PAM特性对砂壤土入渗及土壤侵蚀的影响

EFFECTS OF MOLECULAR WEIGHT AND DEGREE OF HYDROLYSIS OF PAM ON INFILTRATION AND EROSION OF SANDY SOIL

选择3种分子量(12×106、15×106和18×106Da)和3种水解度(7%、20%和35%)聚丙烯酰胺(PAM),测试PAM特性对土壤入渗和侵蚀的影响。结果表明,3种不同分子量PAM均能明显提高土壤入渗,与对照相比,稳定入渗率分别增加了58.9%、92.2%和83.3%。中分子量和高分子量PAM处理增加入渗效果明显大于低分子量处理,但前两者之间差异不显著。同样不同分子量PAM处理可显著降低土壤侵蚀量,与对照相比,土壤侵蚀量分别降低26.3%、52.6%和26.3%。3种分子量之间比较,中等分子量效果明显好于其他两种分子量。3种水解度PAM提高稳定入渗率分别为对照的1.9倍、2.4倍和2.3倍,20%中等水解度增加初始入渗效果明显高于7%与35%水解度,PAM的水解度对侵蚀量影响不明显。低分子量PAM链长较短,不能在相邻的黏粒之间形成"搭接桥",使黏结作用减弱,而高分子量PAM分子链过长,难穿透进入土壤团聚体之间的空隙,中等分子量的分子链长处于中间尺度,较易穿透土壤空隙,也可形成土壤颗粒之间搭接,产生较好黏结效果。PAM水解度小,电荷密度小,吸附作用弱,但水解度大,电荷密度大,造成分子链之间互斥作用增强,反而导致PAM黏结作用减弱,因而,中等水解度施用效果较好。

Effects of PAMs different in molecular weight （MW） （ 12 ×10^6 , 15 ×10^6and 18×10^6Da） and hydrolysis degree （7% , 20% and 35% ） on soil infiltration and soil erosion were investigated. Results show that all the PAMs, regardless of MW, demonstrated pronounced effect on infiltration and increased steady infiltration rate by 58.9% ,92.2% and 83.3% , separately, over the control. The effect of PAM medium or high in molecular weight was more significant than that of PAM low in molecular weight, but no big difference was observed between the former two. All the three PAMs decreased soil erosion by 26.3% ,52.6% and 26.3% separately as compared with the control. PAM medium in molecular weight was more effective than the other two. PAMs, though different in degree of hydrolysis, all increased steady infiltra- tion rate by 1.9, 2.4 and 2.3 times, separate over the control. The PAM 20% in hydrolysis was more effective than the other two in increasing initial infiltration rate, but they did not show much difference in affecting soil erosion. PAMs low in molecular weight have short chains and hence are unable to form bridges between two adjoining soil particles, thus weakening their function of cohesion, while PAMs high in molecular weight are long in chain and hence unable to pene- trate into the space between soil aggregates. However, PAM moderate in molecular weight have chains moderate in length, and can easily go into soil pores and bridge soil particles, thus enhancing their function of cohesion. PAMs low in hydroly- sis are low in charge density and in adsorption, too, while PAMs high in hydrolysis are high in charge density, thus form- ing high repulsion between molecular chains, which in turn leads to reduced adsorption. Therefore, PAMs, 20% in hy- drolysis, are the most suitable sort for field application.