Evaluation of Warm Season Grasses for Biomass Potential in Vermont

Transcription

1 Research Report Evaluation of Warm Season Grasses for Biomass Potential in Vermont Support for this project was provided by the U.S. Department of Energy. Thanks for the generous support from the office of U.S. Senator Patrick Leahy and the Vermont Sustainable Jobs Fund for ongoing renewable energy research and education. 1 March 2013, University of Vermont Extension

2 Evaluation of Warm Season Grasses for Biomass Potential in Vermont Prepared by Sid Bosworth, Extension Agronomist, and Tim Kelly, Research Assistant Many warm season grasses have the potential for biomass production because of their high yield potential and efficient utilization of soil nutrients. In order to evaluate grasses that could potentially be used for biomass production in Vermont, a total of four evaluation field trials were planted in 2009 and The selection of the grass species and cultivars that were included in these trials (Table 1) was based on discussions with various agronomists in the Northeast region who have been conducting grass biomass research and/or seed production. These included Dr. Jerry Cherney from Cornell University, Mr. Paul Salon, USDA-NRCS Big Flats Plant Material Station in New York, Mr. Calvin Ernst, Ernst Conversation Seed Company of Meadville, PA, Mr. Roger Sampson, REAP Canada, and Dr. Steve Herbert, University of Massachusetts. Two field sites were planted in 2009, on in South Burlington at the University of Vermont Horticultural Farm (UVM) and the other in Shelburne at Meach Cove Farm Trust (Meach Cove). Two additional studies were planted in 2010, one in Randolph Center at the Vermont Technical College (VTC) and the other in Alburgh. The Alburgh site was unsuccessful due to very heavy weed pressures; therefore, the rest of this report is based on the three locations. The species and cultivars planted in these trials are found in Table 1 and a description of each site is found in Table 2. Each site was prepared with primary tillage using a moldboard plow followed by two to three passes with a disc harrow. Previous crops in South Burlington and Randolph Center were field corn and sorghum-sudangrass, respectively. The Shelburne site had been in permanent grass sod that was minimally managed, usually just mowed and/or harvested for hay once a year. Each location represented three common soil types (Table 2), a well drained sandy loam (Hort Farm), a poorly drained silt loam (Meach Cove), and a stony loam (VTC). Trial Establishment - All plots, except for Giant Miscanthus, were planted by seed at recommended seeding rates for the Northeast using a Carter small plot cone seeder (Figure 1). The UVM and Meach Cove sites were planted in 2009 on June 2 and June 17, respectively. At each location, treatments were planted in 15 by 23 plots, replicated four times and arranged in a randomized block design. The VTC site was planted in 2010 Prior to planting, a composite soil sample was collected across the whole Fig. 1. Carter small plot planter study area at each location. At the UVM Farm, the soils were adequate for P but low to moderate for K; whereas, at the Shelburne site, P was low to moderate but K was adequate. However, since the objective of this project was to evaluate these grasses under marginal conditions, no additional fertilizer was applied that year since these grasses have been shown to grow in low fertile soils. At all three sites, germination and seedling growth was very good for most species producing vigorous stands for most treatments. High quality seed, planting at the right soil temperature, relatively low weed 2

3 Table 1. Description of grass species and cultivars evaluated in the Warm Season Grass Evaluation Trials, Vermont Grass Biomass Project, Table 2. Location and description of warm season grass biomass trials. 3

