| These experiments were carried out in the farm of AnHui Province SuZHou Vocational and Technal College from 2004 October to 2006 June. The wheat variety Yannong19 was studied with and sowing density, nitrogen amount are arranged as experimental factors, each of them has four levels, the total experiment involves 15 treatments. In the course of the experiment, wheat was confronted with warm winter in the winter of 2004. So I took it and none warm winter(2005) as well as the two experimental factors , density and nitrogen fertilizer into account to study the effects of them on the wheat population quality and yield .The experiment results indicate that the warm winter results in some bad effects such as exvigourous growth, advance in growth course before overwinter, and increasment in frostbite harm during overwinter. The weather also leads to larger population, more slow deterioration rate of invalid, lower spikes ratio on tillers. More quick deterioration rate, shorter growth time, falling in the later stage and so on. Some measures are brought out in this argumentative in order to promote the stable yield under tendency of warm winter. There are some wheat population dynamic index such as population number, the amount of dry material, leaf area index(LAI) and so on . These index all improve with the level elevant of sowing density and nitrogen fertilizer in the front growth course, and the difference among different density and nitrogen level comes to significance or remarkable significance. In the later growth course, the influence of density and nitrogen is different from one index to another index, and the two factors show interaction effect strongly. wheat communities of high density and nitrogen deteriorate more fast, of which all the index are increasingly under unfavorable situation, production capacity is small. Although the communities of lower density and nitrogen deteriorate more slowly, they still lack enough production capacity.With the heightance of density and nitrogen level, the spikes ratio on tillers declines and the community quality becomes worse, resistance ability decreases, the incidence of diseases and falling rises increasingly, and at the same time, root vitality drops, the rate of deterioration accelerates, maturing time shortens. The difference among different experimental levels of the index mentioned above achieves significant criterion. Though the spikes number will increase with the level heightance of nitrogen and density, the production capacity of every spike will decline. This can be seen that both thousand-grain weight and grains'number every spike drop with the increasement of experimental level. The difference among treatments'production capacity comes to significance, this can be seen that the difference among the yield of a large part of the treatments comes to significant degree . The yield of all treatments is over the high yield criterion of 500kg/667m2. This indicates that the pricision sowing and half pricision sowing communities have superiority of high yield. The yield increases at first then decreases when the density increases. The treatments of the density level, 180 ten thousand/hm2 reach higher yield. According to the analysis of all treatments'comprehensive benefits, we know that in this experiment the treatment of 180 ten thousand/hm2 density level and 195kg/ hm2 ,225 kg/ hm2nitrogen level are the best treatments and the treatment of 225 ten thousand/hm2 density level and 255kg/ hm2 nitrogen level is the worst.Based on experiment results, there are several pairs of indexes such as high-efficiency leaf rate and valid leaf rate, spike's length and grains number, the two parameters of grain-leaf rate. Of which every pair of parameters takes on high degree of synchronism and harmony, and both parameters of each pair have positive phase correlation significantly. Experiment results indicate that the effects of density and nitrogen on high-efficiency leaf rate( valid leaf rate), grain-leaf rate, dry matter amount after earing and the realgrains-spike neck bleeding and the percent of node below spike are similar to yield. These indexes take on remarkably positive correlation with each other.In these experiments the spikes ratio on tillers takes on certain of positive correlation with yield, but the correlation dosen't come to significance. Grain weight-spike neck bleeding under different density dosen't have remarkably positive correlation with yield, but the index takes on very significantly positive correlation with yield under the same sowing density.According to the two years'results, the high yield population quality indexes in huaibei area are as follows, in warm winter, spike number is 44.39～45.26ten thousand/667m2,grain number per spike is 33.28～34.79, thousand grains weigh 41.6～43.9g. in common year spike number is 41.34～43.64 ten thousand/667m2,grain number per spike is 36.28-37.19, thousand grains weigh 42.4～43.6g.The max LAI in warm winter is 6.40～7.30 and that is 6.71~6.89 in commom year. Spike nech ratio is 32.4%～32.9%. dry matter amount after earing is 414～438kg/667m2 in warm winter and that is436～470 kg/667m2 in commom year.The dry matter amount of maturing stage is 1205.8-1226.6 kg/667m2 in warm winter and in commom year that is 1240.5～1287.5 kg/667m2. The spikes ratio on tillers is 36.18%～42.34% in warm winter and that is 54.44%～56.44% in commom year.The spike neck bleeding real-grains is 1.626～1.632 mg / grains.h , spike neck bleeding- Grain weight is 33.843～34.294 mg / g.h. Grain-leaf ratio is 0.35grain number/cm2.leaf and 15.20mg/cm2.leaf. high-efficiency leaf rate is73.41%～73.92% and valid leaf rate is 96.89%～97.22%.
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