Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2006
Publication Date: 5/1/2007
Citation: Jiang, P., Anderson, S.H., Kitchen, N.R., Sadler, E.J., Sudduth, K.A. 2007. Landscape and conservation management effects on hydraulic properties on a claypan-soil toposequence. Soil Science Society of America Journal. 71:803-811. Interpretive Summary: Knowledge of how rainfall (or snowmelt) acts as it comes in contact with different soil types is essential for understanding water movement in watersheds. A number of different soil properties (e.g., water storage, rate of water movement within a soil profile, and number and size of soil pores) are typically used to estimate soil-water relationships. These properties are used to help estimate the source of water runoff within watersheds. They are often referred to as “soil hydraulic properties”. These properties are also used to determine the capacity of the soil to provide water for plant growth. Although these properties vary from point to point in a landscape, these differences are often overlooked because of the time and cost required in making measurements. Crop management practices can also alter these properties. Seldom is research done that examines both soil landscape variability and crop management practices together. The purpose of this research was to examine, using long-term cropping system research plots, the impact of cropping practices and soil landscape (summit, side slope or backslope, and foot slope) on soil hydraulic properties. The soil type investigated was a claypan soil, one similar to about 10 million acres in the U.S. Midwest. We found that the depth of the claypan horizon in the landscape was the main controlling factor for practically all of the soil hydraulic properties examined below the surface 4 inches. The depth where the claypan occurs (or the thickness of the surface horizon) is not random with regard to landscape position. Usually, the claypan controls hydraulic properties at the backslope position at a shallower depth than it does at the summit and footslope positions. We further found that management mostly affected soil hydraulic properties in the top 4 inches of soil, but the effect was not the same at all landscape positions. As an example, for the mulch till grain crop system, the rate of water movement and the number of large soil pores were significantly lower at the backslope position than with the other management systems evaluated, including no-till. The implication of these results is that at the backslope position, where topsoil is the shallowest, even conservation tillage (i.e. mulch tillage) may result in degraded soil hydraulic properties. Such effects leave the soil even more susceptible to runoff and erosion. On the other hand, with systems managed in permanent grass (such as with the Conservation Reserve Program (CRP)), the rate of water movement and water retention were improved the most, primarily at this same backslope position. The findings of this study show that landscape position and management practices interact to alter soil hydraulic properties. Both effects are important for characterizing soil hydraulic properties and for developing new soil-water conservation practices. This information can be used to help identify within watersheds those soils and management practices that are most prone to surface runoff and erosion. Understanding this will benefit the general public since many watersheds in the U.S. Midwest empty into lakes and rivers used for drinking water and recreation. These findings will also benefit producers as new management systems are developed that embrace long-term sustainability goals.
Technical Abstract: Information on effects of landscape and its interaction with management on soil hydraulic properties is scarce. This study investigated effects and interactions of landscape position and conservation management systems on soil bulk density, saturated hydraulic conductivity (Ksat), soil water retention, and pore-size distribution for claypan soils in Central Missouri. Landscape positions included summit, backslope, and footslope. Management included mulch tillage with a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation (MTCS); no-till with a corn-soybean-wheat (Triticum aestivum) rotation (NTCSW) with a red clover (Trifolium pretense) cover crop following wheat; conservation reserve program system (CRP; primarily tall fescue (Festuca arundinacea)); and a hay crop system (HAY; white clover (Trifolium repens), orchard grass, big bluestem (Andropogon gerardii), and Canadian wildrye (Elymus canadensis)). Intact soil cores (76 mm × 76 mm) were collected from the 0-10, 10-20, and 20-30 cm soil depths. Bulk density was the lowest for the CRP at the 0-10 cm depth, and was the highest for the footslope at the 10-20 and 20-30 cm depths. Ksat was the highest for CRP (20.2 mm hr-1) and lowest for MTCS (4.3 mm hr-1) averaged for all depths. The management by landscape position interaction indicated at the backslope, Ksat for CRP and HAY were 16 and 10 times higher than that for MTCS. CRP retained the most water at water pressures from saturation to -1 kPa at the 0-10 cm depth. The fraction of larger pores was the highest for CRP at the 0-10 cm depth. The findings suggest effects of landscape and its interactions with management and soil depth should be considered to develop soil water conservation practices for claypan soil landscapes.