Low-input High-diversity Research Articles

Climate Benefits of Increasing Plant Diversity in Perennial Bioenergy Crops

Bioenergy from perennial grasses mitigates climate change via displacing fossil fuels and storing atmospheric CO2 belowground as soil carbon. Here, we conduct a critical review to examine whether increasing plant diversity in bioenergy grassland systems can further increase their climate change mitigation potential. We find that compared with highly productive monocultures, diverse mixtures tend to produce as great or greater yields. In particular, there is strong evidence that legume addition improves yield, in some cases equivalent to mineral nitrogen fertilization at 33–150 kg per ha. Plant diversity can also promote soil carbon storage in the long term, reduce soil N2O emissions by 30%–40%, and suppress weed invasion, hence reducing herbicide use. These potential benefits of plant diversity translate to 50%–65% greater life-cycle greenhouse gas savings for biofuels from more diverse grassland biomass grown on degraded soils. In addition, there is growing evidence that plant diversity can accelerate land restoration.

Restoring low-input high-diversity grasslands as a potential global resource for biofuels

Reducing meat consumption by humans and shifting to more efficient plant and animal protein sources could potentially free up large areas of pasture and feedcrop agricultural land for restoration or conversion to low-input high-diversity (LIHD) grasslands. LIHD grasslands improve biodiversity, carbon sequestration, erosion control, water storage, while also providing opportunities to produce biofuels. We examined the potential of converting pastures globally, and animal feedstock agricultural lands in the USA and Brazil, to LIHD biomass sources and the capacity of these systems to meet national energy demands via (1) cellulosic ethanol and (2) integrated gasification and combined cycle technology with Fischer-Tropsch hydrocarbon synthesis (IGCC-FT) processing. Our analyses, which we argue are conservative, indicate that large amounts of energy, far in excess of many country's current demands, can potentially be produced from IGCC-FT processing of grassland biomass grown on converted pastures, especially in tropical developing countries. Over 40 countries could meet ≥100% of their domestic demands for electricity, gasoline, and diesel. If energy products were shared between countries, the 95 countries with positive energy production yields could meet 46%, 28%, and 39% of their combined electricity, gasoline, and diesel demands, respectively. While it is clearly unrealistic to propose a 100% conversion of pasture lands to biofuel production, these analyses highlight the potential gains in ecosystem services and energy production that could theoretically be achieved on already-managed lands.

Perennial Plant Establishment and Productivity Can Be Influenced by Previous Annual Crops

Core Ideas Perennial treatments established into soybean residue had the highest stand frequency measured. Warm‐season mixtures tended to have higher biomass production following soybean. Previous annual crops affected biomass yields for switchgrass, intermediate wheatgrass–alfalfa, and a cool‐season mixture. Developing efficient, economical methods of perennial mixture establishment is needed for grazing and conservation purposes. Study objectives were to evaluate different perennial monocultures and mixtures planted into spring wheat (Triticum aestivum L.), corn (Zea mays L.), soybean (Glycine max L. Merr.), dry pea (Pisum sativum L.), and spring canola (Brassica napus subsp. Rapifera) residue to determine establishment and subsequent production variation near Mandan, ND. Perennial treatments were two monocultures, binary mixtures (grass + legume), a warm‐season moderate‐input moderate diversity (MIMD) grass mixture, a cool‐season MIMD grass mixture, and a low‐input high diversity (LIHD) mixture consisting of 16 native species. Seeding rate was 450 pure live seed (PLS) m−2 for all perennial treatments and were managed according to best management practices. Stand establishment, measured using the frequency grid method, indicated perennial treatments established into soybean residue had the highest stand frequency (59%). Cool‐season grass treatments tended to have higher stand frequencies than warm‐season grass treatments and LIHD. Biomass yields were highest for intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey] (8.2 ± 1.2 Mg ha−1). Switchgrass (Panicum virgatum L.) produced the highest average biomass yield of the warm‐season grass treatments with 6.7 ± 1.2 Mg ha−1. The LIHD mixture was primarily cool‐season grasses followed by weeds, warm‐season grasses, and forb/legumes. This study highlights how transitioning from an annual cropping system to perennials can be influenced by the previous annual crop in a semiarid environment. Further research on establishing diverse, pollinator‐friendly perennial mixtures following annual crops is warranted.

