This thesis combines experimental work on heterogeneous crop populations (HP) and species mixtures (SM) with a social scientific and participatory approach. Chapter 1 introduces crop communities as a concept to integrate multiple approaches to diversify farming systems. HPs provide intraspecific and SM interspecific diversity in crop communities. A key challenge for the genetic improvement of HPs, especially for root traits is to combine effective selection to improve HPs while maintaining intraspecific diversity. ...