Many urban agriculture programs, and the organizations that run them, require substantial resources to remain viable and provide the multifunctional benefits that practitioners and supporters hope to achieve. As urban agriculture activity expands, practitioners and supporters face significant challenges, including how to match resources to the needs of practitioners and expectations of municipalities, and how to distribute those resources effectively and equitably so that communities, and the city as a whole, capture the benefits of these projects. This is particularly important as cities face increasing pressure to reduce costs and maximize the return on public expenditures. A 2-year study called Five Borough Farm documented the goals and objectives of urban agriculture projects in New York City and the resources for their success. The data showed that resource needs go beyond the material and financial needs discussed in the urban agriculture literature (e.g., land, soil, money). Interviews documented that urban agriculture projects have broader goals than merely producing food, and that attaining these goals (e.g., environmental improvements, community development, social justice) requires the support of government and networks of practitioners, non-profit organizations and philanthropies. Moreover, interviewee comments suggested that significant disparities in access to resources make the urban agriculture system in New York unequal and constrain the efforts of some farms and gardens. This paper, based on the Five Borough Farm research, examines the resource needs of urban agriculture operations in terms of farm and garden viability and equity among practitioners. It describes the goals, expectations and resource needs of New York City urban agriculture from the perspectives of farmers and gardeners, and from the views of city officials, funders and supporting non-profits. It discusses the need for attention to the political and social structures that create disparity and precariousness to ensure a sustainable and just urban agricultural system, in addition to the financial and technical assistance resources that enable farmers and gardeners to produce food. The paper concludes with recommended strategies to align resource needs and urban agriculture goals and expectations in New York and other cities.

The living soil is the basis for crop production in organic agriculture. Biopores are voids in the soil which were formed by the activity of soil life. The first scientific studies on biopores were published in the 1870s–90s by Victor Hensen who stated that earthworms were opening channels to the subsoil and coating them with humus, thus creating a beneficial environment for root growth. His work was originally widely recognized, but then research on biopores was neglected for many decades and was only revitalized with the rise of ecological concerns in the 1960s. In recent times, biopores have attracted the attention of agronomists with a focus on organic agriculture. New visualization techniques, such as X-ray micro computed tomography, in-situ endoscopy and nuclear magnetic resonance imaging have been applied. Biopores contribute to air transport through the soil, increase water infiltration, reduce water runoff and soil erosion, serve as preferential pathways for root elongation and can facilitate the acquisition of water and nutrients from the subsoil. The relevance of biopores for nutrient acquisition can be pronounced particularly in organic production systems, where crops are more dependent on nutrient acquisition from the solid soil phase than under conditions of conventional agriculture. Organic land-use strategies should aim to increase number, stability and quality of biopores. The biopore density can be increased by the share of dicotyledons in the crop rotation and by cultivating perennial crops with taproot systems. Moreover, density and—in particular—the quality of biopores, e.g., the nutrient contents of pore walls, can be influenced by anecic earthworms which can be promoted by adapted tillage practices.

Intensive fertilizer usage of KCl has been inculcated as a prerequisite for maximizing crop yield and quality, and relies on a soil test for exchangeable K in the plow layer to ensure that soil productivity will not be limited by nutrient depletion. The interpretive value of this soil test was rigorously evaluated by: (1) field sampling to quantify biweekly changes and seasonal trends, (2) characterizing the variability induced by air drying and the dynamic nature of soil K reserves and (3) calculating the K balance in numerous cropping experiments. These evaluations leave no alternative but to question the practical utility of soil K testing because test values cannot account for the highly dynamic interchange between exchangeable and non-exchangeable K, exhibit serious temporal instability with or without air drying and do not differentiate soil K buildup from depletion. The need for routine K fertilization should also be questioned, considering the magnitude and inorganic occurrence of profile reserves, the recycling of K in crop residues and the preferential nature of K uptake. An extensive survey of more than 2100 yield response trials confirmed that KCl fertilization is unlikely to increase crop yield. Contrary to the inculcated perception of KCl as a qualitative commodity, more than 1400 field trials predominately documented a detrimental effect of this fertilizer on the quality of major food, feed and fiber crops, with serious implications for soil productivity and human health.