Assessing top- and subsoil organic carbon stocks of Low-Input High-Diversity systems using soil and vegetation characteristics

The soil organic carbon (SOC) stock is an important indicator in ecosystem service assessments. Even though a considerable fraction of the total stock is stored in the subsoil, current assessments often consider the topsoil only. Furthermore, mapping efforts are hampered by the limited spatial density of these topsoil measurements. The aim of this study was to assess the SOC stock in the upper 100cm of soil in 30,556ha of Low-Input High-Diversity systems, such as nature reserves, in Flanders (Belgium) and compare this estimate with the stock found in the topsoil (upper 15cm). To this end, we combined depth extrapolation of 139 measurements limited to the topsoil with four digital soil mapping techniques: multiple linear regression, boosted regression trees, artificial neural networks and least-squares support vector machines. Particular attention was given to vegetation characteristics as predictors. For both the stock in the upper 15cm and 100cm, a boosted regression trees approach was most informative as it resulted in the lowest cross-validation errors and provided insights in the relative importance of predictors. The predictors of the stock in the upper 100cm were soil type, groundwater level, clay fraction and community weighted mean (CWM) and variance (CWV) of plant height. These predictors, together with the CWM of specific leaf area, aboveground biomass production, CWV and CWM of rooting depth, terrain slope, CWM of mycorrhizal associations and species diversity also explained the topsoil stock. Our total stock estimates show that focusing on the topsoil (1.63Tg OC) only considers 36% of the stock in the upper 100cm (4.53Tg OC). Given the magnitude of subsoil OC and its dependency on typical ecosystem characteristics, it should not be neglected in regional ecosystem service assessments.

Expanding the biomass resource: sustainable oil production via fast pyrolysis of low input high diversity biomass and the potential integration of thermochemical and biological conversion routes

Waste biomass is generated during the conservation management of semi-natural habitats, and represents an unused resource and potential bioenergy feedstock that does not compete with food production. Thermogravimetric analysis was used to characterise a representative range of biomass generated during conservation management in Wales. Of the biomass types assessed, those dominated by rush (Juncus effuses) and bracken (Pteridium aquilinum) exhibited the highest and lowest volatile compositions respectively and were selected for bench scale conversion via fast pyrolysis. Each biomass type was ensiled and a sub-sample of silage was washed and pressed. Demineralization of conservation biomass through washing and pressing was associated with higher oil yields following fast pyrolysis. The oil yields were within the published range established for the dedicated energy crops miscanthus and willow. In order to examine the potential a multiple output energy system was developed with gross power production estimates following valorisation of the press fluid, char and oil. If used in multi fuel industrial burners the char and oil alone would displace 3.9×105tonnes per year of No. 2 light oil using Welsh biomass from conservation management. Bioenergy and product development using these feedstocks could simultaneously support biodiversity management and displace fossil fuels, thereby reducing GHG emissions. Gross power generation predictions show good potential.

Press fluid pre-treatment optimisation of the integrated generation of solid fuel and biogas from biomass (IFBB) process approach

The integrated generation of solid fuel and biogas from biomass (IFBB) system is an innovative approach to maximising energy conversion from low input high diversity (LIHD) biomass. In this system water pre-treated and ensiled LIHD biomass is pressed. The press fluid is anaerobically digested to produce methane that is used to power the process. The fibrous fraction is densified and then sold as a combustion fuel. Two process options designed to concentrate the press fluid were assessed to ascertain their influence on productivity in an IFBB like system: sedimentation and the omission of pre-treatment water. By concentrating press fluid and not adding water during processing, energy production from methane was increased by 75% per unit time and solid fuel productivity increased by 80% per unit of fluid produced. The additional energy requirements for pressing more biomass in order to generate equal volumes of feedstock were accounted for in these calculations.

Energy potential for combustion and anaerobic digestion of biomass from low‐input high‐diversity systems in conservation areas

AbstractIn this study, we assessed the potential for bioenergy production of Low‐Input High‐Diversity (LIHD) systems in temperate West‐European conservation areas. A wide range of seminatural ecosystems (wet and dry grasslands, marshes, tall‐herb vegetation and heathlands) was sampled. Because LIHD biomass is often scattered and discontinuously available, we only considered the potential for anaerobic digestion and combustion. Both technologies are suitable for decentralized biomass utilization. The gross energy yield showed a promising range between 46–277 GJ per hectare per mowing cycle (MC). The energy efficiency of the anaerobic digestion process was rather low (10–30%) with a methane energy yield of 5.5–35.5 GJ ha−1 MC−1, experimentally determined by batch digestion tests. The water content, functional group composition and biochemical composition (hemicellulose, cellulose, lignin and Kjeldahl nitrogen) of the biomass were analyzed to assess the suitability of different valorization pathways. On the basis of the results, we were able to propose recommendations regarding the appropriate conversion techniques. Biomass from plant communities with ‘late’ harvest dates (August–October) or a high fraction of woody species like heathland and dune slacks, is best valorized through combustion, while herbaceous biomass of ‘early’ harvested grasslands (June–July) and tall‐herb vegetation can better be digested. The main advantages of the production of bioenergy from LIHD biomass originating from conservation management are the minimization of the competition with food production and its potential to reconcile renewable energy policies and biodiversity goals.

