Effect of Gypsum and Polyacrylamide Application on Erodibility of an Acid Kunigami Mahji Soil

Acid soil covers one third of the world arable lands. Excess Al and H in acid soil are not favorable for most plants. Calcium carbonates and gypsum (CaSO4) are used to improve chemical status of the acid soil. However, application of Ca cation may sometimes enhance dispersion and deteriorate soil physical properties. Presenting study discusses effect of non-ionic polyacrylamide (PAM) application on erodibility of a gypsum amended Japanese acid soil. Acid Kunigami mahji soil (Hapludult), pH(H2O):4.4, from Okinawa, Japan was used in this study. The soil was sieved through 3 mm mesh screen and packed into an acrylic plastic box of 30cm 50cm 10cm in depth with bulk density of 1.15 Mg/m. Prior to the simulated rainfall, a 2.5t/ha of gypsum and/or 15 kg/ha of non-ionic PAM were applied onto soil surface. Intensity of the simulated rainfall were 40 mm/hr. During a rainfall, surface runoff was collected periodically, and after the halt of rainfall sediment concentration, pH, and electric conductivity (EC) of surface runoff was measured. Gypsum application enhanced runoff significantly. It caused quick and more surface runoff than without the amendment. During rainfall, electrolyte concentration of the runoff was greater than 15 mmolc/L, and this concentration was greater than the critical coagulation concentration of the clay fraction of the soil material, however the soil became dispersive with gypsum application. When only non-ionic PAM was applied prior to the rainfall, it could reinforce soil structure. The PAM application could thus improve infiltration of gypsum amended Kunigami mahji soil and the soil could storage more rainfall. Gypsum application caused greater sediment concentration (10 g/L) than that without the gypsum amendment (5g/L). Applying PAM made gypsum-amended soil to show lower sediment concentration of surface runoff.