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Soil-water Regimes of a Typic Haplaquoll under Conventional and No-tillage

ABSTRACT

Computer simulation models are needed to help describe the dynamic nature of soil-water regimes. A simple water budget and an integrated soil-plant-atmosphere simulation model (NTRM) were each evaluated for predicting water regimes under no-till (NT) and conventional tillage (CN) of a well-structured soil. Estimates of soil physical properties related to the retention and movement of water, which were required as input for the models, were obtained from laboratory measurements on undisturbed soil cores. An in situ drainage experiment, using Br^- labeled water, also provided information on field capacity water retention properties. Ponded water containing Br^- moved rapidly through the surface 0.5-m profiles of both tillage treatments. Redistribution of the added water was effectively completed within about 8 h. Field capacity matric potentials of both profiles were above –6 kPa. Chromatography theory indicated that the labeled water may have mixed with only 43 and 25% of the initial soil water in the CN and NT profiles, respectively. Despite these observations, both models, which assumed complete mixing within each soil layer, were reasonably satisfactory at predicting soil-water contents under corn (Zea mays L.) through the 1984 growing season at a southern Minnesota location. Output from the NTRM model agreed better with experimental data showing water contents lower under CN than NT.

¹ Land Resource Research Centre Contribution no. 86–67 and Scientific Journal Series Paper no. 15 054, Minnesota Agric. Exp. Stn.

² Physical Scientist, Land Resource Research Centre, Central Experimental Farm, Ottawa, Canada K1A 0C6; Professor and Head, Dep. of Soil Science; Soil Scientist, USDA-ARS, Crop Res. Lab., 1701 Center Ave., Fort Collins, CO 80526.

Received for publication October 14, 1986.