Effect Of Polyacrylamide On The Slope Phosphorus Loss In Purple Soils And Its Mechanism Analysis

In this thesis,the regulating effect of Polyacrylamide on the phosphorus loss from purple soil and its influencing factors was studied by synthesis methods of isotherm adsorption and desorption,artificial soil column leaching experiment,simulation of rainfall and field runoff plot experiment,and preliminary analysis was taked on the action mechanisms.Then,the PAM optimum utilization technique aiming at controlling phosphorus loess of agricultural non-point pollution was established according to the natural conditions of Three Gorges Reservoir,and it provided a scientific basic for the application of PAM in controlling agricultural non=point pollution.The main conclusions have been drawn as follows.1.PAM had no effect on phosphorus chemisorption,but inhibited the physisorption and decreased the adsoption strength among the low dosage range(0.1-0.5%),the higher the PAM dosage was,the less the adsorbed amount was.The adsoption of 0.5%PAM treated was the largest,and decreased by 27.1%compared with control(200μg·g^-1).Among the high dosage range(1.0-1.5%),the adsoption could be increased with more PAM.This phenomenon might be due to a different a proportion of two kinds of function,phosphorus chemisorption for PAM itself and for improved soil.2.The concentration and cumulant of eluviationing phosphorus were significantly lowered with PAM,and the vertical migration was inhibited.Effect would be more obvious with more PAM.With the phosphate fertilizer application of 0.91g·kg^-1,after 9 times as simulated rainfall eluviation,the concentration variation of eluviationing phosphorus from the control was among 111.17-158.93μg·mL^-1,and the total amounts was 540.75mg in each column.When treated with 0.01-0.20%PAM,the concentration variation of eluviationing phosphorus would be decreased by -6.7-66.37mg.The 0.20%PAM took the best,the concentration of eluviationing phosphorus could be decreased by 36.2%,with the maximum 51.29%,and the cumulant was just 43%of CK. PAM took effect by improving soil and its reticular bound.3.In the artificial simulation of rainfall text,compared with PAM dosage,slop,rainfall intensity,fortifier had the most significant influence on the effect of PAM,and the second was PAM dosage.When PAM was applied with fortifier plaster or lime,the concentration and cumulant of runoff were significantly lowered,and the cumulant of phosphorus loss was 30.37% and 28.32%of just being treated with PAM,respectively;but the runoff was increased and the producing runoff time was advanced.The runoff Volume of the "plaster and PAM" was 9136mL, being 55.47%more than the treatment with only PAM,and the "lime and PAM" was just 25.47%more.In the process,Ca²⁺played an important role,it hah bridge effect between PAM and soil particle,and fixed the PO₄^3-to be Ca-P on the soil colloid,and transformed into stable Ca₁₀-P.When with different slop or rainfall intensity,PAM always took better effect under larger slop or greater rainfall intensity.In slope experiments,the producing runoff time was advanced as the increasing of slop,and the runoff of the 15°was always the least,just 17380mL and 19970mL respectively in the two time rainfall cases;in the total of phosphorus loss,the 20°was the largest while the 8°was the least and was just of 81.84%the 20°s.But at the same time,the difference between 15°and20°was smaller.Under different rainfall intensity,while treated with PAM,the larger the rainfall intensity was,the quicker the velocity was and the earlier the producing runoff time was;PAM took the best effect with the rainfall intensity of 34mm·h^-1,and its phosphorus loss was the least,just 77.37%of the rainfall intensity of 17mm·h^-1,while the 84mm·h^-1was the most;the difference between 34mm·h^-1and 84mm·h^-1was also smaller.Under 15°and 33.7mm·h,8g·m^-2PAM took the best effect,its runoff volume was just 36.7%and 77.22%of CK's(23135ml)respectively,and the least was 22.92%;its phosphorus loss was just 11.80%of CKs(207.45mg).So PAM will be better application value in Three Gorges Reservoir where slope farmland was universal and the rainfall was concentrated,and when under the general slop of 15°and moderate rainfall intensity of about 33.7mm·h^-1,8g·m^-2PAM was the best choice.4.The field experiment in the effect of PAM application was further confirmed.However, PAM application with lime or plaster was unfavorable to the growth of crop,though it also had good effect on controlling phosphorus loess.The phosphorus loess of the treatment with only PAM was decreased by 57.71%with CK's(8676.2mg).Compared with the treatment with only PAM,when PAM was used with plaster or lime,the phosphorus loess was decreased by 43.91%å’Œ48.30%.The growth condition of wheat was best with only PAM,and CK was the second.The plant height in wheat treated with only PAM increased 6.79%over CK on the average,a great increase of leaf length and leaf width.The results indicated that application methods of PAM on the farmland must be different from wasteland.