UNDERSTANDING THE WEATHER- AND SOIL-RELATED VARIABILITY IN AGRICULTURAL WATER FOOTPRINTS: CASE STUDY OF MAIZE AND SOYBEANS GROWN IN THE ST. JOSEPH WATERSHED

Introduced in 2002, the water footprint is a valuable tool for understanding the consumption of freshwater resources. The traditional approach to quantifying the water footprint is to sum the green, blue, and gray water footprint components. The green water footprint is the volume of water that comes from precipitation, is stored in the soil, and used by vegetation. The blue water footprint is the volume of surface or ground water that is withdrawn and applied to cultivated lands via irrigation. These components are based on the evapotranspiration of green and blue water resources, respectively. The gray water footprint is the volume of water that is needed to dilute the resultant pollutants to ensure compliance with water quality standards in natural water bodies. Though applicable to many products and at a range of scales, the water footprint methodology is most commonly applied to agricultural products. This is because of the large volumes of water that products from this industry require. For example, in the U.S., maize and soybeans require 190 x 109 and 120 x 109 m3 in total water per year. Due to the large demands of water, applying the water footprint to an area with intensive agriculture is beneficial to effective resource management, even in areas with abundant water resources such as the Great Lakes Basin, which contains 21% of the world’s freshwater resources. Thus, the St. Joseph watershed, which is located in this area, will be investigated for how maize and soybean produced affect the freshwater resources. Because of the lack of insight gained from the traditional water footprint regarding the effects that water depletion has on local landscapes, a new approach is proposed, called the relative water footprint. Using this approach, it is shown that relative to a natural landscape of woody vegetation and deciduous trees, the agricultural water demands of the St. Joseph watershed are greatly reduced, at least in terms of the green water footprint. However, the blue and gray water footprints for maize and soybeans may still be significant and highly variable, with blue water footprints dependent on rainfall patterns, soil types, and irrigation scheduling, and gray water footprints dependent on fertilizer application rates

A high solids field-to-fuel research pipeline to identify interactions between feedstocks and biofuel production

Background: Environmental factors, such as weather extremes, have the potential to cause adverse effects on plant biomass quality and quantity. Beyond adversely affecting feedstock yield and composition, which have been extensively studied, environmental factors can have detrimental effects on saccharification and fermentation processes in biofuel production. Only a few studies have evaluated the effect of these factors on biomass deconstruction into biofuel and resulting fuel yields. This field-to-fuel evaluation of various feedstocks requires rigorous coordination of pretreatment, enzymatic hydrolysis, and fermentation experiments. A large number of biomass samples, often in limited quantity, are needed to thoroughly understand the effect of environmental conditions on biofuel production. This requires greater processing and analytical throughput of industrially relevant, high solids loading hydrolysates for fermentation, and led to the need for a laboratory-scale high solids experimentation platform. Results: A field-to-fuel platform was developed to provide sufficient volumes of high solids loading enzymatic hydrolysate for fermentation. AFEX pretreatment was conducted in custom pretreatment reactors, followed by high solids enzymatic hydrolysis. To accommodate enzymatic hydrolysis of multiple samples, roller bottles were used to overcome the bottlenecks of mixing and reduced sugar yields at high solids loading, while allowing greater sample throughput than possible in bioreactors. The roller bottle method provided 42–47% greater liquefaction compared to the batch shake flask method for the same solids loading. In fermentation experiments, hydrolysates from roller bottles were fermented more rapidly, with greater xylose consumption, but lower final ethanol yields and CO2 production than hydrolysates generated with shake flasks. The entire platform was tested and was able to replicate patterns of fermentation inhibition previously observed for experiments conducted in larger-scale reactors and bioreactors, showing divergent fermentation patterns for drought and normal year switchgrass hydrolysates. Conclusion: A pipeline of small-scale AFEX pretreatment and roller bottle enzymatic hydrolysis was able to provide adequate quantities of hydrolysate for respirometer fermentation experiments and was able to overcome hydrolysis bottlenecks at high solids loading by obtaining greater liquefaction compared to batch shake flask hydrolysis. Thus, the roller bottle method can be effectively utilized to compare divergent feedstocks and diverse process conditions

High temperatures and low soil moisture synergistically reduce switchgrass yields from marginal field sites and inhibit fermentation

‘Marginal lands’ are low productivity sites abandoned from agriculture for reasons such as low or high soil water content, challenging topography, or nutrient deficiency. To avoid competition with crop production, cellulosic bioenergy crops have been proposed for cultivation on marginal lands, however on these sites they may be more strongly affected by environmental stresses such as low soil water content. In this study we used rainout shelters to induce low soil moisture on marginal lands and determine the effect of soil water stress on switchgrass growth and the subsequent production of bioethanol. Five marginal land sites that span a latitudinal gradient in Michigan and Wisconsin were planted to switchgrass in 2013 and during the 2018–2021 growing seasons were exposed to reduced precipitation under rainout shelters in comparison to ambient precipitation. The effect of reduced precipitation was related to the environmental conditions at each site and biofuel production metrics (switchgrass biomass yields and composition and ethanol production). During the first year (2018), the rainout shelters were designed with 60% rain exclusion, which did not affect biomass yields compared to ambient conditions at any of the field sites, but decreased switchgrass fermentability at the Wisconsin Central–Hancock site. In subsequent years, the shelters were redesigned to fully exclude rainfall, which led to reduced biomass yields and inhibited fermentation for three sites. When switchgrass was grown in soils with large reductions in moisture and increases in temperature, the potential for biofuel production was significantly reduced, exposing some of the challenges associated with producing biofuels from lignocellulosic biomass grown under drought conditions