Study On Soil Nutrient Dynamics Of Vegetable Greenhouses In Baiyin

Greenhouses are artificially established and controlled fancilities for vegetable production, characterized by rain shading, fertilizer riching and intensive cropping. The soil quality and conditions may therefore siginificantly differ from that in the open fields. Soil physical and chemical properties, such as pH, solute salts, macro and micro nutrients, may become unfavorable for vegetable growth. Soil acidification, salinization, pathogens increase, and nutrient unbalance have been reported to have negative impacts on soil quality and environment, resulting in lower yield, inferior quality, and even unsafe produce of vegetables.Soil samples from different depth of vegetable greenhouses in Baiyin City, central Gansu Province, were collected to investigate dunamics of physical, chemical and nutrimental changes in soil profile and after different production years. The major findings are as followings:1. Except soil pH which decreased, the EC, the cation exchange capacity, contents of organic matter, soluble salts, total nitrogen, phosphates and potassium, as well as readily available nutrients at surface layers increased as the production years prolonged, indicating that acidification, salinization and nutrient enrichment at surface soil layers were remarkable of greenhouses.2. Analysis of soil profile from 0-200cm in 10 years old greenhouse showed that soil pH increased gradually, while the cation exchange capacity, contents of soluble salts, organic matter, total and readily available nutrients decreased steadly before stabilized at about 80cm, The results indicated that soil acidification, salinization and nutrient enrichment were obvious at surface layers, and are transmiting gradually to the deep layers.3. From the three major charactical indicators (EC, nitrate, pH) of soil quality, it can be concluded that soil quality in greenhouses of Baiyin is degrading gradually under present soil mananging and fertilizing practices, due to salt accumulation, nitrate enrichment and soil acidification in cropping layer.