Effects Of Optimum Fertilization On Vegetable Yeild And Environment In Protected Soil

In recent years, with the adjustment of the agricultural crop and plant cultivation structure, the vegetable production in protectorate has been developed rapidly in all parts of the county. A great deal of fertilizer, especially nitrogen fertilizer, was used by farmers in order to pursue the maximum economic benefit, which not only lead reduce the nitrogen use efficiency, but also increase the degradation of soil quality and environment pollution. Aiming at resolving these questions, a 4-year located experiment was carried out in protected field in Beijing suburb to investigate the effects of optimized fertilization on crop yield, quality, N use efficiency, soil inorganic nitrogen distribution and apparent N balance of soil-crop system. These optimized fertilization measures were nitrogen-reducing added regulating soil C/N ratio and planting catch crop and using the controlled-release urea. The main results showed as follows:(1) The effects of optimized fertilization on yields were studied on vegetable rotation system. The results showed that: In normal growth seasons (less than five months), there were no significant influence on vegetable yields when common urea dose reduce to 75% of the conventional fertilization and the controlled-release urea dose reduce to 37.50% and 56.25% respectively of the conventional fertilization under the experimental condition. Comparing with a longer growing season (more than ten months), the nitrogen provided by the controlled-release urea cannot meet the crop needs, so the fields declined.(2) The nitrate distribution characteristics in the depth of 0-200 cm soil profiles were studied on vegetable rotation system. As time goes by, the soil profiles inorganic N content in the depth of 20-140 cm, 100-120 cm, 20-40 cm, 100-120 cm of conventional fertilization and three optimized fertilization all accumulated the highest inorganic N content at the end of the first year. After that, the soil inorganic N content fell apparently. Nitrogen reducing added regulating soil C/N ratio and planting catch crop and using the controlled-release urea all could reduce the residue nitrogen accumulation amount. The residue nitrogen accumulation amount in 0-200 cm soil profile was in the order as follows: OCC<CRFL<CRFH<CON. (3) The results of the apparent nitrogen balance in soil vegetable system indicated: the main N resource was from the input of nitrogen fertilizer, occupied in the total nitrogen from 32.40% to 5 9.86%. Crop absorption is the main output item, accounting from 79.62% to 90.97% of the output. In the rotation period, the apparent nitrogen losses were in an order as follows:CON>OCC>CRFH>CRFL.Compared with conventional fertilization, the apparent nitrogen balance of optimized fertilization in system were decreased 689.59 kg/hm~2,1084.68 kg/hm~2 and 1484.81 kg/hm~2 respectively.