This paper uses a hypothetical choice experiment to investigate Italian consumer preferences and willingness-to-pay (WTP) for organic, conventional and genetically modified (GM)-fed beef, utilizing intrinsic, search cues (price, color and visible fat) and extrinsic, credence cues. Data are gathered from three different locations in northern, central and southern Italy using a sequential Bayesian approach. Results showed that consumers attach higher value to organic meat. WTP for GM-fed beef, which is not yet sold in Italy, is well below current conventional beef prices. Organic beef is attractive to consumers because it is associated with higher animal welfare standards and environment-related issues (food miles and biodiversity preservation). No differences are found in marginal WTP estimates by gender, age, education, being a parent or having a higher level of knowledge about organic production. Ethical/environmental issues (credence cues) appear to be more relevant in explaining variation in WTP for organic beef than ordinary product characteristics (search cues).

The Western diet is characterized by high meat consumption, which negatively affects the environment and human health. Transitioning toward eating more plant-based products in Western societies has been identified as a key instrument to tackle these problems. However, one potential concern is that radically reducing meat in the current diet might lead to deficiencies in nutritional intake. In this paper, we explore a scenario in which meat consumption in Sweden is reduced by 50% and replaced by domestically grown grain legumes. We quantify and discuss the implications for nutritional intake on population level, consequences for agricultural production systems and environmental performance. The reduction in meat consumption is assumed to come primarily from a decrease in imported meat. We use data representing current Swedish conditions including the Swedish dietary survey, the Swedish food composition database, Statistics Sweden and existing life cycle assessments for different food items. At population level, average daily intake of energy and most macro- and micro-nutrients would be maintained within the Nordic Nutrition Recommendations after the proposed transition (e.g., for protein, fat, zinc, vitamin B12 and total iron). The transition would also provide a considerable increase in dietary fiber and some increase in folate intake, which are currently below the recommended levels. The transition scenario would increase total area of grain legume cultivation from 2.2% (current level) to 3.2% of Swedish arable land and is considered technically feasible. The climate impact of the average Swedish diet would be reduced by 20% and the land use requirement by 23%. There would be a net surplus of approximately 21,500 ha that could be used for bioenergy production, crop production for export, nature conservation, etc. Implementation of this scenario faces challenges, such as lack of suitable varieties for varying conditions, lack of processing facilities to supply functional legume-based ingredients to food industries and low consumer awareness about the benefits of eating grain legumes. In sum, joint efforts from multiple actors are needed to stimulate a decrease in meat consumption and to increase cultivation and use of domestically grown grain legumes.

Soils perform a number of essential functions affecting management goals. Soil functions were assessed by measuring physical, chemical, and biological properties in a regional assessment of conventional (CON) and alternative (ALT) management practices at eight sites within the Great Plains. The results, reported in accompanying papers, provide excellent data for assessing how management practices collectively affect agronomic and environmental soil functions that benefit both farmers and society. Our objective was to use the regional data as an input for two new assessment tools to evaluate their potential and sensitivity for detecting differences (aggradation or degradation) in management systems. The soil management assessment framework (SMAF) and the agro-ecosystem performance assessment tool (AEPAT) were used to score individual soil properties at each location relative to expected conditions based on inherent soil-forming factors and to compute index values that provide an overall assessment of the agronomic and environmental impact of the CON and ALT practices. SMAF index values were positively correlated with grain yield (an agronomic function) and total organic matter (an agronomic and environmental function). They were negatively correlated with soil nitrate concentration at harvest (an indicator of environmental function). There was general agreement between the two assessment tools when used to compare management practices. Users can measure a small number of soil properties and use one of these tools to easily assess the effectiveness of soil management practices. A higher score in either tool identifies more environmentally and agronomically sustainable management. Temporal variability in measured indicators makes dynamic assessments of management practices essential. Water-filled pore space, aggregate stability, particulate organic matter, and microbial biomass were sensitive to management and should be included in studies aimed at improving soil management. Reductions in both tillage and fallow combined with crop rotation has resulted in improved soil function (e.g., nutrient cycling, organic C content, and productivity) throughout the Great Plains.

