Development of agroforest systems for bioenergy crop production and ecosystem services in the lower Mississippi Alluvial Valley
The purpose of this project is to develop economically viable agroforest systems for producing cellulosic bioenergy crops that will also enhance ecosystems. The project focuses on determining the amount and quality of biofuels that can be produced by cottonwood and switchgrass grown in agroforest systems as well as assessing the effects of these crops on carbon sequestration, small mammal populations/habitat, and water quality. We are in the final stages of data analysis and summarization of the information produced to date. Growing of cottonwoods and switchgrass biofuels were found to reduce the amounts of nitrogen loss in soil water compared to typical row crop rotations grown on marginal soils in the Lower Mississippi Alluvial Valley. Growing these bioenergy crops appeared to enhance small mammal populations but did not significantly increase carbon sequestration in comparison to that in soybean-grain sorghum rotations that are typically grown in this region.
The objectives of this project are to:
- quantify biomass production, potential bioenergy (ethanol, syndiesel, etc.) yields, and economics of agroforest systems with a variety of cottonwood and switchgrass compositions.
quantify ecosystem services (carbon sequestration, nitrogen retention, wildlife habitat, and biodiversity) provided by agroforest systems with a variety of relative cottonwood and switchgrass compositions.
provide information to farmers, bioenergy industry professionals, county agents, natural resource managers, and regional public officials on the production potential, financial viability, and ecological impacts of cottonwood/switchgrass agroforest biofeedstock systems; demonstrate establishment, harvesting, and bioenergy conversion technologies appropriate for these agroforest systems; and establish stakeholder research and outreach steering committees to direct current and future project activities concerning these cropping systems.
Average annual aboveground production during the first three years of the study (2009-2011) in soybean-grain sorghum, switchgrass and cottonwood cropping systems was estimated to be respectively 6.51, 4.78, and 1.43 dry Mg/ha. Switchgrass production includes only two of three study sites because switchgrass could not be successfully established until late 2011 at the third study site. Estimates of cottonwood production were determined by tree inventories at each of the sites and cottonwood biomass equations developed from studies outside the Lower Mississippi Alluvial Valley. To better estimate cottonwood biomass for the cottonwood grown at our study sites, a subsample of trees were destructively harvested to develop allometric biomass equations. Work on these equations and overall estimates of productivity of cottonwood for the fourth year of this study has not been completed but all necessary data has been collected.
Switchgrass yield during the fourth growing season (2012) averaged between 7.8 and 10.9 dry Mg/ha which was greater than at any other year during the study. Soybean total production (grain and plant residue) during the fourth growing season was between 3.4 and 6.1 dry Mg/ha. Grain yields represented between 32.4 and 41.2% of the total aboveground biomass of the soybean crop.
These results indicate that given the variability of marginal soils in the Lower Mississippi Alluvial Valley, the specific bioenergy crop planted to a given site will need to be carefully considered. Within the three sites studied, cottonwood and switchgrass establishment success and production varied considerably. Even at the best sites, an extended establishment time (at least three years) may be needed before maximum biomass production levels are attained. Such establishment difficulties may make landowners reluctant to alter current management practices on these marginal soils.
Switchgrass and cottonwood samples have been collected for biofuel analysis. A series of gasification experiments are being conducted for each selected bioenergy crop using a 125 kW thermal gasification unit. The producer gas composition, char production, and tar yield is being determined as well as the hdrogen, methane, carbon monoxide, carbon dioxide and oxygen composition of the producer gas. The overall crop mass and energy balances for each bioenergy crop sample will be determined when all measurements are completed. Analysis is currently near completion.
Soil water nutrient concentrations were monitored during the winter and spring of 2012, approximately three years following initial crop establishment. Concentrations of N in soil water were consistently greater within the soybean-grain sorghum rotation than any of the bioenergy cropping systems. Average nitrate-N concentrations in the soybean-grain sorghum rotation were approximately 5 to 6 times greater than in the switchgrass or cottonwood bioenergy crops. Total N concentrations, like nitrate-N, were significantly greater in the soybean-grain sorghum rotation. Concentrations of ammonium, organic N, and total P were numerically but not significantly (p<0.10) greater in the soybean grain sorghum rotation than the other two cropping systems.
These higher levels of soil water N in the soybean-grain sorghum rotation likely reflected the nitrogen fixing ability of the soybeans and the fertilizer applied to these row crops. In addition, soybeans and grain sorghum are annual crops characterized by rapid decomposition of harvest residues and below-ground tissues. Comparisons of root biomass among the three cropping systems during the winter of 2012 indicated significantly higher levels of living roots in the bioenergy crops (3.39-4.84 Mg/ha) than in the soybean-grain sorghum rotation (0.40 Mg/ha). The maintenance of living roots in the perennial cottonwood and switchgrass crops would likely help to absorb available N, reduce N inputs from decomposing roots, and thus increase N retention. Soil water C concentrations were also higher in the soybean-grain sorghum cropping system than in the perennial bioenergy crops, indicating a greater level of organic residue and root decomposition with this traditional row cropping system than with the bioenergy cropping systems.
Average annual aboveground C sequestration of the soybean-grain sorghum, switchgrass, and cottonwood cropping systems was respectively 2.83, 2.11, and 0.66 Mg/ha/yr. However, the majority of the C sequestered by the aboveground soybean-grain sorghum crops (80%) was returned to the soil as crop residues. Aboveground C produced by the bioenergy crops was either harvested (switchgrass) or remained in living aboveground biomass (cottonwood). The different cropping systems appeared to have a minimal impact on soil C by the end of the third growing season. Mineral soil C (to a depth of 30 cm) prior to initial crop establishment (2009) was respectively 33.4, 33.8, and 35.2 Mg/ha in the soybean-grain sorghum, switchgrass, and cottonwood cropping systems. In 2012, the C contents of the soil of these three cropping systems were respectively 35.2, 36.1, and 38.5 Mg/ha and did not significantly differ from that in 2009. Changes in the form of soil C among the cropping systems were also not evident. Soil labile C and potential organic matter turnover rates were similar between the bioenergy crops and the row crop rotation.
