Scientific Literature

2017

Title: Organic farming enhances soil microbial abundance and activity–A meta-analysis and meta-regression.

Journal: PLoS ONE

Authors: Lori M, Symnaczik S, Mäder P, De Deyn G, Gattinger, A

Date:  July 12, 2017

Abstract: Population growth and climate change challenge our food and farming systems and provide arguments for an increased intensification of agriculture. A promising option is eco-functional intensification through organic farming, an approach based on using and enhancing internal natural resources and processes to secure and improve agricultural productivity, while minimizing negative environmental impacts. In this concept an active soil microbiota plays an important role for various soil based ecosystem services such as nutrient cycling, erosion control and pest and disease regulation. Several studies have reported a positive effect of organic farming on soil health and quality including microbial community traits. However, so far no systematic quantification of whether organic farming systems comprise larger and more active soil microbial communities compared to conventional farming systems was performed on a global scale. Therefore, we conducted a meta-analysis on current literature to quantify possible differences in key indicators for soil microbial abundance and activity in organic and conventional cropping systems. All together we integrated data from 56 mainly peer-reviewed papers into our analysis, including 149 pairwise comparisons originating from different climatic zones and experimental duration ranging from 3 to more than 100 years. Overall, we found that organic systems had 32% to 84% greater microbial biomass carbon, microbial biomass nitrogen, total phospholipid fatty-acids, and dehydrogenase, urease and protease activities than conventional systems. Exclusively the metabolic quotient as an indicator for stresses on microbial communities remained unaffected by the farming systems. Categorical subgroup analysis revealed that crop rotation, the inclusion of legumes in the crop rotation and organic inputs are important farming practices affecting soil microbial community size and activity. Furthermore, we show that differences in microbial size and activity between organic and conventional farming systems vary as a function of land use (arable, orchards, and grassland), plant life cycle (annual and perennial) and climatic zone. In summary, this study shows that overall organic farming enhances total microbial abundance and activity in agricultural soils on a global scale.

Full Paper

Title: Low-cost agricultural waste accelerates tropical forest regeneration

Journal: Restoration Ecology

Authors: Timothy L. H. Treuer, Jonathan J. Choi, Daniel H. Janzen, Winnie Hallwachs, Daniel Peréz-Aviles, Andrew P. Dobson, Jennifer S. Powers, Laura C. Shanks, Leland K. Werden, David S. Wilcove

Date: 21 August 2017

Abstract: Lower-cost tropical forest restoration methods, particularly those framed as win–win business-protected area partnerships, could dramatically increase the scale of tropical forest restoration activities, thereby providing a variety of societal and ecosystem benefits, including slowing both global biodiversity loss and climate change. Here we describe the long-term regenerative effects of a direct application of agricultural waste on tropical dry forest. In 1998, as part of an innovative agricultural waste disposal service contract, an estimated 12,000 Mg of processed orange peels and pulp were applied to a 3 ha portion of a former cattle pasture with compacted, rocky, nutrient-poor soils characteristic of prolonged fire-based land management and overgrazing in Área de Conservación Guanacaste, northwestern Costa Rica. After 16 years, the experimental plot showed a threefold increase in woody plant species richness, a tripling of tree species evenness (Shannon Index), and a 176% increase in aboveground woody biomass over an adjacent control plot. Hemispheric photography showed significant increases in canopy closure in the area where orange waste was applied relative to control. Orange waste deposition significantly elevated levels of soil macronutrients and important micronutrients in samples taken 2 and 16 years after initial orange waste application. Our results point to promising opportunities for valuable synergisms between agricultural waste disposal and tropical forest restoration and carbon sequestration.

