Paul R. Adler

Life-cycle assessment of net greenhouse-gas flux for bioenergy cropping systems.

Bioenergy cropping systems could help offset greenhouse gas emissions, but quantifying that offset is complex. Bioenergy crops offset carbon dioxide emissions by converting atmospheric CO2 to organic C in crop biomass and soil, but they also emit nitrous oxide and vary in their effects on soil oxidation of methane. Growing the crops requires energy (e.g., to operate farm machinery, produce inputs such as fertilizer) and so does converting the harvested product to usable fuels (feedstock conversion efficiency). The objective of this study was to quantify all these factors to determine the net effect of several bioenergy cropping systems on greenhouse-gas (GHG) emissions. We used the DAYCENT biogeochemistry model to assess soil GHG fluxes and biomass yields for corn, soybean, alfalfa, hybrid poplar, reed canarygrass, and switchgrass as bioenergy crops in Pennsylvania, USA. DAYCENT results were combined with estimates of fossil fuels used to provide farm inputs and operate agricultural machinery and fossil-fuel offsets from biomass yields to calculate net GHG fluxes for each cropping system considered. Displaced fossil fuel was the largest GHG sink, followed by soil carbon sequestration. N20 emissions were the largest GHG source. All cropping systems considered provided net GHG sinks, even when soil C was assumed to reach a new steady state and C sequestration in soil was not counted. Hybrid poplar and switchgrass provided the largest net GHG sinks, >200 g CO2e-C x m(-2) x yr(-1) for biomass conversion to ethanol, and >400 g CO2e-C x m(-2) x yr(-1) for biomass gasification for electricity generation. Compared with the life cycle of gasoline and diesel, ethanol and biodiesel from corn rotations reduced GHG emissions by approximately 40%, reed canarygrass by approximately 85%, and switchgrass and hybrid poplar by approximately 115%.

Sustainable Biofuels Redux

Science-based policy is essential for guiding an environmentally sustainable approach to cellulosic biofuels.

Switchgrass as a biofuels feedstock in the USA.

Switchgrass (Panicum virgatum L.) has been identified as a model herbaceous energy crop for the USA. In this review, we selectively highlight current USDA-ARS research on switchgrass for biomass energy. Intensive research on switchgrass as a biomass feedstock in the 1990s greatly improved our understanding of the adaptation of switchgrass cultivars, production practices, and environmental benefits. Several constraints still remain in terms of economic production of switchgrass for biomass feedstock including reliable establishment practices to ensure productive stands in the seeding year, efficient use of fertilizers, and more efficient methods to convert lignocellulose to biofuels. Overcoming the biological constraints will require genetic enhancement, molecular biology, and plant breeding efforts to improve switchgrass cultivars. New genomic resources will aid in developing molecular markers, and should allow for marker-assisted selection of improved germplasm. Research is also needed on profitable mana...

Perennial Forages as Second Generation Bioenergy Crops

The lignocellulose in forage crops represents a second generation of biomass feedstock for conversion into energy-related end products. Some of the most extensively studied species for cellulosic feedstock production include forages such as switchgrass (Panicum virgatum L.), reed canarygrass (Phalaris arundinacea L.), and alfalfa (Medicago sativa L.). An advantage of using forages as bioenergy crops is that farmers are familiar with their management and already have the capacity to grow, harvest, store, and transport them. Forage crops offer additional flexibility in management because they can be used for biomass or forage and the land can be returned to other uses or put into crop rotation. Estimates indicate about 22.3 million ha of cropland, idle cropland, and cropland pasture will be needed for biomass production in 2030. Converting these lands to large scale cellulosic energy farming could push the traditional forage-livestock industry to ever more marginal lands. Furthermore, encouraging bioenergy production from marginal lands could directly compete with forage-livestock production.

Impact of second-generation biofuel agriculture on greenhouse-gas emissions in the corn-growing regions of the US.

In the US, 95% of biofuel is produced from corn (Zea mays L), an intensively managed annual crop that is also grown for food and animal feed. Using the DAYCENT model, we estimated the effects on ecosystem services of replacing corn ethanol feedstocks with the perennial cellulosic feedstocks switchgrass (Panicum virgatum L) and miscanthus (Miscanthus × giganteus Greef et Deuter). If cellulosic feedstocks were planted on cropland that is currently used for ethanol production in the US, more ethanol (+82%) and grain for food (+4%) could be produced while at the same time reducing nitrogen leaching (−15 to −22%) and greenhouse-gas (GHG) emissions (−29 to −473%). The GHG reduction was large even after accounting for emissions associated with indirect land-use change. Conversion from a high-input annual crop to a low-input perennial crop for biofuel production can thus transition the central US from a net source to a net sink for GHGs.

Aquaculture sludge removal and stabilization within created wetlands

The objective of this research was to investigate treatment of the concentrated solids discharge produced during clarifier backwash within an aquaculture facility. Solids removal and stabilization were investigated within two types of created wetlands where water flowed either: (1) vertically, down through a porous substrate; or (2) horizontally, over soil and through plant hedges. Six 3.7×1.2×0.8-m (L×W×H) wetland cells were used to provide three replicates for both types of wetland. Approximately equal numbers of vetiver grass (Vetiveria zizanioides) tillers were planted on both wetlands types in November of 1994. Sludge (7500 mg l−1 solids) was loaded onto both wetland types six times day−1, with no scheduled drying cycle, from 12 May 1995 until 28 February 1996. Sludge was applied at a rate of about 1.35 cm day−1, or about 30 kg dry solids m−2 year−1. Results from this short study indicated that the vertical flow and horizontal flow wetlands, respectively, removed 98 and 96% TSS, 91 and 72% total COD, and 81 and 30% dissolved COD. Both types of wetland cells removed most (82–93%) of the total kjeldahl nitrogen, phosphorus, and dissolved phosphate. Measurements of sludge depths and TVS at the end of the study indicated considerable mineralization occurred in the wetlands; stored sludge at the end of the study had 50% less TVS than untreated sludge.

