Individual study: Addition of sawdust to raise soil carbon levels and reduce available nitrogen enhances tallgrass prairie restoration at Ohio State University, Ohio, USA
Averett J.M., Klips R.A., Nave L.E., Frey S.D. & Curtis P.S. (2004) Effects of soil carbon amendment on nitrogen availability and plant growth in an experimental tallgrass prairie restoration. Restoration Ecology, 12, 568-574
Restoration of North American tallgrass prairie on former agricultural land is often impeded by failure to establish a diverse native plant community, often in part due to competition from exotic species. High levels of soil nitrogen (N) on may favour fast-growing non-natives at the expense of slower growing prairie species characteristic of low-N soils. This study tested whether reducing N availability through soil carbon (C) amendments could be useful in facilitating successful prairie restoration.
Study area: The study was conducted at the Ohio State University Marion campus, Marion, Ohio, USA in a 0.5 ha area of former tallgrass prairie and savannah known as the Sandusky Plains. The study site was last cultivated in 1989 and then became dominated by native forbs such as Canada goldenrod Solidago Canadensis and goblet aster Aster lateriflorus, alien weeds including wild carrot Daucus carota and common teasel Dipsacus sylvestris and a variety of scattered tree saplings and blackberry Rubus shrubs. In summer 1998, woody plants were mechanically removed, followed by tilling, mowing and spring 1999 applications of Roundup herbicide.
Sawdust addition: In autumn 2000, 32, 2 x 2 m plots (separated by a 2 m buffer strip) were established and soil carbon treatments randomly assigned within each of eight blocks (16 plots of each soil type). To each high-C plot, was added 6 kg/m² hardwood sawdust (mainly Quercus wood). Sawdust was incorporated by tilling with a small tractor and rototiller. The aim was to raise soil C content of high-C plots by approximately 50%. Low-C plots received the same tillage.
Seed mix and planting: Plots were broadcast seeded by hand in January 2001 at 3,230 seeds/m² with a mix of prairie species comprising six forbs (nodding onion Allium cernuum, smooth milkweed Asclepias sullivantii, bottle-gentian Gentiana andrewsii, globular coneflower Ratibida pinnata, wild pink Silene regia and basal-leaved rosin-weed Silphium terebinthinaceum) and four grasses (big bluestem Andropogon gerardii, Canada wild rye Elymus canadensis, little bluestem Schizachyrium scoparium and Indian grass Sorghastrum nutans). Seeding density was chosen based on prior germination rate data. Plots were lightly raked after seeding and covered with straw mulch. To test for differences in nitrogen incorporation, three 2-month-old seedlings of the prairie forb Riddell's goldenrod Solidago riddellii were planted at random within each plot.
The addition of the hardwood sawdust increased soil C by 67% in the upper 15 cm of the treated soil. This caused a 94% reduction in annual net N mineralization and a 27% increase in soil moisture but had no effect on total N or pH. Overall, plant weight after one growing season was reduced by 64% on amended compared with unamended soil, but this effect was less for prairie forbs (−34%) than for prairie grasses (−67%) or exotics (−62%). After the second growing season, only exotics responded significantly to the C amendment, with a 40% reduction in mass. The N concentration of green-leaf tissue and leaf litter was also reduced by the C treatment in most cases.
Conclusions: The addition of soil carbon through sawdust addition gave several benefits for tallgrass prairie target species, most notably by reducing N availability which slowed plant growth but less so for the native prairie forbs, and importantly lowered competition from exotic species.
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