In this prospective article, an international consortium coordinated by researchers from the University of Copenhagen examines the prospects for using the “third dimension” of agricultural land, i.e. the possibility, without resorting to new land, of increasing the volume of soil exploited by the root system of crops, thereby increasing the resource base available for agricultural production while minimizing the undesirable externalities frequently associated with current agroecosystems.

In response to the challenge of growing food demand in a context of global climate change and shrinking land availability, few options exist to sustainably intensify agricultural production. Among these options, a largely neglected aspect consists of increasing the use of deep soil resources through the selection of new genotypes and the development of cropping systems whose effective rooting depth is significantly greater than that of the systems current. This article thus explores the prospects for extending the “3^rd dimension’’ of agricultural land, i.e. the possibility, without resorting to new land, of increasing the volume of soil exploited by crops’ root system, thereby increasing the resource base available for agricultural production while minimizing losses of external input. More particularly, we thus examine: (i) the modalities through which deeper rooted crops could be obtained, (ii) the potential impact of deep rooting on the acquisition of usually untapped resources, (iii) the possible effects of a deeper-rooted agriculture on soil fertility, ecology and C storage. We conclude that current knowledge of deep roots of crops and wild plants clearly indicates that there is a potential to extend the third dimension of agricultural land and that improvement in the utilization of deeper soil resources could be achieved in various ways. It is clear that the most significant improvements may be reached by relying more on inherently deep rooted species, which could result from a shift from annual to perennial crop species. However, improving deep rooting of current crop species is more likely to bring significant improvements in the shorter term.

Key-words : sustainable intensification; deep roots; perennial crops