| At present, it is very popular to deal with the problem of lodging and high yield of maize by chemical regulation. We took two representative varieties ZhongDan808 and JingDan28 as material, soaking seed with PP and foliage spraying plant growth regulator as treatment. We imposed 60000 Plants·hm-2,75000 Plants·hm-2,90000 Plants·hm-2,105000 Plants·hm-2 to study the effect of chemical regulation on maize yield.The experiment had been done at LangFang base of CAAS in 2007. The main results of this experiment were follows:1 It changed the level of endo-hormone by chemical regulationCompared with CK,it decreased the content of IAA,GAS,CTK in maize under every density from seedling to big trumpet stage for two variety. From 60000 Plants·hm-2 to 105000 Plants·hm-2, the content of IAA decreased by 45.2%～96.7%,the content of GAS decreased by 56.1%～86.7% and CTK decreased by 70.5%～83.9% in ZhongDan808 compared with CK.The content of IAA decreased by 29.7%～73.7%,the content of GAS decreased 25.7%～74.7% and CTK decreased by 40.9%～77.4% in JingDan28compared with CK.So the plant was short and the leaf area was diminished.But after big trumpet stage, the content of IAA,GAS,CTK were higher than CK. The content of IAA improved by 14.9%～34.3%, the content of GAS improved by 10.7%～59.8%,the content of CTK improved by 11.21%～43.1% in Zhongdan808 compared with ck. The content of IAA improved by 14.7%～60.6%, the content of GAS improved by 24.1%～78.2%,the content of CTK improved by 7.04%～25.8% in Jingdan28 compared with ck. The plant by chemical regulation grew fast from big trumpet stage to tisseling stage.2 It licked into ideal shape by chemical regulationSoaking seed before sowing and foliage spraying plant growth regulator at jointing stage, the length of 1st to 4th internodes was shortened.The plant height was lower than CK from seedling stage to big trumpet stage. The plant height was decreased 5.6%～12.6% for zhongdan808 and 34.8%～37.6% for Jingdan28. The ear height was decreased by 7.5%～12.6% for zhongdan808 and 18.7%～34.2% for jingdan28.The diameter of 3rd internodes was added compared with CK. It increased by 4.9%～13.8% for zhongdan808 and 4.7%～10.7% for jingdan28.The bottom and middle leaf area were decreased. After the big trumpet stage, the maize took up"compensative growth". 7～10 internodes and top leaf open out, meliorating the plant shape. It increased photosynthesis efficiency.3 It improved the lodging resistant ability by chemical regulationJingDan28 is compact variety. Lodging did not happen in CK and treatment block. Lodging happened when the density>75000plants·hm-2 for ZhongDan808 under normal condition, the lodging percent was 40.1%,62.6%,72.7% at the density 75000 plants·hm-2,90000 plants·hm-2,105000 plants·hm-2. Lodging did not happen under the density 60000 plants·hm-2,75000 plants·hm-2 in treatment block and the lodging percent was 10.3% and 9.4% under the density 90000 plants·hm-2 ,105000 plants·hm-2. compared with CK. the bending strength of stalk improved 14.8%～35.1% for zhongdan808 and 6.4%～18.7% for jingdan28.It increased the content of crude fiber and total-N in maize stalk. So it increased the ability to resist lodging by chemical regulation.4 It enhanced physiological function, accelerating carbon and nitrogen metabolism by chemical regulationIt decreased single plant of maize by chemical regulation,meliorating the airiness and light distribution. So it enhanced the physiological function of maize. It improved the content of chlorophyll in leaf compared with CK. At seedling, jointing, big trumpet,tisseling and grain filling stage,it improved 0.5%～18.7%,1.1%～2.6%,0.2%～4.2%,0.8%～7.9%,0.5%～2.2% for zhongdan808 and 2.07%,3.56%～4.12%,4.66%～7.61%,3.38%～7.7%,4.66%～7.61%for jingdan28. It maintained high physiological function of leaf. Form seedling stage to big trumpet stage, it decreased the content of soluble sugar but increased it after tisseling stage. It accelerated the carbonic transformation to stalk and ear by chemical regulation. It improved the activity of key enzyme of carbon and nitrogen metabolize at jointing stage big trumpet stage tisseling stage and grain filling stage.The activity of NR improved by 4.9%～55.4%,8.3%～21.2%,18.1%～44.8%,10.2%～59.1% for zhongdan808 and 16.9%～44.1%,44.1%～73.6%,12.9～47.4%,6.68%～45.8% for jingdan28.It Accelerated carbon and nitrogen metabolize by chemical regulation.5 It accelerated the accumulation of dry matter after big trumpet stage, diminished the response of ear to high density and improved yield under high densityAt seedling stage,jointing stage and big trumpet stage, it decreased the dry matter accumulation rate by chemical regulation compared with CK. During the period from big trumpet stage to tasselling stage, it accelerated the dry matter accumulation. Under the density of 60000 plants·hm-2,it decreased the dry weight of single maize by chemical regulation. But improved dry weight under other density at harvest stage. It improved lodging resistant ability,added harvest ears by chemical regulation. It accelerated assimilation matter transportation to ear and improved weight of kernel. It decreased the yield by 7.1% of ZhongDan808 under 60000 plants·hm-2 and improved yield by 8.1%,22.9%,66.4% under the density 75000 plants·hm-2 ,90000 plants·hm-2and 105000 plants·hm-2 .It decreased the yield by 9.9% and 8.1%under the density 60000plants·hm-2 and 75000plants·hm-2,but improved the yield by 1.1% and 4.7% under the density of 90000 plants·hm-2 and 105000 plants·hm-2.
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