Relative Erodibility of Soils on Hillp Lands in Tawan Part I. Properties of the Soils Affecting Soil Erosion

Abstract

To evaluate their relative erodibility, six soils from cultivated lands on the slopes ranging from 15% to 25% were subjected to the field study on their soil profile characteristics and infiltration capacity. Analyses on their physical and chemical properties including porosity, particle size distribution, dispersion ratio, aggregate stability, clay ratio and contents of organic matter and -free iron in the soils were carried out. The results revealed that: 1) Highly porous profile of the soil resulted in higher infiltration capacity of the soil. The infiltration rates of all soils were decreased rapidly in first 30 minutes and then gradually decreased to the stable minimum values in 100 minutes. Higher infiltration rates were found for Tsao-tun (草屯) soil and Feng-san (鳳山) soil, but lower rates for Ah-kung-tien (阿公店) and Yen-chao (燕巢) soils. 2) All of the soils tested are highly dispersible according to their dispersion ratios and aggregate stabilities. Lower dispersion ratios were found for Tsao-tun (草屯), Tai-tung(臺東) and Pin-chen (平鎭) soils and higher ratios for Feng-san (鳳山) , Yen-chao (燕巢) and Ah-kung-tien (阿公店) soils. 3) According to the result of higher dispersion ratios of subsoils, it is expected that soils will he easily eroded once the subsoils are exposed and cultivated. 4) The resistance to dispersion of the soils were increased directly with the contents of organic matter and clay in the soils and no evident relationships were found for free iron content. 5) Based on the infiltration rate and dispersion ratio of the soils, Tsao-tun (草屯) soil is regarded as the least erosive and soils of Ah-kung-tien (阿公店) and Yen-chao (燕巢)as easily erosive.