Studies On The Major Of Nitrogen Loss In The Protected Soil Under Different Nitrogen Fertilization And Irrigation Strategies During Tomato Growing Season

This study was conducted to determine the effect of different N application and irrigation rates on N₂O emissions, ammonia volatilization, nitrogen accumulation and utilization efficiency in 0¹00 cm deep layer, tomato yield and fruit quality from a loamy fluvo-aquic soil in North China Plain from 2008 to 2009.Tomato were planted under two different irrigation levels W1 and W1(traditional and water-saving). Three nitrogen levels were set under W1 and W₂ (N₀:0 kg/ha, N₆₇₅: 675 kg/ha, N900:900 kg/ha) respectively. In this experiment, the main results were as follows:1. The results indicated that reduction of nitrogen regardless of low or high irrigation rate can reduce N₂O fluxes, however, only if low N fertilization was applied, low irrigation result lower N₂O fluxes. In this study condition, Total N₂O emission from the different treatments arrangement as follows: W₁N₉₀₀ (5.304 kg/ha)>W₂N₉₀₀ (4.913 kg/ha)>>W₁N₆₇₅ (3.616 kg/ha)>> W₂N₆₇₅ (2.901 kg/ha)>> W1 N0 (0.563 kg/ha)> W2 N0 (0.511 kg/ha). The high N₂O emissions from greenhouse tomatoes plots were due to high N₂O losses from the fertilized treatments during the summer and early autumn (Aug, Sept and Oct) and high soil nitrate contents after the N application. The emissions of N₂O per unit N fertilizer applied (low and the conventional rates of N fertilization)were 0.35% 0.53%.2. Decreased N application can significantly reduced the amount of ammonia volatilization in the protection soil of tomato. Total ammonia volatilization from the different treatments arrangement as follows: W₂N₉₀₀ (21.362 kg/ kg/ha)> W₁N₉₀₀ (20.878 kg/ha) >> W₂N₆₇₅ (17.632 kg/ha) > W₁N₆₇₅ (17.466 kg/ha) >> W₁N₀ (6.591 kg/ha > W₂ N₀ (6.390 kg/ha). Reduced nitrogen fertilizer application is an effective way to reduced ammonia volatilization in greenhouse soil. There is no significant between low and conventional irrigation if the N application rates are same. The reason that the peak of ammonia volatilization is found at 1-3 d after fertilization is the rapid increase of pH after fertilization. In addition ammonia volatilization is higher during high temperature period (August to October).The volatilization of ammonia per unit N fertilizer applied (low and the conventional rates of N fertilization) were 1.59%¹.68%.3. The results showed that protected vegetable soils from high nitrogen treatments accumulated large pools of nitrates in each layer from 0 to 100 cm soil layer, especially from 0 to 40 cm, meanwhile, leaching out of 40 cm soil layer was large when high irrigation was applied. Nitrate residual in vegetable soils may be cause serious threats to underground water in vegetable growing areas.4. Irrigation and N application had important influence on tomato yield and dry matter accumulatio. In this study condition, no N-application have maintained yield however low quality. No significant increase of yield in high N application (900 kg/ha)treatments,but also increased the content of nitrate in fruit.In summary, the experiment showed that it had the potential of saving water and fertilizer under the premise of maintaining the yield and quality in greenhouse in Xinji city, Hebei province. Reduced N application not reduced the yield significantly, but improved fruit quality, reduce the gas losses of N₂O and ammonia, reduced the accumulation and leaching amount of nitrogen of root zone soil. In this experiment, the best treatment is W₂N₆₇₅ which reduce the N₂O fluxes and ammonia volatilization by 45.3% and 15.5% compare with W1N900 treatment, in addition, W₂N₆₇₅ has highest utilization rate and lowest lossing rate of nitrogen.