Sustainability of a Short-Rotation Woody Biofuel System Compared to Grass Biofuel and Grain Cropping Systems

Sustainability of a Short-Rotation Woody Biofuel System Compared to Grass Biofuel and Grain Cropping Systems

Summary

Water quality equipment continues to function well at the Centralia Research Farm and rain event samples continue to be taken. Lab analyses for sediment, nutrient, and herbicide losses are ongoing and entered into the database as they are completed. This study is long-term in nature and will extend beyond the life of this grant. However, preliminary modeling results will be presented in the final report.

Switchgrass yields in 2014 were typical for other studies on claypan soil sites and ranged between 5 and 6 tons per acre. Very little differences were observed among the three landscape positions.

In 2014, some replanting was done in the miscanthus plots with good success. 

Regarding the miscanthus portion of this project, this is the second and concluding year of two main studies: (1) determine miscanthus and yield response to nitrogen (N) fertilizer for marginal claypan soils in order to determine N fertilizer application rates; and (2) quantify the impact of rhizome quality and depth to the claypan horizon on miscanthus emergence and early growth.

Highlights from Study 1 include: this year’s data confirming with 2013 year data that suggest yield is generally not improved by N fertilization. Study 2 highlights include: 83% establishment rates of newly planted miscanthus rhizomes, rhizomes grow well in even the most eroded portions of the landscape, and rhizomes that are bigger (> 18 g) produce more biomass.

Objectives/Performance Targets

The objectives of this project, as started earlier, have been divided into two separate studies, hereafter refereed to as the ‘N study’ and ‘rhizome quality study’; and will be addressed sequentially.

Nitrogen (N) Study.  The objective of the N study is to assess miscanthus N needs on claypan soils.  The N study was conducted as two different experiments.  The first is an N rate experiment initiated on a mature miscanthus stand grown on a claypan soil site at the Jefferson Farm, adjacent to the University of Missouri South Farm (located near Columbia). For this study, a block of miscanthus was planted in 2007 with plots overlaid for N rate treatments in 2012. A randomized complete block design was used to further divide the area into three main blocks (i.e., reps), each block was then divided into four separate main plots of 3.7 x 13.7 m dimensions. Treatments of 0, 40, 80 and 120 lbs N/ac. were hand applied once in 2012 shortly after green-up (around May). No additional N fertilizer was applied because N build-up in the soil and miscanthus rhizome was thought sufficient to sustain this year’s growth while still providing treatment difference from N fertilizer but down in 2012. SPAD chlorophyll readings were taken at four-week intervals throughout the growing season (June, July, August, and September). In mid December each plot was harvested individually to determine yield quantities. A 1.4 m sickle mower was used to cut against the rows removing approximately 0.7 m on the ends of each plot to form a buffer row. One 1.4 m swath with the sickle mower then cut down the center of the plot forming an average harvestable plot area of 16.7m². The canes from each plot were bundled and weighed using a scale attached to the bucket of a tractor and elevated as to leave the bundled biomass in unaided suspension while a weight was recoded. Subsamples were taken to determine moisture and nutrient content.

The second experiment is also an N rate experiment that is being conducted over the 2012-2015 growing seasons at The University of Missouri South Farm (Mexico silt loam), and two producer fields, one in Cooper County (Weller silt loam) and one in Moniteau County (Menfro silt loam). Each of these sites were selected because they represent the unique characteristics of claypan soils, which as discussed earlier exhibit a pronounced enriched-clay soil horizon, which is restrictive to root growth and grain production and in turn impacts grain yield negatively when topsoil overtop this claypn is eroded. Each of these sites had existing one-year-old miscanthus stands and were organized using a randomized complete block design with four main blocks divided into six separate plots. Plot dimensions varied between location and were as follows: South Farm, 3.8 m x 9.1 m; Cooper and Moniteau County, 3 m x 4 m. Treatments of 0, 30, 60 and 120 lbs N/ac. were applied shortly after green-up in early May. Similarly to Jefferson Farm SPAD chlorophyll readings were taken at four-week intervals throughout the growing season (June, July, August, and September). In mid December plots were harvested to determine yield quantities. A 1.4 m sickle mower was used to cut against the rows removing approximately 0.7 m on the ends of each plot to form a buffer row. One 54 in. swath with the sickle mower then cut down the center of the plot forming an average harvestable plot area of 9.9m², 3.5m², and 3.9m² for Lone Tree, Cooper County, and Moniteau County, respectively. The canes from each plot were bundled and weighed using a scale fixed to the center of a pole and then elevated by two people as to leave the bundled biomass in unaided suspension while a weight was recoded. Subsamples were taken to determine moisture and nutrient content.

