600 ?s/cm) for vegetable in normal growth, and 9.5% and 14.9% of respective total soil samples at very high salinity evaluation level (≧1000 ?s/cm). One of the most important reasons accounting for this was due to soil nitrate accumulation resulting from long-term use of excessive nitrogen fertilizer. Significant correlation relationships between soil electrical conductivity and nitrate-N contents were observed for the vegetable soils of greenhouse with wall and without wall, with correlation coefficients being 0.76 for the vegetable soils of greenhouse with wall (n = 285) and 0.86 for the vegetable soils of greenhouse without wall (n = 348). Medium and low OM evaluation levels in most soils in main vegetable production regions in China were found, with 36.9% of the soils in OM contents being below its critical value (20 g/kg) and only 10.0% of the soils at high OM evaluation level (≧40 g/kg), respectively. High accumulations of nitrate-N and available P were observed in the vegetable soils of greenhouse with wall and without wall in main vegetable production regions in China, with 33.0% and 30.7% of respective total soil samples from greenhouse with wall and without wall for soil nitrate-N at high evaluation level (≧150 mg/kg), and 59.3% and 35.3% of respective total soil samples for soil available P at high evaluation level (≧150 mg/kg). These data indicated that high accumulations of nitrate-N and available P in the vegetable soils of greenhouse with wall and without wall would lead to potential threat to vegetable and environment. Significant neutralization of pH was found in the vegetable soils of greenhouse with wall and without wall in northern main vegetable production regions in China, with lower pH values in the vegetable soils of greenhouse with wall (pH 7.2, n = 270) and without wall (pH 7.3, n = 143) compared with the open vegetable soils (pH 7.7, n = 155).