Quantification and Prediction of Biomass Yield of Temperate Low-Input High-Diversity Ecosystems

Little is known about the biomass production and bioenergy potential of low-input high-diversity (LIHD) systems in temperate nonforest conservation areas. In order to assess the potential of the biomass for energetic or other purposes, accurate yield data from LIHD systems are needed. We quantified the biomass yield in a wide range of seminatural systems (grasslands, marshes, tall-herb vegetation, and heathlands). Our results show a considerable variation in annual biomass yield ranging between 0.69 and 6.49 tDM ha−1 year−1. In addition, we provide an accurate method to determine the standing stock of harvestable biomass in the field. We developed four predictive models: one multiple linear regression (MLR) model and three boosted regression tree (BRT) models: (i) a vegetation model with variables that are easy to measure in the field, (ii) a soil model with soil physical and chemical variables, and (iii) a vegsoil model with all available variables. Due to its ability to fit nonlinear response functions and threshold values, the boosted regression tree technique outperformed the classical multiple linear regression. The vegetation model is the preferred model because it combines a good predictive performance (R2adj = 0.75 and R2adjCV = 0.51) with a relatively simple application.

Biomass yield, energy values, and chemical composition of hybrid poplars in short rotation woody crop production and native perennial grasses in Minnesota, USA

The increasing cost of fossil fuels such as petroleum, and a desire to curtail greenhouse gas emissions are driving the expansion of bioenergy. Plant biomass, including woody crops and grasses, are potential energy sources. We examined the biomass production, chemical composition, and energy content of selected hybrid poplar commercial clones such as NM6 (Populus nigra × Populus maximowiczii), D105 (Populus deltoides) and DN34 (P. deltoides × P. nigra) and native grasses and forbs established in polyculture systems in Minnesota, USA. In our study, we found that at the end of the 13-year growing season, NM6 had significantly greater (P = 0.0122) biomass production than D105 and DN34 with a total biomass production of 11.46 Mg ha−1. The chemical composition (mass fraction % on dry basis) of hybrid poplar clones generally contained 39% cellulose, 21% hemicellulose, 27% lignin, 1.3% ash content, and about 17,900–18,031 kJ kg−1 of dry wood. In contrast, after 7 years of growth, biomass such as that from the 5 grass mixture (5G), produced the highest amount of biomass (7.9 Mg ha−1) and largest theoretical ethanol yield (425 L Mg−1 of dry biomass), and contained mass fraction of 36% cellulose, 28% hemicellulose, 20% lignin, 6.04% ash content and about 16,731 kJ kg−1 of dry grass. Our data also showed that the slash left on site constituted a significant source of biomass (theoretically 375–390 L of ethanol for every megagram of biomass) that could be utilized for bioenergy. Seasonal timing of native grasses harvest significantly affected ethanol yield (P = 0.020) and energy content (P = 0.020). Strips of native grasses harvested in Spring 2009 that were allowed to re-grow and harvested in Fall 2009 showed greater potential for ethanol production than those harvested in Spring 2009. Thus, we suggest that hybrid poplars and native perennial grasses offer promising potential as alternative sources of renewable energy. Results of our study indicate that low-input high diversity systems can be utilized as an alternative source of biomass for energy and it could facilitate commercial production of the crops.

Land Availability for Biofuel Production

Marginal agricultural land is estimated for biofuel production in Africa, China, Europe, India, South America, and the continental United States, which have major agricultural production capacities. These countries/regions can have 320-702 million hectares of land available if only abandoned and degraded cropland and mixed crop and vegetation land, which are usually of low quality, are accounted. If grassland, savanna, and shrubland with marginal productivity are considered for planting low-input high-diversity (LIHD) mixtures of native perennials as energy crops, the total land availability can increase from 1107-1411 million hectares, depending on if the pasture land is discounted. Planting the second generation of biofuel feedstocks on abandoned and degraded cropland and LIHD perennials on grassland with marginal productivity may fulfill 26-55% of the current world liquid fuel consumption, without affecting the use of land with regular productivity for conventional crops and without affecting the current pasture land. Under the various land use scenarios, Africa may have more than one-third, and Africa and Brazil, together, may have more than half of the total land available for biofuel production. These estimations are based on physical conditions such as soil productivity, land slope, and climate.

