We provide a review of sustainable coffee certifications and results from a quantitative analysis of the effects of Fair Trade, organic and combined Fair Trade/organic certifications on the livelihood strategies of 469 households and 18 cooperatives of Central America and Mexico. Certified households were also compared with a non-certified group in each country. To analyze the differences in coffee price, volume, gross revenue and education between certifications, we used the Kruskal–Wallis (K–W) non-parametric test and the Mann–Whitney U non-parametric test as a post-hoc procedure. Household savings, credit, food security and incidence of migration were analyzed through Pearson's chi-square test. Our study corroborated the conditions of economic poverty among small-scale coffee farmer households in Central America and Mexico. All certifications provided a higher price per pound and higher gross coffee revenue than non-certified coffee. However, the average volumes of coffee sold by individual households were low, and many certified farmers did not sell their entire production at certified prices. Certifications did not have a discernable effect on other livelihood-related variables, such as education, and incidence of migration at the household level, although they had a positive influence on savings and credit. Sales to certified markets offer farmers and cooperatives better prices, but the contribution derived from these premiums has limited effects on household livelihoods. This demonstrates that certifications will not single-handedly bring significant poverty alleviation to most coffee-farming families. Although certified coffee markets alone will not resolve the livelihood challenges faced by smallholder households, they could still contribute to broad-based sustainable livelihoods, rural development and conservation processes in coffee regions. This can be done by developing more active partnerships between farmers, cooperatives, certifications and environmental and rural development organizations and researchers in coffee regions. Certifications, especially Fair Trade/organic, have proven effective in supporting capacity building and in serving as networks that leverage global development funding for small-scale coffee-producing households.

Agriculture faces a multitude of challenges in the 21st century, and new tools are needed to help determine how it should respond. Among these challenges is a need to reconcile how human food consumption patterns should change to both improve human nutrition and reduce agriculture's environmental footprint. A complete-diet framework is needed for better understanding how diet influences demand for a fundamental agricultural resource, land. We tested such a model, measuring the impact of fat and meat consumption on the land requirements of food production in New York State (NYS). Analysis was confined to this geographic area to simplify the modeling procedure and to examine the state's ability to reduce environmental impact by supplying food locally. Per capita land resource requirements were calculated with a spreadsheet model for 42 diets ranging from 0 to 381 g d−1 (0 to 12 oz d−1) of meat and eggs and 20 to 45% total calories from fat. Many of these diets meet national dietary recommendations. The potential human carrying capacity of the NYS land base was then derived, based on recent estimates of available agricultural land. A nearly fivefold difference (0.18–0.86 ha) in per capita land requirements was observed across the diets. Increasing meat in the diet increased per capita land requirements, while increasing total dietary fat increased the land requirements of low meat diets but reduced the land needed for high meat diets. Higher meat diets used a larger share of the available cropland suited only to pasture and perennial crops. Thus, only a threefold difference was observed for the potential number of people fed from the NYS land base (2.0–6.2 million). In addition, some high-fat vegetarian diets supported fewer people than lower fat diets containing 63–127 g d−1 of meat (approximately one- to two-thirds of the national average per capita consumption in the US). These results support the assertion that diet should be considered in its entirety when assessing environmental impact. To more completely understand how diet influences land requirements and potential carrying capacity, this model should be applied across a larger geographic area that encompasses a wider variety of climates and soil resources. To better understand the ability of a local region to supply more of its own food, the model should be moved into a geospatial framework.

There is growing recognition that the direct marketing initiatives favored by many local food activists and proponents often lack the capacity to meet rapidly expanding consumer demand for local food. To address these needs, some food systems researchers have identified a role for ‘transitional’ food systems that piggyback on the pre-existing, conventional local food system infrastructure, while moving toward the social and economic benefits of direct marketing. This paper uses a value chain model (based on business management studies and adapted to the context of agrifood enterprises) as a framework for investigating how actors who are accustomed to working within the logic of the traditional produce industry incorporate local food into their overall operations. Using a qualitative comparative case study approach, the paper examines how features of the value chain structure and governance mechanisms operate in two food distribution networks that are transitioning toward localization in a rural and an urban region of Pennsylvania, respectively. Case study analysis focuses on conventional wholesale produce distributors as the link between local producers and local buyers. Interviews with the distributors, producers and buyers reveal the sources and outcomes of challenges affecting how the distributors organize their purchasing and selling of local produce. Network practices, in turn, have equity implications as distributors struggle to pay producers enough to maintain their economic viability, while still making local produce accessible to a wide range of consumers. Policy-makers and practitioners seeking to support the ‘scaling up’ of local and regional food systems should consider targeted development of technical infrastructure in processing and distribution, as well as outreach on appropriate shared ownership models. Future research should be longitudinal to determine the longer-term role and contribution of the conventional food system infrastructure in transitioning to more sustainable local and regional food systems.

