Tillage and soil ecology: Partners for sustainable agriculture

Much of the biodiversity of agroecosystems lies in the soil. The functions performed by soil biota have major direct and indirect effects on crop growth and quality, soil and residue-borne pests, diseases incidence, the quality of nutrient cycling and water transfer, and, thus, on the sustainability of crop management systems. Farmers use tillage, consciously or inadvertently, to manage soil biodiversity. Given the importance of soil biota, one of the key challenges in tillage research is understanding and predicting the effects of tillage on soil ecology, not only for assessments of the impact of tillage on soil organisms and functions, but also for the design of tillage systems to make the best use of soil biodiversity, particularly for crop protection. In this paper, we first address the complexity of soil ecosystems, the descriptions of which vary between studies, in terms of the size of organisms, the structure of food webs and functions. We then examine the impact of tillage on various groups of soil biota, outlining, through examples, the crucial effects of tillage on population dynamics and species diversity. Finally, we tackle the question of the design of tillage systems to enhance biological control in cultivated fields. Identification of the optimal tillage system requires a global consideration of soil management, rather than an analysis focusing on tillage alone, taking into account soil ecology. Organic residue management, the prevention of compaction, crop rotation and the timing of cultivation must all be considered together, taking into account their impact on pest populations and on the natural enemies of pests and ecosystem engineers. This approach requires more detailed research and careful experimental design than traditional comparisons of conventional and reduced tillage systems. We propose the development of population modeling in cultivated fields, as the available ecological models rarely include parameters linked to the soil management system.