Full Paper

Title: Clay illuviation provides a long-term sink for C sequestration in subsoils

Journal: Scientific Reports

Authors: Gemma Torres-Sallan, Rogier P.O. Schulte, Gary J. Lanigan, Kenneth A. Byrne, Brian Reidy, Iolanda Simó, Johan Six & Rachel E. Creamer

Date: 06 April 2017

Abstract: Soil plays a key role in the global carbon (C) cycle. Most current assessments of SOC stocks and the guidelines given by Intergovernmental Panel on Climate Change (IPCC) focus on the top 30 cm of soil. Our research shows that, when considering only total quantities, most of the SOC stocks are found in this top layer. However, not all forms of SOC are equally valuable as long-term stable stores of carbon: the majority of SOC is available for mineralisation and can potentially be re-emitted to the atmosphere. SOC associated with micro-aggregates and silt plus clay fractions is more stable and therefore represents a long-term carbon store. Our research shows that most of this stable carbon is located at depths below 30 cm (42% of subsoil SOC is located in microaggregates and silt and clay, compared to 16% in the topsoil), specifically in soils that are subject to clay illuviation. This has implications for land management decisions in temperate grassland regions, defining the trade-offs between primary productivity and C emissions in clay-illuviated soils, as a result of drainage. Therefore, climate smart land management should consider the balance between SOC stabilisation in topsoils for productivity versus sequestration in subsoils for climate mitigation.

Full Paper

Title: Soil networks become more connected and take up more carbon as nature restoration progresses

Journal: Nature Communications

Authors: Elly Morriën, S. Emilia Hannula, L. Basten Snoek, Nico R. Helmsing, Hans Zweers, Mattia de Hollander, Raquel Luján Soto, Marie-Lara Bouffard, Marc Buée, Wim Dimmers, Henk Duyts, Stefan Geisen, Mariangela Girlanda, Rob I. Griffiths, Helene-Bracht Jørgensen, John Jensen, Pierre Plassart, Dirk Redecker, Rudiger M. Schmelz, Olaf Schmidt, Bruce C. Thomson, Emilie Tisserant, Stephane Uroz, Anne Winding, Mark J. Bailey, Michael Bonkowski, Jack H. Faber, Francis Martin, Philippe Lemanceau, Wietse de Boer, Johannes A. van Veen & Wim H. van der Putten

Date: 08 February 2017

Abstract: Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.

Full Paper

Title: Historical carbon dioxide emissions caused by land-use changes are possibly larger than assumed

Journal: Nature Geoscience

Authors: A. Arneth, S. Sitch, J. Pongratz, B.D. Stocker, P. Ciais, B. Poulter, A. D. Bayer, A. Bondeau, L. Calle, L. P. Chini, T. Gasser, M. Fader, P. Friedlingstein, E. Kato, W. Li, M. Lindeskog, J. E. M. S. Nabel, T. A. M. Pugh, E. Robertson, N. Viovy, C. Yue & S. Zaehle

Date: 30 January 2017

Abstract: The terrestrial biosphere absorbs about 20% of fossil-fuel CO2 emissions. The overall magnitude of this sink is constrained by the difference between emissions, the rate of increase in atmospheric CO2concentrations, and the ocean sink. However, the land sink is actually composed of two largely counteracting fluxes that are poorly quantified: fluxes from land-use change and CO2 uptake by terrestrial ecosystems. Dynamic global vegetation model simulations suggest that CO2 emissions from land-use change have been substantially underestimated because processes such as tree harvesting and land clearing from shifting cultivation have not been considered. As the overall terrestrial sink is constrained, a larger net flux as a result of land-use change implies that terrestrial uptake of CO2 is also larger, and that terrestrial ecosystems might have greater potential to sequester carbon in the future. Consequently, reforestation projects and efforts to avoid further deforestation could represent important mitigation pathways, with co-benefits for biodiversity. It is unclear whether a larger land carbon sink can be reconciled with our current understanding of terrestrial carbon cycling. Our possible underestimation of the historical residual terrestrial carbon sink adds further uncertainty to our capacity to predict the future of terrestrial carbon uptake and losses.

