The cultivated land soil quality change and mechanism in the Pearl River Delta

The soil quality change and mechanism of cultivated land was studied by soil survey of typical region in the Pearl River Delta. The results showed that,comparing with the second generalsoil survey in 1980s,the content of soil organic matter and total nitrogen had no significant change but performed decrease trend; the available-N(NO3--N) and available-P increased obviously,especially the accumulations of available-P adding up to very rich level; the available-K increased slightly,but being still at lower level; the available-Mg,available-B,and available-Mo were still seriously insufficient,some of the soils were poor in available-Si and available-Mn. It was indicated,along with the cropping system change,intensive continuous cultivation,the over fertilization and applying caustic lime in vegetable field for control of plant disease and insects,might be the main factors of the degrease of soil organic matter and the presenting of news nutrient imbalance.