Regulation Effect Of Different Irrigation And Nitrogen Fertilization On Nitrogen Uptake And Utilization Of Rape (Brassica Campestris L.)

Unreasonable irrigation and fertilization practices have led to tremendous waste of water and nutrient resources, thus hindering the sustainable development of agriculture. A pot experiment with completely randomized design of irrigation and nitrogen was conducted to study the utilization of nitrogen for rape (Brassica campestris L.) with the technique of stable isotope 15N-traced urea. The study included three irrigation levels (W1,60%9f (field capacity); W2,75%θf; W3,90%θf) and four nitrogen rates (No, OgN/kg soil; N1,0.1 gN/kg soil; N2,0.2 gN/kg soil; N3,0.3 gN/kg soil). The results were as follows:(1) Both irrigation level and nitrogen rate had significant effects on water soluble sugar and nitrate concentration. Water soluble sugar content decreased and nitrate concentration increased with the increasing of irrigation level. Irrespective of irrigation, as nitrogen rate enhanced gradually, water soluble sugar showed a deceasing trend, while nitrate concentration increased. Vitamin C content, water soluble sugar and nitrate concentration were both highly affected by the interaction of irrigation and nitrogen. W2N1 treatment, which performed well for both growth and quality, was the optimal combination.(2) Irrigation level, nitrogen rates and their interaction had different effects on nitrogen, phosphorus and potassium content. The maximum nutrient concentration were observed at W2N1 treatment. Nitrogen content showed a decreasing trend except for several treatment. The yield of rape were significantly affected by irrigation level and nitrogen rate. Yield increased with the increasing irrigation level and significant parabolic relationship were found between nitrogen rates and yield. Nitrogen rates and the interaction effect of irrigation and nitrogen were found to be significant for irrigation water use efficiency and the relationship between IWUE and nitrogen rates were same as that between yield and nitrogen.(3) Irrigation level, nitrogen rates or their interaction had significant effects on nitrogen accumulation and the source of nitrogen. The maximum nitrogen accumulation, fertilizer nitrogen accumulation and the percentage of that were both observed in W3N2 treatment. Over seventy percent of nitrogen derived from soil and the percentage of nitrogen derived from fertilizer exhibited different trend as growth period progressed under different treatments.(4) The recovery rate of fertilizer nitrogen was 5.30%～23.00%, soil residual rate was 56.22～71.29%, and loss rate was 13.17%～37.10% in the first season, while the corresponding data for total two season was9.07%-26.17%,32.53%～46.37% and 17.83%～50.22%. Nitrogen fate of the two rape crops were both highly affected by irrigation, nitrogen or their interaction effect. The maximum fertilizer nitrogen recovery rate and minimum loss rate were found in W3N1 treatment for the two rape crops.