Full Paper

2016

Title: Emergent crowns and light-use complementarity lead to global maximum biomass and leaf area in Sequoia sempervirens forests

Journal: Forest Ecology and Management

Authors: Robert Van Pelt, Stephen C. Sillett, William A. Kruse, James A. Freund, Russell D. Kramer

Date: 1 September 2016

Abstract: Forests >80 m tall have the highest biomass, and individual trees in these forests are Earth’s largest with deep crowns emerging above neighboring vegetation, but it is unclear to what degree these maxima depend on the emergent trees themselves or a broader-scale forest structure. Here we advance the concept of emergent facilitation, whereby emergent trees benefit co-occurring species. Trees reorganize foliage within crowns to optimize available light and, if long-lived, can reiterate after crown damage to become emergent. The height, depth, and spacing of emergent trees in turn allows for abundant light to pass through the canopy, leading to light-use complementarity as well as elevated biomass, leaf area, and species diversity of the forest as a whole. We chose Sequoia sempervirens to develop this concept and installed eleven 1-ha plots in old-growth forests spanning nearly six degrees of latitude in California. Each plot was based off a 316-m-long centerline where biomass and leaf area of all vegetation were quantified. We employed hierarchical measurements and stratified random sampling spanning the full size range of individuals to generate 180 equations for determining biomass and leaf area of all dominant plant species in these forests. Biomass (5190 Mg ha⁻¹), leaf area (LAI = 19.4), and aboveground carbon (2600 Mg ha⁻¹) are global maxima, occurring in plots with the highest proportion of emergent trees. Decay-resistant Sequoia heartwood contributes the bulk of this mass, ranging from 61.5 to 76.7% of plot totals. Heartwood is a key contributor to the development of trees with emergent crowns, since its durability enables trees to recover leaf area and to re-grow crowns after damage so that they can continue expanding for millennia. By distributing leaf area among fewer trees with deeper crowns, Sequoia maintains very high leaf area itself (LAI up to 14.5) while simultaneously allowing other species to flourish underneath (non-Sequoia LAI up to 8.0). Because Sequoia is not replaced by other species, aboveground biomass, leaf area, and carbon content of these forests are essentially asymptotic over time.

Full Paper

Title: The underestimated biodiversity of tropical grassy biomes

Journal: Scientific Reports

Authors: Brett P. Murphy, Alan N. Andersen, Catherine L. Parr

Date: 08 August 2016

Abstract: For decades, there has been enormous scientific interest in tropical savannahs and grasslands, fuelled by the recognition that they are a dynamic and potentially unstable biome, requiring periodic disturbance for their maintenance. However, that scientific interest has not translated into widespread appreciation of, and concern about threats to, their biodiversity. In terms of biodiversity, grassy biomes are considered poor cousins of the other dominant biome of the tropics—forests. Simple notions of grassy biomes being species-poor cannot be supported; for some key taxa, such as vascular plants, this may be valid, but for others it is not. Here, we use an analysis of existing data to demonstrate that high-rainfall tropical grassy biomes (TGBs) have vertebrate species richness comparable with that of forests, despite having lower plant diversity. The Neotropics stand out in terms of both overall vertebrate species richness and number of range-restricted vertebrate species in TGBs. Given high rates of land-cover conversion in Neotropical grassy biomes, they should be a high priority for conservation and greater inclusion in protected areas. Fire needs to be actively maintained in these systems, and in many cases re-introduced after decades of inappropriate fire exclusion. The relative intactness of TGBs in Africa and Australia make them the least vulnerable to biodiversity loss in the immediate future. We argue that, like forests, TGBs should be recognized as a critical—but increasingly threatened—store of global biodiversity.

This article is part of the themed issue ‘Tropical grassy biomes: linking ecology, human use and conservation’.

