|Gibbs, F - USDA-NRCS|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 15, 2000
Publication Date: N/A
Interpretive Summary: Injection of liquid animal wastes into the soil greatly reduces odors and nutrient losses and is a recommended Best Management Practice (BMP). In some tile drained fields, however, injected wastes have been found in the tile outlets shortly after application even though the soil was not dry and cracked and recommended application rates were not exceeded. This appears to be a particular concern in no-till fields where increased earthworm populations are frequently noted. These earthworms can benefit the soil and crop in a number of ways such as improving soil structure and the cycling of nutrients. The common nightcrawler (one of many species of earthworms), however, creates and lives in large diameter burrows that penetrate three feet or more into the soil. In an experiment conducted in a no-till soybean field at a commercial swine production facility we found that nightcrawler burrows about 1 to 2 feet either side of a buried tile rapidly transmitted water to the tile and probably contribute to the rapid movement of injected wastes offsite. Burrows further away didn't transmit water to the tile. In fields where this is a problem, precision farming technology (to till only the soil above the tile or to avoid waste application in the immediate vicinity of tile lines in order to reduce movement of injected wastes into the tile) or alternatively, blocking the tiles when animal manure is being injected which might allow any wastes that enter the tile time to reenter the soil, are methods suggested to farmers by this research to help reduce this concern.
Technical Abstract: Subsurface injection of animal manure is a recommended BMP that helps control odors and promotes efficient nutrient usage. In tile drained fields, however, injected wastes have been observed emerging from tile outlets shortly after application. This appears to be a particular concern in no-till fields where populations of Lumbricus terrestris L. are often high. Our objective was to determine if burrows created by this earthworm contribute to rapid movement of injected wastes to tile drains. A turbine blower was used to force smoke into a 0.6 m deep tile line in a no-till field and 20 burrows 0.02 to 0.5 m from the tile that emitted smoke and 18 burrows 0.8 to 4.7 m from the tile that did not produce smoke were flagged. A Mariotte device filled with dyed water was then used to measure infiltration rate for each burrow. Afterwards, plastic replicas of the burrows were made so their proximity to the buried tile and geometrical properties could be determined. The average infiltration rate for smoke-emitting burrows (128 mL min**-1 burrow**-1) was twice that of the more distant burrows. Additionally, dyed water was observed in the tile outlet when added to smoke-emitting burrows, but not when added to burrows that didn't produce smoke. Thus, earthworm burrows in close proximity to tile lines can expedite transmission of injected wastes offsite. Use of precision farming technology to avoid waste application in the immediate vicinity of tile lines or alternative application procedures may help reduce this concern.