Curtis L. Larson

Tilled soil subsidence during repeated wetting.

ABSTRACT A total of 15.2 cm of water was applied without raindrop impact energy to six replicates of four freshly tilled soils to determine its effect on subsidence, random roughness, bulk density, and hydraulic conductivity. Texture of the soils ranged from sandy loam to clay loam. Random roughness degraded to a relatively constant value about 0.5 cm below initial values for all soils except one which was degraded to 1.3 cm below the initial value. Bulk density increased about 0.1 g/cm3 for three soils while the fourth increased 0.2 g/cm3. Regression equations were developed to predict these changes. Coefficients of determination ranged from 0.84 to 0.97 for both random roughness and bulk density. Hydraulic conductivity also decreased with added water. Maximum decreases ranged from 3.0 cm/h to 8.9 cm/h...

Modeling Soil Moisture and Effects of Basin Tillage

ABSTRACT A soil-water model was developed and tested. The model provides satisfactory predictions of soil-water content at various depths for corn at a location in south-west Minnesota. The model was used to study the poten-tial effects of basin tillage on soil moisture levels at two locations, one in Minnesota and another in south central Texas. Results of these projections indicated that basin tillage increases soil moisture and decreases crop stress significantly as compared to conventional tillage by in-creasing infiltration of excess precipitation during the growing season, the off-season or both.

Experimental Evaluation of Two Infiltration Models

ABSTRACT INFILTRATION from constant application rates as predicted by the Holtan model and the Green-Ampt model as modified by Mein and Larson (GAML model) was compared to values determined experimentally. The Holtan model parameters were evaluated by fitting. The Campbell method was used to determine unsaturated conductivities for use in evaluating the Sav parameter for the GAML model. Both models did a good job of predic-ting infiltration during the latter and middle portions of the experimental runs. The GAML model did a good job of predicting time to start of run-off, while the Holtan equation generally failed to predict the delay in ponding.

Modelling infiltration: a measurable parameter approach.

Abstract Development of a 2-stage, measured parameter, infiltration model is reviewed. The model has been verified against finite difference solutions of the unsaturated flow equation, by laboratory tests and has been evaluated under field conditions. Progress of recent research utilizing this model is discussed. Results of recent research indicate that the effects of air entrapment on hydraulic conductivity must be taken into account. A reasonable approach to this problem is to evaluate relative conductivity as a function of relative moisture content and use this relationship to evaluate hydraulic conductivity at field saturation. Additional factors which have been investigated include air viscous effects and the effects of tillage and surface sealing. While significant progress has been made toward including these effects in the model, additional research is required. An attractive attribute of the model is that all parameters utilized in the model are measurable and thus no parameter fitting is required. The paper discusses how parameters may be evaluated and how the model operates, and presents some examples of model predictions under different conditions of soil composition and rainfall pattern.

Hydraulic Conductivity and Green-Ampt Infiltration Modeling for Tilled Soils

ABSTRACT Athree layer infiltration model was formulated using the Green-Ampt approach. The characteristics of the surface and tilled layers are transient, being subject to surface sealing and consolidation, respectively. A relationship for the hydraulic conductivity of the tilled layer as a function of soil and applied rainfall characteristics was developed.

INFILTRATION MODEL: DEVELOPMENT AND EVALUATION OF ITS PARAMETERS.

ABSTRACT AN infiltration model is developed which considers air viscous forces. The Buckley-Leverett soil moisture profile is used at surface ponding and thereafter. A viscous correction factor, p, and an effec-tive gravity correction factor, £, were utilized to simplify the resistance and gravity components respectively. These parameters proved to be extremely difficult to evaluate and were sensitive to values of moisture content upstream of the Buckley-Leverett wetting front.