| In order to clarify the effects of irrigation and nitrogen on population dry matter production and grain yield formation of winter wheat under water-saving conditions, two experiments were carried out during 2006-2007 in Baoding and 2007-2008 in Gaocheng County with locally commecial winter wheat cultivar Henong 822 and Shixin 616 respectively. The experiments during the two winter wheat growing seasons were arranged as split plot arrangement, with irrigation frequency as main plots ( including 0, 1, 2 and 3 times during the growing period on the basis of suitable pre-sowing soil moisture, expressed as W0, W1, W2 and W3, respectively ), and nitrogen application amounts as split plots ( including N 0, 112.5 and 225 kg/ha, respectively). The main results were summarized as follows:1. During 2006-2007, irrigation frequency and nitrogen amounts had significant effects on population culm number. The culm numbers of W1, W2 and W3 with irrigation was significantly higher than those without irrigation in W0. The difference of culm numbers among W1, W2 and W3 was not significant although that of W1 was the highest. The culm number among the three levels of nitrogen application amounts were different significantly and increased with the increasing nitrogen. The difference of LAI among the four irrigation levels was insignificant at most growing stages, but the difference of LAI among the three nitrogen application amounts was significantly different, with the LAI of N2 significantly higher than those of N1 and N0. In 2007-2008 experiment, however, the effects of irrigation frequency and nitrogen application amounts on population culm number and LAI at various growing stages were all statistically insignificant.2. In 2006-2007 experiment, dry matter accumulation increased with the increasing irrigation in early grain filling period. The dry matter accumulation were almost the highest under the irrigation rigimes of W3, W1, W2 and W0 at maturity. The effects of nitrogen application on dry matter accumulation of wheat were statistically significant, and increased with the increasing nitrogen. During 2007-2008, irrigation frequency only had significant effect on dry matter accumulation of maturity stage. Dry matter accumulation of W1 was the highest in the four irrigation levels, and the effects of nitrogen application amounts on dry matter accumulation was statistically insignificant.3. During 2006-2007, irrigation frequency and nitrogen amounts had significant effect on the characters of wheat plant. The numbers of secondary roots and culms per plant per plant of W1 rigime was the highest in the four irrigation levels. The characters of wheat plant among the three levels of nitrogen application amounts were different significantly in few growing stages and increased with the increasing nitrogen. In 2007-2008 experiment, however, the effects of irrigation frequency and nitrogen application amounts on such characters of wheat plants were all statistically insignificant.4. During 2006-2007, irrigation frequency and nitrogen amounts had significant effect on leaf chlorophyll SPAD and photosynthetic rate of leaves. The chlorophyll SPAD and photosynthetic rate among the four levels of irrigation amounts increased with the increasing irrigation, and decreased slowly with the increasing irrigation in late growth stage. The effects of nitrogen application on chlorophyll SPAD and photosynthetic rate of wheat were statistically significant, and increased with the increasing nitrogen. The duration of chlorophyll SPAD value and photosynthetic rate of leaves were longer and decreased slowly in late growth stage with the increasing nitrogen. In 2007-2008 experiment, however, the effects of irrigation frequency and nitrogen application amounts on chlorophyll SPAD and photosynthetic rate were all statistically insignificant. The dynamics of chlorophyll SPAD and photosynthetic rate of leaves were basically identical in different treatments.5. The effects of irrigation frequency on spike number per ha and grain weight were statistically significant, and the effects of nitrogen application amount on spike number per ha and grain number per spike were significant, so that the main effects of irrigation frequency and nitrogen application amounts on grain yield were all statistically significant. The grain yield of W3 was the highest, and that of W0 the lowest among the four levels of irrigation, and the grain yield of N1 was the highest, and that of N0 the lowest among the three levels of nitrogen amounts. The interaction of irrigation frequency and nitrogen application amounts on grain yield and yield components was statistically significant. The grain yield increased with the increase of nitrogen application under W0 and W1 rigimes, i.e. higher nitrogen application could offset the yeild decrease by less irrigation. Under W2 and W3 rigimes, however, the grain yield of N1 with middle nitrogen application was the highest, and was significantly higher than that of N0. In 2007-2008 experiment, however, the effects of irrigation frequency and nitrogen application amounts on grain yield of wheat were all statistically insignificant.6. In the two experiments, irrigation frequency and nitrogen amounts had significant effect on water use efficiency, and the water use efficiency decreased with the increasing nitrogen. The water use efficiency among the four levels of irrigation frequency were different significantly. During 2006-2007, the water use efficiency among the three levels of nitrogen application amounts were different significantly and increased with the increasing nitrogen. In 2007-2008 experiment, the effects of nitrogen application amounts on water use efficiency were all statistically insignificant, although that of N0 was slightly higher among the three levels of nitrogen application amounts. Analysis indicated that during 2006-2007, irrigation frequency and nitrogen amounts had significant effect on population quality and yield of wheat. The population quality and yield of wheat were best with moderate irrigation frequency and higher nitrogen amounts. In 2007-2008 experiment, the population quality and yield of wheat decreased with the increasing irrigation frequency and nitrogen amounts. So it is necessary to make decisions of irrigation and fertilization based on precipitation type and soil fertility, so as to increase water production efficiency.
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