聚丙烯酰胺对H_2PO_4^-和HPO_4^(2-)在土壤中吸附-解吸特性的影响

Effects of Polyacrylamide on Adsorption and Desorption of H_2PO_4^-and HPO_4^(2-) in the Soil

采用批量平衡法研究聚丙烯酰胺(PAM)对两种形态磷(HPO2-4、H2PO-4)在土壤中吸附和解吸特性的影响,以明确PAM对输入土壤中肥料磷素的固持效果。结果表明:施入PAM土壤对磷的吸附动力学过程符合二级动力学方程(平均R2=0.998 4),包括快速反应和慢速平衡两个阶段。在低(20mg/kg)和高(100mg/kg)磷浓度条件下,原土或施入PAM处理土壤对HPO2-4、H2PO-4的吸附均可在反应进行12h时达到平衡,仅高浓度磷条件的H2PO-4处理需要24h达到吸附平衡。Langmuir模型可对等温吸附数据进行很好的拟合(平均R2=0.940 4)。相比原土对照处理,PAM处理可提高土壤对H2PO-4吸附,降低对HPO2-4的吸附,使得HPO2-4的最大吸附量和吸附强度降低,而H2PO-4的最大吸附量和吸附强度升高。PAM处理土壤对磷的解吸受施磷量影响不同,中低施磷条件(磷含量低于80mg/kg)下,NaCl和柠檬酸对PAM处理土壤中磷解吸率均低于原土对照,而在高施磷量条件下,NaCl和柠檬酸对PAM处理土壤中磷素的解吸率均高于原土对照,说明中低施磷条件下,施用PAM不利于土壤对H2PO-4和HPO2-4的释放。PAM施入土壤后,H2PO-4的解吸率(NaCl、柠檬酸)始终高于HPO2-4,说明H2PO-4较不易被土壤固定。

Batch equilibrium methods were employed to reveal the impacts of polyacrylamide（PAM） on ad sorption and desorption characteristics of H2PO4-and HPO4^2- in the soil. The results showed that the adsorp- tion kinetics of phosphorus after soil applied PAM conformed to the secondary dynamics equation （average R2 was 0. 998 4）, included the two stages of rapid response and slow balance. Twelve hours was taken to reach the retention equilibrium in every treatment, only under the condition of high phosphorus concentration （P content 100 mg/L）, twenty-four hours was taken to the retention equilibrium for H2PO4 treatment. The re- tention isotherm in each treatment fitted Langmuir model （average R2 was 0. 940 4） well. Compared to corre- sponding soil untreated PAM, PAM treatment could improve the adsorption of H2PO4, reduce the adsorp- tion of HPO4^- , and decrease the maximum adsorption capacity and adsorption intensity of HPO4^2- , while in- crease those of H2PO4. Desorption of phosphorus in soil treated with PAM was influenced by different ap- plication quantities of phosphorus, under the medium and low P conditions （P content less than 80 mg/kg）, the desorption rate of phosphorus in soil treated PAM were lower than soil untreated with PAM, while under the high P conditions, the desorption rate of phosphorus in soil treated with PAM were higher than soil un- treated with PAM, these showed that in medium and low phosphorus condition, the application of PAM was beneficial to the mobilization of HPO4^2- and H2 PO4^- in soil. Desorption rate of H2 PO4^- in soil treated PAM in different application quantities of phosphorus were always higher than HPO4^2- , this showed that H2 PO2- was harder to immobilization than HPO42 in soil.