Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2009
Publication Date: 10/12/2009
Citation: Cullum, R.F. 2009. Macropore flow estimations under no-till and till systems. Catena 78(1): 87-91. Elsevier Science Publishers B.V. Doi:10.1016/j.catena.2009.03.004. Amsterdam, Netherlands. (available online at www.sciencedirect.com).
Interpretive Summary: Vertically continuous paths in soils caused by tillage management, worm holes, root holes, large pores calle macropores, and cracks in the soil layer play an important role in chemical pollutants reaching groundwater. An ionic compound, potassium bromide, was used to tract the water movement entering subsurface drains from these pathways under till and no-till conditions. The no-till plots produced more macropore flow than the tilled plots. Even though macropore flow contributed relatively small amounts of outflow from the drains as compared to the flow from the main wetting front, macropore flow contributed a large quantity of bromide in the drainage. These results will be useful to extension personnel, action agencies involved in water quality planning, to those modeling chemical transport, and to farmers applying agrichemicals.
Technical Abstract: The processes associated with water movement through silt loam soils involve both the flow through macropores as preferential flow or macropore flow and flow through the micropore as matrix flow. Macropore and matrix flow components were separated from total flow by a hydrograph-separation technique which used the assumption of dual porosity and a tracer mass balance. The magnitude of water and bromide (Br-) transported by macropore flow to a drain line from irrigations applied by a rain simulator were estimated and the resulting hydrographs provided an indication of the potential significance of macropore flow in transporting water and non-reactive chemicals through macropores to the shallow groundwater system. Matrix flow appears to contribute the majority of the water moving to the drains even during the early stages of the drain flow hydrographs. The no-till plots produced more macropore flow than the tilled plots, independent of how the drains were installed. Macropore flow in the drainage at any time was small as compared to the matrix flow; however it contributed a disproportionate amount of Br- tracer. These data support the concept that models used to predict mass balances using only the matrix flow will underestimate those chemicals that move like bromide into the soil profile.