Study On The Form Distribution And Bioavailability Of Cadmium In Rice-vegetable Rotation Soil In Tropical Area Under Different Factors

In this study pakchoi and rice were used as experimental materials and rice-vegetable rotation pot experiment was carried out to study the effect of different environmental conditions(water management,soil pH value,fertilization model)on the form distribution and transformation of Cd in farmland soil in tropical area and its bioavailability.Explored for the changes of total content of Cd,different for:ms of Cd content,Cd content in crop,crop growth indicators,quality indicators and soil enzyme activity with the applied Cd levels under different treatments of the three factors,the results of the study were as follow:(1)The pot experiments showed that with the increase of exogenous Cd concentration,the total amount of Cd in first season pakchoi and second season rice soils increased significantly under different water management methods,soil pH values and fertilization modes.And the total Cd content of Chinese cabbage treated with submersion,pH6.5 and organic fertilizer were higher than the other treatments.Under submersion treatment,Cd contents of Fe-Mn oxide form in pakchoi and rice soil were the highest,and the ability of pakchoi to enrich Cd was the weakest.Under pH6.5 treatment,Cd contents of carbonate and organic form in pakchoi and rice soil were the highest,and the ability of pakchoi to enrich and transport Cd was the weakest.Under organic fertilizer treatment,Cd contents of exchangeable form in pakchoi and rice soil were the lowest,and the ability of pakchoi to enrich Cd was the weakest.(2)The Cd contents in the stems and leaves of pakchoi in first season were significantly correlated with the total contents of Cd and the five forms of Cd contents under the three factors.Under different water management treatments,Cd contents in stems and leaves of pakchoi had the best correlation with exchangeable form of Cd.Under different soil pH treatments,Cd contents in stems and leaves of pakchoi had the best correlation with carbonate form of Cd.Under different fertilization treatments,Cd contents in stems and leaves of pakchoi had the best correlation with exchangeable and carbonate form of Cd.(3)Under the three influence factors,the plant height and leaf number of pakchoi decreased significantly with the increase of exogenous Cd concentration,but had no significant influence on the maximum leaf width of pakchoi.The plant height and leaf number of pakchoi treated with controlling water,pH6.5 and organic plus inorganic fertilizer were the largest.The yield of pakchoi was lower than that of CK and decreased with the increase of Cd concentration.Under the condition of flooding,pH4.5 and organic fertilizer,the decrease rates of pakchoi yield were the largest.The effect of Cd and the three factors on the plant height,tiller number and yield of rice in second season was not significant,and there were slight decrease compared with CK.(4)With the increase of Cd concentration,the contents of Vc and soluble protein in first season pakchoi showed a significant decrease under the three factors of water management,soil pH and fertilization model,while the contents of crude protein and amylose in second season rice had no significant change.Under the same Cd concentration level,the contents of Vc and soluble protein in pakchoi treated with controlling water,pH6.5 and organic plus inorganic fertilizer were the highest.(5)The soil invertase activities of pakchoi and rice rose at first,then decreased with the increase of exogenous Cd concentration,and the peak concentration was affected by the Cd concentration in soil and crop types.The soil catalase and urease activities of pakchoi decreased with the increase of exogenous Cd concentration.While the concentration of exogenous Cd in rice soil decreased so the the inhibitory effect of Cd on those two kinds of soil enzyme was reduced,Cd promoted the enzyme activities at low concentrations and inhibited the enzyme activities at high concentrations.The activities of catalase,urease and invertase were the lowest in pakchoi and rice soil under the treatments of flooding,pH4.5 and inorganic fertilizer.