Control of rainfall-induced soil erosion with various types of polyacrylamide

Background. Several types of organic polymers with various molecular weights and surface charges are produced for various industrial and agricultural purposes, and recent studies have shown that high molecular weight anionic polymers are the most effective in reducing runoff and soil loss. However, anionic polyacrylamide (PAM) is marketed under various commercial names with variable molecular weight and length according to its chemistry (Barvenik 1994). Consequently, its interactions with soil and efficiency in reducing soil erosion arc expected to vary. Moreover, types of PAM other than those recommended for erosion control may also be effective in reducing soil erosion. Objectives. The objective of this research is to test the influence of 9 types of polyacrylamide (PAM) on water infiltration and soil loss of an and silt loam soil under simulated rainfall conditions. Methodology. Nine types of organic polymers varied in surface charge, ranging from +20 to -75, and molecular weight ranging from very low to very high were used in this study. Soil plots with dimensions of 60 cm by 120 cm having moderate slope of 3 to 5% were constructed in the field and equipped with runoff collection installations. A specific type of PAM was spread on soil plots at a rate of 10 kg/ha. Rainfall was supplied from a drip type rainfall simulator at constant intensity and duration of 80 mm/h and 50 min, respectively. Runoff, infiltration and soil loss were measured for each plot subjected to a specific type of PAM and compared to control plots. Results and Conclusions. Land application of PAMs significantly increased infiltration prior to runoff but had insignificant effect on total infiltration volume and final infiltration rate under the present experimental conditions. Experimental results confirmed that anionic polymers were more effective in reducing soil loss than that of nonionic or cationic polymers. In fact the cationic, low molecular weight and low surface charge non-ionic PAMs had insignificant effect on soil loss. High molecular weight anionic PAM with 30% surface charge (A-130) was more effective (46% reduction) than those having a high molecular weight and a lower surface charge of 20% (A-110 and A-120) with an average soil loss reduction of 24%. The PAM A-836, described as soil erosion polymer with 20% surface charge and high molecular weight, reduced soil erosion by 41%. Unexpectedly, the anionic PAM with low molecular weight but very high surface charge was also effective in reducing soil loss (47% reduction). Recommendations and Perspectives. Land application of PAM improves water infiltration and highly reduces soil erosion thus improving agricultural production. Application of PAM could be the only viable way to improve arid land farming. It seemed that various types of PAMs, other than those specifically produced for erosion protection can be used to combat soil erosion. This means that farmers in poor countries can use any type of PAM that is available to them to improve agricultural production.