Adsorption And Desorption Characters Of Zinc And Effect Of Zinc On The Growth Of Brassica Chinensis In Several Typical Soils Of China

Zinc(Zn)migration in the environment is mainly through the food chain of soil-plants (animal)-food to affect health of human being.Therefore,the soil-plant system is the main research field of controlling Zn.This thesis studied adsorption and desorption of Zn,and effects of different soil types and different soil utilization types on the adsorption and desorption of Zn in nine soils,which were collected from six typical soil types of China.A pot experiment planted with Brassica Chinensis was conducted in four typical cropland soils (Loess soil,Lou soil,red calcareous soil and red soil)of China to examine effect of Zn supply on growth of Brassica Chinensis,and Zn ubtake by Brassica Chinensis.The mainly achieved results were as follows:1.This paper studied adsorption-desorption characteristics of zinc(Zn)by three typical types of soil in northwest China,namely the old manured loessal soil,yellow loessal soil and calcareous cinnamon soil.The results showed that the amount of soil adsorbed Zn increased with the initial concentrations of Zn.The Zn isothermal adsorption curves for these three types of soil fitted very well with Langmuir equation,Freundlich equation and Temkin equation as well.The coefficients are all＞0.9.It was also observed that the amount of desorbed Zn from Zn absorbed soil increased with the amount of soil adsorbed Zn.The relationship between soil Zn adsorption and desorption was well fitted with linear regression (R2 was＞0.9 for every soil.).Among the three types of soil,the old manured loessal soil exhibited the greatest ability in the maximun Zn adsorbed by soil,the maximum soil Zn buffering capacity,the intensity of soil Zn adsorption and the amount of soil Zn rentention. The maximun adsorbed Zn by the calcareous cinnamon soil was greater than yellow loessal soil,but the maximum soil buffering capacity,the intensity of soil Zn adsorption and the amount of soil Zn retention was less than yellow loessal soil.Modern land use(farmland soil) showed small influence on these soil characteristics compared to the effect of soil type.2.This paper deals with Zinc(Zn)adsorption-desorption characteristics of six typical cropland soils from northwest China and southeast China.The results showed that Zn adsorbed by soils increased with the initial concentrations of Zinc added.The isothermal curves of Zn adsorption by these six soils fitted very well with Langmuir equation,Freundlich equation and Temkin equation.All the coefficients were＞0.9 except blue-purple paddy soil. The maximun adsorbed Zn by southeast Chinese soils was greater than the northwest Chinese soils,but the maximum soil buffering capacity,the intensity of soil Zn adsorption and the amount of soil fixed Zn were smaller except calcareous soil collected from Zhejiang,which had similar maximum buffering capacity to those from northwest Chinese soils,the intensity of soil Zn adsorption and the amount of soil Zn2+fixed to the northwest Chinese soils due to its high organic content,CEC and pH.It was also observed that soil Zn desorption rate increased with the soil adsorbed Zn.3.The fresh and dry weights of Brassica Chinensis shoots increased first and then decreased in four typical soils(Loess soil,Lou soil,red calcareous soil,red soil)with increasing soil Zn application rate.The growth,fresh and dry weights,of the shoots were better grown in the typical cropland soils of southeast China than those in typical cropland soils of northwest China.The threshold for plant growth in response to Zn differed between different soils.4.With increase of Zn application,the change of chlorophyll content in leaves of Brassica Chinensis also showed different in the four typical soils,with the same pattern as exhibited in plant mass growth except that in the red soil which the chlorophyll content reduced at first,and then increased..5.In the four typical soils,Zn concentrations in Brassica Chinensis increased with the increase of Zn application.The plant shoots contained the higest Zn level when grown in red soil compared to the other 2 calcareous soils.When Zn application rate was less than 28mg/kg, the shoot Zn concentrations of Brassica Chinensis were significantly lower in plant grown in northwest China soil than those in southeast China soils.6.Similar to shoot Zn concentration,Zn accumulation in shoots of Brassica Chinensis also increased with increasing Zn rate.The Zn amount in Brassica Chinensis shoots was siginificantly less in plant grown in northwest China soils than that in southeast China soil. Amongst all the 4 tested soils,shoots accumulated Zn most in plant grown in the red soil, compared to the other 3 calcareous soil.The Zn accumulation was up to 1.119 mg/pot in the red soil when soil Zn at 561 mg/kg.7.The soil available Zn and plant Zn were well correlated.The correlation between soil available Zn and plant shoot Zn concentration(correlation coefficient＞0.798;R_0.01=0.798) was better than that between soil available Zn and shoot Zn accumulation in Brassica Chinensis.The best correlation was shown in soil available Zn with Zn accumulation in plants grown in red soil which was up to 0.9808. 属性不符...