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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #45713
Title: EFFECT OF ROOT SYSTEMS ON PREFERENTIAL FLOW IN SWELLING SOIL

Author
item MITCHELL A R - OREGON STATE U, MADRAS
item ELLSWORTH T R - U OF ILLINOIS, URBANA
item MEEK B D - 5368-20-00

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Slow infiltration rates are a problem in many swelling soils. The slow rates make it difficult to replenish water used by plants and adequately leach for salt control. In non-swelling soils it has been shown that plant roots increase the infiltration rates when they decay and leave channels. There has been a question whether swelling soil responds similarly to decaying root systems because lateral swelling of the soil may close preferential flow channels. The objective of this study was to observe, using methylene blue, preferential water flow paths in a swelling soil following two crops (wheat and alfalfa) which have contrasting root systems. Wheat possesses fine fibrous roots; alfalfa, on the other hand, has a tap root system. Cracks and earthworm channels were not stable because of the lateral pressure of the swelling soil; however, alfalfa produced stable macropores consisting of decaying roots, while wheat- cropped soil had no such macropores. Macropores that did not contain stabilizing root remains of alfalfa were apparently not stable during flood irrigation. These findings emphasize the importance of having alfalfa in the rotation to improve infiltration rate even in swelling soils.

Technical Abstract: Root systems can have a profound effect on water flow in fields by creating macropores. Infiltration rates and solute flow have been shown to increase where plant roots decay and leave macropores that serve as preferential flow paths. There is a question whether swelling soil responds similarly to decaying root systems, because lateral swelling of the soil may close preferential flow channels. The objective of this study was to observe preferential water flow paths in a swelling soil during the later stages of irrigation. A Holtville silty clay (clayey- over-loam, montmorillonitic Typic Torrifluvent) was observed in the field. Two crops, alfalfa (Medicago sativa, L.) and wheat (Triticum turgidum, L.) provided sharply contrasting root systems, with wheat possessing fine, fibrous roots; alfalfa on the other hand, has a taproot system. Macropores were observed by applying soil-adsorbing, methylene blue dye to irrigation water. Cracks and earthworm channels were not stable because of the lateral pressure of the swelling soil; however, alfalfa produced stable macropores consisting of decaying roots, while wheat-cropped soil had no such macropores. Measured final infiltration rates increased during alfalfa cropping, which agrees with Meek et al.'s (1989, 1990) findings on sandy loam soils.