Closed and Semi-closed Systems in Agriculture

Agriculture is the endeavor that served for thousands of years as a cradle for human civilizations. However, it may also act as a brake. Indeed, climate change is increasingly constraining the available pool of land and water resources. The current agriculture has become highly dependent on a flow of chemical input from pesticide and insecticide industry, itself remaining as a source of a problem both for human and global health. Protected agriculture is among the answers to the looming crisis in water and climate change. We reviewed the current systems of protected agriculture as they migrate from 'open' to 'semi-closed' and 'fully-closed' systems of plant production from the sustainability point of view. Not a long time ago, the problems related to the soilborne diseases acted as a trigger for a remarkable shift to use of simpler growth media. Now the plant factories and similar approaches are applying the state of the art techniques of fertilization and lighting to deliver a clean product; but still they remain dependent on a large flow of external inputs, as well as an intensive monitoring and management platform. On the other side are the emerging agroecological perspectives that are in support of a concept of disease management based on higher biodiversity in the plant culture media and the surrounding environment. Such systems try to address the pest and disease issue by use of a much more complex media, and a high biodiversity in the production environment that could reduce the management intensity and thus reduce the cost. As these systems are more self-sufficient, they have the ability to create more 'closed' systems of production. However, there is no a consensus in the scientific society in this regard, therefore a clear dilemma between a selection of simple or complex growing media exists, which determines the technologies to be developed and used. The same problem persists in the studies of bio-regenerative life support system where sophisticated designs for plant production units destined for potential use in outer space are attempted. This review tries to shed light on the future image of both approaches from the sustainability outlook based on the degree of inherent self-sufficiency or recyclability of inputs, which could be further interpreted as the level of 'closedness' of the systems.