The Studies On The Soil Moisture Index And Economy Irrigation Method In Tobacco

The effect of different soil moisture on some physiological characteristics of tobacco leaf was studied by the pot experiment with flue-cured tobacco c. v. K326 in 1998-1999. The results showed that reduction of soil moisture cause the decrease in the growth of tobacco plants, the leaf water potential, the moisture content of leaf , the stomatal conductance , net photo-synthetic rate and transpiration rate , the increase in natural saturation deficiency , the stomatal density, the thickness of leaf , the number of cells in the palisade tissues and the chlorophyll con-tent , but it caused that the activity of SOD rose at first , then decrease and that the activity of POD kept increasing .During the mature stage, when soil moisture was under 60 percent, the total nitrogen and nicotine content increased, but the total sugar and the reducing sugar content decreased, the ratio of sugar and nicotine was low. When it was over 80 percent, the nicotine content decreased .when it was between 60-80 percent ,all chemical components harmonized relatively, the content of Ca, CL decreased , and that of other elements kept steady . so the 60-80 percent of soil moisture should be kept during the maturing stage .The soil moisture index of different stages is not the same . The suitable soil moisture index is 61.90 percent during the root spreading stage, 81.30 percent during the vigorous growing stage and 77.25 percent during the maturing stage .The drought index is 50.1 percent , 69. 00 percent and 58.43 percent respectively.The total sugar, reducing sugar and the content of K were high, the contents of nicotine and total nitrogen were appreciate, each ratio was suitable, and the contents of Ca and Cl were decreasing under the drip irrigation, but under the ditch irrigation, the ratio47of sugar and nicotine and the contents of Fe and Mg were low, the content of Ca was over distinctly the those of drip irrigation and spray irrigation .at the same time, the account of drip irrigation is 48 percent less than that of the ditch irrigation and 21. 7 percent less than that of the spray irrigation .The drip irrigation can improve effectively the yield and the quality of tobacco .