Evolution of soil nutrient and salts in vegetable field ofgreenhouse in Xinxiang

Abstract: The production history of greenhouse was more than 30 years in Muye vegetable production base in Henan Xinxiang. The main planting pattern of this region was wheat and maize rotation before building a greenhouse, but now it is the production of cucumbers and tomatoes in a greenhouse in spring and autumn. In order to study the evolution characteristics of soil fertility and salt of the vegetable field in the greenhouse, the soil sample of the vegetable field in the greenhouse (0-20, >20-40 cm) in different cultivating years (0, 5, 10, 15, 20, 25, and 30) were collected and the main soil fertility index and soluble salt and soil pH values were measured. The results showed that the fertilization period of plastic house soil in Xinxiang is usually around 15 age of cultivating where the content of organic matter therein is ideal, exceeding 30 g/kg. However, at the 15th cultivating years, the contents of alkali-hydrolyzable nitrogen and rapidly available phosphorus are slightly high, exceeding 150 and 90 mg·kg-1 respectively. Regarding the quantity of rapidly available potassium, the soil is in serious shortage of rapidly available potassium whose content is lower than 100 mg/kg, and this continues to decline after 15 cultivating years. The contents of nutrients decline as the depth of soil rises. The contents of organic matter, alkali-hydrolyzable nitrogen, and rapidly available phosphorus in soil of 0-20 cm in depth are 33%, 39.79%, and 18% higher than their contents in soil of 20-40 cm in depth. Judging from the contents of nitrogen phosphorus potassium in soil, plastic houses of different cultivating years are all in serious shortage of potassium, having an oversupply of phosphorus. Hence, great attention should be paid to the fertilization management of plastic house soil in Xinxiang city. The salinization speed of plastic house vegetable field soil slows down within the first 15 years of plantation, and it reaches 0.3% and exceeds the critical value of 0.296% at the 15th cultivating year. Then the salinization speed rises at an annual speed of 0.05%/a during the cultivating period from 15 to 30 years. Changes of contents of SO42-, NO3-, Cl-, K+, and Na+ agree with the change of content of water soluble salt, comprising of the main element of salt ions. The content of SO42- goes up stably at an annual speed of 33 mg/kg after cultivating of vegetables, and it always exceeds 43% of the total content of salt ions, becoming the ion leading to salinization of soil by the largest margin. pH value of the soil declines by approximately 0.03 each year after cultivating, but stays above 7.0 all the time without any occurrence of soil acidification. The analysis indicates that soil salinization tends to synchronize with a decline of pH value of soil, which directly resulted from the application of a large amount of fertilizer. The research conclusions tend to provide a theoretical basis for fertilization decisions of the vegetable greenhouse soil of Xinxiang.