Variation of nutrient contents in protected cultivation soil with different planting years in north area of Shanxi Province

With farmland and open vegetable fields as control,soil pH value,nutrient contents and its relations in protected cultivation soil with continuous planting years(1,4,7,11,14,17 a) in Yanggao County were studied.The results indicated that pH value significantly decreased,nutrient contents obviously increased in protected cultivation soil in comparison with farmland.With increasing of cropping years,organic matter,alkali-hydrolyzable N and available P contents in 0~20 cm and 20~40 cm soil increased within short-term and reduced beyond some years.According to the criteria of soil nutrient contents for protected vegetable soil,pH value,organic matter and available K contents were appropriate,alkali-hydrolyzable N was high,and available P was seriously over proof in protected cultivation soil in Yanggao County.Correlation analysis showed that there were negative correlation between pH value and available K content,and positive correlation between every two soil nutrient contents.In short,soil chemical properties had been changed clearly due to irrational fertilization in protected cultivation,we should promote scientific fertilization in the future.