Measurement Methods And Of Available Zinc And Its Influencing Factors Of Main Type Soils In The Loess Plateau

The fact that about 50% of the world population suffers from micronutrient deficiencies makes plant nutrition research becoming indispensable. As total contents in soil have not correlation with the metal amount absorbed by plants, so, the amount which extracted by extracting agents was preferred to chose to reflect the.available metals in soil Though many extracting agent has been used before in the research, no method has yet been widely acceptable in extracting available Zn in soil of Loess Plateau.Main soil types in the Loess Plateau combining with three different complexing agent (1) 0.005M DTPA+ 0.1M CaCl2+0.1M TEA(pH7.3),(2)0.01M DTPA+1M NH₄HCO₃(PH7.6),(3) 0.07MEDTA+ 1MNH₄OAc (pH7.0) were selected in the experiment to mesuare the extractable Zn and analyze the influence on the process of extracting Zn by different extracting conditions (the ratio of solution to soil was:1:1,2:1,5:1 and 10:1 respectively;the shaking time was:1h,1.5h,2h and 3h respectively)in Loess Plateau soils.The effects of these combinations on extraction of Zn may provide theory basis for determination of soil available Zn in the Loess Plateau soil.The results were as follows:(1) The results indicated that: in the treatments of 1:1,2:1,5:1,10:1 solution-soil ratio and comparatively short shaking time(1h,1.5 and 2h) , extractable Zn was increased with increasing solution-soil ratio and oscillation time. The maximum value was observed at the treatments of 10:1 and 5:1 solution-soil ratio while the minimum value was observed at the treatment of 1:1 solution-soil ratio. And there was well correlation among soil available Zn under different combinations.(2) The quantity of soil available Zn under different extracting agent followed the order: DTPA+TEA > DTPA+ NH₄HCO₃> EDTA+CH₃COONH₄;the effects of solution-soil ration and shaking time have significantly effect (p<0.01) on the amount of extractable Zn respectively, while interactive effect of solution-soil ration with shaking time have different effects on amount of extractable Zn by these three extracting agents, in the treatment of DTPA+TEA, interactive effect showed significant effect (p<0.001), while interactive effect have little influence(p>0.05)on the amount of extractable Zn in the treatment of EDTA+CH₃COONH₄ and DTPA+NH₄HCO₃;(3) The correlation analysis between soil extractable Zn and Zn in the plant indicated that: there were optimum extraction conditions existed in the treatment of extracting agent DTPA+TEA combined with 2:1 solution-soil ration under 3h shaking, ,in the treatment of extracting agent EDTA+CH₃COONH₄ under the same condition and in the treatment of extracting agent DTPA+NH₄HCO₃ with 2:1solution-soil ration under 1h shaking;(4) Total soil zinc was mostly within the range 50-100 mg·kg^-1. Available zinc was low with 20.7 % below the critical value and 37.9 % beneath the (0.5^-1 mg·kg^-1) level. Power functions, linear and exponential regression equations were established to relate available zinc to other soil properties. For the Loess Plateau soils, soil available zinc was positively correlated with total zinc, total nitrogen, total phosphorus, and organic matter. A significant negative correlation existed with soil pH. Power functions provided a better fit between available zinc and total nitrogen or soil organic matter. The regression equations were LogY=0.1433+0.6779LogX (r=0.6948) and LogY=0.9656+0.7959LogX (r=0.7745), respectively. The relationships between soil available zinc and total zinc, total phosphorus and pH could be expressed by exponential functions. The regression equations were LogY=^-1.0061+0.0126X (r=0.6549), LogY=-0.5348+0.086X (r=0.4807), LogY=5.0214-0.6073X (r=-0.5834), respectively. The results of path analysis indicated that the direct acting coefficient of soil chemical and physical factors on soil available zinc was in the following order: total nitrogen>total zinc>pH>total phosphorus.