Full Paper

Title: Global Tree Cover and Biomass Carbon on Agricultural Land: The contribution of agroforestry to global and national carbon budgets

Journal: Scientific Reports

Authors: Rober J. Zomer, Henry Neufeldt, Jianchu Xu, Antje Ahrends, Deborah Bossio, Antonio Trabucco, Meine van Noordwijk & Mingcheng Wang

Date: 20 July 2016

Abstract: Agroforestry systems and tree cover on agricultural land make an important contribution to climate change mitigation, but are not systematically accounted for in either global carbon budgets or national carbon accounting. This paper assesses the role of trees on agricultural land and their significance for carbon sequestration at a global level, along with recent change trends. Remote sensing data show that in 2010, 43% of all agricultural land globally had at least 10% tree cover and that this has increased by 2% over the previous ten years. Combining geographically and bioclimatically stratified Intergovernmental Panel on Climate Change (IPCC) Tier 1 default estimates of carbon storage with this tree cover analysis, we estimated 45.3 PgC on agricultural land globally, with trees contributing >75%. Between 2000 and 2010 tree cover increased by 3.7%, resulting in an increase of >2 PgC (or 4.6%) of biomass carbon. On average, globally, biomass carbon increased from 20.4 to 21.4 tC ha−1. Regional and country-level variation in stocks and trends were mapped and tabulated globally, and for all countries. Brazil, Indonesia, China and India had the largest increases in biomass carbon stored on agricultural land, while Argentina, Myanmar, and Sierra Leone had the largest decreases.

Full Paper

Title: Legacy effects of grassland management on soil carbon to depth

Journal: Global Change Biology

Authors: Susan E. Ward, Simon M. Smart, Helen Quirk, Jerry R.B. Tallowin, Simon R. Mortimer, Rober S. Shiel, Andrew Wilmby, Richard D. Bardgett

Date: 9 May 2016

Abstract: The importance of managing land to optimize carbon sequestration for climate change mitigation is widely recognized, with grasslands being identified as having the potential to sequester additional carbon. However, most soil carbon inventories only consider surface soils, and most large-scale surveys group ecosystems into broad habitats without considering management intensity. Consequently, little is known about the quantity of deep soil carbon and its sensitivity to management. From a nationwide survey of grassland soils to 1 m depth, we show that carbon in grassland soils is vulnerable to management and that these management effects can be detected to considerable depth down the soil profile, albeit at decreasing significance with depth. Carbon concentrations in soil decreased as management intensity increased, but greatest soil carbon stocks (accounting for bulk density differences), were at intermediate levels of management. Our study also highlights the considerable amounts of carbon in subsurface soil below 30 cm, which is missed by standard carbon inventories. We estimate grassland soil carbon in Great Britain to be 2097 Tg C to a depth of 1 m, with ~60% of this carbon being below 30 cm. Total stocks of soil carbon (t ha−1) to 1 m depth were 10.7% greater at intermediate relative to intensive management, which equates to 10.1 t ha−1 in surface soils (0–30 cm), and 13.7 t ha−1 in soils from 30 to 100 cm depth. Our findings highlight the existence of substantial carbon stocks at depth in grassland soils that are sensitive to management. This is of high relevance globally, given the extent of land cover and large stocks of carbon held in temperate managed grasslands. Our findings have implications for the future management of grasslands for carbon storage and climate mitigation, and for global carbon models which do not currently account for changes in soil carbon to depth with management.

Full Paper (requires journal access)

Title: Climate-smart soils

Journal: Nature

Authors: Keith Paustian, Johannes Lehmann, Stephen Ogle, David Reay, G. Philip Robertson & Pete Smith

Date: 06 April 2016

Abstract: Soils are integral to the function of all terrestrial ecosystems and to food and fibre production. An overlooked aspect of soils is their potential to mitigate greenhouse gas emissions. Although proven practices exist, the implementation of soil-based greenhouse gas mitigation activities are at an early stage and accurately quantifying emissions and reductions remains a substantial challenge. Emerging research and information technology developments provide the potential for a broader inclusion of soils in greenhouse gas policies. Here we highlight ‘state of the art’ soil greenhouse gas research, summarize mitigation practices and potentials, identify gaps in data and understanding and suggest ways to close such gaps through new research, technology and collaboration.