Quarterly small mammal trapping and habitat data collection was conducted at the Rohwer Experimental Station in 2012. All data analysis for this portion of the project will be completed in 2013. A thesis, “Small mammal habitat utilization of a feedstock agroforest system in southeast Arkansas,” is expected to be submitted in May 2013.
During May of 2012 an advisory committee meeting was held at one of the Arkansas research sites. During this meeting, project updates were provided to the members of the committee.
Personnel from the project assisted two companies in their interests in growing switchgrass for biofuels in Louisiana. One company has interest in building a switchgrass-based jet fuel facility in northwest Louisiana, and the other is building a switchgrass-based pellet mill in southeast Louisiana. To assist in their efforts, personnel provided visits to study sites, shared yield data and management methods, and provided switchgrass biomass and soil samples. These efforts were requested to help the pellet company in developing a system for removing chlorine from switchgrass to protect pelletizing machinery.
The LSU AgCenter communications department made TV, radio, and news print releases of this project that included footage of switchgrass harvesting and interviews with Michael Blazier and Hal Liechty. The news print release was picked up by Gannett and Associated Press and distributed to newspapers nationally.
A fact sheet titled “Establishing Cottonwood Plantations” was written and published by the University of Arkansas, Division of Agriculture. Information was written and collected by project personnel.
Impacts and Contributions/Outcomes
This project has supported two graduate students during 2012. One student completed his work on small mammal population dynamics and wrote a thesis which was accepted in 2012. The other student initiated his research in January 2012 at the Rohwer Division of the Southeast Research and Extension Center in Desha County, Arkansas.
- Robinson, Zackary. 2012. Small mammal occurrence and utilization of a cottonwood/switchgrass agroforest system in the Lower Mississippi Alluvial Valley. M.S. Thesis, University of Arkansas at Monticello, Monticello, Arkansas, USA.
Liechty, H.O., M. Blazier, M. Pelkki, D. White Jr. and Z. Robinson. 2012. The potential for using agroforests for bioenergy production in the Lower Mississippi Alluvial Valley . In: Meyer, S. R., ed. 2012. Proceedings of IUFRO 3.08.00 Small Scale Forestry Conference 2012: Science for Solutions. Sept. 24-27. Amherst, Ma. P 88-92.
Barry, Jon. Establishing Cottonwood Plantations. University of Arkansas, Division of Agriculture Research and Extension Factsheet. FSA5031
- Bioenergy crops. Louisiana Agricultural Technology and Management Conference. Marksville, LA, February 15, 2012.
Biofuels from forests: Management, Policy, and Economic Issues. Four-state Forestry on the Grow Meeting. Idabel, OK. . March 7, 2012.
Biofuels from forests: Management, Policy, and Economic Issues. Mississippi Society of American Foresters Annual Meeting. Tupelo, MS. April 12, 2012
The potential for using agroforests for bioenergy production in the Lower Mississippi Alluvial Valley . IUFRO 3.08.00 Small Scale Forestry Conference 2012: Science for Solutions. Sept. 24-27. Amherst, Ma.
Building a better biomass ecosystem: cottonwood-switchgrass agroforests. Sungrant National Conference, 10/2-5/2012, New Orleans, LA.
Soil carbon dynamics three years following conversion of marginal soils to cottonwood and switchgrass bioenergy crops. . Sungrant National Conference, 10/2-5/2012, New Orleans, LA.
Carbon sequestration and greenhouse gas emissions associated with cellulosic bioenergy feedstock production on marginal agricultural lands in the Lower Mississippi Alluvial Valley. Project Director Meeting for Agriculture and Natural Resources Science for Climate Variability and Change. Oct. 22, 2012 Cincinnati, OH.
Soil carbon, nitrogen, and water chemistry three years after conversion of marginal agricultural soils to switchgrass and cottonwood bioenergy cropping systems. ASA, SSSA, CSA 2012 annual meeting Oct. 21-25, 2012, Cincinnati, OH
Alley cropping management systems for producing switchgrass as biofuel feedstock in the Southeast U.S. Society of American Foresters Annual Meeting. Spokane, WA. October 26, 2012.
Short-rotation forestry and growing biofuel crops between trees-LSU AgCenter “success stories” project highlights. LSU AgCenter Annual Conference. December 18, 2012.
- Short-rotation forestry and growing biofuel crops between trees. USDA Natural Resource Conservation Service landowner workshop. Shreveport, LA. August 10, 2012.
- “Establishing Cottonwood Plantations” University of Arkansas Fact Sheet FSA5031
- The Potential for Using Agroforests for Bioenergy Production in the Lower Mississippi Alluvial Valley. IUFRO Proceedings 2012
- Small mammal occurrence and utilization of a cottonwood/switchgrass agroforest system in the Lower Mississippi Alluvial Valley. M.S. Thesis, UAM. Robinson 2012
Associate Professor of Wildlife
University of Arkansas
Arkansas Forest Resources Center, PO Box 3468
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Professor of Agronomy
University of Arkansas
Crop, Soil, and Environmental Sciences
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University of Arkansas Extension
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University of Arkansas, Division of Agriculture
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Louisiana State University Agricultural Center
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University of Arkansas
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University of Arkansas
Division of Agriculture
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