Perennial grain crops would address many agricultural problems, including soil erosion, nutrient loss and pesticide contamination. Doubts about the possibility of perennial grain crops rest upon two assumptions: (1) that the relationship between yield and longevity is a fixed function that cannot be influenced by selection, mutation or environmental changes; and (2) that yield and longevity trade off in a bivariate manner to the exclusion of all other traits. These assumptions are consistent with the phenotypic trade-off model, but recent research suggests that a quantitative genetic model is a more appropriate approach to trade-offs. In the quantitative genetic model, environmental and genetic changes can result in increases in two traits simultaneously even when a trade-off, or negative correlation, exists between the two traits. Empirical evidence that the trade-off between perenniality and reproductive allocation is not fixed comes from wild, herbaceous perennials that can produce more than 2000 kg seed ha−1 in the temperate zone, and herbaceous perennial crops that produce on average 8900 kg fruit ha−1 in the tropics. Ecological literature suggests that most perennials produce small amounts of seed relative to their vegetative growth not as a physiological absolute, but rather as a result of natural selection in a stable, competitive environment favoring longevity. By selecting strongly for seed yield in a population of perennial plants, the plant breeder can likely achieve that which is rare in nature—a high seed-yielding perennial plant. The same general methodologies that have allowed annual grain breeders to increase grain yield and push many combinations of negatively correlated traits to levels of expression not seen in nature are available to the perennial grain breeder. Perennial grain breeders are integrating ecological principles and traditional plant breeding methods in their efforts to develop perennial grain wheat (Triticum spp.), sorghum (Sorghum spp.), sunflower (Helianthus spp.), Illinois bundleflower (Desmanthus illinoensis) and rice (Oryza spp.).

Conservation agricultural systems rely on three principles to enhance ecosystem services: (1) minimizing soil disturbance, (2) maximizing soil surface cover and (3) stimulating biological activity. In this paper, we explore the concept of diversity and its role in maximizing ecosystem services from managed grasslands and integrated agricultural systems (i.e., integrated crop–livestock–forage systems) at the field and farm level. We also examine trade-offs that may be involved in realizing greater ecosystem services. Previous research on livestock production systems, particularly in pastureland, has shown improvements in herbage productivity and reduced weed invasion with increased forage diversity but little response in terms of animal production. Managing forage diversity in pastureland requires new tools to guide the selection and placement of plant mixtures across a farm according to site suitability and the goals of the producer. Integrated agricultural systems embrace the concept of dynamic cropping systems, which incorporates a long-term strategy of annual crop sequencing that optimizes crop and soil use options to attain production, economic and resource conservation goals by using sound ecological management principles. Integrating dynamic cropping systems with livestock production increases the complexity of management, but also creates synergies among system components that may improve resilience and sustainability while fulfilling multiple ecosystem functions. Diversified conservation agricultural systems can sustain crop and livestock production and provide additional ecosystem services such as soil C storage, efficient nutrient cycling and conservation of biodiversity.

Organic and low-input farmers often plant seed varieties that have been selected under conventional practices, traditionally including high inputs of artificial fertilizers, crop protection chemicals and/or water. In addition, these crops are often selected in environments that may or may not represent the local environment of the farmer. An evolutionary participatory breeding (EPB) method emphasizes the utilization of natural selection in combination with site-specific farmer selection in early segregating generations of a heterogeneous crop population. EPB is a combination of two specific breeding methods, evolutionary breeding and participatory plant breeding. Evolutionary breeding has been shown to increase yield, disease resistance, genetic diversity and adaptability of a crop population over time. It is based on a mass selection technique used by farmers for over 10,000 years of crop improvement. Participatory plant breeding programs originated in developing countries to meet the needs of low-input, small-scale farmers in marginal environments who were often overlooked by conventional crop breeders. The EPB method is an efficient breeding system uniquely suited to improving crop varieties for the low-input and organic farmer. The EPB method utilizes the skills and knowledge of both breeders and farmers to develop heterogeneous landrace populations, and is an effective breeding method for both traditional and modern farmers throughout the world.