Technological advances have contributed to impressive yield gains and have greatly altered US agriculture. Selective breeding and directed molecular techniques address biological shortcomings of plants and animals and overcome environmental limitations. Improvements in mechanization, particularly of power sources and harvest equipment, reduce labor requirements and increase productivity and worker safety. Conservation systems, often designed to overcome problems introduced from other technologies, reduce negative impacts on soil and water and improve the environmental sustainability of production systems. Advances in information systems, largely developed in other disciplines and adapted to agriculture, are only beginning to impact US production practices. This paper is the fourth in the series of manuscripts exploring drivers of US agricultural systems. While development of technology is still largely driven by a need to address a problem, adoption is closely linked with other drivers of agricultural systems, most notably social, political and economic. Here, we explore the processes of innovation and adoption of technologies and how they have shaped agriculture. Technologies have increased yield and net output, and have also resulted in decreased control by producers, increased intensification, specialization and complexity of production, greater dependence on non-renewable resources, increased production inputs and hence decreased return, and an enhanced reliance on future technology. Future technologies will need to address emerging issues in land use, decline in work force and societal support of farming, global competition, changing social values in both taste and convenience of food, and increasing concerns for food safety and the environment. The challenge for farmers and researchers is to address these issues and develop technologies that balance the needs of producers with the expectations of society and create economically and environmentally sustainable production systems.

No-tillage and reduced tillage are considered sustainable options of conservation tillage. While US organic farming researchers have focused on no-tillage, European organic farming researchers have concentrated on reduced tillage through the reduction of tillage depth or the application of noninversion tillage practices. Combinations of these two approaches have been implemented by the use of the two-layer plow or the layer cultivator. These innovations often came from farmers, aiming at reducing off-farm inputs such as fuel, and saving costs and labor, while at the same time building up soil fertility. Systematic, documented research on reduced tillage systems in Europe started only 1–2 decades ago, with experiments in Germany, Switzerland and France. While most experiments mimic stockless farms, other experiments include fodder crops such as grass–clover ley and applications of manure and slurry as is typical for mixed farms with animals and crops. Soil organic carbon, microbial activity and soil structure are often improved in the upper soil layer under reduced tillage compared with plowed soils. However, these positive findings were confounded by lower yields in some cases and enhanced weed pressure, except for the two-layer plow. Often it was not possible to determine whether and to what extent yield reduction was due to weed competition or to nitrogen shortage, because of retarded nitrogen mineralization in spring in reduced tillage systems. In systems with manure use, also higher soil fertility measures concomitant with increased yields were reported under reduced tillage. Indeed, it is difficult to gain an overview on research activities dealing with reduced tillage in organic farming in Europe due to dispersed experimental infrastructures and the scarcity of peer-reviewed published literature. To close this knowledge gap a European Network is being established aiming at further developing reduced tillage systems in organic farming, addressing the issue of carbon sequestration and N2O emissions, as well as weed and nutrient management.

