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Title: Enhancement of plant establishment on dredged material sites with mycorrhizal fungi and clay amendments
Authors: Mitchell, James K., 1943-
Keywords: Revegetation
Dredging spoil
Soil conservation
Publisher: Environmental Laboratory (U.S.)
U.S. Army Engineer Waterways Experiment Station.
Series/Report no.: Technical Report;EL-89-16
Abstract: The effect of vesicular-arbuscular mycorrhizae (VAM) and clay amendments on the growth in sandy substrates of selected plant species was investigated in greenhouse experiments and a field trial. VAM were applied as commercially available preparations of the fungi Glomus deserticola, G. etunicatum, and G. intraradices. The clays attapulgite, bentonite, kaolinite, and montmorillonite from various commercial sources were used as sediment amendments at rates from 5 to 15 percent (equivalent to 19 to 57 tons/acre). Apparent host specificity, and the effects of inoculum density, fertilizer, clay type, clay particle size, and calcining of clays were evaluated in greenhouse experiments. In general, the 12 plant species tested (11 grasses and 1 herb) exhibited enhanced shoot and/or root growth when inoculated with any of the three VAM species. Only 4 of the 48 plant-VAM combinations did not result in higher plant yields than in uninoculated controls. Maximum effect of VAM required an inoculum density of at least 25 x 10³ chlamydospores/pot. Inoculation with VAM increased the yield of alfalfa at all fertilizer application rates tested (0.0 to 2.0 g Osmocote per liter of potting mix, equivalent to 0 to 2,500 lb/acre). Applied at rates of 5 to 15 percent (equivalent to 19 to 57 tons/acre), the clays bentonite and montmorillonite enhanced the growth of smooth brome grass. Top soil, the clays attapulgite and kaolinite, and the commercial products Agrosoke and Stawet were relatively ineffective in promoting plant growth. Montmorillonite of 16/30 and >40 mesh sizes enhanced growth of smooth brome grass more than coarser clay particles (6/30 mesh); Non-calcined montmorillonite promoted growth of smooth brome grass to a greater extent than calcined (heat-treated) montmorillonite. Field trials evaluated the effect of VAM and clay amendments on establishment of seeded and transplanted plants in a sandy, upland dredged material disposal site near Oakville, IA. Trial plots received VAM inoculant, inoculant plus montmorillonite clay, or inoculant, clay, and oat straw mulch. Transplants in all treatments died, presumably owing to the severe drought which occurred during the summer of 1988. Plants became successfully established in the areas that received VAM/clay and VAM/clay/mulch treatment, but not in the VAM-only plot. At 160 days after planting, plant cover and biomass in the 2 VAM/clay/mulch treated area (64 percent and 32 g/ft²) were higher than in the VAM/clay area (42 percent and 18 g/ft²). The combination of VAM with clay amendments and mulch provides a practical, low-maintenance revegetation scheme for sandy dredged materials. It is recommended that sandy substrates be amended with ca. 25 tons montorillonite or bentonite clay per acre, that VAM inoculation be applied while seeding, and that mulching take place after planting. This regimen successfully revegetated sandy dredged materials without further attention during a severe drought and should readily succeed under more moderate conditions.
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