Tradeoffs in Biomass and Nutrient Allocation in Prairies and Corn Managed for Bioenergy Production

Abstract

Prairie vegetation has the potential to serve as a bioenergy feedstock with favorable environmental impacts but generally yields less than corn (Zea mays L.). To more fully assess the potential of prairie vegetation to serve as a biofuel feedstock, more needs to be understood about prairie responses to different management strategies, including fertilization. We hypothesized that (i) N fertilization would increase prairie productivity and nutrient content and (ii) fertilized prairie would produce similar amounts of total biomass as corn but would allocate more biomass and nutrients to roots. Our hypotheses were tested in a field experiment using prairie species representing different functional groups—C3 grasses, C4 grasses, legumes, and multifunctional group mixtures—grown with and without N fertilizer as well as fertilized corn. Fertilized and unfertilized C4 prairie grasses produced as much total biomass as corn but allocated up to 65% of their biomass belowground compared to 3% for corn. Corn yields decreased over the 3‐yr period of the study whereas yields of fertilized C4 grasses and multifunctional group mixtures were stable, and yields of unfertilized C4 grasses and mixtures increased and became equal to their fertilized counterparts. Calculated annual costs for replacing nutrients removed in the harvested portions of corn and fertilized and unfertilized C4 grasses were US$403, $137, and $40 ha−1, respectively. Results of this experiment show tradeoffs among corn and prairie systems with respect to harvested biomass, root production, and nutrient exports, emphasizing the need for a multifaceted approach to fully evaluate bioenergy feedstock production systems.

How Does Nitrogen and Perenniality Influence Belowground Biomass and Nitrogen Use Efficiency in Small Grain Cereals?

“…Our findings also contrast with at least one in situ study; Jarchow and Liebman (2012) reported greater root biomass of C 4 grasses in unfertilized systems compared with their fertilized system. Our findings also contrast with at least one in situ study; Jarchow and Liebman (2012) reported greater root biomass of C 4 grasses in unfertilized systems compared with their fertilized system.…”

“…In annuals, Russell et al (2009) reported no change in corn (Zea mays L.) root biomass with increasing N additions, whereas Durieux et al (1994) reported a decrease in root mass with increasing N rates at corn harvest, especially in drier growing seasons. In a perennial system, Jarchow and Liebman (2012) found that inorganic N fertilizer additions significantly reduced root biomass in a perennial C 4 grass system. At the same site, Dietzel et al (2015) found that inorganic fertilizer significantly increased root biomass in a mixed prairie system.…”

“…There is evidence to support each of these competing theories; thus, belowground crop responses to N fertilizers in both annual and perennial crops remain poorly understood and contradictory (Heggenstaller et al, 2009;Jung and Lal, 2011;Jarchow and Liebman, 2012). In annuals, Russell et al (2009) reported no change in corn (Zea mays L.) root biomass with increasing N additions, whereas Durieux et al (1994) reported a decrease in root mass with increasing N rates at corn harvest, especially in drier growing seasons.…”

Strategic use of native species on environmental gradients increases diversity and biomass relative to switchgrass monocultures

“…Tilman et al, 2001Tilman et al, , 2006 has supported the theory that yield increased with diversity. However, other research has found yield of specific monocultures or simple mixtures often equals or exceeds highdiversity mixes (Jarchow and Liebman, 2012;Johnson et al, 2010;Picasso et al, 2008;Springer et al, 2001). In particular, mixtures that include a warm-season perennial grass (often switchgrass) and a high-yielding legume (such as alfalfa [Medicago sativa]) often yield more than monocultures of the same species or higherdiversity mixtures (DeHaan et al, 2010;Wang et al, 2010).…”

Prairies Thrive Where Row Crops Drown: A Comparison of Yields in Upland and Lowland Topographies in the Upper Midwest US

“…While leguminous forbs produce relatively little harvestable biomass, they may provide sufficient plant-available nitrogen to maintain high graminoid biomass yields in the absence of nitrogen fertilizer [43]. Grasses provide higher potential ethanol yields per unit biomass [21,44], but forbs offer greater energy content per unit biomass when the biomass is directly combusted or thermochemically converted to other fuels [44].…”