Sustainable intensification of smallholder farms in Africa is highly dependent on enhancing biological nitrogen fixation (BNF). Legume diversification of maize-based systems is a core example of sustainable intensification, with the food security of millions of farm families at stake. This study highlights the constraints and opportunities associated with the adoption of legumes by smallholder farmers in southern Africa. A two-part survey of households and farm fields (n=88) was conducted in the Ekwendeni watershed of northern Malawi. Participatory research and education activities have been underway for over a decade in this region, resulting in expanded uptake of a range of legume species as intercrops and in rotation with the staple maize crop. Farmer adoption has occurred to a varying extent for soybean (Glycine max), pigeon pea (Cajanus cajan), velvet bean (Mucuna pruriens) and fish bean (Tephrosia vogelii). Farmers, working with the project valued pigeon pea and other legumes for soil fertility purposes to a greater extent than farmers not working with the project. Legumes were valued for a wide range of purposes beyond soil cover and fertility enhancement, notably for infant nutrition (at least for soybean), insect control, and vegetable and grain production for both market and home consumption. Literature values for BNF in tropical legumes range up to 170 kg N ha−1 for grain and 300 kg N ha−1 for green manure species; however, our field interviews illustrated the extent of constraints imposed by soil properties on smallholder fields in Malawi. The key edaphic constraints observed were very deficient to moderate phosphorus levels (range 4–142, average 33 mg kg−1), and moderately acid soils (range pH 5.1–7.9, average 6.2). The per farm hectarage devoted to legume production relative to maize production was also low (0.15 versus 0.35 ha), a surprising find in an area with demonstrated interest in novel legume species. Further, farmers showed a strong preference for legumes that produced edible grain, regardless of the associated nutrient removal in the harvested grain, and did not sow large areas to legume crops. These farm-level decisions act as constraints to BNF inputs in maize-based smallholder cropping systems. Overall, we found that legume productivity could be enhanced. We documented the value of policies and educational efforts that support farmers gaining access to high-quality seeds, amendments for phosphorus-deficient soils, and promotion of multipurpose legumes that build soils through leafy residues and roots, as well as providing grain for food security and sales.

Local food system potentials were studied in Washington County, Nebraska. As a departure from most studies of locally based systems, farmers were surveyed in addition to consumers for potential participation. Data about the current food system and opinions and preferences for local production, marketing, and purchasing of food were collected using self-administered mail questionnaires. The response rate was 35% for the farmer survey and 37% for the consumer survey. Results indicated that, on the farming side of the food system, conventional corn and soybean production and marketing predominated in Washington County, and farmer interest in producing for local markets was low. Consumers reported a high level of interest in purchasing food from farmers' markets, local grocery stores, local restaurants and directly from farms, and indicated a willingness to pay a price premium for local foods. They also reported that quality and taste were the most important factors in food purchase decisions, but environmentally friendly production and support for local farmers were also important. We conclude that there is tremendous potential for local marketing of farm products, but that there is a large gap between consumer demand and willingness of farmers to meet this demand. Further study of motivations and opinions of farmers is needed, in addition to determining production thresholds for the number of farms and farmers needed to meet local food demands.

Soil biological quality can affect key soil functions that support food production and environmental quality. The objective of this study was to determine the effects of management and time on soil biological quality in contrasting dryland cropping systems at eight locations in the North American Great Plains. Alternative (ALT) cropping systems were characterized by greater cropping intensity (less fallow), more diverse crop sequences, and/or reduced tillage than conventional (CON) cropping systems. Soil biological properties were assessed at depths of 0–7.5, 7.5–15, and 15–30 cm from 1999 to 2002 up to three times per year. Compared to CON, ALT cropping systems had greater microbial biomass and potentially mineralizable N. ALT cropping systems also had greater water stable aggregates in the surface 7.5 cm, but only at four locations. Total glomalin (TG), an organic fraction produced by fungi associated with aggregate stability, differed only at one location (Mandan), where the ALT cropping system had 27% more TG than the CON cropping system. Fatty acid methyl ester (FAME) profiles were highly location dependent, but total extracted FAME tended to be higher in ALT cropping systems. Soil biological properties fluctuated over time at all locations, possibly in response to weather, apparent changes in soil condition at sampling, and the presence or absence of fallow and/or legumes in rotation. Consequently, preplant and post-harvest sampling, when weather and soil conditions are most stable, is recommended for comparison of soil biological properties among management practices. Overall, ALT cropping systems enhanced soil function through: (1) improved retention and cycling of nutrients and (2) maintenance of biodiversity and habitat, implying improved agro-ecosystem performance over time.

