Development of agroforest systems for bioenergy crop production and ecosystem services in the lower Mississippi Alluvial Valley

Development of agroforest systems for bioenergy crop production and ecosystem services in the lower Mississippi Alluvial Valley

Summary

The purpose of this project is to develop economically viable agroforest systems for producing cellulosic bioenergy crops that will also enhance ecosystem services. 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 and sample collection. Studies near completion have indicated that small mammals utilize these agroforest systems to a greater extent than current row cropping systems.

Objectives/Performance Targets

1. 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.

Accomplishments/Milestones

Objective 1: Crop Production and Biofuel Yields

The second harvest of switchgrass occurred in 2011 (3rd growing season) at two of the study sites. Inventories indicated switchgrass yields averaged 3.8 oven dry tons/acre at one site and 7.2 oven dry tons/acre at the other site. Switchgrass densities were greatest at the site with the greatest switchgrass production.

Adequate switchgrass establishment has not occurred at the third site. The soil at this site is heavy clay and has proven difficult for switchgrass establishment. It appears that the surface soil dries and develops a crust which retards the emergence of the weak switchgrass seedlings. In fall of 2010 winter wheat was planted followed by an herbicide application of glyphosate in early April of 2011 to kill the wheat, followed by no-till drilling of switchgrass seed into the wheat residue. The purpose was to promote a stand of wheat residue and stubble that would minimize the crusting that normally forms on the surface of the clay soil at this site. It was surmised that the clayey crust offered excessive resistance to switchgrass seedling emergence, thus preventing stand establishment. Unfortunately, the wheat stubble did not reduce the clay crust adequately to promote switchgrass emergence and therefore again we failed to establish the switchgrass at this site. In an effort to produce some switchgrass for quality measurements and future yield measurements, we transplanted approximately 200 plugs of 8 week old switchgrass seedlings by hand on June 1, 2011. There was 100% survival. Biomass yield on October 6 was estimated to be 700 oven dry lbs./acre and average plant height was 3-4 ft. The plan for 2012 is to plant approximately 44,000 additional 8 week old switchgrass seedlings in May to establish more than one full acre of switchgrass at this site.

Aboveground cottonwood biomass and production was determined for the 3rd growing season (2011). Cottonwood survival ranged between 30% and 82% among the three study sites. Survival was lowest at the site in Louisiana where soils had a shallow hardpan and had most recently been cropped as a hay meadow. This site has also been subject to two years of severe drought. Survival in the most northern site averaged 64% which would provide an adequate level of cottonwood production if growth rates were suitable. Although survival of the cottonwood was lowest at these two study sites, there was adequate stocking in some locations at these sites but little or no survival in other locations. Aboveground standing biomass was greatest at the southern Arkansas site (3.23 tons/acre) and least at the Louisiana site (0.25 tons/acre). Standing aboveground biomass at the northern Arkansas site averaged 0.40 tons/acre; the low biomass accumulation at this site reflected a recurring damage associated with herbicide drift. Facet herbicide is applied to a nearby rice field which is owned by a private landowner. Although the distance to this field is in excess of 1,000 feet, drift from aerial application of the herbicide is stunting the growth of these trees. Annual biomass production (2011) at the southern Arkansas site, which had the highest biomass accumulation, was 2.1 tons/acre which represents approximately 65% of the total accumulated aboveground biomass. We expect that annual production at this site will double during 2012.

Average aboveground biomass yield of grain sorghum at the three sites during the 2nd year of the study (2010) was 5.97 oven dry tons/acre. Approximately 11.9% of the biomass was grain while the remainder was in stem, foliage, and seed head remains. During the third year of the study (2011) soybeans were planted as part of the soybean-grain sorghum rotation. Average soybean aboveground production was 1.80 oven dry tons/acre. Soybean grain represented approximately 42% of the total aboveground biomass.

Analysis of fuel quantity and quality has begun. Six bales of switchgrass collected in the fall of 2011 are being utilized for these analyses. Currently only the most basic analyses have been completed. In regard to physical characteristics, the average moisture content, particle length after initial chopping with a hammer mill, and bulk density were respectively 23.1%, 0.335 in., and 6.85 lbs./ft3. Initial proximate analysis of the switchgrass indicated that volatile matter, fixed carbon, and ash represented 74.9, 20.9, and 4.2% of the dry weight of the switchgrass. The lower heating value of this material was 6,329 BTU/lb. Cottonwood has been harvested at the sites for fuel analyses. These materials are being dried and processed in preparation of the fuel analysis.

Objective 2: Ecosystems Services

Soil sampling occurred in December 2011 and January 2012 to assess the amount of carbon sequestered in the soil of each agroforest system. Analyses of these samples have not been completed. The amount of aboveground C sequestered during the second year of the study (2010) was estimated to be on 5,043, 1,531, 1,155, 651, and 405 lbs/acre of carbon for the soybean-grain sorghum rotation, switchgrass (100%), switchgrass (67%)-cottonwood (33%), cottonwood (67%)-switchgrass (33%), and cottonwood (100%) cropping systems respectively. We expect with the large increases in switchgrass and cottonwood biomass in 2011 that the amounts of carbon sequestered by the bioenergy crops will increase.