4 pressures due to past cropping history, and timely rain in July and August, were all major factors in stand success. All the sites were hand weeded at least once within the first few weeks after emergence. The only cultivar that did very poorly at both of these sites was Sutter big bluestem; therefore, in 2010, these plots were tilled and used to plant Giant Miscanthus. Rhizome cuttings of Giant Miscanthus were purchased from Kurt Bluemel Nursery (Baldwin, MD) in April 2010 and transplanted in six inch containers with potting soil, grown in the UVM greenhouse until a tiller emerged, and transplanted into a thirty-six inch spaced grid in each plot in early June. They were watered about twice a week for a month after transplanting. Figure 2. Miscanthus tillers transplanted in thirty six inch spaced grids Trial Maintenance There was relatively little maintenance after the seeding year. In the year after establishment in 2010, all plots at in South Burlington and Shelburne were fertilized in May when the grasses had grown about four inches, using a broadcast method with an application rate of fifty pounds of nitrogen (28-0-0) per acre. Some research had shown that these warm season grasses do not respond to N in their first couple of years, therefore, no fertilizer was applied in 2011 at any site. However, in 2012, all three sites received the same rates of N as previously applied using the same methods. In 2011 at the Hort farm and Meach Cove, creeping perennial weeds, especially cool season grasses such as reed canarygrass or bluegrass, started becaming a problem. These species would invade in the spring before the warm season grasses have begun their spring growth which usually is mid-may. In 2012, both trial locations were sprayed with one quart per acre of glyphosate in early May to control these early-growing, invading species. Harvest Method For biomass, there was only one harvest each year, in the fall (October or November) once the majority of the plants were drying down after frost. In the seeding year, only switchgrass plots at the Hort Farm and Meach Cove were harvest. At VTC, most of the plots were sampled for yield the establishment year using a 6 x 36 quadrat and hand clippers. Otherwise, all plots were harvested using a Carter self propelled research harvester which flail chops and collects a 3 foot wide swath. Subsamples were collected, weighed fresh, then dried and reweighed to determine dry matter content. The same samples were ground and used for determining ash (and mineral content in 2011). Statistical analysis included an analysis of variance (ANOVA) to compare treatment means of each parameter using a Least Significant Difference (LSD) test (P<0.05). Field notes of observations such as diseases and lodging of stands were also recorded throughout each season. Figure 3. Carter small plot harvester 4

5 Results Weather data for the experimental period is shown in Table 3. At the Hort Farm and Meach Cove, temperatures were generally at or above average except for June and July of During June, July and August, the major growth period of switchgrass, rainfall was at or below average in all four years except for June of 1010 and August of At VTC, temperatures were above average all three years and rainfall was mixed. Table 3. Average monthly temperature and precipitation and departure from normal (DFN), thirty year average, near the site locations. Weather conditions were similar at the South Burlington and Shelburne sites. Yield Results of Seeding Year - In the seeding year in 2009 at UVM and Meach Cove, only the switchgrass plots had enough growth at the end of the season to warrant a harvest (Table 4). Adequate and timely rainfall helped promote seedling growth during the July and August. One cultivar, Kanlow, exceeded four feet in height. It was the only lowland cultivar in the study and never went into a seedhead stage that year. Yield was low in the seeding year (about 1 to 1.5 tons per acre), probably not enough to offset the cost to harvest. The other species at the Hort Farm and Meach Cover were not harvested in 2009 due to slow seedling growth and inadequate yield in the seeding year. However, tiller counts taken at the end of the season did show that the stands for all the species and cultivars except for Sutter big bluestem (data not shown) were high enough for an adequate stand (Table 6). In the seeding year at VTC, 2010, most all the species were harvested (Table 5) and yields were comparable to the seeding year yields of switchgrass at Meach Cove in This was 5

6 Table 4. Biomass yield of warm season grass trials harvested from 2009 to 2012 in South Burlington and Shelburne, Vermont. Both sites were planted in June of

7 Table 5. Biomass yield a warm season grass trial harvested from 2010 to 2012 in Randolph Center, VT. This site was planted in June of Table 6. Tiller populations after harvests in 2010 and 2011 in S. Burlington and Shelburne, VT. 7

