Considering global trends such as climate change and resource scarcity, a major challenge of future cities will be to reduce urban footprints. Moreover, cities have to become or remain livable for their inhabitants and offer social and economic opportunities. Thus, reconnecting food production and cities offers promising potential. The diffusion of urban farming reflects a rising awareness of how food and farming can shape our cities. A growing number of urban farming projects exist in and on urban buildings, including open rooftop farms, rooftop greenhouses and indoor farming. These projects are characterized by the non-use of land or acreage for farming activities. We use the term ‘Zero-Acreage Farming’ (ZFarming) to represent these farms. The objective of this paper is to: (1) illustrate and systemize present practices of ZFarming and (2) discuss specific novelties of ZFarming in the wider context of urban agriculture. We analyzed 73 ZFarms in cities of North America, Asia, Australia and Europe using a set of criteria, and developed a typology of ZFarming, complemented by in-depth interviews with pioneers in rooftop farming in New York. The results illustrate that ZFarming generates innovative practices that may contribute to a sustainable urban agriculture. Besides growing food, it produces a range of non-food and non-market goods. It involves new opportunities for resource efficiency, new farming technologies, specific implementation processes and networks, new patterns of food supply and new urban spaces.

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.

Synergy between dry pea and corn can reduce the density of corn needed for optimum yield. Lower crop density may accrue an additional benefit, as after-harvest residues of corn lying on the soil surface can reduce yield of crops planted the next year. This study evaluated impact of corn residue levels on growth and yield of three cool-season crops in no-till. Corn was grown at two densities, 52,000 and 73,000 plants ha−1, leading to after-harvest residue levels designated as low and high residue. Residue quantity on the soil surface differed by 21%. Controls were included for each residue level by burying residue with tillage. Spring wheat, dry pea and red clover were planted the following year. Grain yield of spring wheat and dry pea and forage yield of red clover were reduced 13–33% by residue on the soil surface. However, yield of cool-season crops were 10–18% higher in the low-residue treatment compared with high residue. Furthermore, yield loss because of weed interference in spring wheat and red clover was greater with high residue. Of the three crops, spring wheat was the least affected by corn residue on the soil surface. One contributing factor to lower yield with high residue was reduced crop seedling establishment. Producers may be able to reduce the negative impact of corn residue on following crops in no-till systems by using synergistic crop sequences in the rotation.

Organic no-till (NT) management strategies generally employ high-residue cover crops that act as weed-suppressing mulch. In temperate, humid regions such as the mid-Atlantic USA, high-residue winter cover crops can hinder early spring field work and immobilize nutrients for cash crops. This makes the integration of cover crops into rotations difficult for farmers, who traditionally rely on tillage to prepare seedbeds for early spring vegetables. Our objectives were to address two separate but related goals of reducing tillage and integrating winter cover crops into early spring vegetable rotations by investigating the feasibility of NT seeding spinach (Spinacia oleracea L.), an early spring vegetable, into winterkilled cover crops. We conducted a four site-year field study in the Piedmont and Coastal Plain regions of Maryland, USA, comparing seedbed conditions and spinach performance after forage radish (FR) (Raphanus sativus L.), a low-residue, winterkilled cover crop, spring oat (Avena sativa L.), the traditional winterkilled cover crop in the area, a mixture of radish and oat, and a no cover crop (NC) treatment. NT seeded spinach after FR had higher yields than all other cover crop and tillage treatments in one site year and was equal to the highest yielding treatments in two site years. Yield for NT spinach after FR was as high as 19 Mg ha−1 fresh weight, whereas the highest yield for spinach seeded into a rototilled seedbed after NC was 10 Mg ha−1. NT seeding spring spinach after a winterkilled radish cover crop is feasible and provides an alternative to both high-residue cover crops and spring tillage.

Although interest in integrating agriculture into the urban landscape in the USA is increasing rapidly, there is a shortage of guidance for agricultural production in this context as well as a unique set of significant biophysical constraints. A common constraint is not being able to grow directly in the soil, making raised-bed gardening a necessity. Subirrigated planters (SIPs) are a style of raised bed with a subsoil reservoir that provides aeration and allows growers to irrigate below the soil where water is pulled up via capillary action. This bed design has vocal advocates; anecdotally, growers find them to be high yielding, water efficient and easier to maintain than standard raised beds. Given their apparent promise, there is interest in promoting SIPs and in utilizing them in larger-scale urban gardening operations but no rigorous tests compare these beds relative to standard raised beds. At one location and for one season, we compared yields for three crops: cayenne pepper (Capsicum annuum), sungold cherry tomatoes (Solanum lycopersicum) and lacinato kale (Brassica oleracea), crop quality and labor input for two styles of SIPs, as well as a sack garden, a variation of a SIP that does not require lightweight soil, with two conventional raised beds (one with a compost and topsoil mix and one with the soilless growing medium ideal for container gardening). Results from our first year of data indicate that both the SIP beds and the conventional beds with the soilless growing medium were more productive overall than conventional raised beds with topsoil and compost (P<0.01). Tomato production in the SIP without the root barrier was greater than both the conventional bed with the compost and topsoil mix (P<0.01) and the conventional bed with the soilless growing medium (P<0.05). The majority of the higher-cost beds had a positive revenue stream in the first summer season; given these results, investing in SIPs or in soil appropriate for raised beds appears to be worth the higher initial cost.