Full Paper (requires journal access)

Title: The role of ruminants in reducing agriculture’s carbon footprint in North America

Journal: Journal of Soil and Water Conservation

Authors: W.R. Teague, S. Apfelbaum, R. Lal, U.P. Kreuter, J. Rowntree, C.A. Davies, R. Conser, M. Rasmussen, J. Hatfield, T. Wang, F. Wang, and P. Byck

Date: April 2016

Abstract:

Full Paper

2015

Title: Increasing beef production could lower greenhouse gas emissions in Brazil if decoupled from deforestation

Journal: Nature Climate Change

Authors: R. de Oliveira Silva, L. G. Barioni, J. A. J. Hall, M. Folegatti Matsuura, T. Zanett Albertini, F.A. Fernandes & D. Moran

Date: 2 October 2015

Abstract: Recent debate about agricultural greenhouse gas emissions mitigation highlights trade-offs inherent in the way we produce and consume food, with increasing scrutiny on emissions-intensive livestock products^1, 2, 3. Although most research has focused on mitigation through improved productivity^4, 5, systemic interactions resulting from reduced beef production at the regional level are still unexplored. A detailed optimization model of beef production encompassing pasture degradation and recovery processes, animal and deforestation emissions, soil organic carbon (SOC) dynamics and upstream life-cycle inventory was developed and parameterized for the Brazilian Cerrado. Economic return was maximized considering two alternative scenarios: decoupled livestock–deforestation (DLD), assuming baseline deforestation rates controlled by effective policy; and coupled livestock–deforestation (CLD), where shifting beef demand alters deforestation rates. In DLD, reduced consumption actually leads to less productive beef systems, associated with higher emissions intensities and total emissions, whereas increased production leads to more efficient systems with boosted SOC stocks, reducing both per kilogram and total emissions. Under CLD, increased production leads to 60% higher emissions than in DLD. The results indicate the extent to which deforestation control contributes to sustainable intensification in Cerrado beef systems, and how alternative life-cycle analytical approaches result in significantly different emission estimates.

Full Paper (requires journal access)

Title: Emerging land use practices rapidly increase soil organic matter

Journal: Nature Communications

Authors: Megan B. Machmuller, Marc G. Kramer, Taylor K. Cyle, Nick Hill, Dennis Hancock & Aaron Thompson

Date: 30 April 2015

Abstract: The loss of organic matter from agricultural lands constrains our ability to sustainably feed a growing population and mitigate the impacts of climate change. Addressing these challenges requires land use activities that accumulate soil carbon (C) while contributing to food production. In a region of extensive soil degradation in the southeastern United States, we evaluated soil C accumulation for 3 years across a 7-year chronosequence of three farms converted to management-intensive grazing. Here we show that these farms accumulated C at 8.0 Mg ha−1 yr−1, increasing cation exchange and water holding capacity by 95% and 34%, respectively. Thus, within a decade of management-intensive grazing practices soil C levels returned to those of native forest soils, and likely decreased fertilizer and irrigation demands. Emerging land uses, such as management-intensive grazing, may offer a rare win–win strategy combining profitable food production with rapid improvement of soil quality and short-term climate mitigation through soil C-accumulation.

Full Paper

Title: Cropland expansion outpaces agricultural and biofuel policies in the United States

Journal: Environmental Research Letters 

Authors: Tyler J. Lark, J Meghan Salmon, and Holly K. Gibbs

Date: 2 April 2015

Abstract: Cultivation of corn and soybeans in the United States reached record high levels following the biofuels boom of the late 2000s. Debate exists about whether the expansion of these crops caused conversion of grasslands and other carbon-rich ecosystems to cropland or instead replaced other crops on existing agricultural land. We tracked crop-specific expansion pathways across the conterminous US and identified the types, amount, and locations of all land converted to and from cropland, 2008–2012. We found that crop expansion resulted in substantial transformation of the landscape, including conversion of long-term unimproved grasslands and land that had not been previously used for agriculture (cropland or pasture) dating back to at least the early 1970s. Corn was the most common crop planted directly on new land, as well as the largest indirect contributor to change through its displacement of other crops. Cropland expansion occurred most rapidly on land that is less suitable for cultivation, raising concerns about adverse environmental and economic costs of conversion. Our results reveal opportunities to increase the efficacy of current federal policy conservation measures by modifying coverage of the 2014 US Farm Bill Sodsaver provision and improving enforcement of the US Renewable Fuels Standard.