The measurement of soil carbon dioxide respiration is a means to gauge biological soil fertility. Test methods for respiration employed in the laboratory vary somewhat, and to date the equipment and labor required have somewhat limited more widespread adoption of such methodologies. The purpose of this research is to compare the results of measured soil CO2 respiration using three methods: (1) titration method; (2) infrared gas analysis (IRGA); and (3) the Solvita gel system for soil CO2 analysis. We acquired 36 soil samples from across the USA for comparison, which ranged in pH from 4.5 to 8.5, organic C from 0.8 to 4.6% and the clay content from 6 to 62%. All three methods were highly correlated with each other after 24-h of incubation (titration and Solvita r2=0.82, respirometer and Solvita r2=0.79 and titration versus respirometer r2=0.95). The 24-h (1-day) CO2 release from all three methods was also highly correlated to both basal soil respiration (7–28 days) and cumulative 28-day CO2 respiration. An additional 24 soil samples were acquired and added to the original 36, for a total of 60 soil samples. These samples were used for calibration of the Solvita gel digital color reader results using CO2-titration results and regression analysis. Regression analysis resulted in the equation y=20.6∗(Solvita number)−16.5 with an r2 of 0.83. The data suggest that the Solvita gel system for soil CO2 analysis could be a simple and easily used method to quantify soil microbial activity. Applications may also exist for the gel system for in situ measurements in surface gas chambers. Once standardized soil sampling and laboratory analysis protocols are established, the Solvita method could be easily adapted to commercial soil testing labs as an index of soil microbial activity.

The organic farming concept developed in the period prior to 1940 and was pioneered by Sir Albert Howard (1873–1947). Howard, born and educated in England, directed agricultural research centers in India (1905–1931) before permanently returning to England. His years of agricultural research experiences and observations gradually evolved into a philosophy and concept of organic farming that he espoused in several books. Howard's thinking on soil fertility and the need to effectively recycle waste materials, including sewage sludge, onto farmland was reinforced by F.H. King's book, Farmers of Forty Centuries. Howard developed a system of composting that became widely adopted. Howard's concept of soil fertility centered on building soil humus with an emphasis on how soil life was connected to the health of crops, livestock, and mankind. Howard argued that crop and animal health was a birthright and that the correct method of dealing with a pathogen was not to destroy the pathogen but to see what could be learned from it or to ‘make use of it for tuning up agricultural practice’. The system of agriculture advocated by Howard was coined ‘organic’ by Walter Northbourne to refer to a system ‘having a complex but necessary interrelationship of parts, similar to that in living things’. Lady Eve Balfour compared organic and non-organic farming and helped to popularize organic farming with the publication of The Living Soil. Jerome Rodale, a publisher and an early convert to organic farming, was instrumental in the diffusion and popularization of organic concepts in the US. Both Howard and Rodale saw organic and non-organic agriculture as a conflict between two different visions of what agriculture should become as they engaged in a war of words with the agricultural establishment. A productive dialogue failed to occur between the organic community and traditional agricultural scientists for several decades. Organic agriculture gained significant recognition and attention in 1980, marked by the USDA publication Report and Recommendations on Organic Farming. The passage of the Federal Organic Foods Production Act in 1990 began the era of accommodation for organic farming in the USA, followed by another milestone with official labeling as USDA Certified Organic in 2002. Organic agriculture will likely continue to evolve in response to ongoing social, environmental, and philosophical concerns of the organic movement.

Providing a wholesome and adequate food supply is the most basic tenet of agricultural sustainability. However, sharp increases in global food prices have occurred in the past 2 years, bringing the real price of food to the highest level seen in 30 years (FAO, 2008). This dramatic shift is a fundamental concern. The role of ‘local food’ in contributing to the solution of underlying problems is currently being debated, and the debate raises a critical question: To what degree can society continue to rely on large-scale, long-distance transportation of food? Growing concerns about climate change, the longevity of fossil fuel supplies and attempts to produce energy from agriculture suggest that energy efficiency will be critical to adapting to resource constraints and mitigating climate impacts. Moreover, these problems are urgent because energy prices, biofuel production and weather-related crop failures are partially responsible for the current world food price situation. Tools are needed to determine how the environmental impact and vulnerability of the food system are related to where food is produced in relation to where it is consumed. To this end, analyses of foodsheds, the geographic areas that feed population centers, can provide useful and unique insights.

