Effects Of Added Maize Straw And Citric Acid On Cu And Cd Availability In Soil

This paper studied on the effects of returning maize straw and adding citric acid on the availability of Cu and Cd in calcareous cinnamon soils, and also studied the effect mechanism between maize straw cultivated, adding citric acid and Cu, Cd availability. The effects of maize straw and citric acid added into soil on the adsorption - desorption of Cu and Cd was studied by indoor cultivated trial. And the effects of different amounts of straw and citric acid added into soil on absorption and availability of Cu and Cd was studied by pot experiment. The main results were as follows:1. The tissues that easy to break down such as roots and leaves began to decompose during the first four weeks, and there was 40% of the total weight of straw was lost after maize straw was added into soil. And then, the rate of decomposition was gradually slow down. The influence of straw decomposition on adsorption - desorption of Cu was mainly in the third week, in the third week the straws would generate some organic matter including organic acid to increase the adsorption of Cu. And the effects of straw decomposition on adsorption-desorption of Cd was also happened during this period, but the influence of soil on adsorption-desorption of Cd was much affected by Cu.2. The Cu absorption amount of soil was increased rapidly at first and then decreased with added citric acid amount increasing, and the turning point was at the citric acid concentration was 1 mmol·L^-1. The Cu desorption amount of soil was decreased with the citric acid increased, and the turning point was at the citric acid concentration was 0.5mmol·L^-1. The effect of citric acid on cadmium sorption was less than competitive adsorption of copper. The effect of citric acid on soil decomposition of Cd was similar to Cu.3. The DTPA - Cd content was decreased at first and then increased with the citric acid added concention increased in the contaminated soil, and the DTPA - Cd content was lowest when citric acid added concention was 0.5mmol·L^-1. there was no significantly affect on Cd content by cultivated time extended.4. The routine straw added amount treatment could reduce the soil DTPA - Cu content, while the double straw added amount treatment could increase the soil DTPA - Cu content. The DTPA - Cd content was increased with the straw added amount increased. The results show that proper quantities of straws could reduce the hazards of heavy metal on plants. But adding superfluous straw could activate heavy metals availability and increase the toxicity of heavy metals in soil.5. Adding citric acid could significantly reduce the Cu content in plants. The Cu content in plants was decreased with the added Cd increase under the higher Cu content treatment. It means that Cd also produced toxic on alfalfa at higher Cu concentration. With the added citric acid amount increased, the DTPA– Cu content was reduced, and especially under the higher Cu added amount treatment. In the treatment of 5mmol·L^-1 citric acid, Cd content in plant was the highest, and the DTPA - Cd content was decreased slowly with the citric acid added amount increased.