Livestock production on grasslands associated with cereal and vegetable cropping on arable lands was the historical basis of the agricultural revolution that helped shape western civilization during the 16th century in Europe. The process of recycling organic matter and nutrients from livestock feces to cropland and through various fodders consumed by livestock created a relatively closed loop that sustained—and sometimes improved—soil fertility. However, with the advancement of the industrial revolution, particularly in the mid-20th century with widespread use of synthetic fertilizers, reliance on mechanical power for field operations, and improved buildings and equipment for livestock wintering, feeding and milking, interest soon waned for such mixed farming systems. Livestock systems tended to become concentrated to capture economy of scale. Cropping systems became narrowly specialized to capture market opportunities and reduce labor requirements. As a result of these rapid technological changes, livestock production and arable cropping systems became increasingly separated onto different farms—and even in different regions—leading to unusual uniformity of regional agricultural landscapes. Intensification of these two types of specialized agricultural systems has led to unacceptable deterioration of the environment due to: (i) excessive concentration of nutrients and pathogens in livestock production systems; and (ii) loss of natural biodiversity and excessive simplification of ecosystem processes with uniform land use in arable cropping systems.

Facing the necessity to increase agricultural production for a burgeoning human population, it will not be socially and economically acceptable to advocate for a decrease in agricultural productivity just to minimize negative environmental consequences of specialized agricultural systemsReference Foley, Ramankutty, Brauman, Cassidy, Gerber, Johnston, Mueller, O'Connell, Ray, West, Balzer, Bennett, Carpenter, Hill, Monfreda, Polasky, Rockström, Sheehan, Siebert, Tilman and Zaks¹. Our hypothesis is that by maintaining or enhancing diversity of agricultural systems—at all levels of organization, i.e., the field, the farm, the landscape and the region—it will be possible to reconcile the seemingly dichotomous goals for achieving high quantity and quality of food production and improve environmental quality. Agricultural diversity at the field, farm, landscape and regional levels may need to be simply maintained in less developed regions and improved in various ways and scales in more developed regions².

The high capacity of grassland ecosystems for feeding domestic herbivores—and for producing essential ecosystem services, such as CO₂ sequestration, soil fertility, water quality, biodiversity—when associated spatially and temporally with arable cropping systems is an essential foundation for integrated crop–livestock systems (ICLS), either within single farms or among specialized farms within a region. Analysis of ICLS at farm or regional levels requires studies on processes governing biogeochemical cycles, environmental fluxes and dynamics of biodiversity in interaction with management options. In this way, it will be possible to answer the question ‘What if … ?’ and to evaluate the impacts of systems both in term of production and ecosystem services. Development and adoption of ICLS by farmers implies the need for entrepreneurial evaluation of system types and analyses of socio-economic constraints to answer the question ‘What is it necessary for … ?’ Hence, advancement of modern ICLS as a concept to promote agricultural productivity and achieve environmental quality will require a multidisciplinary approach linking strongly process-based and system-management analyses from local to regional scales.

An international effort to move ICLS forward as an agricultural sustainability concept has been gaining ground through a series of symposia—the first of which was held in Curitiba, Brazil in August 2007 and the second of which was in Porto Alegre, Brazil in October 2012. The first symposium was organized by the Federal University of Parana (UFPR) and was divided into invited oral sessions focused on: (i) the fundamental concept, (ii) the crop component, (iii) the soil component, (iv) the animal component and (v) a worldwide context. Many volunteered posters were also presented, primarily by researchers in Brazil and neighboring Latin American countries, and a tour of research stations and farms in Parana was organized. The second symposium was organized by the Federal University of Rio Grande do Sul (UFRGS) organized into themes of: (i) introduction and summaries of ICLS in different regions of the world, (ii) ecological and environmental processes from fields to landscapes, (iii) issues and tools for integration between livestock and arable cropping systems, (iv) long-term experimental platforms for quantification and prediction of impacts from land use and climate change, (v) management and policies for ICLS at farm to regional levels and (vi) summary comments. Invited speakers came from nine countries, many posters were presented from research being conducted primarily in South America, and a mid-week tour of farms using ICLS principles was organized. From the enthusiasm and success of the first two symposia, a third symposium is already being planned for 2015 in Columbia.