A large body of research has explored opportunities to mitigate climate change in agricultural systems; however, less research has explored opportunities across the food system. Here we expand the existing research with a review of potential mitigation opportunities across the entire food system, including in pre-production, production, processing, transport, consumption and loss and waste. We detail and synthesize recent research on the topic, and explore the applicability of different climate mitigation strategies in varying country contexts with different economic and agricultural systems. Further, we highlight some potential adaptation co-benefits of food system mitigation strategies and explore the potential implications of such strategies on food systems as a whole. We suggest that a food systems research approach is greatly needed to capture such potential synergies, and highlight key areas of additional research including a greater focus on low- and middle-income countries in particular. We conclude by discussing the policy and finance opportunities needed to advance mitigation strategies in food systems.

Agricultural diversification has been identified as one of the mechanisms for managing household food security and poverty in developing economies, because it can spread the risk among multiple production enterprises and provide a range of food items for the households. By examining the integrated farming systems of 608 smallholders in Ghana, this paper presents empirical evidence to support the development of effective strategies that enhance diversified farming systems. The estimated mean diversification indices were 0.45, 0.32 and 0.59 for crop, livestock and crop–livestock diversification systems, respectively. Using the Cragg two-step regression model, this paper shows that the decision to diversify and the extent of diversification are distinct decisions affected by different sets of factors. Likewise, the effect of these factors also varied across the three categories of diversification examined. Careful consideration needs to be given to the selection of factors and the methods for examining the diversification process to avoid confounding recommendations. The findings underscore the importance of households’ access to tillage equipment, fertilizers, credit and market information in encouraging farmers to diversify.

In Ghana, studies on the use of organic materials to increase soil productivity have focused on crop-residue management, use of green and animal manures, and legume cover cropping. Few studies have assessed the use of human waste for agriculture, even though this is widely practiced by farmers in the northern part of the country. This study was carried out to investigate the stakeholders in the use of faecal sludge (FS) for crop production in Tamale and Bolgatanga municipalities in the guinea savanna agroecological zone of Ghana. The aim was to determine the driving factors, constraints and potentials for this practice. Field survey and focus group discussions were carried out among 90 farmers who use FS, and officials of the Municipal Sanitation Unit were interviewed. Sixty-four percent of farmers interviewed used FS as a cost-effective way to improve soil fertility and increase yields of maize and sorghum. Sludge is discharged by spreading it on the soil surface, or it is stored and dried in pits during the dry season and incorporated into the soil at the onset of the rainy season. The high temperatures of the savanna climate and this long period of drying allow sludge to be handled easily. Although this treatment is perceived to reduce the number of pathogens in dried sludge, 22% of farmers complained of itching feet and foot rot after working with FS, which is done without wearing protective foot covering. This constraint is coupled with the foul smell, transport problem and public mockery associated with the use of human waste for agriculture. In spite of these problems, there is competition for FS among farmers, due to benefits derived from its use. Further investigation is required to ascertain the causes of itching feet and foot rot, and there is a need for education on proper handling and appropriate hygiene practices when working with FS. Information regarding optimal FS application rates is also required.

No-tillage (NT) and reduced tillage (RT) systems are well-known management tools for reducing soil erosion and improving soil fertility. NT and RT may improve the environmental and economic performance of organic farming, but they are still not common practice among organic farmers. This paper presents the effects of tillage [RT versus conventional tillage (CT)], fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators such as soil organic carbon (Corg), microbial biomass and microbial activity, soil nutrients and nutrient budgets in an organic farming system during the first six-year crop rotation period of a long-term experiment on a clayey soil in a temperate climate. RT caused stratification of soil organic carbon (Corg), microbial properties and soil nutrients in the soil profile. Under RT, Corg in the 0–10 cm soil layer increased from 2.19 to 2.61% (w/w) from 2002 to 2008, whereas it remained constant under CT. In both tillage treatments, Corg remained constant in the 10–20 cm soil depth. Microbial biomass C increased by 37% under RT in the 0–10 cm soil depth and microbial activity [dehydrogenase activity (DHA)] was enhanced by 57%. Soil microbial biomass C and DHA in the 10–20 cm soil depth were also higher under RT (+10 and +17%, respectively). Soluble soil P and K were 72 and 40%, respectively, higher in 0–10 cm soil depth under RT when compared with CT. Fertilization showed no effects on the measured soil properties. Biodynamic preparations increased solely the Cmic-to-Nmic (soil microbial biomass C to soil microbial biomass N) ratio by 7% in the 0–10 cm soil depth. Nutrient budgets for P were balanced in all treatments, but N and K exports were higher under RT compared to CT. We conclude that RT is a suitable method for increasing indicators of soil fertility in organic farming systems. The combined effects of RT and an organic farming system with a diverse, ley-based crop rotation and organic fertilization merit further promotion and it may be considered for supporting actions by the agricultural policy schemes.

