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Transcript
EARTHWORMS AND SOIL HEALTH Jodi Johnson-Maynard 1/21/14 UNIVERSITY OF IDAHO SOIL HEALTH • “The capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation” –USDA • Key elements • • • • Sustain productivity- long term Relationship to water and air quality Human health Soil biology SOIL HEALTH “We should allow the soil to work for us and not work against it”. (Elliott and Coleman,1988) Recommendations 1) reduce tillage more and better quality SOM increase microbial biomass increase macroporosity 2) minimize use of biocidal compounds CHALLENGES • • • • Long-term, may not see immediate benefit Dynamic Site-specific Quantification SOIL HEALTH Example Indicators Soil structure Infiltration rate Bulk density Water retention pH Extractable N-P-K Microbial biomass C and N Soil respiration Soil organic matter 20 – 30 x’s biomass d-1 Ingest 100 to 1000 Mg of dry soil ha-1 yr-1 Surface casting species move 40 t ha-1 yr-1 (Feller et al . 2003) Annual flux of N through biomass =10 to 74 kg ha–1 year–1 (Whalen & Parmelee, 2000) Earthworm Jim Across the globe: length - 2 m to a few mm weight - 10 mg to a kg diameter - up to 40 mm Across the IPNW: Driloleirus sp. Photo: Brita Olson Photo: Andre a Zcisi A. trapezoides EARTHWORM ECOLOGICAL GROUPS • Epigeic species feed on undecomposed litter and live within the first few cm of soil; <10 cm in length Anecic species feed on surface litter and live in permanent burrow systems that may extend several meters; > 15 cm in length Endogeic species feed on soil and associated organic matter and live in horizontal, non-permanent, branching burrow systems; 10-20 cm in length (Bouche, 1977) Casts Burrows BURROWS Increase infiltration, reducing runoff Increase movement of air and water within profile Habitat for other organisms anecic endogeic (Figure from Blouin et al., 2013) DRILOSPHERE Enriched C and N Increased microbial activity Residue, mucus and casts Increased populations of grazers(protozoa, nematodes, and collembola) Increased C and N mineralization CASTS Enhance aggregate stability Stabilize C Mesopores and micropores N mineralization EXAMPLE: EARTHWORM ACTIVITY AND SOM Increase microbial activity and decomposition Increase respired CO2 Loss of soil organic matter Increase nutrient availability Increase plant biomass Cast production Increase physically protected C Gain of soil organic matter PREDICTING EARTHWORM IMPACTS What do we need to know? Species present • Ecological habit • Typical density and biomass values • Activity periods MEAN ANNUAL PRECIPITATION SPECIES • Aporrectodea trapezoides • Aporrectodea tuberculata 90% of adults over a 2-year survey Endogeic or epi-endogeic • Aporrectodea calignosa DENSITY REGIONAL DISTRIBUTION ACTIVITY FUTURE WORK • Controlled mesocosm experiment to quantify the impact of temperature and moisture on earthworm survival, reproduction and aestivation rates • Use of 15N labeled wheat residue to determine the impact of earthworm activity on N uptake by wheat • Continued field sampling to determine, more specifically, seasonal changes in activity SUMMARY • Earthworms can have strong positive impacts on chemical and physical indicators of soil health • These impacts depend on earthworm density, species and feeding/burrowing behavior • Must consider density and activity period in climates with significant dry periods • The most common species in IPNW agroecosystems may have greater influence over chemical/fertility indicators than physical • Specific soil quality indicators may change at different rates and be more or less sensitive to management