Salt accumulation,translocation and ion composition in greenhouse soil profiles

By investigating greenhouse cultivation in different regions of China and analyzing both greenhouse and open field soil samples,salt accumulation and translocation in greenhouse soils was studied.The results indicated that salt content in greenhouse soils was higher than that in open field soils.The salt content in 40%～89% of greenhouse soil samples reached the stunt point for vegetables.Salt accumulation is a main limiting factor for sustainable development of greenhouse cropping.The highest salt content was found in greenhouse soils used for about 4 years,when salt content might reach the threshold value limiting normal growth of crops,then it would decrease by some countermeasures but still higher than open-field soil.Compared with neighboring open field soils,the salt content of the greenhouse soil decreased with depth.Greenhouse soils displayed apparent phenomena of salt accumulation in topsoil(0-20cm) and salt leaching downwards to the bottom of the soil(80-100cm),especially NO3- that seriously affected the quality of groundwater in the area.Apart from HCO3-,the contents of NO3-、SO42-、Cl-、Ca2+、Mg2+、K+、Na+ were increased to different degree in greenhouse soils,and NO3- 、SO42- and Ca2+ were the major ions in the soils.The large accumulation of salt and some salt ions might cause induce other limiting factors of greenhouse cropping system,such as the nutritional disorders,acidification of soil and the short supply of CO2 etc.