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United States Department of Agriculture

Agricultural Research Service

Research Project: DETERMINING MAXIMUM SUSTAINABLE PRODUCTION OF BIOMASS WITH MIXTURE OF PRAIRIE SPECIES
2011 Annual Report


1a.Objectives (from AD-416)
The objective of this project is to determine the optimal mixture of native prairie vegetation for the most efficient means of sustainable production of biomass for electrical generation while maintaining wildlife habitat and other prairie conservation benefits.


1b.Approach (from AD-416)
We propose to develp a native biomass fuel mixture that will produce large quantities of biomass over a variety of margnal soil types under variable annual weather conditions. This mixture would also be easily established, persist in mixed stands for the long term (10-30 years), be harvested efficiently by machine, be easily processed and used in stocker furnaces for elecrical generation. The"biofuels prairie mix" will contain 16 species from at least five plant functional groups (C4 and C3 grasses, sedges, legumes and forbs). The "biofuels mix" will be compared with three other mixes: a control consisting of a pure stand of switchgrass, a stand of five species of productive warm-season grasses, and a "prairie reconstruction mix" comprised of 32 species typically used in prairie plantings. Treatments will be imposed in randomized, replicated plots, large enough for harvest with farm equiment and to provide sufficient material for test burning by Cedar Falls Utilities. The experimental design will be stratified by soil type. Baseline soil carbon data will be collected from the plots prior to planting prairie vegetation in the spring of 2008. Species composition, aboveground- and root biomass will be quantified in 2009, 2010, 2011, and 2012. Soil cores will be taken in 2012, to assess soil carbon changes under the vegetation treatments. Wildlife monitoring will begin in 2008 and continue through 2012.


3.Progress Report

Experiments were implemented at two research sites in 2008 and 2009: an alluvial site located in the Cedar River Natural Resource Area and an upland site located on the University of Northern Iowa campus. Deep soil cores were taken in May 2008 (200 cores: alluvial site) and April 2009 (16 cores: upland site) and surface soil cores were taken in May 2009 (200 cores: alluvial site) and June 2009 (80 cores: upland site). Analysis for total soil C and nitrogen (N) (~2,000 samples), soil inorganic C (~2,000 samples), particulate organic matter C and N (~200 samples), potentially mineralizable C and N (~40 samples), pH (~1,000 samples), Mehlich-extractable macro- and micronutrients (~1,000 samples), and bulk density (~2,000 samples) was completed by early summer 2011. Preliminary results indicate that at the alluvial site, soil organic C and total N content decreased significantly to a depth of 120 cm. The C:N ratio was highest in the top two soil depths and lowest in the bottom two depths of the soil profile, with the 30-60 cm depth falling in between. At the upland site, which had been planted to alfalfa/bromegrass for 10 years prior to soil sampling, soil organic C and total N also decreased with soil depth, although the pattern of change was different than observed for the alluvial site. Total N decreased significantly with depth, but soil organic C didn’t decrease until the 60-90 cm depth increment. The C:N ratio was not significantly different among the top three depth increments and decreased significantly below 60 cm which suggests the alfalfa/bromegrass vegetation impacts soil organic matter to a depth of 60 cm at this site.


Last Modified: 10/21/2014
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