Publication from the first symposium was as proceedings papers on CD-ROM. From the 2nd International Symposium on Integrated Crop-Livestock Systems, we wanted to reach a broader scientific community, and therefore, organized a series of three special issues in international journals under the following general themes:

1. i. Environmental outcomes (special issue in Agriculture, Ecosystems and Environment);

2. ii. Production responses (special section in European Journal of Agronomy);

3. iii. Social aspects (special section in Renewable Agriculture and Food Systems).

Five papers from the symposium in Porto Alegre are presented in this issue and summarized in the following. Coquil et al. outlined an approach aimed at understanding the transition to autonomy in mixed crop–livestock systems with progressive mobilization of external inputs and acquisition of experience through trials and problem solving. New ways of thinking and acting by farmers were developed by mobilizing various resources, some of them shared: introducing rotational grazing, diversifying the winter diets of the dairy cows and diversifying the composition of the sown pastures. In spite of sharing resources, operation of many farms is still unique; requiring reliance on various internal resources available on the farm.

Torre and Darly analyzed the role of territorial governance, which is the engine of local development, and the tool for better local compromises, involving periods of opposition and streams of negotiation to help overcome conflicts and tensions at the interfaces of rural, natural and peri-urban areas. This evaluation of conflicts in land use within a peri-urban context was based on studies in the Greater Paris region, and a case study on the use of agricultural soils on the urban fringe.

Poccard-Chapuis et al. used historical changes in Southern Mali, Brazilian Cerrados and the Amazon frontier to illustrate the potential for greater crop–livestock integration in the tropical region. Spatial and social arrangements of integrated systems were characterized within a landscape context. This approach provided a retrospective view to discuss four key points about the future of integrated systems in the tropics: (i) importance of landscape structure for design and adaptation of the integrated systems; (ii) key role of local institutions in supporting such integrated systems; (iii) trade-offs between external and internal resources; and (iv) role of nitrogen to improve system efficiency.

Oliveira et al. determined the economic responses of different grazing intensity levels of winter pastures in a long-term experiment in Rio Grande do Sul, Brazil. Soybean yield was not affected by grazing intensity, but cattle's average daily gain declined with increasing grazing intensity, cattle gain per hectare increased with increasing grazing intensity and gross margin was optimized when grazing intensity was moderate (i.e., sward height was between 10 and 20 cm). The ICLS improved economic performance compared with grain cropping only.

Duru et al. proposed a conceptual framework based on plant functional traits to better describe interactions of diverse agricultural components on community structure responses to disturbances and resources, as well as to define their effects on ecosystem functioning and services. The approach was used in grassland-based livestock farms in France to predict forage provision and non-market services according to environmental and management drivers. Environmental gradients were weakly predicted, while soil microbial functional traits need to be developed. An adaptive management approach was suggested rather than relying on a prescriptive scheme.

We thank the sponsors of the 2nd International Symposium on Integrated Crop-Livestock Systems: Ministry of Education (http://www.mec.gov.br/), Ministry of Agriculture, Livestock and Food Supply (http://www.agricultura.gov.br/), Government of Brazil (http://www.brasil.gov.br/), Rio Grande Institute of Rice (http://www.irga.rs.gov.br/), Secretariat of Agriculture, Livestock and Agribusiness (http://www.agricultura.rs.gov.br/), Program to Compete Together (Juntos Para Competir), FARSUL (http://www.farsul.org.br/), SENAR (http://www.canaldoprodutor.com.br/internacional/senar), SEBRAE (http://www.sebrae.com.br/), CAPES (http://www.capes.gov.br/), CNPq (http://www.cnpq.br/), Agrisus (http://www.agrisus.org.br/), FAO (http://www.fao.org/), USDA-Agricultural Research Service (http://www.ars.usda.gov/), CIRAD (http://www.cirad.fr/), MARFRIG (http://www.marfrig.com.br/), INRA (http://www.inra.fr/), Federal University of Parana (http://www.ufpr.br/) and Federal University of Rio Grande do Sul (http://www.ufrgs.br/).

We also thank the participants of the symposium for bringing up their ideas for discussion. We thank the authors of these papers for working diligently to assemble high-quality contributions and we thank the many reviewers who devoted their time and expertise to note deficiencies in presentations and to suggest improvements. We hope that this set of special issues is the beginning of fruitful research and development among scientific colleagues and with industry partners to improve agriculture for the benefit of humankind.