Abstract:

Application of nitrogen (N) fertilizer is one of the most important measures to increase grain yield and protein content in winter wheat (Triticum aestivum L.) production. However, misuse of N fertilizer will not only affect grain yield and quality, but also cause the decline of economic effects and related environmental effects. It is essential to study reasonable nitrogen applying regimes for profitable yields, efficient N utilization, and reduction of possible environment pollution. The objectives of this study were to determine the N uptake and translocation in wheat plant by using 15N isotope tracer in PVC cylinders (2.05 m length, Ф0.2 m, without bottom) with seven treatments: without applying N fertilizer (N0); N application rate of 168 kg N·ha^-1 (0.527 g/pot), ratios of base fertilizer to topdressing of 1:1 (N1), 1:2 (N2) and 0:1(N3); N application rate of 240 kg N·ha^-1 (0.753 g/pot), ratios of base fertilizer to topdressing of 1:1(N4), 1:2(N5) and 0:1(N6). Treatment N4 is a regime applied now in local wheat production. At the same time, the field experiment was conducted in the same field, and experimental design is same as that of the 15N isotope tracer experiment with three repetitions. The plot area was 3 m×8 m=24 m². At the three-leaf stages, the seedlings were thinned to a density of 150 plants per m².
¹⁵N tracer experiment showed that main basal nitrogen absorbed by plant from sowing to jointing stage accounted for 78.04%–89.67%; fertilizer-N use efficiency (N fertilizer accumulation in plant/N supplied, FNUE) of topdressing was markedly higher than that of basal nitrogen; reducing basal nitrogen amount and increasing topdressing nitrogen amount could appropriately promote plant to absorb more fertilizer nitrogen, and enhance FNUE, of which treatment N2 was the highest. In high-yield condition this study concerned, when nitrogen (N) fertilizer rate increased from 168 kg·ha^-1 to 240 kg·ha^-1, the amount of N accumulation in plant and in grain had no significant difference between treatments with the same ratio of base fertilizer to topdressing; with reducing basal nitrogen amount and increasing topdressing nitrogen amount appropriately, the translocation efficiency (accumulation amount from vegetative organs to grain/N accumulation in vegetative organs on anthesis, TE) heightened, and the amount of nitrogen assimilation for grain after anthesis and its contribution proportion (the amount of nitrogen assimilation to grain after anthesis/N accumulation in grain) also increased, in other words grain N accumulation amount increased with increasing amount of topdressing nitrogen in the same nitrogen fertilizer rate. There was no significant difference among treatments N2, N3, N5 and N6 in grain nitrogen accumulation. Appropriate N fertilizer rate with reducing basal nitrogen amount and increasing topdressing nitrogen amount such as in N2, N5 and N6 increased grain yield and protein content. In conclusion, under the condition of this experiment, as far as grain yield, protein content and fertilizer-N use efficiency are concerned, the most appropriate nitrogen fertilizer applying regime recommended is treatment N2, its nitrogen fertilizer rate is 168 kg·ha^-1 and ratio of base fertilizer to topdressing is 1:2.

Key words: Nitrogen fertilizer rate, Ratio of base and topdressing, ¹⁵N, Nitrogen uptake, Translocation, Yield