Urban agriculture is a global and growing pursuit that can contribute to economic development, job creation, food security and community building. It can, however, be limited by competition for space with other forms of urban development, a lack of formalized land use rights and health hazards related to food contamination. The use of green roof technology in urban agriculture has the potential to alleviate some of these problems, without adversely affecting the benefits provided by urban agriculture. It would not only enable the use of land for development and agriculture, but may also facilitate the formation of formal space and water use agreements, and enable redistribution of ground-level resources among urban farmers. This could decrease the use of contaminated land and water at ground level and alleviate health concerns. Before green roof technology can be incorporated into urban agriculture on a larger scale, installation costs must be reduced, roof weight limitations should be assessed, and appropriate management practices should be developed which will ensure that the benefits of green roofs, such as energy savings and storm water management, are still provided to urban communities.

Growing interest in local food has sparked debate about the merits of attempting to reduce the distance food travels. One point of contention is the capacity of local agriculture to meet the food needs of local people. In hopes of informing this debate, this research presents a method for mapping potential foodsheds, land areas that could theoretically feed urban centers. The model was applied to New York State (NYS). Geographic information systems were used to estimate the spatial distribution of food production capacity relative to the food needs of NYS population centers. Optimization tools were then applied to allocate production potential to meet food needs in the minimum distance possible. Overall, the model showed that NYS could provide 34% of its total food needs within an average distance of just 49 km. However, the model did not allocate production potential evenly. Most NYS population centers could have the majority of their food needs sourced in-state, except for the greater New York City (NYC) area. Thus, the study presents a mixed review of the potential for local food systems to reduce the distance food travels. While small- to medium-sized cities of NYS could theoretically meet their food needs within distances two orders of magnitude smaller than the current American food system, NYC must draw on more distant food-producing resources. Nonetheless, the foodshed model provides a successful template for considering the geography of food production and food consumption simultaneously. Such a tool could be valuable for examining how cities might change their food procurement to curb greenhouse gas emissions and adapt to depletion of petroleum and other energy resources necessary for long-distance transport of food.

Integrated crop–livestock systems are often considered a promising way to address agricultural sustainability issues. Many authors claim that complementarities and synergies between crops and livestock can improve nutrient cycling and delivery of ecosystem services (ES) in agricultural systems. They have analyzed effects of interactions at the farm level and affirmed the potential advantage of developing crop–livestock interactions at the territory level. However, potential benefits of developing synergies beyond the farm level have not been clearly identified. Thus, we developed a conceptual framework that can be used to analyze, design and perform integrated assessment of crop–livestock systems at the territory level. To address crop–livestock interaction issues, we define it as a social-ecological system called the territorial crop–livestock system (TCLS). The ecological system is represented as three interacting components, crops, grasslands and animals, allowing description of various land uses and their potential effects on nutrient cycling and ES. The social system, represented as farmers interacting with natural-resource managers and agro-food chain actors, determines land use and the nature and intensity of ES delivered. We highlight the importance of coordination and learning among actors to support implementation of complex adaptive systems such as TCLSs. We illustrate the expressive power of our conceptual framework through development of a generic typology of crop–livestock systems. Then we show how our conceptual framework can be used as an intermediary object with stakeholders in participatory design approaches. We illustrate this process by representing four archetypal TCLSs. We provide an example of the design approach implemented in Southwestern France to address severe recurrent water shortages, which includes analysis of land use in the current crop–livestock system and the associated key metabolic and ES issues, identification of options for change and multi-criteria analysis of these options. We conclude that this framework shows great potential to support development of sustainable farming systems at the territory level.

