Effect Of Application Rate Of Nitrogen On Yield And Quality Of Several Vegetables

A field trial was established to investigate the effects of nitrogen (N) fertilizer on vegetable yields and qualities, and to develop fast N-diagnosing techniques. Nitrogen fertilizer was applied to a yellow-brown soil at five rates: N0, N1, N2, N3, N4, and Chinese cabbage, Spinach, Capsicum and Radish were grown in turn. The results of this study were following:1. The application of nitrogen fertilizer could increase the yields of Chinese cabbage, Spinach, Capsicum and Radish, but would decrease vegetable yields when N was over-applied. The following equations described the relationship among N application rates, vegetable yields and available-N before planting.Chinese cabbage, Y=3257.11+223.61x-0.33x~2; Spinach, Y= -4382.23+328.67z-3.61z~2+35.27x-0.18x~2;Capsicum, Y= 4261.75-4.91z+25.23x-0.046x~2;Radish, Y=2447.29+111.72z-0.29z~2+l 19x+0.47x~2.2. The application of N fertilizer at an appropriate rate facilitated the plant up-take, utilization and accumulation of nitrogen, phosphorus and potassium, improving the qualities and flavors of vegetables, and the synthesis and accumulation of protein in vegetables.3. Nitrate concentrations in vegetables increased with the application rate of nitrogen fertilizer. The application of N fertilizer had significantly elevated concentrations of nitrate in Chinese cabbage, Spinach and Radish. Concentrations of nitrate in Capsicum hadn't been affected significantly by N application, but still showed some increasing trend with the application rates.4. The application of nitrogen fertilizer at an appropriate rate could elevate the concentrations of chlorophyll in Chinese cabbage, Spinach, Capsicum and Radish, facilitating the synthesis and accumulation of carbohydrate in vegetables. As the application rate increased, concentrations of chlorophyll in vegetable leaves increased first but then decreased.5. Nitrogen efficiency in Chinese cabbage, Spinach, Capsicum and Radish declined with the application rate increasing. There was a significantly negative relationship between nitrogen efficiency and nitrogen application rates.6. To achieve high yields and good qualities of vegetables as well as low contamination of environment, we suggested that the optimum application rates of N fertilizer be 90-270, 40-100, 150-300, and 60-120 kgN/ha for Chinese cabbage, Spinach, Capsicum and Radish, respectively.