[Change characteristics of soil available nitrogen and phosphorus and heavy metal contents after long-term cultivation of vegetables].

Soil samples were collected from three vegetable fields under different years of cultivation in Changsha suburbs of Hunan Province, South-central China to study the accumulation characteristics, risks, and sources of soil available nitrogen and phosphorus and heavy metals in the fields. With the increasing year of vegetable cultivation, the soil NO3(-)-N, Olsen-P, and heavy metals contents in the fields increased significantly. The average contents of soil NO3(-)-N, Olsen-P, and Cd in the vegetable fields having been cultivated for 1-2 years in Ningxiang County, 10-15 years in Changsha County, and 30 years in Kaifu District were 21.1, 31.9 and 0.33 mg x kg(-1), 42.0, 146.9 and 0.52 mg x kg(-1), and 49.5, 219.9 and 1.40 mg x kg(-1), respectively. The cumulative index (CI) of soil heavy metals generally followed the sequence of Cd >> Cu > Pb > Ni > Zn. Principal component analysis and cluster analysis showed that compared with soil NH4 OAc-extracted potassium, pH, organic matter and NH4(+)-N, that were dominated by natural factors, the soil Olsen-P and NO3(-)-N had the similar accumulation characteristics with the soil heavy metals, being mainly controlled by fertilization. It was considered that the soil environment and health quality of the vegetable fields in Changsha suburbs were not optimistic. The longer the cultivation year of vegetables, the more the soil NO3(-)-N, Olsen-P, and heavy metals accumulated in the fields. The accumulation of these elements in the fields could be primarily due to the long-term fertilization.