Rhizome Quality Study.   The objective of this study was to quantify the impact of rhizome quality and depth to the claypan horizon on miscanthus emergence and early growth. The second year of this study was conducted at the Centralia Missouri Research Farm. The research site used for cooperative research by the USDA-ARS and University of Missouri since 1991 investigates the effects of tillage, rotation, and other management practices on crop production and soil and water quality. The site is also mapped as a Mexico silt loam. The research site is12-ha area with 3 replications of 10 large cropping system treatment plots (18 m × 189 m; 0.35 ha/plot; 30 total), oriented so each plot contains summit, backslope, and footslope landscape positions of a typical claypan soil landscape. The cropping systems at this site are arranged in a randomized complete block design with landscape position as a fixed effect.  Additionally, depth to the claypan layer (DTC) was done using soil ECa.

Starting in 2010 potential perennial bioenergy crops were included in investigations at the site. In 2013 M. x giganteus was planted on three plots (one in each block) that previously had been planted to bioenergy willow the two previous years (2011 and 2012), but had failed.  Planting of M. x giganteus in 2013 was also unsuccessful, presumably because of herbicide damage and drought. Replanting occurred on 21 May 2014 and was used to initiate the second study. After rhizome quality characterization, 10 randomly-selected rhizomes were hand-planted to a 10 cm depth, on ~ 5-m spacing, on each of the three landscape positions.

Rhizome quality was characterized by measuring the mass, total length (found by summing the lengths of all protruding parts), diameter, and number of active buds. In order to insure accuracy of measurements each rhizome was rinsed in water to cleanse it of soil and debris.  Rhizomes were selected at random from the population.

The first week following planting, characterized rhizomes were visited every other day to record new shoot emergence. Visits to the site were lengthened to two weeks and then monthly intervals as new shoot emergence slowed. Yield data was obtained for each characterized plant at the end of the growing season. Basal circumference was also taken prior to harvest. Weekly soil temperature and seasonally soil moisture measurements were also taken during the initial months following planting. In the spring of 2015 mortality rates among the characterized plants will be evaluated.

• Centralia plot research shows large plots instrumented with surface runoff monitoring weirs and samplers for both grain (corn and soybean) and bioenergy (switchgrass and miscanthus) cropping systems. One cropping system as seen in the photo is a mix, with grain on the summit and footslope landscaped positions, and switchgrass on the most erodible backslope.

Accomplishments/Milestones

Nitrogen (N) Study. For the N Study, miscanthus yield was not increased by higher N fertilizer rates (Figure 1) for all location except for Boone County (LT).  These results matched our finding from 2013.  This could be due in part to the perennial nutrients that were recycled from last year’s growth, which supplied adequate nutrients even for those treatments with no N. Early season measurements of chlorophyll content using SPAD readings were found to be impacted by N rates (Figure 2).  As the season progressed, N rate treatments diminished. These results again matched our finding in from 2013.

Rhizome Quality Study. The second year of the rhizome quality study had 83% establishment rates of newly planted miscanthus rhizomes. A general trend of rhizomes with a larger length, mass, and diameter performed better as indicated by end-of-season, plant basal circumference and the numbers of tillers they produced (Figure 3). Early in the season DTC and viable bud count was important for developing into new tillers, but the effect of these properties faded as the growing season progressed. Rhizomes were shown to perform best in the most eroded parts of the landscape at both locations. Though this phenomenon is difficult to explain, it is encouraging that M. x giganteus is not sensitive to these highly vulnerable and degraded portions of the landscape for establishment.

2014 Field Day. Over 100 farmers and educators attended the 2014 Field Day held in early September at the USDA ARS Centralia Research Farm (Figure 4). Presentations were made both on the establishment and management of switchgrass and the miscanthus nitrogen study results. Post-event surveys revealed that participants increased their level of knowledge on producing these bioenergy crops.

• Figure 1: Yield for 2014 by location and nitrogen fertilizer rate.
• Figure 2: Leaf chlorophyll measurements (SPAD) for 2014 by location in relation to month and N fertilizer rate.
• Figure 3: Early and late season shoot counts in relation to rhizome length, weight, and rhizome score.
• Figure 4. More than 100 people attended the 2014 Field Day.
• Figure 5. Dr. Hank Stelzer talked on the environmental and soil health benefits of growing switchgrass.
• Figure 6. Graduate student, Bryan Randall, discusses the results of his miscanthus nitrogen study at the 2014 Field Day.

Impacts and Contributions/Outcomes

Post-event surveys revealed that farmers and educators who attended the field day increased their knowledge of the soil-enhancing benefits of producing dedicated energy crops on marginal claypan soils. They further learned some of the “do’s” and “don’ts” in establishing and maintaining these crops. Early-adopter farmers working in concert with MFA Oil have established pilot plantings of miscanthus. Their goal is to provide feedstock to potential markets in Mid-Missouri. The less-intensive management in producing energy crops compared to conventional grain cropping systems will reduce soil erosion and improve both soil structure and health.

Collaborators: