Great Plains Agroforestry: Evaluation of Bioenergy Feedstock and Carbon Sequestration as Potential Long-term Revenue Streams to Diversify Landowner Income
Activities in Year 3 shifted from Years 1 and 2 that focused on landowner surveys, focus groups, and economic analyses to field measurements of changes in soil properties following tree planting and estimation of aboveground tree biomass. Eight sites were selected, two each in North Dakota, South Dakota, Nebraska, and Kansas. These sites provided a range of climate, soils, tree age and species and cropping practices. Site selection was intended to obtain representative soils, tree plantings, and cropping practices for the respective areas. Soil samples were collected and soil profile descriptions were prepared for tree plantings and agricultural fields at each site. Due to landowner limitations and site restrictions, only four of the sites were potentially suitable for the destructive tree sampling. Observations of tree and stand conditions were made on all four sites and sampling was completed on the Stromsburg, NE site. Soil analyses and biomass estimation efforts are ongoing. Preliminary results of soil organic carbon (SOC) analyses provide a range of results from little difference between soils beneath trees and in crop or grazing land to much greater SOC beneath trees compared to cropland, likely due to losses of soil organic matter due to cultivation and erosion.
1) Windbreak Tree Biomass
The intent of this portion of the project was to develop one or more new equations that would be more useful to landowners when they consider potential revenues from the biomass that would be removed in the renovation or replacement of a windbreak.
2) Tree Windbreak Effects on Soil Properties
The objective of this portion of the project was to determine the effects of tree planting on soil properties. The goal for Year 3 was to collect and analyze soil samples from two sites in each of the four states in the study.
1) Windbreak Tree Biomass Obstacles have been encountered and at least partially overcome. Of the eight windbreak sites used in the main project, the owner of two sites would not allow any trees to be cut at all. Another three sites had significant limitations on what was available, one site owner placed a limit of 3 ash trees as all that could be harvested, not enough for producing a reliable regression equation. Another site under the management of the U.S. Forest Service had old Ponderosa Pine and would have allowed only limited removals to thin the windbreak, meaning only poor quality trees could be destructively analyzed. So, on July 21-23, 2015 Dr. Hall made a trip to visit the four remaining sites with possibilities for fitting the study criteria. One site had an impressive osage orange (Maclura pomifera) windbreak that was over 90 years old. On further inspection it was obvious that some of the trees were re-sprouts of the original planting. It was also clear that most of the trees were too big and two armed with thorns to handle with detailed measurements of branches and bole. Two sites in Nebraska had red cedar windbreaks where essentially all the trees were available for harvest. The older site at the Mead Farm was a multispecies windbreak that also included Austrian Pine and Green Ash. It was starting to breakup and every tree seemed to have its own unique form and surrounding competition or lack thereof. Fortunately, a 20+ year old red cedar site near Stromsburg was entirely available for harvest (see later results). The remaining site at Marquette, KS has a number of Angiosperm tree species that are about 29 years old. The most promising and somewhat unique species is a cultivar of a hybrid red x silver maple (Acer freemanii). As a cultivar it has less phenotypic variation and should yield a good regression equation to predict biomass. It also has commercial value as an ornamental tree, so a windbreak owner could plant it on a closer spacing and thin by removing trees with a large mechanical tree spade. That might cover the cost of establishing the windbreak. The current plan is to harvest trees from that stand in March, 2016. The Stromsburg red cedar windbreak consisted of two rows running east-west. The row to the south had significant damage from heavy equipment and the storage of round bales close to the tree boles. The north row was in much better shape and we were able to harvest 18 trees and separate the material in stem segments, live and dead branches, and stem “cookies” for image analysis of stem form. The image analysis and dry weight determinations have not been completed, awaiting equipment availability. The samples are in cold storage. Table 1 shows averages and standard deviations for height and fresh weights of the stems. 2015 Annual Report Final Table 1The windbreak owner wanted high stumps left to make it easier for the total removal he had planned. We left a 65 cm stump which is included in the height column. A conservative estimate for the un-harvested biomass in the stump was determined from the average weight for the next 65 cm of stem; that amounts to 14.8 + 3.5 kg of fresh weight. The rot resistance of red cedar accounts for the large amount of dead branches that would still be a part of the harvestable biomass and their drier status would be an advantage if the wood is used in direct combustion or pyrolysis systems. 2) Tree Windbreak Effects on Soil Properties Eight tree windbreak sites were identified and sampled in the summer of 2015. Table 2 summarizes the general site characteristics. 2015 Annual Report Final Table 2 Selection of sampling sites was accomplished through a combination of identifying areas with extensive historical tree windbreak plantings and discussions with local soil and water conservation district, Natural Resources Conservation Service (NRCS), and state forestry agency personnel. Only then were landowners contacted and permission requested for site access. After site selection, four expeditions were organized to collect samples at both sites in each state during the same visit. Soil conditions, weather, and availability of NRCS soil scientists to assist with the soil profile descriptions made the scheduling of visits quite challenging. At each site a soil pit to a depth of ~5’ was dug by hand or with a backhoe inside the tree planting and in the adjacent cropped area, which included cultivated fields, alfalfa, grass hay and pasture. Soil samples were collected from the three walls of the soil pit and from two hand auger holes adjacent to each pit. Figure 1 shows examples of the soil pits and an NRCS soil scientist with student assistants analyzing the soil profile. 2015 Annual Report Final Fig 1.
Over 600 soil samples were collected for analysis. Samples were transported back to Ames and processed for the different analytical procedures. Analyses completed so far include total, organic, and inorganic soil carbon, total nitrogen, pH, soil texture, and bulk density. The graduate student and undergraduate student worker supported by the grant have been responsible for most of the soil sample processing and analyses. An example of the results are shown in Figure 2. 2015 Annual Report Final Fig 2 These SOC data are from the McPherson, KS site comparing an osage orange hedgerow soil (Tree) with the adjacent row crop field (Crop) on a Ladysmith silty clay loam soil. This site is unique as the hedgerow was planted into virgin prairie, thus the soil has never been cultivated. There is a dramatic difference in SOC that can be attributed to loss of soil organic matter during over a century of small grain and row crop production. The landowner, due to concern for what he felt was the loss of soil quality, stopped tilling this field three years ago and now practices no-tillage on his farm. This data shows that ~ ½ of the original SOC through the entire soil profile has been lost due to cropping and cultivation.
Impacts and Contributions/Outcomes
Data analysis and interpretation are still underway. The PI’s plan to present results of the study at the Society of American Foresters conference in November 2016. Two manuscripts will be prepared for publication and a second M.S. thesis in Sustainable Agriculture is also in preparation.
One manuscript has already been submitted from the first M.S. thesis:
Hand, A., Bowman, T., JC Tyndall. (In review) Influences on farmer and rancher interest in supplying woody biomass in the US Northern Great Plains. Submitted to Great Plains Research (December 2015).
National Soil Survey Center
100 Centennial Mall North, Room 152
Lincoln, NE 68508
Office Phone: 4024374149
Iowa State University
Dept. of Natural Resources, Ecology and Management
Ames, IA 50011
Office Phone: 5152941453
Iowa State University
Dept. of Natural Resources, Ecology and Management
Ames, IA 50011
Office Phone: 5152944912
Univ. of Nebraska-Lincoln
Agronomy and Horticulture
Lincoln, NE 68583
Office Phone: 4024726626