Assessment of sustainable biomass resource for energy use in China

This paper assesses the sustainable biomass resource for energy in China. Assessment has been carried out for the following resources: (i) agricultural residues, (ii) forest residues, and (iii) municipal solid waste (MSW). The potential of each resource is estimated for the base years 2008, 2008, and 2007. The energy potentials of these resources in 2008, 2008, and 2007 are estimated to be 14.7, 3.9, and 0.2 EJ, respectively. The total potential including the energy of 6.4 EJ from the proposed low-input high-diversity (LIHD) grassland biomass on the untilled lands for the base years 1996 is equal to about 30.2% of China’s energy consumption in 2008. Furthermore it is projected that sustainable biomass use for energy will reduce net emissions of green house gases (GHG) of 3276.7 million tonnes, and help in emission-reduction target of China and the world.

Comparing Biomass Yields of Low-Input High-Diversity Communities with Managed Monocultures Across the Central United States

Biofuel cropping expansion is increasing pressure on food, grazing, and conservation lands. Debate over the efficacy of converting diverse native plant communities to managed monocultures prompted us to explore the extensive crop and ecological site productivity databases maintained by US Department of Agriculture-Natural Resources Conservation Service. We compared annual net primary productivity (ANPP) of diverse native plant communities to ANPP of alfalfa (Medicago sativa L.) in Nebraska, Kansas, and Oklahoma; to coastal bermudagrass (Cynodon dactylon [L.] Pers.) in northern and central Texas; and to buffelgrass (Pennisetum ciliare [L.] Link.) in extreme southern Texas. In only 21% of the 1,238 sites in Nebraska, Kansas, and Oklahoma did native communities produce more or equivalent ANPP compared with managed alfalfa or coastal bermudagrass. In contrast, southern Texas native communities had greater ANPP than did buffelgrass at 81% of the sites. Regression analyses based on these results suggested that managed switchgrass (Panicum virgatum L.) ANPP would consistently exceed native community ANPP. We identified the type of sites that could remain in diverse communities or be converted to diverse communities and have productivity as great as or greater than highly managed monocultures of alfalfa, coastal bermudagrass, or buffelgrass. However, because of the low ANPP on these sites, biomass production may not be the optimal use of such sites. These lands may be better suited to providing other ecosystem services.

Soil Carbon Sequestration or Biofuel Production: New Land-Use Opportunities for Mitigating Climate over Abandoned Soviet Farmlands

Although the CO(2) mitigation potential of biofuels has been studied by extrapolation of small-scale studies, few estimates exist of the net regional-scale carbon balance implications of biofuel cultivations programs, either growing conventional biofuel crops or applying new advanced technologies. Here we used a spatially distributed process-driven model over the 20 Mha of recently abandoned agricultural lands of the Former Soviet Union to quantify the GHG mitigation by biofuel production from Low Input/High Diversity (LIHD) grass-legume prairies and to compare this GHG mitigation with the one of soil C sequestration as it currently occurs. LIHD has recently received a lot of attention as an emerging opportunity to produce biofuels over marginal lands leading to a good energy efficiency with minimal adverse consequences on food security and ecosystem services. We found that, depending on the time horizon over which one seeks to maximize the GHG benefit, the optimal time for implementing biofuel production shifts from "never" (short-term horizon) to "as soon as possible" (longer-term horizon). These results highlight the importance of reaching agreement a priori on the target time interval during which biofuels are expected to play a role within the global energy system, to avoid deploying biofuel technology over a time interval for which it has a detrimental impact on the GHG mitigation objective. The window of opportunity for growing LIHD also stresses the need to reduce uncertainties in soil C inputs, turnover, and soil organic matter stability under current and future climate and management practices.

Effects of hay management and native species sowing on grassland community structure, biomass, and restoration

