Influence of coated urea on yield and quality of celery and nitrogen balance

The effectiveness of soil-applied fertilizers depends mainly on their ability to maintain a sufficient concentration of the nutrients within the plant root zone for desired period of time. In most commercial fertilizers, the nutrient concentrations of fertilizers after applied in soil rapidly diminish prior to sufficient plant uptake due to degradation (e.g. chemical, photochemical and biological), volatilization, leaching, adsorption or immobilization. In order to increase crop production, large dosage is often applied, thus increasing environmental risk. Coated slow-release fertilizers have recently been developed aiming at retarding the release rate of the nutrients in soil.In this paper pot experiment was conducted to determine the effect of coated fertilizers in grey fluvo-aquic soil on uptake and balance of nitrogen, yield and quality of celery ( Apium graveolens ) , in order to gain better insight into the mechanisms of coated urea in increasing nitrogen utilization rate and reducing environment pollution by fertilization. The results indicated that the treatment with coated urea in 2 kinds of texture grey fluvo-aquic soils (sandy loam soil and loamy sand soil) increased celery yield by 11.5%-15.2% , and N uptake by celery by 5.9%-9.5% , but ammonia volatilization was reduced by 14.2%-14.9%,and N loss via leaching and de-nitrification was reduced by 25.5%-28.3%, soil retained N was enhanced by 32.0%-37.3%, and the utilization efficiency of physiological nitrogen element,i.e. total N uptake by crop/(total N of soil before experiment - total N of soil after crop harvest) + N rate applied 100,increased by 20.1%-27.9% compared with the treatment with urea. Moreover, the concentration of NO3--N decreased fay 44.2%-58.9%, but vitamin C increased obviously in celery shoots and the product quality of celery was improved significantly. More importantly, the yield of second season crop romaine lettuce (Lactuca sativa var. longifolia) increased by 14.4%-35.2% .