Abstract

Three different experiments were designed to study the effects of N fertilizer rate, timing and splitting, and the response to combined application of N and S fertilizer on the quality of durum wheat (Triticum turgidum L.) over a 3-year period in Vertisols under rainfed Mediterranean conditions. The following parameters were analyzed: grain yield, test weight, grain protein concentration, gluten index, yellow index, ash content and vitreousness. The N rate experiment included rates of 0, 100, 150, and 200 kg N ha⁻¹ carried out on 4 different sites. The experiment was designed as a randomized complete block with four blocks. For the experiment on N timing and splitting, a single rate of 150 kg N ha⁻¹ was used, different fractions being applied at sowing, tillering and stem elongation, at a single site; again, experimental design was a randomized complete block with four blocks. Finally, for the experiment on the response to combined application of N and S fertilizer, a single fertilizer dose of 150 kg N ha⁻¹ was applied in two forms (urea + ammonium nitrate and urea + ammonium nitrosulfate) with one leaf application at ear emergence (zero, 25 kg S ha⁻¹, 25 kg N ha⁻¹, 25 kg S ha⁻¹ + 25 kg N ha⁻¹, and 50 kg N ha⁻¹), also at a single site, using a split-plot design with four replications. Year-on-year variation in rainfall led to marked variations in wheat yield, grain protein concentration and quality indices. Rainfall and temperatures during grain formation and ripening (April and May) were critical for durum wheat quality. N fertilizer rate modified the behavior pattern of some quality indices as a function of climate, and had a more consistent effect on durum wheat quality than on grain yield. The highest values for grain yield were recorded at an N rate of 100 kg ha⁻¹, while maximum grain protein concentration values were recorded at 200 kg ha⁻¹. Increasing N rates also prompted an increase in vitreous kernel count, which was highest at 150 kg N ha⁻¹. The timing and splitting of N fertilizer had no clear effect on either grain yield or quality indices. Leaf application of N at ear emergence increased only grain protein concentration, vitreous kernel count and grain ash content. Soil or leaf application of S had no effect on quality indices, with the exception of ash content, which rose with leaf application at ear emergence. The response of grain yield and grain protein concentration to fertilizer N differed from that reported for temperate climates.

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.

应用¹⁵N示踪技术研究了高产麦田中施氮量和底施与追施氮肥的比例对小麦氮素吸收转运及籽粒产量的影响。共设7个处理，对照为不施氮肥(N0)；在施纯氮量为168和240 kg/hm²条件下，各设底肥氮量与追肥氮量比例（底追比例）为1∶1 (N1和N4)、1∶2 (N2和N5)、0∶1(N3和N6)。结果表明，播种至拔节期植株积累的底施氮占植株全生育期积累底施氮总量的78.04%~89.67%；小麦植株对追肥氮的利用率显著高于对底肥氮的利用率，适当增加追施氮肥的比例可提高氮肥利用率，其中N2处理的最高。在相同底追比例下，不同施氮量处理相比较，植株与籽粒中的氮素积累量均无显著差异；施氮量相同，随追施氮肥比例的增加，开花前贮存氮素的转运量和转运效率呈先增加后降低的趋势，N2和N5的转运量及转运效率最高；开花后氮素的同化量及对籽粒的贡献率则随追施氮比例的增加而提高；籽粒氮素积累量在N2、N3、N5和N6处理间无显著差异，但显著高于N1和N4。适量施氮并增加追施氮肥的比例可显著提高籽粒产量、蛋白质含量，N2、N5和N6均效果较好。在本试验条件下，施氮量为168 kg/hm²及底追比例为1∶2的处理是兼顾产量、品质和效益的最佳氮肥运筹方式。