CROPPING AND TILLAGE EFFECTS ON SOIL ROUGHNESS INDEXES

Several soil roughness indexes have been proposed or are being used in wind erosion prediction models, yet little is known about the effects of tillage, soils and cropping systems on the indexes. In this study, we test the hypotheses that roughness indexes related to the wind erosion process vary with type of tillage, can be functionally related to precipitation, and can be estimated by a random roughness (RR) index. We measured roughness using a pin–type microrelief meter for three seasons on fallow, cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench] fields on three soils (two Paleustalfs and a Paleustoll) of west Texas. Roughness was characterized by RR expressed as the standard deviation of adjusted surface elevations, a ridge height index, and the fraction of the surface susceptible to particle abrasion measured parallel and perpendicular to the tillage direction. These indexes varied considerably in their ability to resolve differences among soils, tillage tools and crops. In nearly every case, each index was significantly affected (P < 0.05) by tillage type and soil. Random roughness, however, did not vary among soils. No significant differences were found among crops when comparing only roughness measured immediately after tillage. In general, the roughness indexes fell into three broad tillage groups. The ridging tools (rolling cultivator and lister) produced the greatest roughness. The chisel, knife sweep and cultivator produced the least roughness and the remaining tillage tools comprised an intermediate group. We were successful in developing models to estimate the four roughness indexes using initial roughness value and the cumulative amount of precipitation as independent variables.