Soil samples were collected in the summer, fall, and winter of 2011 to assess nitrogen mineralization. One additional sample will be collected in 2012. With the final collection completed, aerobic incubations will be initiated.

Lysimeter samples are currently being collected to assess changes in soil water chemistry in response to cottonwood and switchgrass bioenergy crop conversion. Sample collection will continue until the end of June, 2012. Analyses of these samples are ongoing.

To determine the effect of bioenergy crop production and agroforests on small mammal diversity and populations, small mammal trapping at the study sites was conducted during five consecutive nights in February, April, July, and November of 2011 at each study site. A total of 289 individuals and 8 species (marsh rice rat, Oryzomys palustris; white-footed mouse, Peromyscus leucopus; hispid cotton rat, Sigmodon hispidus; eastern wood rat, Neotoma floridana; least shrew, Crypototis parva; woodland vole, Microtu pinetorum; harvest mouse, Reithrodontomys spp.; and house mouse, Mus musculus) were captured during this time period. Approximately 63% of these captures occurred at the southern Arkansas study site. House mice were the most frequently captured individuals. Where switchgrass was successfully established, the majority of the captures occurred within this crop (55-75%). At the site where switchgrass was not established, over 60% of the individuals were captured in the cottonwoods. The smallest proportion of individuals (8-16%) was captured in the soybean-grain sorghum cropping system at each study site. Species diversity (shannons index) was similar among the study sites (1.01-1.05). However, the diversity of small mammals that were captured at the sites where switchgrass was successfully established was greater in the agroforest cropping system that included both the switchgrass and cottonwoods (1.04-1.27) than in the areas where only cottonwood (0.00-0.67), switchgrass (0.52-0.69), or the soybean-grain sorghum crops (0.00-0.50) were planted.

Objective 3: Outreach and Extension

During 2011 advisory committee meetings were held at each of the two Arkansas research sites. During these meetings project updates were provided to the members of these committees.

On August 9th two project investigators participated in an in-service training event for Arkansas County Extension agents. Project personnel made presentations on the economics of bioenergy and the current issues faced by those who grow bioenergy crops.

On October 6th a “field day” was conducted at the Rohwer Research Station in southeast Arkansas. Most of these producers that attended the “field day” had not grown bioenergy crops in the past, but after the field day, several reported that they would consider or were considering bioenergy crop production. This could be considered an accomplishment in light of the current near absence of markets for bioenergy products in our area. The use of biodiesel was discussed during the field day. Our discussion reduced the number who refused to use biodiesel by 60% and increased the number who said they would use it in trucks and farm equipment.

Project personnel participated in several workshops and meetings involving the use of agroforests for bioenergy production. One of the workshops focused on “training the trainers” and involved USDA NRCS personnel. Two other workshops were held at LSU Agcenter research stations and organized to inform landowners and professional forest managers on the use of wood and agricultural crops for fuel.

• Left Photo: Soil surface at southern Arkansas study site showing clay crust, dead wheat stubble, and no switchgrass seedlings. Right Photo: Transplanting switchgrass seedlings at the southern Arkansas site on June 1, 2011.
• Left photo: average height of switchgrass stand at northern Arkansas site. Right Photo: highest yielding plot. Photos taken on July 18, 2011

Impacts and Contributions/Outcomes

This project has supported two graduate students. One student is comparing the different lysimeter methodologies for monitoring soil water chemistry at the research sites. The other student is determining small mammal population dynamics in relation to the different cropping systems.

Several presentations concerning the project and/or initial results of the project were presented at professional meetings. Below is a list these presentations.

• Extension programming to foster awareness of emerging agroforestry methods for producing biofuels in the Western Gulf region. Annual National Agroforestry Conference. June 6-8, 2011. Athens, GA.

  Establishing alley cropping systems for producing switchgrass and cottonwood on marginal agricultural soils of the Lower Mississippi Alluvial Valley. Annual National Agroforestry Conference. June 6-8, 2011. Athens, GA.

  Short-rotation forestry and growing biofuel crops between trees. Forest landowner meeting. June 27, 2011. Eldorado, AR.

  Emerging crops for biofuels. Louisiana Soil and Water Conservation Society Annual Meeting. November 18, 2011. Alexandria, LA.

  Biomass market update. Forest Practices Tour, UA Livestock and Forestry Research Station, Batesville, AR. April 28, 2011

  Alternatives and risks for Arkansas’s landowners in the woody biomass markets. University of Arkansas Biomass Conference, 9 August 2011, Little Rock, AR

  Carbon sequestration and greenhouse gas emission associated with cellulosic bioenergy feedstock production on marginal agricultural lands in the Lower Mississippi Alluvial Valley. Presented at USDA Agriculture and Food Research Initiative Director’s Meeting, October 26, 2011, Washington, DC

Below is a list of workshops where project personnel provided presentations concerning the use of agroforests for bioenergy production:

• Forest biofuels workshop. LSU AgCenter Hammond Research Station. November 2, 2011. Hammond, LA.

  Biofuels in agriculture and forestry. LSU AgCenter Dean Lee Research Station. November 15, 2011. Alexandria, LA.

  Biofuels in agriculture and forestry. LSU AgCenter Macon Ridge Research Station. November 29, 2011. Winnsboro, LA.

Collaborators: