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A comparison of aggregate stability and biological activity in earthworm casts and uningested soil as affected by amendment with wheat or lucerne straw
Author(s) -
HAYNES R. J.,
FRASER P. M.
Publication year - 1998
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1046/j.1365-2389.1998.4940629.x
Subject(s) - earthworm , amendment , straw , chemistry , soil water , agronomy , zoology , biomass (ecology) , incubation , respiratory quotient , hay , biology , ecology , biochemistry , political science , law
Summary The mechanisms responsible for stabilization of earthworm casts were investigated in a laboratory study. Earthworms ( Aporrectodea caliginosa ) were fed soil or soil amended with either ground wheat straw or lucerne hay. Cast material and uningested soil material were incubated for 56 days, and changes in aggregate stability (measured by wet sieving), soil biological activity and macronutrient availability were measured periodically. In general, aggregate stability and microbial biomass C tended to increase during the incubation for both cast and soil material, whereas hot‐water extractable carbohydrate content declined. For amended treatments, basal respiration rate and microbial metabolic quotient were large at the first sampling (7 days) but declined rapidly thereafter. There was a transitory increase in extractable P in fresh casts compared with uningested material, a sustained increase in mineral N concentrations but no change in exchangeable K content. For unamended treatments, the casts were less stable than soil material, but this difference diminished during incubation. Drying aggregates before analysing them did not reverse this trend. The casts contained more microbial biomass C than soil material did, but the basal respiratory rate, respiratory quotient and hot‐water extractable carbohydrate content were less. By contrast, for wheat‐ and lucerne‐amended treatments casts were more stable than soil material, and the microbial biomass was less at all sampling times. For wheat treatments, respiratory quotient and hot‐water extractable carbohydrate content were larger for cast than soil material, but the opposite was the case for lucerne treatments. We attribute the stability of casts in amended treatments to the intimate mixing of part‐decomposed organic fragments with comminuted soil particles, binding by microbial mucilage associated with the organic fragments and linking and binding by fungal hyphae.