Full Paper (requires journal access)

Title: Development of soil microbial communities for promoting sustainability in agriculture and a global carbon fix

Journal: PreJ PrePrints — “PeerJ Preprints” is a venue for early communication or feedback before peer review. Data may be preliminary.

Authors: David Johnson, Joe Ellington, Wesley Eaton

Date: 13 January 2015

Abstract: The goals of this research were to explore alternative agriculture management practices in both greenhouse and field trials that do not require the use of synthetic and/or inorganic nutrient amendments but instead would emulate mechanisms operating in natural ecosystems, between plant and Soil Microbial Communities (SMC), for plant nutrient acquisition and growth.

Greenhouse plant-growth trials, implementing a progression of soil conditions with increasing soil carbon (C) (C= 0.14% to 5.3%) and associated SMC population with increasing Fungal to Bacterial ratios (F:B) ( from 0.04 to 3.68), promoted a) increased C partitioning into plant shoot and plant fruit partitions (m=4.41, r2=0.99), b) significant quantities of plant photosynthate, 49%-97% of Total System New C (CTSN), partitioned towards increasing soil C c) four times reduction in soil C respiration (CR) as F:B ratios increased, starting with 44% of initial treatment soil C content respired in bacterial-dominant soils (low F:B), to 11% of soil C content respired in higher fertility fungal-dominant soils (Power Regression, r2=0.90; p=0.003).

Plant growth trials in fields managed for increased soil C content and enhanced SMC population and structure (increased F:B) demonstrated: a) dry aboveground biomass production rates (g m-2) of ~1,980 g in soils initiating SMC enhancement (soil C=0.87, F:B= 0.80) with observed potentials of 8,450 g in advanced soils (soil C=7.6%, F:B=4.3) b) a 25-times increase in active soil fungal biomass and a ~7.5 times increase in F:B over a 19 month application period to enhance SMC and c) reduced soil C respiration rates, from 1.25 g C m-2 day-1 in low fertility soils (soil C= 0.6%, F:B= 0.25) with only a doubling of respiration rates to 2.5 g C m-2 day-1 in a high-fertility soil with an enhanced SMC (F:B= 4.3) and >7 times more soil C content (soil C= 7.6%).

Enhancing SMC population and F:B structure in a 4.5 year agricultural field study promoted annual average capture and storage of 10.27 metric tons soil C ha-1 year -1 while increasing soil macro-, meso- and micro-nutrient availability offering a robust, cost-effective carbon sequestration mechanism within a more productive and long-term sustainable agriculture management approach.

Full Paper

2014

Title: Emerging land use practices rapidly increase soil organic matter

Journal: Nature Communications

Authors: R. de Oliveira Silva, L. G. Barioni, J. A. J. Hall, M. Folegatti Matsuura, T. Zanett Albertini, F.A. Fernandes & D. Moran

Date: 30 April 2014

Abstract: The loss of organic matter from agricultural lands constrains our ability to sustainably feed a growing population and mitigate the impacts of climate change. Addressing these challenges requires land use activities that accumulate soil carbon (C) while contributing to food production. In a region of extensive soil degradation in the southeastern United States, we evaluated soil C accumulation for 3 years across a 7-year chronosequence of three farms converted to management-intensive grazing. Here we show that these farms accumulated C at 8.0 Mg ha⁻¹ yr⁻¹, increasing cation exchange and water holding capacity by 95% and 34%, respectively. Thus, within a decade of management-intensive grazing practices soil C levels returned to those of native forest soils, and likely decreased fertilizer and irrigation demands. Emerging land uses, such as management-intensive grazing, may offer a rare win–win strategy combining profitable food production with rapid improvement of soil quality and short-term climate mitigation through soil C-accumulation.

