| Reasonable nitrogen fertilizer management can improve nitrogen use efficiency and realize high wheat yield and less environmental effect. The study investigated the effect of nitrogen application rate and timing on wheat growth development, yield and nitrogen use efficiency in order to provide theoretical basis for the reasonable application of nitrogen fertilizer on dry-land wheat in the Loess Plateau. Field experiment was carried out from June in 2014 to June in 2015 under straw mulching with two nitrogen(N) levels(150 and 200 kg/ha) and three application times, a total of 6 treatments. The main results obtained were as follows:1) The yield range of wheat grain was from 3667 to 4096 kg/ha. With the increase of nitrogen application rate, the grain yield, ear number, grain number and grain weight showed a trend of increase or decrease, while both N rate and application times had no significant effect on the yield of wheat. The wheat harvest index varied between 0.33 and 0.35, but wheat harvest index was similar at different nitrogen levels and nitrogen application times. The water consumption was 441-493 mm, the water use efficiency was 7.70-8.71 kg/ha/mm, nitrogen application rate and times had no significant effect on water consumption and water use efficiency.2) The effects of nitrogen application rate and times on relative chlorophyll content, photosynthetic rate and transpiration rate of wheat flag leaf were not significant, but three split applications showed the highest values in above three parameters in the grain filling stage. The soluble protein content of wheat flag leaf was gradually decreased with the age increase of flag leaf, both nitrogen application rate and nitrogen application times did not significantly affect its content. The content of MDA in flag leaf of wheat increased gradually with the age increase of flag leaf, and the content of MDA in flag leaf was not significant at different nitrogen levels and different nitrogen application times either.3) Wheat nitrogen partial factor productivity(PFPN) were 25.2-27.3 kg/kg and 18.3-19.5 kg/kg in low and high N treatments, and high N rate significantly reduce PFPN, but N split applications had no significant effects on PFPN. Nitrogen uptake efficiency were 0.70-0.76 in high N and 0.93-1.04 in low N treatments, at low N rate two applications had the highest value which was significantly higher than those of others at low or high N rates with one or more applications. Nitrogen use efficiency at high and low N treatments were 24.58-25.38 kg/kg and 23.48-27.10 kg/kg, respectively. The nitrogen harvest index of wheat was from 0.56 to 0.63.4) Nitrogen uptake at high N(200 kg/ha) and low N(150 kg/ha) was 141-152 kg/ha and 144-156 kg/ha, respectively. The results indicted the nitrogen balance of all treatments appeared surplus.On the whole, under wet year in dry-land area of Loess Plateau N rate and application times had no significant effects on winter wheat yield, yield component factors and physiological and photosynthetic characteristics of flag leaf after flowering. The tested low N rate met the demand for wheat growth, combined with the previous experimental results, thus, it is concluded that one application of N before sowing is feasible for the studied area under straw mulching. |
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