One of the key questions of primary importance to global agriculture and food security is how to optimize sustainable intensification to balance competing demands on land for food and energy production, while ensuring the provision of ecosystem services and maintaining or increasing yields. Integrating trees and agriculture through agroforestry has been attracting increasing interest as an agroecological approach to sustainable intensification. Trees have traditionally been important elements of temperate agricultural systems around the world, but there has been increasing separation of agriculture, forestry and nature over the past few decades. This paper discusses what we can learn from traditional agroforestry systems to help develop modern systems that integrate ecological farming and agroecological advances to achieve sustainable intensification. We also discuss the existing barriers to wider adoption of agroforestry, and identify how these barriers can be overcome to promote agroforestry as a mainstream land-use system.

Cocoa-based small-scale agriculture is the most important source of income for most farming families in the region of Alto Beni in the sub-humid foothills of the Andes. Cocoa is grown in cultivation systems of varying ecological complexity. The plantations are highly susceptible to climate change impacts. Local cocoa producers mention heat waves, droughts, floods and plant diseases as the main impacts affecting plants and working conditions, and they associate these impacts with global climate change. From a sustainable regional development point of view, cocoa farms need to become more resilient in order to cope with the climate change related effects that are putting cocoa-based livelihoods at risk. This study assesses agroecosystem resilience under three different cocoa cultivation systems (successional agroforestry, simple agroforestry and common practice monocultures). In a first step, farmers’ perceptions of climate change impacts were assessed and eight indicators of agroecological resilience were derived in a transdisciplinary process (focus groups and workshop) based on farmers’ and scientists’ knowledge. These indicators (soil organic matter, depth of Ah horizon, soil bulk density, tree species diversity, crop varieties diversity, ant species diversity, cocoa yields and infestation of cocoa trees with Moniliophthora perniciosa) were then surveyed on 15 cocoa farms and compared for the three different cultivation systems. Parts of the socio-economic aspects of resilience were covered by evaluating the role of cocoa cooperatives and organic certification in transitioning to more resilient cocoa farms (interviews with 15 cocoa farmers combined with five expert interviews). Agroecosystem resilience was higher under the two agroforestry systems than under common practice monoculture, especially under successional agroforestry. Both agroforestry systems achieved higher cocoa yields than common practice monoculture due to agroforestry farmers’ enhanced knowledge regarding cocoa cultivation. Knowledge sharing was promoted by local organizations facilitating organic certification. These organizations were thus found to enhance the social process of farmers’ integration into cooperatives and their reorientation toward organic principles and diversified agroforestry.