Plant species composition and biofuel yields of conservation grasslands

Marginal croplands, such as those in the Conservation Reserve Program (CRP), have been suggested as a source of biomass for biofuel production. However, little is known about the composition of plant species on these conservation grasslands or their potential for ethanol production. Our objective was to assess the potential of CRP and other conservation grasslands for biofuel production, describing the relationships of plant species richness and tall native C4 prairie grass abundance with plant chemical composition and the resulting potential ethanol yield. We determined plant species composition and diversity at multiple scales with the modified Whittaker plot technique, aboveground biomass, plant chemical composition, and potential ethanol yield at 34 sites across the major ecological regions of the northeastern USA. Conservation grasslands with higher numbers of plant species had lower biomass yields and a lower ethanol yield per unit biomass compared with sites with fewer species. Thus, biofuel yield per unit land area decreased by 77% as plant species richness increased from 3 to 12.8 species per m2. We found that, as tall native C4 prairie grass abundance increased from 1.7% to 81.6%, the number of plant species decreased and aboveground biomass per unit land area and ethanol yield per unit biomass increased resulting in a 500% increased biofuel yield per unit land area. Plant species richness and composition are key determinants of biomass and ethanol yields from conservation grasslands and have implications for low-input high-diversity systems. Designing systems to include a large proportion of species with undesirable fermentation characteristics could reduce ethanol yields.

Mechanistic approach to phytoremediation of water

Conventional thinking regarding the use of food crops to clean aquaculture effluents has been that plants cannot remove nutrients in water to low levels without a reduction in productivity and quality. Because greenhouse space is expensive, productivity is critical for a profitable operation. A production strategy, called the conveyor production system (CPS), was developed using thin-film technology for plant production in dilute aquaculture effluents. With the CPS, young plants were positioned near the solution inlet in a gutter receiving the effluent and moved progressively, like along a conveyor belt, towards the outlet as they grew. Luxury consumption by lettuce plants (Lactuca sativa L. cv. Ostinata) enabled them to store P in their tissues early in their growth cycle for use later as water P levels decreased and influx could no longer meet current demands. If water is distributed in a horizontal plug-flow pattern, without the CPS, all nutrients will be luxury consumed at the inlet, making nutrients limiting at the outlet and significant greenhouse space will be dedicated to growing plants that have no market value. The object of this study was to construct and operate a pilot-scale CPS, collect data demonstrating its potential to clean effluent and produce a marketable product, and develop a mechanistic model describing the process. Greenhouse studies demonstrated that by using the CPS, phosphorus could be reduced from 0.52 to <0.01 mg l−1 by lettuce without an apparent reduction in production or quality. The mechanistic model described in this paper simulated experimental data collected during the operation of the CPS growing lettuce and defines critical data necessary for the general comparison of effluents for treatment.

Ammonium decreases muskmelon root system hydraulic conductivity

Abstract The flow of water through plant roots is controlled by two driving forces, the transpiration rate (?P) and osmotic potential difference between the soil solution and inside the root (?π), and the root system hydraulic conductivity [Lroot (L•m‐2)]. Plant water status is affected by the source of nitrogen (N) supplied to the plant. This study was undertaken to isolate the effect of ammonium (NH4)‐N on Lroot from other factors affecting water transport through plants. The effect of NH4‐N on muskmelon (Cucumis melo L.) Lroot was determined by estimating conductance at high water flux rates where osmotic effects are negligible. Ammonium decreased Lroot by about 50%. At a given transpiration rate, the NH4‐N‐induced decrease in Lroot decreased leaf water potential [ψleaf (MPa)] which, in turn, may alter the behavior of the leaves as observed in other studies.

Changes in Soil Phosphorus Availability with Poultry Compost Age

Composting reduces the available nitrogen (N) content of organic materials by immobilizing it and converting it to a slow release form. The effect of composting on phosphorus (P) is less clear. Adding compost to soil can increase water extractable soil P by direct addition, dissolution, displacing sorbed, or reducing sorption capacity for P. Organic acids can affect soil P and vary with compost maturity. The objective of this study was to examine the effect of poultry manure compost on available soil P levels. Compost of different maturities was studied to evaluate the effect of biological activity on extractable P levels in two contrasting soils, a loam and clay. Turkey litter was mixed with orchard grass hay at a 3:1 volume ratio and turned frequently, and temperature, carbon dioxide, and oxygen were measured regularly. Compost samples were taken at day 0 when the compost was made, and at weeks 2, 4, and 8. Compost maturity determined by the Dewar self-heating and oxygen uptake tests indicated that two-week old compost had greater biological activity than compost at 4 or 8 weeks. Compost samples were added to a loam or clay soil at 0.15 and 0.30-g total P kg soil−1 and then incubated for 8 weeks. At 1 d and at 2, 4, and 8 weeks, water-extractable and Mehlich-1 extractable P were determined. The effect of compost age was most pronounced in the loam on day 1 with water-extractable P compared to the Mehlich-1 extractable P fraction. These data suggest that water-extractable P may increase when loam soils are amended with biologically active, immature compost or when the sorption capacity of the soil is not sufficient to offset the effects of the compost addition. Because water-extractable P is implicated in runoff events, caution should be exercised in applying immature composts to critical source areas within the watershed, which are most vulnerable to P loss in surface runoff and erosion.