Chi-hua Huang

Soil detachment and transport processes from interrill and rill areas

Abstract The objective of this work is to investigate effects of rainfall intensity, slope steepness and soil surface condition on soil detachment and transport. All experiments were conducted in the laboratory using programmable rainfall simulation troughs equipped with oscillating nozzles. Interrill soil erosion experiments were conducted in Austria for six different soils. Sediment transport processes in a rill channel were studied for an Ava silt loam at the NSERL, USA. Experiments were conducted for different soil hydrologic conditions, rainfall intensities and slope steepness. Data showed the importance of raindrop impact as well as slope steepness, hydrologic conditions, and their complex interactions on erosion processes from interrill and rill areas.

Quantifying Intrinsic and Extrinsic Factors Affecting Soil Erodibility

Soil erodibility has traditionally been conceived as a soil dependent parameter that can be quantified from intrinsic soil properties that usually stay constant. Development of erosion prediction equations, from the empirical-based Universal Soil Loss Equation (USLE) to a more process-based Water Erosion Prediction Project (WEPP), all used erodibility terms based on the same perception that the erodibility is a soil dependent property that remains constant. Both USLE and WEPP erodibilities are derived either experimentally or through statistical regression from field plots under the most erodible condition which is defined as leaving the plot bare fallow under natural rainfall or freshly tilled seed-bed condition under simulated rain storms. This most erodible condition only considers the state of soil aggregates or particles without the influence of soil water that may in fact impose additional forces on the soil particles causing the soil to respond differently under erosive forces. If soil erodibility is defined as a measure of a soil’s susceptibility against erosive forces, then this erodibility concept will encompass both intrinsic and extrinsic factors affecting the strength of the soil.

Tools for Ephemeral Gully Erosion Research

Techniques to quantify ephemeral gully erosion have been identified by USDA Natural Resources Conservation Service (NRCS) as one of the gaps in current erosion assessment tools. One reason that may have contributed to this technology gap is the difficulty to quantify changes in channel geometry to assess the amount of erosion from the gully channels. Another reason that may have also contributed to the NRCS’ interest in ephemeral gully erosion assessment is the fact that fields implemented with reduced tillage or no-till may have mitigated the surface erosion problem but some of these fields still have ephemeral gullies. Since most conservation practices are designed to minimize erosion from raindrop impact and flow shear as a part of the surface hydrologic processes, gullies at no-till field indicates that subsurface hydrology may have contributed to the formation of these gullies.

Erosion as Affected by Soil Inherent Properties and Extrinsic Conditions

Soil erosion and subsequent pollution by water from agricultural lands is still in need for better understanding and evaluating the impacts of various processes involved. We have summarized, in a systematic manner, the contribution of soil inherent properties and extrinsic conditions on soil erosion from numerous soils collected from the top cultivated layer. The soil inherent properties studied included: (1) predominant clay mineralogy (kaolinitic, illitic and smectitic); (2) soil texture (4-6 typical textural classes from sandy to heavy clay); and (3) organic matter content. The extrinsic conditions studied included: (1) 4-5 levels of rain kinetic energy (KE, 0-22 kJ/m3); (2) 3-4 wetting rates (WR) of dry soil by rainfall and irrigation water; (3) water quality (rain, fresh, effluent or saline irrigation water); (4) 4-8 antecedent moisture contents (from dry to full saturation) combined with different aging durations between two wettings; (5) tillage intensity (conventional and minimum tillage); and (6) soil sodicity, and use of soil amendments (polymer, gypsum).