Residue Cover and Surface-Sealing Effects on Infiltration: Numerical Simulations for Field Applications Huanxiang Ruan,* Laj R. Ahuja, Timothy R. Green, and Joseph G. Benjamin ABSTRACT may decrease infiltration (Savabi and Stott, 1994) and is an issue we do not consider in this study. Surface sealing of bare soils often reduces rain infiltration, and The relationship between the mass or extent of resi- crop-residue cover is commonly used to reduce surface sealing. We due cover and the increase in infiltration is an important conducted numerical experiments to quantify effects of the percentage and distribution of residue cover on infiltration, and to provide guide- issue in dealing with the surface-sealing problem. lines for residue management. Residue cover was simulated over the Baumhardt and Lascano (1996) conducted a field exper- soil surface in circular patches. Excess surface water from the bare iment near Lubbock, TX. Simulated rain was applied surface-sealed areas was available for infiltration in nonsealed areas. at 65 mm h -1 for 1 h on a bare and residue-covered Numerical simulations were conducted for combinations of (i) soil Olton clay loam soil. They found that cumulative infil- type, either a clay loam or loamy sand soil; (ii) percentage residue tration was lowest (28.7 mm) on bare soil, and increased cover (P rc ); (iii) saturated hydraulic conductivity of the surface seal curvilinearly with increasing residue amounts, leveling (K c ) relative to bulk soil (K s ); (iv) residue-patch size with a constant off to a limit (49.0 mm). The leveling off (asymptotic P rc ; and (v) rainfall intensity. The K c values had the greatest influence limit) occurred at a residue amount of 2.4 ton ha -1 . on infiltration as a function of P rc . This influence increased with rainfall Increases in infiltration were related to the residue intensity. For a given P rc , smaller patches gave greater relative infiltra- amount and not influenced by residue geometry, or their tion due to differences in the lateral redistribution of infiltrated water. The target values of P rc that provided 95% relative infiltration varied location on the bed or furrow. Lang and Mallett (1984) from 40 to 80% for most combinations. Changing the geometry of compared six levels of maize stover, expressed as a per- the residues made no significant difference. We also tested a one- centage ground cover (0, 10, 20, 30, 45, and 75%) under dimensional model with a spatially averaged saturated hydraulic con- a rainfall simulator (rainfall intensity of 63.5 mm h -1 ) ductivity (K ce ) for both covered and surface-sealed areas, and found to assess the effect of surface residues on infiltration that infiltration into a partially residue-covered soil could be estimated and soil loss on a clay loam soil with a 3.5% slope. The by the one-dimensional model for all cases of this study, when K c  increase of infiltration was curvilinearly related to the 0. Finally, simulated infiltration qualitatively agreed with data sets of ground-cover percentage, and the infiltration was 54% two independent field experiments under similar soil and rainfall con- greater with 45% residue cover than without residue ditions. cover. It would be extremely useful to know what level of W ater availability is a major factor in crop produc- residue cover would be adequate to achieve maximum tivity in the vast arid and semiarid regions of the infiltration, or perhaps 95% of the maximum. This infil- world. Water use efficiency, which is defined in terms tration would be especially important in arid and semi- of the proportion of total available water transpired by arid regions, where water is the most limiting factor for a crop, is critical in an era of increasing competition for crop production. It is surprising that only a few studies water use. Practices that increase rain infiltration and have been conducted to quantify the residue-cover effi- minimize runoff are important to increase water use effi- ciency. ciency. A number of modeling studies on infiltration into The impact of raindrops on a bare soil surface forms surface-sealed soils have been reported (e.g., Mualem a thin layer known as a surface seal on the soil surface and Assouline, 1989; Baumhardt et al., 1990). Without due to a combination of physical and chemical processes. residues, surface seals are formed uniformly over the The surface seal is denser and has a lower saturated soil surface and the water infiltration and redistribution hydraulic conductivity than that of the bulk soil (Tackett in soils are in one dimension, if the soil is otherwise and Pearson, 1965). Water infiltration into the bare soil homogeneous and flat. Several other studies have mod- is most often determined by the surface seal (Duley, eled the water infiltration into the surface-sealed or 1939; Ellison and Slater, 1945; McIntyre, 1958; Ahuja, crusted soil using one-dimensional methods (Ahuja, 1974; Morin and Benyamini, 1977; Ahuja, 1983; Eigel 1973; Ahuja, 1983; Ahuja and Swartzendruber, 1992; and Moore, 1983; Smith et al., 1999). Crop residues Mualem et al., 1993; Philip, 1998; Smith et al., 1999). protect the soil surface from physical raindrop impact, Most models such as the RZWQM (RZWQM Develop- which can reduce the formation of surface seals and ment Team, 1998) use one-dimensional approaches. increase the infiltration rate (Unger and Stewart, 1983). Infiltration into soil partially covered by crop residues On the other hand, rainfall interception by residue cover is a two-dimensional problem for which we need to use a two-dimensional model. However, if we can determine an effective saturated hydraulic conductivity for the soil Huanxiang Ruan, Laj R. Ahuja, and Timothy R. Green, USDA-ARS- surface that allows the same amount of infiltration as NPA, Great Plains Systems Research Unit, P.O. Box E, 301 S. Howes St., Fort Collins, CO 80522; Joseph G. Benjamin, USDA-ARS-NPA, Abbreviations: P rc , percentage residue cover; K c , saturated hydraulic Central Great Plains Research Unit, Akron, CO 80720. Received 15 conductivity of the surface seal; K s , saturated hydraulic conductivity Mar. 1999. *Corresponding author (ruan@gpsr.colostate.edu). of bulk soil; K ce , spatially averaged saturated hydraulic conductivity; R 1 , radius of the residue patch; R 2 , radius of the cylinder. Published in Soil Sci. Soc. Am. J. 65:853–861 (2001). 853