Organic agriculture has the potential to provide improved livelihood opportunities, increased income and social benefits for resource-poor small-scale farmers. It has thus become a popular strategy for economic development and poverty reduction in many areas of the global south. However, there has been limited empirical research regarding the actual benefits of certified organic production, particularly when organic is combined with fair trade certification, and for small-scale farmers who are not engaged in coffee or banana production. Further research is needed to demonstrate experiences of farmers under diverse socioeconomic conditions, organizational contexts and degrees of market access. To address these gaps, two surveys of certified organic and fair trade tea producers in China and Sri Lanka were undertaken to investigate the contributions of organic crops to the household economy. In both cases, organic production required lower investment in terms of external inputs but a higher input of farmers’ labor. The price premium received by farmers for the organic tea compensated for the extra labor input and lower yield, resulting in a net profit. However, given the relatively small plots of tea gardens of each household, organic production could not fully provide for the households’ livelihood. Non-farm income dominated the total income of the households across the study cases, despite the earnings from organic farming. In both sites, market-oriented organic tea projects have created more options for paid work locally, which benefits women of reproductive age. Social benefits of organic farming were also reported. Pursuing fair trade certification on top of organic production facilitated farmer organizing, training and community development. Organic agriculture and fair trade certification offer important prospects to improve the livelihoods of small-scale farmers in other, less favored areas of Asia. These forms of certified production could provide economic and social benefits in instances where farm income is the main source of household income.

Cropping systems that rely on renewable energy and resources and are based on ecological principles could be more stable and productive into the future than current monoculture systems with serious unintended environmental consequences such as soil erosion and water pollution. In nonagricultural systems, communities with higher species diversity have higher productivity and provide other ecosystem services. However, communities of well-adapted crop species selected for biomass production may respond differently to increasing diversity. Diversity effects may be due to complementarity among species (complementary resource use and facilitative interactions) or positive selection effects (e.g., species with higher productivity dominate the mixture), and these effects may change over time or across environments. Our goal was to identify the ecological mechanisms causing diversity effects in a biodiversity experiment using agriculturally relevant species, and evaluate the implications for the design of sustainable cropping systems. We seeded seven perennial forage species in a replicated field experiment at two locations in Iowa, USA, and evaluated biomass productivity of monocultures and two- to six-species mixtures over 3 years after the establishment year under management systems of contrasting intensity: one or three harvests per year. Productivity increased with seeded species richness in all environments, and the positive relationship did not change over time. Polyculture overyielding was due to complementarity among species in the community rather than to selection effects of individual species. Complementarity increased as a log-linear function of species richness in all environments, and this trend was consistent across years. Legume–grass facilitation may explain much of this complementarity effect. Although individual species with high biomass production had a major effect on productivity of mixtures, the species producing the highest biomass in monoculture changed over the years in most environments. Furthermore, transgressive overyielding was observed and was more prevalent in later years, in some environments. We conclude that choosing a single well-adapted species for maximizing productivity may not be the best alternative over the long term and that high levels of species diversity should be included in the design of productive and ecologically sound agricultural systems.

The influence of farm management practices on ground-dwelling natural enemy communities and predation of insects and weed seeds was investigated over the first 2 years of the transition from conventional to organic production. Three transition strategies were selected that differed in their management and input intensities, and were characteristic of pasture/ley systems (low intensity), cash grain systems (intermediate intensity), and vegetable production (high intensity). Beneficial arthropods (insectivores and granivores) were monitored using pitfall (arthropod activity) and quadrat (arthropod density) samples. The frequency of predation on restrained larvae of Galleria mellonella and the species observed feeding were recorded. Weekly removal rates of weed seeds representative of abundant species at our site were monitored over a 3-week period during fall. Management intensity affected the activity and abundance of biological control agents. In year two of the transition, biological control agent densities were higher in the low-intensity treatment than in the other two treatments, but activity of insectivores and granivores was reduced in this treatment relative to the higher intensity systems. The patterns in the abundances of biological control agents may be explained by habitat stability within the different cropping systems. Quadrat samples were strongly correlated with the insectivory index, although pitfall samples were not. Insectivory rates were highest (>80% of G. mellonella larvae) in the low-intensity treatment. Predation patterns over a 17-h period differed substantially among the management treatments, indicating behaviorally distinct insectivore communities. Seed removal was also highest in the low-intensity treatment. We conclude that low-intensity cropping systems are most favorable to the abundance and function of beneficial ground-dwelling arthropod communities (insectivores and granivores) during the transition process.