8 probably due to excellent weed control and timely rainfall patterns in June and July which promoted seedling growth. Kanlow switchgrass had the highest yield, probably due to its lack of reproductive development that year. While the other species were in a heading stage by mid-september, Kanlow continued to grow. Yield Results Post Seeding Year - As expected, yields improved each year with the highest in the third and fourth year of collecting data (Tables 4 and 5). Of the switchgrass cultivars, Cave-N-Rock and Shawnee have been the most productive in biomass yield across all locations. Kanlow, a lowland cultivar, did well at UVM, moderate at Meach Cove and poorly at VTC. As noted from the seeding year, this cultivar matures very late and will continue to put on dry matter later into the season compared to the other cultivars (Figure 4). Blackwell yielded well at VTC, its only location, but based on data from other northern states, it should be a viable cultivar for Vermont. Sunburst generally yielded less than Figure 5. Prairieview big bluestem at the UVM Hort Farm, Figure 4. Stand of Cave In Rock (left) and Kanlow (right) switchgrass in 2012 at the UVM Hort Farm. other switchgrass cultivars except at VTC in It matures the earliest of the cultivars in the trial and consistently showed more leaf diseases. Bowmaster was killed in the first winter. Of the big bluestem cultivars (Figure 5), Prairieview yielded well at Meach Cove in 2010 and 2011 and had the highest yields compared to any of the grass species at the Hort Farm in those years (Table 4). In 2012, its yields were lower than the best switchgrass cultivars and were more comparable to Niagara big bluestem. Both cultivars showed a steady decrease in tiller populations over time but especially Prairieview (Table 6). By the end of 2011, it had the lowest reproductive tiller population amongst all the cultivars. Niagara big bluestem has had moderate yields. Indiangrass generally had poor yields in the first three years (Table 4, Table 5); however, its yield was excellent at UVM in 2012 and good at VTC where the sites are moderate to well-drained. But at Meach Cove, which tends to be wet, it has done poorly (Figure 6). It is also very slow to mature and probably is more suited for including in a mixture rather as a monoculture biomass crop. Figure 6. Good stand of Indiangrass at the UVM Hort Farm (left) and poor stand at Meach Cove (right),

9 The polyculture mixture, Figure 7, (consisting of Cave In Rock switchgrass, one of the two cultivars of big bluestem depending on location, and Desmodium spp., a native prairie legume) yielded as well or sometimes slightly better than the monoculture of Cave In Rock during the same years and locations (Table 4, Table 5). The dominate specie in this mixture was consistently the switchgrass. The big bluestem made up Figure 7. Polyculture mixture about 25% of the mixture and the Desmodium did not really contribute much to the biomass; however, it has continued to persist each year (Figure 8). It does fix atmospheric nitrogen; however, it would need to make up a great amount of the stand to contribute to the N needs of the stand. Figure 8. Desmodium spp. Giant Miscanthus had the highest yield at Meach Cove with over 7 tons of yield in However, yields were inconsistent across locations. At UVM, it showed signs of serious water deficit stress and at VTC, it had serious winter injury with an 8% to 10% loss of plants. It requires a greater amount of water compared to the other warm season species. It needs several more years of evaluation before being considered as a viable option in Vermont (Figure 9). Figure 9. Giant Miscanthus at Meach Cove (left), UVM Hort farm (center) and VTC (right) in Coastal panicgrass and Prairie cordgrass were only located at the VTC site (Table 5). They both had moderate yields but not as well as the best cultivars of switchgrass. The prairie cordgrass was the earliest to green up in the spring but tended to lodge easily. The reed canarygrass at UVM and Meach Cove was only added to be a control since it is so commonly found in marginal sites in Vermont and has biomass potential. It did not do well in this study because its optimum harvest time is much earlier and the late fall harvest affected its reproductive cycle. In the last two years of the study, very few of the plants produced seed heads. Ash and Mineral Content - Ash content and certain minerals (Tables 7, 8, and 9) can have a significant effect on the fuel properties of grasses used for combustion. There is generally a high correlation between ash content of biomass combustion fuels with levels of undesirable minerals such as potassium (K), silicon (Si), chloride (Cl), and sulfur (S) that affect burn efficiency, fouling and slagging (Cherney and Verma, 2013). Generally, ash content in perennial grasses can range from 2% up to over 10 % 9

10 Table 7. Ash content of biomass at harvest from warm season grass trials from 2009 to 2012 in South Burlington and Shelburne Vermont. Both sites were planted in June of

11 Table 8. Ash content of biomass at harvest from a warm season grass trial harvested from 2010 to 2012 in Randolph Center, VT. This site was planted in June of Table 9. Potassium, nitrogen, and sulfur content of biomass from warm season grass trials,