Full Paper

Title: Greenhouse Gas Mitigation Opportunities for California Agriculture: Review of California Rangeland Emissions and Mitigation Potential

Publisher: Nicholas Institute

Authors: Marcia S. DeLonge, Justine J. Owen, and Whendee L. Silver

Date: February 2014

Abstract: Rangelands cover approximately 50% of California and have considerable potential to mitigate climate change. Several management strategies offer opportunities to build soil carbon and reduce greenhouse gas emissions. Grazing management can increase soil carbon, but significant uncertainties remain and best management practices are unknown. Long-term, well-replicated studies are urgently needed to explore the potential of grazing management for climate change mitigation. Organic amendments, particularly compost, can enhance biomass and sequester carbon on grasslands while reducing emissions from the waste sector. This strategy shows significant potential but requires additional research, particularly in arid rangelands. High-efficiency synthetic fertilizer use, plant community management, fire management, and irrigation can also influence soil carbon; however, these strategies could be challenging to scale up over large areas, and their net greenhouse gas impacts are uncertain. Remote sensing, biogeochemical modeling, and life-cycle assessments should be leveraged to identify and implement mitigation strategies.

Full Paper

2013

Title: Redefining agricultural yields: from tonnes to people nourished per hectare

Journal: Environmental Research Letters

Authors: Emily S. Cassidy, Paul C. West, James S. Gerber, and Jonathan A. Foley

Date: 1 August 2013

Abstract: Worldwide demand for crops is increasing rapidly due to global population growth, increased biofuel production, and changing dietary preferences. Meeting these growing demands will be a substantial challenge that will tax the capability of our food system and prompt calls to dramatically boost global crop production. However, to increase food availability, we may also consider how the world’s crops are allocated to different uses and whether it is possible to feed more people with current levels of crop production. Of particular interest are the uses of crops as animal feed and as biofuel feedstocks. Currently, 36% of the calories produced by the world’s crops are being used for animal feed, and only 12% of those feed calories ultimately contribute to the human diet (as meat and other animal products). Additionally, human-edible calories used for biofuel production increased fourfold between the years 2000 and 2010, from 1% to 4%, representing a net reduction of available food globally. In this study, we re-examine agricultural productivity, going from using the standard definition of yield (in tonnes per hectare, or similar units) to using the number of people actually fed per hectare of cropland. We find that, given the current mix of crop uses, growing food exclusively for direct human consumption could, in principle, increase available food calories by as much as 70%, which could feed an additional 4 billion people (more than the projected 2–3 billion people arriving through population growth). Even small shifts in our allocation of crops to animal feed and biofuels could significantly increase global food availability, and could be an instrumental tool in meeting the challenges of ensuring global food security.

Full Paper

Title: A Lifecycle Model to Evaluate Carbon Sequestration Potential and Greenhouse Gas Dynamics of Managed Grasslands

