Investigation And Assessment Of Safety On Vegetable Soil Fertiltiy And Environment Quality In Suburbs Of Nanjing

The growing of vegetables is an intensive way of land use. The amounts of agrochemicals and farm film used in vegetable growing are usually dozens of times of those used for growing cereals. Excessive fertilizers are unbalanced applied on vegetable soil. Suburbs of cities are the most important bases for the supply of vegetables and subsidiary food to downtowns. However, suburban areas suffer the most severe industrial and agricultural pollution. The problems of the degrading of soil environmental quality and soil pollution are becoming increasingly prominent. Reports on the acidification and secondary salinization of vegetable soil are on the rise. Consequently, we investigated nutrient accumulation, environmental quality of vegetable soil and pollution of main varieties of vegetables in the suburbs of Nanjing.Results obtained showed that compared to paddy soil, the concentrations of organic matter, total nitrogen, total phosphorous, readily available phosphorous, nitrate were accumulated to some extent, especially the soil readily available phosphorous and nitrate. However, in comparison with the data acquired in the Second National Soil Survey, soil organic matter and total potassium content decreased, whereas soil total phosphorous concentration increased slightly.According to the national requirements on the locality of non-polluted vegetable, 40 percent of the vegetable growing area investigated met the requirements,30 percent of the soil investigated approached the warning line, while 30 percent of the soil were polluted and failed to meet the requirments. Cd pollution contributed the most to the soil contamination, and Hg pollution was also severe in certain area.Under the circumstances of huge amounts of chemical and organic fertilizers being applied to the fields, soil pH of farmland in the open air rose slightly. Greenhouse vegetable soil pH was 0.30 to 0.87 lower than that of open-air farmland soil, and was 0.12 to 0.52 lower than that of open-air vegetable soil in times of Second National Soil Survey. In the meanwhile, severe accumulation of salinity was found in open-air vegetable soil, with nitrate being accumulated the most.Analysis on the pollution of vegetable samples collected from Jiangxinzhou, Xishan, Suangzha and Banqiao showed, except for some samples from Jiangxinzhou, Cr, Cd, As, Pb, nitrate and nitrite residues in samples of other three towns were within the limits set on the National Standard for heavy metal and hazardous substances concentration in non-polluted vegetable. However, certain substance contents were close to the limits, which should be considered immediately.