Rainfall effects on erosion of earthworm casts and phosphorus transfers by water runoff |
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| Authors: | R C Le Bayon F Binet |
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| Institution: | (1) CNRS, UMR 6553 Ecobio, Laboratoire d'Ecologie du Sol et de Biologie des Populations, Station Biologique, F-35380 Paimpont, France e-mail:claire.le-bayon@univ-rennes1.fr, FR |
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| Abstract: | We investigated whether, under a temperate climate and in a maize crop, earthworm casts could contribute to soil erosion
and further favour the exportation of phosphorus by runoff waters. Recording of casts was made in compacted (wheel-tracks)
and non-compacted inter-rows, for a 2-month period in spring. To assess the rainfall impact on cast evolution, half of the
observation sites were protected against rain splash by a nylon mesh placed above the soil surface. The water runoff was collected
and analysed for sediment contents and phosphorus concentration. The mean annual production of surface casts was calculated
to be 34 kg (dry weight) year–1 kg–1 earthworm (fresh weight). Synchronization between cast erosion and rainfall events was shown under natural conditions (unprotected
sites). The erosion rate was 4 times greater over rainy periods than dry ones, reaching 80% of cast numbers. It appeared that
not the runoff effect but the splash effect, due to the kinetics of the drops, disrupted casts. Newly formed casts disappeared
first, with the erosion rate decreasing twofold for casts more than 10 days old. Cast erosion and runoff, as well as worm
casting activity, were greater under compacted sites than under non-compacted sites, indicating an influence of earthworms
on soil erosion from compacted soils. The total phosphorus content was similar in casts and uningested soil (0.80 mg phosphorus
g–1). Potential phosphorus losses from cast erosion was calculated to reach 25–49 mg phosphorus m–2 per rainfall event depending on soil compaction. The amounts of particulate phosphorus recovered in water runoff after each
rainfall event varied from 1 mg to 11 mg phosphorus. These results are compared and discussed.
Received: 20 October 1998 |
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| Keywords: | Earthworm Surface casts Rainfall events Soil erosion Phosphorus |
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