Do cover crops increasethe resilience and sustainability of the agri-food system?

Over a third of the World's soil resources are degraded, compromising food production. Additional future threats including environmental change will also affect the capability of soil systems to deliver a variety of ecosystem services, including food production. We have soil management tools available in agricultural systems to reduce soil degradation yet there is little understanding whether they can increase soil resilience in light of these future threats. Cover crops (crops grown between cash crops in an arable rotation to provide environmental benefits) are one such tool which generates biomass that enters the soil and feeds the soil food web. Cover crops offer a tractable means to increase the botanical diversity of arable landscapes because a polyculture of contrasting species can be simultaneously cropped without changing the agronomic management of the cash crop. Cover crop polycultures can comprise plants that provide different environmental benefits to one another and include species from different plant families that produce different plant secondary metabolites. However, it is unclear to what extent the resulting biochemical diversity of the biomass that enters the shared rhizpsphere and detritosphere of a polyculture results in interactions that shape the structure of the soil food web to form a community that is more capable of delivering soil functions and securing resilience against environmental change than the sum of the individual members of the polyculture. The overarching hypothesis is that increased plant diversity in cover crop polycultures results in a soil food web response that provides greater soil resilience to environmental change and short term perturbations. The hypothesis is justifiedbecause when providing a single source of crop residues and root exudates to
a soil, a food webthat is most adapted to exploiting that resource will be activated, but when applying a mixture of several biochemically contrasting substrates, the number of ecological niches increases and groups of organisms capable of competitively exploiting each of these niches are stimulated. This hypothesis will be tested by conducting experiments at the laboratory scale, field-plot scale, and the landscape scale with the following objectives: 1.Identify whether polycultures alter soil food webs, provide greater soil functions, and increase cash crop yield, compared to the sum of the parts, or a control.2.Determine whether polycultures engineer more resilient soil microbial communities 3.Investigate the impact of soil type on the benefits provided by cover crop polyculturesField-plot scale: This PhD project will make use, and extend the lifetime, of an already established field experiment on the University of Reading experimental farm at Sonning. Berseem clover, Buckwheat, Oil radish and Sunflower are grown annually in plots either as single species monocultures or as a quaternary polyculture between autumn-sown cereal crops in rotation. Annual measurements of the biomass, composition and activity of the soil microbial, mesofauna, and macrofauna community and its relationship with soil structure, nutrient availability and crop yield will be made to address Objective 1.Laboratory scale: Open top chambers will be installed on the plots of the field experiment described above to simulate winter warming and summer heatwaves consistent with projected environmental change in the UK. The resilience of soil from underneath and adjacent to the chambers will be assayed periodically using a laboratory respirometer and a recent methodology to quantify soil resilience to address Objective 2. Landscape scale: A network of farmers will be recruited to establish field trials on contrasting soil types across a landscape.