Towards crop communities: exploring wheat diversity, wheat-pea species mixtures and farming practice in a food system context

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. In Chapter 2 a hydroponic system was tested for its suitability to non-destructively assess root traits on a population level in order to achieve genetic gain and maintain diversity. The hydroponic selection for long seminal roots led to an increase of seminal root length by 1.6 cm (11.6%) in a single generation with a heritability of 0.59, thus providing a method for population level selection of root traits. Chapter three reports on a multifunctional evaluation of SM. Seven wheat HP and eight line cultivars from central Europe and Hungary were tested as pure stands (100% sowing density) and in SM with a winter pea cultivar with 70% wheat and 50% pea sowing density under organic conditions. SM increased cereal grain quality, weed suppression, resource use efficiency, yield gain and reduced lodging relative to pea pure stands, indicating multifunctionality. Effects were greater in 2018/19, characterized by dry and nutrient poor conditions than in 2019/20 when nutrient levels were higher. Wheat entries varied considerably for protein content and yield in both, SM and monocultures. Under higher nutrient availability, entry-based variation was reduced in both systems and peas were suppressed. HPs were more stable across environments for yield and protein than line cultivars. Depending on year, different line cultivars outperformed the HPs for either protein content or yield. Results have to be interpreted with caution due to limited number of environments. Chapter 4 reports on a qualitative social scientific investigation. Socially shared models of SM adoption were built from interview data with farmers to identify the main factors for SM adoption: (1) perceived relative mixture performance, (2) suitability within the farm context, (3) challenges and opportunities in mixture management due to increased complexity, (4) knowledge and technology as resources to handle mixture management and (5) quality standards in the food value chain. The final chapter 5 engages in a broader discussion of the contribution of complementarity and facilitation to the studied systems and identifies the spatiotemporal design of crop communities and its interplay with agroecological interactions, farm management and economics as research priority. The thesis is concluded by delivering an explicit definition and conceptual model for crop communities and crop community systems.