Effect of continuous vegetable cropping on soil nutrient variation in plastic greenhouse

It was studied that the soil nutrient variation tendency and accumulation situation in plastic greenhouse with different cultivation years and different soil layers in Harbin City.The results showed that with the increasing of using period of the protect vegetable filed,the content of the slowly released potassium and available phosphorus in each layer were increased with the period of tillage,the total phosphorus and available potassium showed periodical variation in the growing season.But the contents of total nitrogen and alkali-hydrolysable nitrogen in each soil layer were different,in the profile of 0-20 cm soil,which were increased and in the profile of 20-40 cm and 40-60 cm were declined.Other soil nutrient contents were all declined gradually with the soil layer depth increasing.