Characterization of middens formed by Lumbricus terrestris
Abstract
Lumbricus terrestris creates middens, an accumulation of cast material and crop residue, on the soil surface above its permanent, vertical burrows. This network of macropores has come under scrutiny as it can contribute towards preferential flow and chemical leaching. Yet, there is a dearth of information regarding the middens found above these vertical burrows. Middens can interact with surface applied chemicals, modify sorption and degradation reactions, and thereby affect the environmental fate of chemicals. This study attempts to understand L. terrestris-induced heterogeneity of selected soil properties. Results indicate midden aggregates contain more total and organic carbon, exchangeable calcium, potassium, magnesium, and the two light- and one heavy fraction of organic matter than the bulk soil, whereas bulk soil aggregates have more extractable iron and aluminum than the midden aggregates. $\sp{13}$C-NMR and FTIR spectra of the heavy fraction of organic matter (HF-OM) shows that both middens and bulk soil samples are composed of similar carbon species. The carbon in HF-OM is largely aliphatic, with a significant carbohydrate component. The subtle differences in HF-OM composition suggests it to be relatively more decomposed in bulk soil than in the middens. Within each soil type the HF-OM in the smallest aggregate fraction is more humified than in the other three aggregate size fractions. Midden samples have higher atrazine sorption and lower imazaquin sorption than in the bulk soil, while bulk soil has more extractable atrazine and less extractable imazaquin than in middens. More atrazine and imazaquin was degraded in bulk soil than in midden samples. These results indicate that even though midden and bulk soil samples from the same vicinity were compared, L. terrestris activity alters the geochemistry of soils. L terrestris-induced heterogeneity of soil properties creates a microenvironment in which factors controlling soil processes and reactions in middens are quite different from that in the corresponding bulk soil.
Degree
Ph.D.
Advisors
Kladivko, Purdue University.
Subject Area
Agronomy|Environmental science|Soil sciences|Zoology|Biogeochemistry
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