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United States Department of Agriculture

Agricultural Research Service

Title: Flow Mechanisms Through Continuous and Buried Macropores

Author
item Logsdon, Sally

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 1995
Publication Date: N/A

Interpretive Summary: Tillage destroys stable macropores (worm channels, root channels, and cracks) within the tilled layer, but creates unstable tillage pores. The buried macropores are maintained below the tilled layer. The purpose of this study was to examine the conditions under which water will flow through macropores buried beneath a tilled layer. Packed columns were constructed with sloped bases to permit separate outflow from artificial wormholes and from the bulk soil. Some columns were artificially tilled by removing part of the soil and repacking more loosely. Outflow from buried wormholes occurred about half of the time, but the rates were slower than for no-till columns (continuous wormhole). Water appeared to flow through large tillage-created macropores, and sometimes these connected with the buried wormholes. This mechanism has important implications for rapid movement of water and farm chemicals through macropores in tilled soils.

Technical Abstract: Tillage destroys stable macropores, but creates unstable tillage pores within the tilled layer. The buried macropores below the tilled layer are maintained stable. Buried macropores are usually considered nonfunctional for preferential flow unless a water pressure head builds up above the buried pores. The objectives of this study were to determine the conditions under which water would flow into a buried macropore in a soil column, and to examine the flow properties within a macropore. Packed columns (450 mm long, 75 mm wide) were constructed with sloping bases to permit separate outflow from the artificial, worm-slicked macropore (6 mm diameter), and from the soil matrix. Some columns were artificially tilled by removing the top 12 cm and repacking at the same or lower density. Macropore outflow rates from no-till columns ranged from 0 to 6 ml/s, but the rates were slower (0 to 0.9 ml/s) for tilled columns with buried macropores in which outflow only occurred about half of the time. Water flowing through tillage-created macropores sometimes connected with a buried macropore, resulting in outflow from the buried macropore. Buried macropores were sometimes connected to the soil surface by tillage pores, although the infiltration rate through the buried pores was reduced because of increased tortuosity and varying pore diameters and necks in tillage pores.

Last Modified: 10/24/2014
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