, Volume 7, Issue 6, pp 672-685
Date: 23 Jun 2004

Earthworms Increase Nitrogen Leaching to Greater Soil Depths in Row Crop Agroecosystems

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Many biological functions of soil organisms are replaced in intensive agricultural systems, but earthworms and other soil invertebrates may continue to have significant effects on nutrient cycling in these disturbed systems. We investigated the influence of earthworms on leaching of water and nitrogen in corn (Zea mays L.) agroecosystems in a long-term (6-year) field experiment in Wooster, Ohio, USA. We employed a split-plot experimental design in which main plots received one of three nutrient treatments (cow manure, legume–grass mixture, inorganic fertilizer) and contained three 4.5 × 4.5-m field enclosures in which earthworm populations were increased, decreased, or unmodified. We installed zero-tension lysimeters beneath enclosures with increased or decreased populations and collected leachates regularly in 1996, analyzing them for water volume and concentrations of NH4 +, NO3 , and dissolved organic nitrogen (DON). Earthworms did not influence concentrations of inorganic N or DON but greatly increased leachate volume. The total flux of N in soil leachates was 2.5-fold greater in plots with increased earthworm populations than in those with decreased populations. Earthworm population density was positively correlated with total N leaching flux (r 2 = 0.49). Leaching losses of N to a depth of 45 cm were greater in the inorganically fertilized than in the organically fertilized plots, possibly due to greater inorganic N concentrations and lower immobilization potential in inorganically fertilized systems. Our results indicate that earthworms can increase the leaching of water and nitrogen to greater soil depths, potentially increasing N leaching from the system.

Present address: Departamento de Ecoloxia e Bioloxía Animal, Universidade de Vigo, E-36200, Spain.
Present address: Archbold Biological Station, 300 Buck Island Ranch Rd., Lake Placid, Florida 33852, USA.
Present address: P.O. Box 303, Yucca Valley, California 92286, USA.