灌溉条件下施氮水平对土壤作物系统中肥料氮素去向的影响

FATE OF FERTILIZER NITROGEN IN SOIL PLANT SYSTEM UNDER IRRIGATING CONDITION Ⅰ. EFFECT OF NITROGEN LEVEL

本试验利用１５Ｎ示踪技术，研究３种施氮水平（适宜施氮量Ｎ１０∶１５０ｋｇＮ·ｈａ－１，低于适宜施氮量的５０％Ｎ０５∶７５ｋｇＮ·ｈａ－１，高于适宜施氮量的５０％Ｎ１５∶２２５ｋｇＮ·ｈａ－１）对灌溉冬小麦氮素利用、去向及作物产量的影响。结果表明：在灌溉条件下，３种施氮水平（Ｎ０５，Ｎ１０，Ｎ１５）的冬小麦氮素利用效率分别为３８５％、３２３％和２２４％，以Ｎ０５水平为最高。Ｎ１０施氮水平获得了最高的作物产量（６８０×１０３ｋｇ籽粒·ｈａ－１，１４７×１０３ｋｇ生物量·ｈａ－１），Ｎ０５水平同Ｎ１０水平相比，在产量上没有显著性差异；而Ｎ１５水平因施氮过量造成籽粒产量明显下降，与不施肥相比，差异不显著。在深层条施（５～８ｍｍ）条件下，仍有３０２％～３６７％的化学氮素通过各种途径而损失。在Ｎ１５水平中，施用氮素的４６％仍存在于０～５０ｃｍ土层中，远远高于其它两种施肥水平。

Three nitrogen fertilization levels including optimum rate of nitrogen applied (N1 0, 150kg N·ha -1 ), 150% of optimum rate (N1 5, 225kg N·ha -1 ) and 50% of optimum rate (N0 5, 75kg N·ha -1 ) were selected to determine the fate of nitrogen in soil plant system by 15 N technique in 1994～1995 field experiment which was conducted in Shijiazhuang. The results showed that under irrigated condition the nitrogen use efficiencies (NUE) of ammonium bicarbonate by winter wheat in fertilized treatments were 38 5%, 32 3% and 22 4% respectively, while the highest NUE of winter wheat was found in N0 5 treatment due to a relatively high fertility. The highest yield (6 8×10 3kg grain·ha -1 , 14 7×10 3 kg top·ha -1 ) was obtained in N1 0 treatment, but nitrogen uptake and grain yield in N1 5 treatment were lower than those of other fertilizer treatments and there was no significant difference between N0 0 and N1 5 in grain yield. The highest residue of fertilizer N was determined in N1 5 treatment, of which 46% existed in the top layer of the soil (0～50cm). There was no significant difference in residual fertilizer N in soil between the other two treatments (31 28% in N0 5, 31 12% in N1 0). In 15 N balance calculation, the unaccounted part of applied N which was leaching down 50cm in the soil profile as nitrate or gaseous loss through volatilization, denitrification were 30 20%, 36 56%, 31 25% in N0 5,N1 0, N1 5 treatments, respectively. It is very important to control residual N in order to prevent N pollution and promote the growth of next crop.