Journal: Ecosystems

Authors: Marcia S. DeLonge, Rebecca Ryals, and Whendee L. Silver

Date: 16 April 2013

Abstract: Soil amendments can increase net primary productivity (NPP) and soil carbon (C) sequestration in grasslands, but the net greenhouse gas fluxes of amendments such as manure, compost, and inorganic fertilizers remain unclear. To evaluate opportunities for climate change mitigation through soil amendment applications, we designed a field-scale model that quantifies greenhouse gas emissions (CO₂, CH₄, and N₂O) from the production, application, and ecosystem response of soil amendments. Using this model, we developed a set of case studies for grazed annual grasslands in California. Sensitivity tests were performed to explore the impacts of model variables and management options. We conducted Monte Carlo simulations to provide estimates of the potential error associated with variables where literature data were sparse or spanned wide ranges. In the base case scenario, application of manure slurries led to net emissions of 14 Mg CO₂e ha⁻¹ over a 3-year period. Inorganic N fertilizer resulted in lower greenhouse gas emissions than the manure (3 Mg CO₂e ha⁻¹), assuming equal rates of N addition and NPP response. In contrast, composted manure and plant waste led to large offsets that exceeded emissions, saving 23 Mg CO₂e ha⁻¹ over 3 years. The diversion of both feedstock materials from traditional high-emission waste management practices was the largest source of the offsets; secondary benefits were also achieved, including increased plant productivity, soil C sequestration, and reduced need for commercial feeds. The greenhouse gas saving rates suggest that compost amendments could result in significant offsets to greenhouse gas emissions, amounting to over 28 MMg CO₂e when scaled to 5% of California rangelands. We found that the model was highly sensitive to manure and landfill management factors and less dependent on C sequestration, NPP, and soil greenhouse gas effluxes. The Monte Carlo analyses indicated that compost application to grasslands is likely to lead to net greenhouse gas offsets across a broad range of potential environmental and management conditions. We conclude that applications of composted organic matter to grasslands can contribute to climate change mitigation while sustaining productive lands and reducing waste loads.

Full Paper

Title: Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands

Journal: Ecological Applications

Authors: Rebecca Ryals, Whendee L. Silver

Date: 1 January 2013

Abstract: Most of the world’s grasslands are managed for livestock production. A critical component of the long-term sustainability and profitability of rangelands (e.g., grazed grassland ecosystems) is the maintenance of plant production. Amending grassland soils with organic waste has been proposed as a means to increase net primary productivity (NPP) and ecosystem carbon (C) storage, while mitigating greenhouse gas emissions from waste management. Few studies have evaluated the effects of amendments on the C balance and greenhouse gas dynamics of grasslands. We used field manipulations replicated within and across two rangelands (a valley grassland and a coastal grassland) to determine the effects of a single application of composted green waste amendments on NPP and greenhouse gas emissions over three years. Amendments elevated total soil respiration by 18% ± 4% at both sites but had no effect on nitrous oxide or methane emissions. Carbon losses were significantly offset by greater and sustained plant production. Amendments stimulated both above- and belowground NPP by 2.1 ± 0.8 Mg C/ha to 4.7 ± 0.7 Mg C/ha (mean ± SE) over the three-year study period. Net ecosystem C storage increased by 25–70% without including the direct addition of compost C. The estimated magnitude of net ecosystem C storage was sensitive to estimates of heterotrophic soil respiration but was greater than controls in five out of six fields that received amendments. The sixth plot was the only one that exhibited lower soil moisture than the control, suggesting an important role of water limitation in these seasonally dry ecosystems. Treatment effects persisted over the course of the study, which were likely derived from increased water-holding capacity in most plots, and slow-release fertilization from compost decomposition. We conclude that a single application of composted organic matter can significantly increase grassland C storage, and that effects of a single application are likely to carry over in time.

Full Paper (requires journal access)

2010

Title: Managing Soils and Ecosystems for Mitigating Anthropogenic Carbon Emissions and Advancing Global Food Security

Journal: BioScience

Authors: Rattan Lal

Date: October 2010

Abstract: Soil carbon (C) is a dynamic and integral part of the global C cycle. It has been a source of atmospheric carbon dioxide (CO₂) since the dawn of settled agriculture, depleting more than 320 billion metric tons (Pg) from the terrestrial pool, 78±12 Pg of which comes from soil. In comparison, approximately 292 Pg C have been emitted through fossil-fuel combustion since about 1750. However, terrestrial pools can act as a sink for as much as 50 parts per million of atmospheric CO₂ for 100 to 150 years. The technical sink capacity of US soils is 0.288 Pg C per year; Earths terrestrial biosphere can act as a sink for up to 3.8 Pg C per year. The economic potential of C storage depends on its costs and cobenefits, such as global food security, water quality, and soil biodive’rsity. Therefore, optimally managing the soil C pool must be the basis of any strategy to improve and sustain agronomic production, especially in developing countries.

Full Paper