Impact Of High Input Of Fertilizers On Soil Secondary Salinization In Protected Agriculture

For a long time, the sustainability of soil production and protected vegetable development were threatened by the continual deterioration of soil quality in protected agriculture, which was caused by the high application of fertilizers for the purpose of obtaining high yields. Firstly, the overused fertilizers exceeded the nutrient absorption ability of crops, which resulted in the nutrient accumulation of nitrogen and phosphorus in the soil. Secondly, the high application of fertilizers caused the severe soil secondary salinization, which strongly influenced the normal growth of vegetables. Thirdly, the salt washing wastewater was discharged directly to the surface water while the salt washing, an un-environmental friendly way, was carried out to reduce the soil salinity to keep the normal growth of crops, which caused severe non-point source pollution. Therefore, it’s greatly meaningful for promoting the sustainable development of protected agriculture, to study on the impact of high application of fertilizers on soil environmental quality in protected agriculture.This research, taking the protected vegetable fields in Shanghai suburbs as the study object, investigated the cropping modes, plantation years, crop yields and fertilization situation of protected vegetables fields, and analyzed the relationship between fertilization amounts and crop yields. Based on the plantation years (0-3years,4-6years,7-10years and>10years), cropping modes (leaf vegetables continuous cropping (LV), leaf vegetables and solanaceous fruit vegetables rotation (LS), and solanaceous fruit vegetables continuous cropping (SF)), fertilizer types (organic fertilizer and chemical fertilizer), the soil samples were collected in the typical protected vegetables fields, and the physical and chemical index, and the characteristics of salinity accumulation were studied. And the impact pattern of soil salinity on the yields and quality of crops was explored. The results were as follows:1. According to the investigation on the greenhouse types, cropping modes, plantation years and fertilization situation of protected vegetables farms with the area of more than200mu, in the protected vegetables fields with the plantation years of less than3years, the application amounts of fertilizers were the largest, and the total pure amounts of nitrogen and phosphorus had reached160.34kg·mu-1. In the protected vegetables fields which mainly used the chemical fertilizer, the total pure amounts of nitrogen and phosphorus were30-120kg·mu-1, while the amounts were50-300kg·mu-1in the protected vegetables fields which mainly used the organic fertilizer. Along with the increase of plantation years, the application amounts of fertilizers were kept in high level, while the proportion of chemical fertilizers increased year by year, from36.25%in the fields with less than3years to53.31%in the fields with more than10years. For the protected vegetables fields with different cropping modes, the total pure amounts of nitrogen and phosphorus followed the pattern of LV>SF>LS, while the application amounts of chemical fertilizers followed the pattern of SF>LS>LV.2. Through the studies on the physical and chemical index of secondary salinization soil and characteristics of salinity accumulation of protected vegetables fields with different plantation years, cropping modes and fertilizer types, the results indicated that, along with the increase of plantation years, the volume weight increased, while the pH, total porosity, maximum field moisture capacity and organic matter decreased, the nutrients of nitrogen and phosphorus accumulated, and the salinity of top soil significantly increased. The high input of fertilizers caused the change of basic physical feature, acidification and hardening, damage of aggregate structure, reduction of moisture capacity and permeability, and secondary salinization of protected vegetables soil. Meanwhile, the soil salinity appeared to accumulate in the top soil, and then accumulated in the soil with the depth of60-80cm along with the increase of plantation years, especially the nitrate and nitrite, which were the potential threats of ground water.3. The results of pot experiment for the relationship between soil salinity and crop yields and quality showed that, the soil salinity inhibited the growth of crop seeds, which caused lower germination rates. The absorption of nitrogen of crops was blocked and the yields gradually deceased, when the soil salinity exceeded3g·kg-1. The nitrate contents in the crops were increased with the soil salinity increased. Therefore, the soil was not suitable for cropping and the soil remediation need to be applied, when the soil salinity reached3g·kg-1...