Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2003
Publication Date: 6/1/2003
Citation: MCINTOSH, G.C., SHARRATT, B.S. OVER WINTER STABILITY AND HYDROLOGY OF MACROPORES IN THE NORTHERN US CORN BELT. SOIL SCIENCE. 2003. V. 168. P. 338-346. Interpretive Summary: Soil macropores allow for the rapid transmission of agricultural chemicals to ground water. Current models that simulate chemical flow through soils assume that macropores remain stable over time, but macropores may deteriorate in cold regions as they are subjected to freezing and thawing or wetting and drying. The stability of various sized macropores was assessed over winter in the northern Corn Belt. Larger macropores collapsed while smaller macropores remained more stable (least change in pore size) over winter. The collapse of macropores was largely due to slaking of the pore wall caused by freezing and thawing. Hydrologists will be able to more accurately simulate water and chemical movement through soil in cold regions by accounting for over winter changes in macropore size and shape. These improved simulations can then aid farmers and land managers in better managing their lands to mitigate groundwater contamination.
Technical Abstract: Macropores created by biological or physical processes can profoundly influence water movement through the soil. In cold regions, macropore stability can be influenced by natural processes such as wetting/drying and freezing/thawing. Little is known, however, concerning the over winter stability of macropores. This study investigated changes in the physical dimensions of macropores from autumn to spring in the northern US Corn Belt. Macropores 30 cm deep having diameters of 5, 10 and 15 mm were created in a Barnes loam soil in October of 1999 and 2000. After snowmelt in the spring, all 5 and 10 mm pores and more than 95% of the 15 mm pores were filled with soil at the surface. Smaller pores retained a greater extent of their overall dimension than larger pores. The 5-mm macropores retained about 65% of their created length while 10-mm macropres retained 50% of their length over winter. The 15-mm macroporse retained about 5 and 45% of the created length during the consecutive winters. This study suggests that macropores are not stable during winter and thus will impact the hydrology of soils.