Local food systems are comprised of networks of actors that work to ensure the sustainability of food supplies within communities. While local food has typically been promoted through direct marketing strategies such as farmers' markets and community-supported agriculture (CSA), retail stores are increasingly carrying and marketing local foods in response to consumer demand and market potential. Given the frequency with which consumers shop at grocery stores, as well as the portion of consumers' food purchases made at these locations, these stores may play a significant role in the success of local agriculture and the shaping of ideology about what is ‘local’. We conducted 27 semi-structured interviews with representatives of food retailers known to source and market local foods in the four major urban centers of Oregon's Willamette Valley. Our results reveal that grocers' perceptions of local food vary significantly from one another. Additionally, our results differed in comparison to the published literature on consumers' and producers' ideas of what constitutes local. Food retailers identified varying distances (frequently a region including several states) that they consider local, as well as diverse reasons for choosing to source and market local foods (most commonly supporting the local economy). Some trends in the variation of responses relate to how the size and form of ownership of the grocery stores influence the level at which decisions are made. These wide-ranging perceptions outline many of the realities of the local food movement, as well as opportunities for change.

Understanding the response of soil quality indicators to changes in management practices is essential for sustainable land management. Soil quality indicators were measured for 2 years under established experiments with varying management histories and durations at four locations in New York State. The Willsboro (clay loam) and Aurora (silt loam) experiments were established in 1992, comparing no-till (NT) to plow-till (PT) management under corn (Zea mays L.)–soybean (Glycine max L.) rotation. The Chazy (silt loam) trial was established in 1973 as a factorial experiment comparing NT versus PT and the crop harvesting method (corn silage versus corn grain). The Geneva (silt loam) experiment was established in 2003 with vegetable rotations with and without intervening soil building crops, each under three tillage methods (NT, PT and zone-till (ZT)) and three cover cropping systems (none, rye and vetch). Physical indicators measured were wet aggregate stability (WAS), available water capacity (AWC) and surface hardness (SH) and subsurface hardness (SSH). Soil biological indicators included organic matter (OM), active carbon (AC), potentially mineralizable nitrogen (PMN) and root disease potential (RDP). Chemical indicators included pH, P, K, Mg, Fe, Mn and Zn. Results from the Willsboro and Aurora sites showed significant tillage effects for several indicators including WAS, AWC, OM, AC, pH, P, K, Mg, Fe and Mn. Generally, the NT treatment had better indicator values than the PT treatments. At the Chazy site, WAS, AWC, OM, AC, pH, K and Mg showed significant differences for tillage and/or harvest method, also with NT showing better indicator values compared to PT and corn grain better than corn silage. Aggregate stability was on average 2.5 times higher in NT compared to PT treatments at Willsboro, Aurora and Chazy sites. OM was also 1.2, 1.1 and 1.5 times higher in NT compared to PT treatments at Willsboro, Aurora and Chazy sites, respectively. At the Geneva site WAS, SH, AC, PMN, pH, P, K and Zn showed significant tillage effects. The cover crop effect was only significant for SH and PMN measurements. Indicators that gave consistent performance across locations included WAS, OM and AC, while PMN and RDP were site and management dependent. The composite soil health index (CSHI) significantly differentiated between contrasting management practices. The CSHI for the Willsboro site was 71% for NT and 59% for PT, while at the Aurora site it was 61% for NT and 48% for PT after 15 years of tillage treatments.

A goal in sustainable agriculture is to use fossil fuel energy more efficiently in crop production. This 12-year study investigated effects of two crop rotations and two crop production systems (organic versus conventional management) on energy use, energy output and energy-use efficiency. The grain-based rotation included wheat (Triticum aestivum L.)–pea (Pisum sativum L.)–wheat–flax (Linum usitatissimum L.), while the integrated rotation included wheat–alfalfa (Medicago sativa L.)–alfalfa–flax. Energy use was 50% lower with organic than with conventional management, and approximately 40% lower with integrated than with the grain-based rotation. Energy use across all treatments averaged 3420 MJ ha−1 yr−1. Energy output (grain and alfalfa herbage only) across treatments averaged 49,947 MJ ha−1 yr−1 and was affected independently by production system and crop rotation. Energy output in the integrated rotation was three times that of the grain-based rotation; however, this difference was largely due to differences in crop type (whole plant alfalfa compared with grain seed). Energy output was 30% lower with organic than with conventional management. Energy efficiency (output energy/input energy) averaged to 17.4 and was highest in the organic and integrated rotations. A significant rotation by production system interaction (P<0.05) indicated that energy efficiency increases due to crop input reduction (i.e., shift from conventional to organic management) were greater in the integrated than in the grain-based rotation. Greater energy efficiency in the integrated rotation under organic management was attributed to the fact that the forage component was less sensitive to chemical input removal than grain crops.

