Amendment Effect of Polyion Complex Against Raindrop Erosion.

Water erosion covers more than 50% of the factor of soil degradation and is resulted from detachment and transport of soil particles by raindrop impact and runoff flow. Reducing soil erosion is essential for sustainable food production and environment.

We examined the prevention effect of polyion complex (PIC) against raindrop erosion on soil surface of sandy loam soil using the rainfall simulator and a compact soil box at the Arid Land Research Center of Tottori University, Japan. The rainfall intensity was 75 mm h^-1, and the < 2 mm fraction of soil was used in this study.

The used PIC solution was composed of polycation (Polydiallyldimethylammonium chloride), polyanion (polyacrylic acid) and electrolyte (KNO₃). In the PIC solution with appropriate salt concentration, attractive electrostatic interaction between polycation and polyanion is suppressed, so that the transparent PIC solution is formed. In low salt concentration, the equilibrium state of the PIC solution changes to PIC gel state.

After the application of the transparent PIC solution onto the soil surface then followed by the simulated rainfall, the salt concentration of transparent PIC solution was decreased, and finally the PIC gel was formed in the soil. This PIC gel acts as binding agent between soil particles.

During the simulated rainfall, we measured the volume of runoff and mass of soil loss periodically.

Experimental results showed that the cumulative runoff and cumulative soil loss decreased dramatically with increasing amount of applied PIC solution. When 3 L/m² of the transparent PIC solution was applied onto the soil surface, cumulative runoff and soil loss were nearly equal to zero after 2 hours rainfall. These results suggest that the PIC improves the stability of the soil structure, and thus reduces the detachment of soil particles because insoluble PIC acts as a binding agent between soil particles.