Characteristic of Soil and Groundwater Nutrient in Different Age Greenhouse Vegetable Cultivation in Tianjin

Recent years,with the rapidly growth of greenhouse coverage area in Tianjin,soil nutrient status in different old greenhouses were investigated for the healthy development of greenhouses.The results showed that available nitrogen,available phosphorus and available potassium were heavy cumulated in soil of greenhouse vegetable.With the planting age increasing,the cumulative intensity was the higher.The contents of soil available nitrogen and available phosphorus were significantly increased in the soil which planting years of greenhouses were more than 10 years.Available nitrogen and available phosphorus accumulation were the same as other districts,but available potassium accumulation was more intensity than other districts.Nitrate was also cumulated in surface layer and deep layer of the soil of greenhouse vegetable.At same time,the content of nitrate in the groundwater was higher.For example,if the greenhouse vegetable lasted more then 10 years,the content of nitrate in the groundwater was up to 149.1 mg/L;however it was only 1.13 mg/L where filed crops were planted.The pH didn't change a lot in the soil where greenhouse vegetables were planted less than 10 years,but if more than 10 years it decreased remarkably.After 10 years of greenhouse vegetable planting,the salt contents of soil were increased obviously.The content of soil organic matter was also increased remarkable after 5 years planting of greenhouse vegetables.These results indicate that soil nutrients were cumulated intensively after 10 year planting of greenhouse vegetables.Simultaneity,ground water pollution was serious in these area,so effective measures should be taken to deal with it.