In the United States, interest in urban farms and community gardens is flourishing, yet the urban home food garden (UHFG) and its contributions to urban systems have been overlooked and understudied. To begin to address this gap, we are conducting a mixed methods study of African American, Chinese-origin and Mexican-origin households with home gardens in Chicago, IL. Study methods include in-depth interviews, participant observation, ethnobotanical surveys and analysis of the chemical and physical properties of garden soils. As of this writing, findings indicate that home gardening has an array of beneficial effects, contributing to household food budgets and community food systems, the reproduction of cultural identity and urban biodiversity. The majority of informants in the study were internal or international migrants. For these individuals, gardening, culture-specific food plant assemblages and the foodways they support represent a continuation of cultural practices and traditional agroecological knowledge associated with their place of origin. The gardens of some migrant households also harbor urban agrobiodiversity with roots in the Global South. At the same time, gardens may have less salubrious effects on urban systems and populations. A lack of knowledge of safe gardening practices may expose vulnerable populations to environmental hazards such as soil contaminants. Gardeners in this study reported using synthetic chemical fertilizers and pesticides, sometimes indiscriminately, and the repeated application of synthetic fertilizers and compost may contribute to the nutrient loading of urban stormwater runoff. These effects may be moderated by the relatively low bulk density and high porosity of garden soils due to tillage and the application of organic matter, which can be expected to enhance stormwater infiltration. While the UHFG's potential contributions to urban systems are significant, outreach and research are needed to help gardeners grow food safely and sustainably in ways that contribute to overall ecosystem health.

Organic systems in the southeastern USA offer unique challenges and solutions to crop production due to regional soil and climate characterized by highly weathered soil types, high precipitation and the capacity to grow cover crops in the winter. Recently, the interest of producers and researchers in high-residue cover crops and conservation tillage systems has increased. Various designs of the roller–crimper to manage cover crops have been invented and demonstrated to growers in the southeastern region of the USA over the past 17 years. The impacts of high-residue cover crop mulches on the agronomic systems in the region are diverse. Legume cover crops assist with meeting N demand from cash crops though they decompose rapidly and are seldom sufficient for N demanding crops such as corn. Cereal cover crop mulches can have the opposite effect by immobilizing N and have a longer impact on soil moisture and weed dynamics. While undesirable for many crops, N immobilization is one possible mechanism for weed suppression in legume cash crops planted into cereal residues. Other cover crop weed suppression mechanisms include physical impedance, light availability, allelopathy and microclimate effects. Regardless of the cause, successful weed control by mulches is highly dependent on having substantial biomass. The southeastern region is capable of producing cover crop biomass in excess of 9000 kg ha−1, which is sufficient for weed control in many cash crops, although supplementary weed control is sometimes necessary. Long-term data are needed to predict when farmers should add supplementary weed control. More work is also needed on how much additional N is required for the cash crops and how best to deliver that N in a high-residue environment using organic sources.

Direct marketing is a popular marketing practice among smaller producers in the United States. We conducted detailed case studies of three organic farming operations of different sizes and compared their marketing costs and profitability in alternative marketing channels. We classified marketing-related activities into three categories: packing and storage, transportation, and selling and administration. By measuring the costs for labor, purchased goods and services, and capital assets associated with these marketing activities, we determined that there are significant variations in marketing costs across marketing channels. For each of our three case-study farms, marketing costs per dollar of revenue were lowest in the wholesale channel and highest in the farmers' market channel. Significant labor costs for the selling activity and transportation expenses offset the higher prices and minimal packaging costs associated with farmers' markets. Profitability can also be significantly affected by marketing factors, such as packing and grading standards, and product that is used for sampling and consumer premiums. Our research demonstrates that the higher prices that producers earn from direct marketing rather than wholesaling are not pure profit; the price premiums are compensation for the costs they incur when direct marketing their produce. Direct marketing channels, such as farmers' markets and Community Supported Agriculture (CSAs), can enable smaller farmers to build financially viable operations, by gaining access to markets, growing their farming operations and reducing their marketing risk. However, to achieve this success, farmers must manage their marketing costs as well as their production costs.

