Effect of N rate on growth and grain filling of wheat in Sichuan Basin

【Objectives】Nitrogen (N) has a significant effect on the accumulation, transport and distribution of photosynthetic products of wheat. In order to improve wheat yield potential in Sichuan Basin, effects of different N rates on dry matter production and grain filling of high-yield wheat cultivars were studied in Jiangyou City, Sichuan Province from 2011 to 2013. 【Methods】 A randomized block design with a split plot experiment was laid out and two cultivars, CM 104 and NM 836, were used as the main plot factors. Five N rates were set as sub plots: 0, 90, 135, 180 and 225 kg/hm2. Individual and population biomass, yield, yield components and filling parameters of the two cultivars were tested.【Results】 The yield, yield components, dry matter accumulation and leaf area index are all significantly affected by the N rates, cultivars and interannual climatic conditions. In the same N rate, the yield of CM 104 is higher than that of NM836. In the control, the average yield of NM 836 and CM 104 is 6638.9 and 6717.7 kg/hm2. In the N 135 kg/hm2 treatment, the yields of two cultivars are more than 9000 kg/hm2 and dry matter accumulation is more than 18000 kg/hm2. When the N rate is higher than 135 kg/hm2, the yield and dry matter accumulation increment become less. The relationship of yields and N rates can be described with a quadratic function, for CM104, y=-0.1056x2+44.023x+6724.6 and for NM836, y=-0.0934x2+35.991x+6651.5 (P0.05). The theoretical maximum yield and the N rate for the highest yield for CM104 are higher than for NM 836. The increased N rates lead to the increment of dry matter accumulation at all the growing stages, but the differences in increment range are not significant from N rate of 135 to 225 kg/hm2 and the highest dry matter accumulation after flowering and the contribution of dry matter translocation is in N rate of 135 kg/hm2. Although higher N rate is beneficial for the formation of effective spikes per hectare and grain numbers per spike, especially for the cultivar of CM 104, but not for the grain filling. The maximum grain-filling rate is decreased substantially in N rate of 180 kg/hm2 for NM836, 225 kg/hm2 for CM104. The 1000-grain weights in all the N treatments are lower than in control, and negative with N application rate increasing.【Conclusions】The difference in the dry matter accumulation after flowering is the main reason for the different response to N rate for the two cultivars. Appropriate N application rate is very important for achieving high population biomass, increasing the dry matter accumulation and translocation to the grains after flowering.Under the fertile and less N loss paddy soil condition in Sichuan Basin, the suitable N rate for high yield is 135-150 kg/hm2.