Prairie hay meadows are important reservoirs of grassland biodiversity in the tallgrass prairie regions of the central United States and are the object of increasing attention for conservation and restoration. In addition, there is growing interest in the potential use of such low-input, high-diversity (LIHD) native grasslands for biofuel production. The uplands of eastern Kansas, USA, which prior to European settlement were dominated by tallgrass prairie, are currently utilized for intensive agriculture or exist in a state of abandonment from agriculture. The dominant grasslands in the region are currently high-input, low-diversity (HILD) hay fields seeded to introduced C3 hay grasses. We present results from a long-term experiment conducted in a recently abandoned HILD hay field in eastern Kansas to evaluate effects of fertilization, haying, and native species sowing on community dynamics, biomass, and potential for restoration to native LIHD hay meadow. Fertilized plots maintained dominance by introduced grasses, maintained low diversity, and were largely resistant to colonization throughout the study. Non-fertilized plots exhibited rapid successional turnover, increased diversity, and increased abundance of C4 grasses over time. Haying led to modest changes in species composition and lessened the negative impact of fertilization on diversity. In non-fertilized plots, sowing increased representation by native species and increased diversity, successional turnover, and biomass production. Our results support the shifting limitations hypothesis of community organization and highlight the importance of species pools and seed limitations in constraining successional turnover, community structure, and ecosystem productivity under conditions of low fertility. Our findings also indicate that several biological and functional aspects of LIHD hay meadows can be restored from abandoned HILD hay fields by ceasing fertilization and reintroducing native species through sowing. Declines in primary production and hay yield that result from the cessation of fertilization may be at least partially compensated for by restoration.

From the petroeconomy to the bioeconomy: Integrating bioenergy production with agricultural demands

AbstractProduction of biomass for bioenergy generation, and in particular production of biologically derived liquid fuels, is attracting great interest as an alternative to the fossil fuel economy. Biofuels represent as yet only 1% of world agricultural output, but this small extension has triggered widespread fears, many now shown to be groundless, such as the fear that it was biofuels that drove up food prices in 2008. This perspective reviews the literature on the extent to which biofuel production can be integrated into agricultural production, taking a global view of the potential for land, water and other resources to be extended beyond current food, feed and fi ber applications. As opposed to the focus on negative impacts, there are benefi cial practices in biofuels that could be expected to propagate to agriculture more generally and have a positive impact on yields and practices. These include (1) promoting a shift from wasteful annual crops to perennials, particularly low‐input high‐diversity (LIHD) crops; (2) sequestering carbon in soil both organically and as biochar; (3) improving conservative water management practices; and (4) recycling resources. The possibilities of encouraging biofuel production (and biomass for bioenergy generally) in the tropical South, for consumption in the temperate North, based on certifi cation of such sustainable practices in the South, could be expanded if global trade in biofuels were liberalized. Copyright © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd

Treatment Variable Effects on Supercritical Gasification of High-Diversity Grassland Perennials

Low-input high-diversity (LIHD) mixtures of native grassland perennials were subjected to a supercritical treatment process with the aim of obtaining hydrogen-rich gases. The process was studied based on the following treatment variables: reaction temperature (374 degrees C to 575 degrees C, corresponding to a pressure range of 22.1 to 40 MPa), residence time (10 to 30 min), biomass content in the feed, and catalysts (0% to 4% NaOH and solid alkali CaO-ZrO(2)). The gaseous phase produced from gasification of LIHD primarily consisted of hydrogen (H(2)), with a mixture of carbon monoxide (CO), methane (CH(4)), and carbon dioxide (CO(2)). The statistical significance of treatment variables was evaluated using analysis of variance (ANOVA). It showed that at the level of P < 0.05, temperature, catalysts, and biomass content in the feed significantly affected gas yields, while residence time was not significant.

Comment on "Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass"

Tilman et al. (Reports, 8 December 2006, p. 1598) argued that low-input high-diversity grasslands can provide a substantial proportion of global energy needs. We contend that their conclusions are not substantiated by their experimental protocol. The authors understated the management inputs required to establish prairies, extrapolated globally from site-specific results, and presented potentially misleading energy accounting.

Response to Comment on "Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass"

We discovered that biofuels from low-input high-diversity mixtures of native perennial prairie plants grown on degraded soil can provide similar bioenergy gains and greater greenhouse gas benefits than current corn ethanol produced from crops grown in monoculture on fertile soil with high inputs. Russelle et al .'s technical concerns are refuted by a substantial body of research on prairie ecosystems and managed perennial grasslands.

Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass

Biofuels derived from low-input high-diversity (LIHD) mixtures of native grassland perennials can provide more usable energy, greater greenhouse gas reductions, and less agrichemical pollution per hectare than can corn grain ethanol or soybean biodiesel. High-diversity grasslands had increasingly higher bioenergy yields that were 238% greater than monoculture yields after a decade. LIHD biofuels are carbon negative because net ecosystem carbon dioxide sequestration (4.4 megagram hectare(-1) year(-1) of carbon dioxide in soil and roots) exceeds fossil carbon dioxide release during biofuel production (0.32 megagram hectare(-1) year(-1)). Moreover, LIHD biofuels can be produced on agriculturally degraded lands and thus need to neither displace food production nor cause loss of biodiversity via habitat destruction.