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%, alkali-hydrolysable 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 m2. The basic seedling rate was 120 plants per m2, with sowing on October 8 in 2002 and October 3 in 2003. In the field plots of N1, N3, N4 treatments, microplots of 15N tracing experiments were set, with the area of 15 cm×44.5 cm and isolated with 30 cm-high iron frame. Each 15N microplot had two replicates, using 10. 13 atom % 15N-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). 15N 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 15N 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.
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