Effects of nitrogen fertilizer rate on uptake, distribution and utilization of nitrogen in winter wheat under high yielding cultivated condition

Chinese. 通过2年田间定位试验，采用. 5N示踪技术，研究了高产条件下不同施氮量处理对冬小麦氮素吸收、分配、利用及产量和品质的影响。结果表明，在本试验土壤肥力条件下，当施氮量超过150kg／ha时，不能显著增加植株氮素积累量，对小麦生育后期植株氮素吸收无显著促进效应。随施氮量增加，氮素在籽粒中的分配比例降低，在茎和叶的分配量及比例显著增加。. 5N示踪试验指出，施氮量由195kg／ha增至240kg／ha，植株吸收的肥料氮素增加，吸收的土壤氮素减少，植株总的氮素积累量无显著差异；施氮量增加，开花后营养器官中的氮素向籽粒的转移无显著差异，而转移效率及氮素转移对籽粒的贡献率降低。施氮量增加，氮素吸收效率和氮素利用效率下降，氮肥生产效率降低，氮素收获指数亦降低。施氮量为105―240kg／ha时，氮肥当季回收率为36.22％-50.54％，其中追肥氮回收率大于基肥氮；施氮量增加，氮肥回收率先增加后降低，195kg／ha处理氮肥当季回收率较高。适量施氮，籽粒产量增加，蛋白质含量提高，加工品质改善；过量施氮，籽粒产量降低，加工品质趋于变劣。本试验条件下，综合考虑产量、品质和氮素利用率，施氮量为150―195kg／ha可供生产中参考。

English. Application of nitrogen （N） fertilizer is one of the most important measures that increase grain yield and improve end-use quality in winter wheat （ Triticum aestivum L. ） production. However, misuse of N fertilizer （particularly overuse） will not only not bring higher yield and better quality, but also cause the decline of economic effects and related environmental effects. Thus choosing N rate for application is essential for profitable yields, efficient N utilization, and reduction of possible environmental effects. The obligations of this study were to determine the effects of N fertilizer rate on N uptake, distribution and utilization in wheat plant, and on the grain yield and quality with high yield, also to elucidate why wheat responded only slightly or negatively to excessive application of N. Two-year field experiments were carried out on high fertile soil with organic matter 1.33 %, total N 0.082 %, alkalihydrolysable N 85.87 mg/kg, available phosphorus 27.48 mg/kg and available potassium 129.7 mg/kg in Qianzhuliu Village, Longkou City, China, using the cultivar ＂Jimai 20＂ which has high yield and strong gluten potential. Seven N treatments （CK1, CK2, N1, N2, N3, N4, N5） were set, with 0, 0, 105, 150, 195, 240, 285 kg N/ha respectively, using urea as the N fertilizer. Half of the N fertilizer was applied before sowing, the other half topdressed at jointing stage. Except CK1, the treatments were supplied with 135 kg P2O5/ha and 105 kg K2O/ha before sowing. Each treatment had three replicates, and the plot area was 3 m × 8 m = 24 m. . The basic seedling rate was 120 plants per m. , with sowing on October 8 in 2002 and October 3 in 2003. In the field plots of N1, N3, N4 treatments, microplots of 13N tracing experiments were set, with the area of 15 cm × 44.5 cm and isolated with 30 cm-hlgh iron frame. Each . 5N microplot had two replicates, using 10.13 atom % . 5N-urea before sowing or topdressed, the rate and date of N application were the same as the field plot. The results showed that on the soil fertile condition this study concerned, more N fertilizer supplied than 150 kg/ha could not increase the amount of N accumulation in plant, owning to the slight effects on N uptake during the later growth stage of wheat （Table 1 ）. With the increase of N fertilizer rate, the proportion of N allocation to grain was decreased, and the amount and proportion of N allocation to stem and leaf were increased dramatically （Table 2）. . 5N tracing experiment showed that when N fertilizer rate ranged from 195 kg/ha to 240 kg/ha, N uptake from fertilizer was increased, that from soil decreased, and no significant difference was found in the total amount of N accumulation in plant （Table 3）. With increased N fertilizer, the amount of N translocation （N accumulation in vegetative organs on anthesis - N accumulation in vegetative organs on maturity, NTA） from vegetative organs to grain after anthesis was changed slightly, but the N translocation efficiency （NTA/N accumulation in vegetative organs on anthesis, TE） and contribution proportion （NTA/ N accumulation in grain, CP） of translocation to grain decreased （Table 4）. With the supplied N increased, N uptake efficiency （N accumulation in plant/N supplied, NUPE）, N utilization efficiency （grain yield/N accumulation in plant, NUTE）, N productive efficiency （grain yield/N supplied, NPE） and N harvest index （N accumulation in grain/ N accumulation in plant, NHI） decreased. When tSN was supplied at the rate of 105 -240 kg/ha, the in-season N recovery efficiency （NRE） was 36.22% -50.54%, and the NRE of topdressed N was higher than that of basal N. With the amount of fertilizer N increased, the NRE was increased first than decreased, the treatment with 195 kg/ha N added had the higher in-season NRE than other treatments （Table 5 ） . Appropriate N fertilizer rate would increase grain yield and protein content, and improve end-use quality, however when supplied with excessive N, grain yield would be decreased and the quality tended to be weaker （Table 6）. With yield, quality and N use efficiency concerned, the N fertilizer rate recommended under the condition of this experiment was 150 - 195 kg/ha.