Effects of irrigation on nitrogen uptake and distribution of wheat using the 15N tracer technique

Field experiments were conducted to determine the effects of irrigation amounts on nitrogen uptake and distribution in wheat by using 15N tracer technique in Wanghai village, Yanzhou, Shandong, China. Jimai 20 was selected as the cultivar. Three irrigation regimes were designed with no irrigation during the whole growth season ( W0); irrigated 2 times, before wintering and at the jointing stage (W1); irrigated 3 times, before wintering, at jointing and anthesis stages (W2), and the irrigation amount is 60 mm every time. The results show that the total amount of nitrogen accumulation in wheat at maturity and the amount of nitrogen derived from soil are both ranked as W2W1W0, while the amount of nitrogen derived from fertilizer in wheat at maturity is ranked as W0 and W1W2. The amounts and proportion of nitrogen derived from basal fertilizer in wheat of W1 are lower than those of W0, the amount and proportion of nitrogen derived from top dressing fertilizer in wheat of W1 are higher than those of W0. The amounts of nitrogen derived from basal and top dressing fertilizer in wheat of W2 are lower than those of W0. At the maturity stage, the amounts of nitrogen distribution derived from fertilizer are ranked as Kernel Stem +Sheath Leaf Spike axis + glume. The percentages of nitrogen derived from basal fertilizer in vegetative organs are higher than those derived from topdressing fertilizer, but, opposite phenomenon occurs in grains. The amounts of nitrogen derived from fertilizer in grains are ranked as W0 and W1 W2. W1 treatment gains the highest grain yield. The amount of nitrogen derived from fertilizer and the recovery of fertilizer nitrogen in plant of W1 are higher than those of W2. These is indicate that irrigation before wintering and at the jointing stage can improve the absorption and accumulation of top dressing nitrogen and soil nitrogen, and increase the fertilizer nitrogen accumulation amount and use efficiency. Adding irrigation at the anthesis stage based on W1 treatment, the amount of top dressing nitrogen accumulation in shoot and the proportion of that distribution to grain are decreased significantly. This is the physiological reason why the yield and nitrogen use efficiency are decreased as more water applied after anthesis.