12 depending on species, stage of maturity at time of harvest, soil texture and drainage, soil fertility and weather conditions, and soil contamination. In this study, ash content varied from as low as 2.0% to as high as 7% across years and studies, reflecting differences in soil type and water availability, species, and harvest date (Tables 7 and 8). All of these levels were above optimum for newly proposed grass pellet fuel standards but still within an acceptable range (Cherney and Verma, 2013). Meach Cove tended to have the highest ash content. This may be explained by the fact that there is usually a higher uptake of minerals with greater soil moisture; however, there was relatively little difference in potassium content between the locations and amongst the cultivars (Table 9). Silicon (not measured in this study), which often makes up half of the minerals in ash, usually has a higher plant uptake in wetter soils and this may explain the differences. At all sites, ash content declined each year. This is probably due to annual mineral uptake from the soil without replacement since no fertilizer was applied except N. Generally, the big bluestem cultivars were lower in ash content than the switchgrass cultivars (Tables 7 and 8) but this was not consistent every year or at every location. Prairie cordgrass also had very low ash content (Table 8). Potassium (K) content of grass biomass, along with other alkali metals and chloride, can have a significant effect on the potential to cause boiler corrosion along with fouling and slagging. In this study (Table 9), K levels ranged from 0.31% to 0.79% which is above both the optimum but within the acceptable range for a newly proposed grass pellet fuel standards (Cherney and Verma, 2013). Sunburst switchgrass was consistently lower in K than the other switchgrass cultivars. Prairie cordgrass had the lowest K content at the VTC site. Big bluestem, Indiangrass and Coastal panicgrass all had K levels similar to switchgrass. Giant Miscanthus consistently had higher K levels. Nitrogen (N) and sulfur (S) content of biomass can indicate potential for NO x and SO x emissions, respectively, and in this study, all the grass species and cultivars (Table 9) were above optimum but within acceptable ranges for quality fuel standards recently proposed for grass pellets (Cherney and Verma, 2013). Giant miscanthus and reed canarygrass had the highest N content. Nutrient Removal Rate Since biomass crops remove the total above ground portions of the crop, it is important to determine the potential removal rate of soil nutrients in order to assess replacement needs over time. Removal rates of macronutrients in 2011 (Table 10) varied by species, cultivar and location. Nitrogen removal rates varied from 28 to 133 lbs/acre. In most cases, yield had the greatest influence over total N removal rates; however, Giant Miscanthus also was much higher in N content than the other species (Table 9) and the combination of high yields at Meach Cove plus the higher concentration resulted in a removal rate almost three times greater than most of the other grasses. Phosphate (P 2 O 5 ) removal rates varied from as low as 9 lbs up to 36 lbs/acre and potash (K 2 O), from 20 lbs up to 98 lbs/acre. Overall, the average removal rates of the warm season grasses not including the Giant Miscanthus were 44 lbs of N, 22 lbs P 2 O 5, and 51 lbs of K 2 O per acre or an average of 14 lbs of N, 6 lbs of P 2 O 5, and 13 lbs of K 2 O per ton of dry matter biomass yield. 12

13 Table 10. Nutrient removal rates of warm season grasses harvested in 2011 Summary - Many warm season grasses appear to be suitable for biomass production in Vermont. The production potential of adapted cultivars can potentially reach 4 to 6 tons per acre per year once the stand is fully established. However, harvest losses should be accounted for and can be as high as twenty to thirty percent. Fuel quality of warm season grasses can be acceptable if soil nutrients are kept at a low to moderate level and harvests are made at the proper time. Nutrient removal is relatively low for these species; however, over time, soil nutrients will need to be replaced to assure adequate yields. References Cherney JH and VK. Verma Grass pellet Quality Index: A tool to evaluate suitability of grass pellets for small scale combustion systems. Applied Energy 103: Special thanks to Tim Kelly, Susan Monahan, Evan Reiss, Devon Snyder and Conner Burke for their assistance with preparation, maintenance and harvesting of plots. A special thanks to the farm collaborators in these trials - Chris Davis of Meach Cove Farm Trust, Sosten Lungu of Vermont Technical College, and Roger Rainville of Borderview Farm. For More Information on Grass Biomass, go to: - Revised April 2013 Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. University of Vermont Extension, Burlington, Vermont. University of Vermont Extension, and U.S. Department of Agriculture, cooperating, offer education and employment to everyone without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status. 13