SOIL TECHNOLOGY vol. 4, p. 197-207 Cremlingen 1991 I THE EFFECTS OF SOIL ORGANIC MATTER CONTENT, RAINFALL DURATION AND AGGREGATE SIZE ON SOIL DETACHMENT E.I. Ekwue, Maiduguri Summary Soil detachment was measured using a factorial experiment involving five soils (with organic matter contents ranging from 1.23 to 5.64%), three rainfall du- rations (4, 12 and 20 mins) and two aggregate sizes (<2 mm and 2-5 mm). Detachment was described in terms of the direct effects and the first and sec- ond order interactions of these variables above. There were significant differences (P<0.01) in the amount of soil detached between the study soils. The mean values of detachment generally declined with in- creasing soil organic matter content from 1.15 kg m -2 in the G1 soil to 0.51 kg m -2 in the G5 soil. For each soil, there were significant increases (P<0.01) in de- tachment with increasing rainfall dura- tion. Soil detachment was smaller for the larger aggregate size. The most significant interactions af- fecting soil detachment were between rainfall duration and aggregate size, or- ganic matter content and aggregate size, and between organic content and rain- fall duration in that order. These in- ISSN 0933-3630 @1991 by CATENA VERLAG, W-3302 Cremlingen-Destedt, Germany 0933-3630/91/5011851/US$ 2.00 + 0.25 teractions were used to make inferences on the effect of organic matter on soil detachment. For each soil and aggregate size, power relationships were established to relate detachment to rainfall total kinetic en- ergy and organic matter content. 1 Introduction Soil erosion process comprises two phases: detachment and transport by raindrop and runoff (Ellison 1947). Soil detachment is the first step in the erosion process. Although the potential ability of or- ganic matter to reduce soil erodibility is well known (Luk 1979), few studies have examined its influence specifically on soil detachment. Previous research has con- centrated on the effect of organic matter on soil aggregate stability and how stable aggregates affect detachment (Chaney & Swift 1984, Bryan 1968). Verhagen (1984) obtained a low corre- lation coefficient (r = -0.26) between soil detachment and organic matter content and attributed it to the low range of or- ganic content (1.11 to 4.87%) in the soils he studied. Chandra & De (1978) work- ing with Indian soils observed a signifi- cant correlation coefficient (r = -0.68) de- SOl L TECHNOLOGY--A cooperating Journal of CATENA