Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2002
Publication Date: 11/1/2003
Citation: SHUSTER, W.D., SHIPITALO, M.J., SUBLER, S., AREF, S., MCCOY, E.L. EARTHWORM ADDITIONS AFFECT LEACHATE PRODUCTION AND NITROGEN LOSSES IN TYPICAL MIDWESTERN AGROECOSYSTEMS. JOURNAL OF ENVIRONMENTAL QUALITY. 2003. v. 32. p. 2132-2139. Interpretive Summary: Earthworms burrow in the soil and ingest crop residues and presumably influence the movement and fate of fertilizer and organic nitrogen in agricultural fields, but there is little quantitative information on these effects. In order to measure these effects we added deep burrowing earthworms to chisel-tilled and ridge-tilled plots where they were previously absent and compared the amount of water and nitrogen lost in leachate to that from plots without added earthworms. We found that the added earthworms significantly increased the amount of leachate and nitrogen lost from the chisel-tilled plots, but not from the ridge-tilled plots. Since the deep burrowing earthworms persisted after the additions stopped in the ridge-tilled, but not in the chisel-tilled plots, this suggests that under natural conditions deep burrowing earthworms are unlikely to have a major impact on nitrogen leaching losses. This information will benefit farmers in that it suggests that management practices that increase earthworm populations will help to improve soil structure, but should not result in increased leaching of nitrogen.
Technical Abstract: Earthworms affect soil structure and the movement of agrochemicals. Yet, there are few field-scale studies that quantify the effect of earthworms on dissolved nitrogen fluxes in agroecosystems. We investigated the influence of biannual deep-burrowing earthworm additions on leachate production and quality in different row crop agroecosystems. Chisel-till (CS) corn-soybean rotation and ridge-till corn-soybean-wheat rotation (CSW) plots were arranged in a complete randomized block design (n=3) with earthworm treatments (addition and ambient) as sub plots where zero-tension lysimeters were placed 45 cm below ground. We assessed earthworm populations biannually and collected leachate biweekly over a 3-year period; and determined leachate volume, concentrations of total inorganic N (TIN) and dissolved organic N (DON). Abundance of deep-burrowing earthworms increased in addition treatments over ambient in both agroecosystems. Leachate loss was similar among agroecosystems, but earthworm additions significantly increased leachate production by 1.1 to 35.0% above ambient in CS cropping. Although leachate TIN and DON concentrations were generally similar between agroecosystems or earthworm treatments, transport of these compounds was significantly increased in addition treatments than ambient, and only in CS cropping. Losses of total nitrogen in leachate loadings were up to 10% of agroecosystem N inputs. The coincidence of soluble N production and availability; and preferential leaching pathways formed by deep-burrowing earthworms thereby increased N losses from the CS agroecosystem. Processing of N compounds and transport in soil water from CSW cropping was largely independent of earthworm activity.