Jim R. Kiniry

Perennial Biomass Grasses and the Mason–Dixon Line: Comparative Productivity across Latitudes in the Southern Great Plains

Understanding latitudinal adaptation of switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthusu2009×u2009giganteus J. M. Greef & Deuter ex Hodk. & Renvoize) to the southern Great Plains is key to maximizing productivity by matching each grass variety to its optimal production environment. The objectives of this study were: (1) to quantify latitudinal variation in production of representative upland switchgrass ecotypes (Blackwell, Cave-in-Rock, and Shawnee), lowland switchgrass ecotypes (Alamo, Kanlow), and Miscanthus in the southern half of the US Great Plains and (2) to investigate the environmental factors affecting yield variation. Leaf area and yield were measured on plots at 10 locations in Missouri, Arkansas, Oklahoma, and Texas. More cold winter days led to decreased subsequent Alamo switchgrass yields and increased subsequent upland switchgrass yields. More hot-growing season days led to decreased Kanlow and Miscanthus yields. Increased drought intensity also contributed to decreased Miscanthus yields. Alamo switchgrass had the greatest radiation use efficiency (RUE) with a mean of 4.3xa0g per megajoule intercepted PAR and water use efficiency (WUE) with a mean of 4.5xa0mg of dry weight per gram of water transpired. The representative RUE values for other varieties ranged from 67 to 80xa0% of Alamo’s RUE value and 67 to 87xa0% of Alamo’s WUE. These results will provide valuable inputs to process-based models to realistically simulate these important perennial grasses in this region and to assess the environmental impacts of production on water use and nutrient demands. In addition, it will also be useful for landowners and companies choosing the most productive perennial grasses for biofuel production.

Switchgrass Biomass Simulation at Diverse Sites in the Northern Great Plains of the U.S.

The Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model, originally developed and tested in Texas, needs to be tested for switchgrass (Panicum virgatum L.) simulation in more northerly locations. The Northern Great Plains of the U.S. has regionally adapted native populations of switchgrass and has excellent potential for growing switchgrass as a biofuel crop. The objective of this study was to adjust switchgrass parameters (potential leaf area index (DMLA) and degree days to maturity (PHU)) for northern sites and populations and to validate the model against switchgrass data from diverse sites in this region. Three or 4xa0years of measured yield data were used from a ten field sites in North Dakota (ND), South Dakota (SD), and Nebraska (NE). ALMANAC realistically simulated mean annual switchgrass yields ranging from means of 4.75 to 9.13xa0Mg ha−1. Mean simulated yields were within 3%, 15%, and 9% of mean measured yields for NE, SD, and ND, respectively. Sensitivity analysis with temperature and rainfall demonstrated variable responses of potential yields depending on whether season duration, soil water, or soil nitrogen was the limiting factor at a site. ALMANAC shows promise as a useful tool for switchgrass evaluation and management in the northern Great Plains and in similar latitudes with low rainfall such as the East European Plain.

Dedicated Energy Crops and Crop Residues for Bioenergy Feedstocks in the Central and Eastern USA

Dedicated energy crops and crop residues will meet herbaceous feedstock demands for the new bioeconomy in the Central and Eastern USA. Perennial warm-season grasses and corn stover are well-suited to the eastern half of the USA and provide opportunities for expanding agricultural operations in the region. A suite of warm-season grasses and associated management practices have been developed by researchers from the Agricultural Research Service of the US Department of Agriculture (USDA) and collaborators associated with USDA Regional Biomass Research Centers. Second generation biofuel feedstocks provide an opportunity to increase the production of transportation fuels from recently fixed plant carbon rather than from fossil fuels. Although there is no “one-size-fits-all” bioenergy feedstock, crop residues like corn (Zea mays L.) stover are the most readily available bioenergy feedstocks. However, on marginally productive cropland, perennial grasses provide a feedstock supply while enhancing ecosystem services. Twenty-five years of research has demonstrated that perennial grasses like switchgrass (Panicum virgatum L.) are profitable and environmentally sustainable on marginally productive cropland in the western Corn Belt and Southeastern USA.

Legacies in Switchgrass Resistance to and Recovery from Drought Suggest That Good Years Can Sustain Plants Through Bad Years

The warm-season perennial switchgrass (Panicum virgatum) is a candidate bioenergy crop. To be successful, switchgrass production must be maintained on low-quality landscapes with minimal inputs while facing future climates that are expected to be more extreme and more variable. We propose that antecedent rainfall constrains how plants respond to drought, as well as subsequently recover from drought. To test this idea, we examined how six switchgrass genotypes responded to a 1-year severe drought and then recovered under normal rainfall in the following year. These plants had previously grown for 3xa0years under a range of dry to wet rainfall levels in a shallow-soil common garden with no fertilizer. Plants previously exposed to drought produced less biomass, and basal area after the severe drought was relieved compared to previously well-watered plants. In addition, there were legacy effects caused by plant size: plants that were larger pre-drought were more likely to survive the severe drought, and plants that were larger during the severe drought recovered more biomass, basal area, and tillers post-drought. Although genotypes differed somewhat in their responses, the size constraint was consistent across genotypes. These findings suggest that we can establish more drought-resilient switchgrass stands by, for example, planning for initial irrigation or planting during a wet year to allow plants to grow larger prior to experiencing drought. Additional studies are needed to understand whether these rainfall and size legacies persist or are transient.

Inter-Annual Precipitation Variability Decreases Switchgrass Productivity from Arid to Mesic Environments

Cellulosic biofuels are an important source of renewable biomass within the alternative energy portfolio. Switchgrass (Panicum virgatum L.), a perennial C4 grass native to North America, is widely studied as a biofuel feedstock for its consistently high yields and minimal input requirements. The influences of precipitation amount and temporal variability on the fertilizer response of switchgrass productivity are not fully understood. Moreover, global climate models predict changes in rainfall patterns towards lower and increasingly variable soil water availability in several productive areas worldwide, which may impact net primary production of biofuel crops. We conducted a meta-analysis of aboveground net primary production of switchgrass from 48 publications encompassing 82 different locations, 11 soil types, 52 switchgrass cultivars, fertilizer inputs between 0 to 896xa0kgxa0Nxa0ha−1xa0year−1, and 1 to 6xa0years of annual productivity measures repeated on the same stand. Productivity of the lowland ecotype doubled with N rates >u2009131xa0kgxa0Nxa0ha−1xa0year−1, but upland ecotype productivity increased only by 50%. Results showed an optimum N rate of 30 to 60xa0kgxa0Nxa0ha−1xa0year−1 for both ecotypes, after which biomass gain per unit of N added decreased. Growing season precipitation (GSPPT) and inter-annual precipitation variability (inter-PPTvar) affected both ecotypes similarly. Long-term mean annual precipitation (MAP) differentially affected lowland and upland productivity, depending on the N level. Productivity responses to MAP and GSPPT were similar for both upland and lowland ecotypes at none or low N rates. When N increased beyond 60xa0kgxa0Nxa0ha−1xa0year−1, lowland cultivars had a greater growth response to MAP than uplands. Productivity increased with increasing GSPPT and MAP and had a positive linear response to MAP ranging from 600 to 1200xa0mmxa0year−1. One third of the variability in switchgrass production was accounted for by inter-PPTvar. After accounting for MAP, sites with higher inter-PPTvar had lower switchgrass productivity than sites with lower inter-PPTvar. Increased inter-annual variation in precipitation reduced production of both ecotypes. Predicted changes in the amount and timing of precipitation thus likely will exert greater influence on production of upland than lowland ecotypes of switchgrass.