A participatory plant breeding (PPB) program involving the French farmers' association ‘Réseau Semences Paysannes’ and the French National Agricultural Research Institute (INRA) at Le Moulon was initiated in 2005. In the process of designing the breeding scheme, we evaluated the impact of farmer selection at an early stage (F2) on bread wheat cross progeny populations. The objectives were to characterize the effect of farmer selection, to evaluate the impact of farmer selection on intra-varietal diversity, to provide farmers with relevant information that they can use to improve their selection practices. Early selection was found efficient for some traits and for some of the 35 F2-derived F3 families. For traits of interest such as thousand kernel weight or grain weight per spike, when the response was significant, it was always positive. For most of the traits studied, the among-family genetic variance increased after selection while the average within-family genetic variance decreased. This study provides the first quantitative results for this PPB program and information that will help optimize it in the future.

Urban agriculture, a current trend in many US cities, is purported to bring enhanced food security, reduction of food waste, community building, open green space in cities and higher property values. However, the literature lacks an understanding of whether urban farming has extended beyond a compelling concept into the practice of farming in the city and peri-urban areas. The exact definition of an urban farm is challenging, since many urban farms have a primary mission of supporting social goals rather than providing food. Use of the USDA definition of farm omits many self-identified urban farms, but the most consistent measure of agriculture is the Census of Agriculture. Using census data, this paper finds that urban farms are smaller than the typical farm, and while the amount of urban and peri-urban farmland declined between 2002 and 2007, the total number of farms increased. Growth in farmland is positively related to land values, suggesting that increases in urban farmland are more likely to take place in population dense, land scarce areas. Spatial analysis of urban and peri-urban farms in the Northeast finds fewer clusters of farms in areas with high land costs. In the most populous Northeastern cities, the farms are more likely to be located in the peri-urban area than in the urban core. Urban farms in the Northeast were more likely to produce vegetables, eggs and goats. Significant levels of vegetable farm clusters were detected surrounding Providence, Boston and Hartford Metropolitan Statistical Areas, which are regions that had no significant level of clustering of total farms. Future analysis, incorporating data from the 2012 census, should provide insight into whether local policy changes have resulted in growth in urban farms and farmland.

A study was conducted on the spatial dimension of crop diversity in Jutpani Village Development Committee (VDC) in central Nepal. Many crop diversity studies focus only on home gardens, but this study aimed to investigate the crop diversity among different production systems, and the factors affecting variations in the crop diversity on a household level. A survey of inter-household variation in cultivated crop diversity in different land-use types among 134 households indicates that 96 different types of annual crops, perennial crops and fruit trees are cultivated. Individual farms cultivated an average of 26 different crops, with this number ranging from 11 to 45. Crops were used as food by the households and, based on their adaptive characters, they were grown either in home gardens or in upland, Tandikhet and lowland. Research showed that home gardens have the highest crop diversity (a total of 78 different crops grown) compared to upland, Tandikhet and lowland. Statistical analysis to understand the factors affecting the variation in crop diversity in the household level showed that the total number of crops grown (crop diversity) on a farm is significantly higher (P<0.001) in the Indo-Aryan ethnic group compared to the Tibeto-Burman group. Farmers with three different production domains maintained higher (P<0.001) crop diversity compared to having only one or two production domains. Poor farmers with small land holdings were associated with higher crop diversity (P<0.001) compared to rich farmers with large land holdings. Therefore, planning for agrobiodiversity management should focus on the production systems, and social and economic settings within the farming community.

Although discussion of the role of urban agriculture in developing nations has occurred over the past decade, dialogue relating to urban agriculture in industrialized countries, including the United States (US) has only recently begun to attract significant attention. The unique factors that influence urban agriculture, including limited and non-traditional land access, use of reclaimed soils and alternative growing mediums, local legal and political environments, social and community-based missions, and involvement of non-traditional farmers, create a production system distinct from rural agricultural enterprises. In many cases, specific local environmental and external factors drive urban farms to develop unique innovations for space-intensive production systems, often creating a dominant paradigm for urban farming for a given location. Furthermore, non-production-related organizational goals are often the primary focus of urban agricultural operations, with the food production becoming a secondary objective. In order to address this information gap regarding the status of urban agriculture in the US, our project, centered at the University of Wisconsin-Madison, gathered data through site visits to and interviews of organizations in seven cities, examining how structural and strategic food system factors shape urban agricultural efforts. A broad range of operations are considered, including diverse business and production models based on both commercial and community-based management strategies and production in parking and vacant lots, warehouses, public land and peri-urban locations. Based on these observations, the unique innovations in space-intensive agricultural production that have arisen in response to urban food system factors are discussed. We conclude with an assessment of the most significant challenges continuing to face urban agriculture.

Throughout the USA, urban agriculture is expanding as a manifestation of an emerging American food politics. Through a case study of Brooklyn, New York, I used mixed qualitative research methods to investigate the political possibilities of urban agriculture for fostering food justice. My findings build on the existing alternative food network (AFN) literature by indicating that problematic contradictions rooted in the neoliberalization of urban agriculture limit the transformative possibilities of farming the city as currently practiced in Brooklyn. I suggest that longstanding agrarian questions—concerns over the relationship between agriculture and capitalism and the politics of small-scale producers—are informative for critical interrogation of urban agriculture as a politicization of food.

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.