The Change of Soil Characteristics After Land Use Change from Paddy to Vegetable-field in the Pearl River Delta

The change of soil characteristics of vegetable transferring from paddy soil was studied by comparing with paddy soil nearby,in which 52-paired soil samples of Boluo county were selected.The results showed that:The soil pH had no significant change but increased slightly;The contents of soil organic matter and total nitrogen both were induced to fall;the contents of alkali-N,total-P,available-P and available-K increased obviously,especially the accumulations of available-P adding up to 98.02 mg/kg;At the same time,the contents of available Cu were induced;The contents of available B and available Mo both performed rising trend;the average contents of available Mn and available Zn increase significantly,and both beyond the national critical values,but there were 32.69% and 26.93% of soil samples below critical values respectively;the content of available Fe dropped distinctly.It was indicated that secondary salinization had performed lightly in some vegetable-field soils,characterized by the accumulations of total salt,NO-3-N.Statistical analysis showed that either the soil total salt content or the vegetable nitrate content was positively correlated with soil NO-3-N content.This means the over fertilization and intensive continuous cultivation might be the main factors of the degradation of soil fertility and the accumulation of nitrate in the leafage of vegetables.Therefore,the equilibrium of soil nutrients through balance fertilization and reasonable management of cultivation should be adopted to increase production and improve the quality of vegetables.