Growing populations and a constrained fossil-manufactured energy supply present a major challenge for society and there is a real need to develop forms of agriculture that are less dependent on finite energy sources. It has been suggested that organic agriculture can provide a more energy efficient approach due to its focus on sustainable production methods. This review has investigated the extent to which this is true for a range of farming systems. Data from about 50 studies were reviewed with results suggesting that organic farming performs better than conventional for nearly all crop types when energy use is expressed on a unit of area basis. Results are more variable per unit of product due to the lower yield for most organic crops. For livestock, ruminant production systems tend to be more energy efficient under organic management due to the production of forage in grass–clover leys. Conversely, organic poultry tend to perform worse in terms of energy use as a result of higher feed conversion ratios and mortality rates compared to conventional fully housed or free-range systems. With regard to energy sources, there is some evidence that organic farms use more renewable energy and have less of an impact on natural ecosystems. Human energy requirements on organic farms are also higher as a result of greater system diversity and manual weed control. Overall this review has found that most organic farming systems are more energy efficient than their conventional counterparts, although there are some notable exceptions.

The paper describes the model software REPRO (REPROduction of soil fertility) designed for analyzing interlinked carbon (C) and nitrogen (N) fluxes in the system soil–plant–animal–environment. The model couples the balancing of C, N and energy fluxes with the target to estimate the climate-relevant CO2, CH4 and N2O sources and sinks of farming systems. For the determination of the net greenhouse effect, calculations of C sequestration in the soil, CO2 emissions from the use of fossil energy, CH4 emissions from livestock keeping and N2O emissions from the soil have been made. The results were converted into CO2 equivalents using its specific global warming potential (GWP). The model has been applied in the experimental farm Scheyern in southern Germany, which had been divided into an organic (org) and a conventional (con) farming system in 1992. Rather detailed series of long-term measuring data are available for the farm in Scheyern, which have been used for validating the software for its efficiency and applicability under very different management yet nearly equal site conditions.

The organic farm is multi-structured with a legume-based crop rotation (N2 fixation: 83 kg ha−1 yr−1). The livestock density (LSU=Livestock Unit according to FAO) is 1.4 LSU ha−1. The farm is oriented on closed mass cycles; from the energetic point of view it represents a low-input system (energy input 4.5 GJ ha−1 yr−1). The conventional farm is a simple-structured cash crop system, based on mineral N (N input 145 kg ha−1 yr−1). Regarding the energy consumption, the system is run on high inputs (energy input 14.0 GJ ha−1 yr−1). The organic crop rotation reaches about 57% (8.3 Mg ha−1 yr−1) of the DM yield, about 66% (163 kg ha−1 yr−1) of the N removal and roughly 56% (3741 kg ha−1 yr−1) of the C fixation of the conventional crop rotation. In the organic rotation, 18 GJ per GJ of fossil energy input are bound in the harvested biomass vis-à-vis 11.1 GJ in the conventional rotation. The strongest influence on the greenhouse effect is exerted by C sequestration and N2O emissions. In Scheyern, C sequestration has set in under organic management (+0.37 Mg ha−1 yr−1), while humus depletion has been recorded in the conventional system (−0.25 Mg ha−1 yr−1).

Greenhouse gas emissions (GGEs) due to fuel consumption and the use of machines are nearly on the same level in both crop rotations. However, the conventional system emits an additional 637 kg CO2 eq ha−1 yr−1, which had been consumed in the manufacture of mineral N and pesticides in the upstream industry.

Besides the analyses in the experimental farm Scheyern, the model has been applied in 28 commercial farms (18 org and 10 con) with comparable soil and climate conditions in the surroundings of Scheyern (mean distance 60 km). The program calculations are aimed at benchmarking the results obtained in the farming systems Scheyern; they are expected to disclose management-specific variations in the emission of climate-relevant gases and to rate the suitability of the model for describing such management-specific effects. In order to make the situation in the farms comparable, only the emissions from cropping systems were analyzed. Livestock keeping remained unconsidered. Due to lower N and energy inputs, clearly lower N2O and CO2 emissions were obtained for the organic farms than for the conventional systems.

The analyses have shown possibilities for the optimization of management and the mitigation of GGE. Our findings underline that organic farming includes a high potential for C sequestration and the reduction of GGEs. Currently, the model REPRO is tested by 90 farms in the Federal Republic of Germany with the aim to apply it in the future not only in the field of research but also in the management of commercial farms.