Managing Rare Arable Weeds to Promote Soil Function and Support Maintenance of Barley Yields

Background: There is increasing concern about an ongoing decline in biodiversity, particularly as a consequence of agricultural intensification [1]. In farmland systems this decline has been observed at many trophic levels, including plants, and one issue is the continued survival of certain rare arable weeds [2]. The reduction in arable weeds is due, in part, to the focus of modern farming practice on removing potential competitors from crop fields. However, we know from ecological theory that coexisting species do not necessarily compete, and certain combinations of species can alternatively have no discernable, or even facilitative, effects on each other. Incorporation of additional species in crop systems may provide wider benefits, for example, improvements in soil quality and function or increased resistance to invasive species, both of which can influence crop yields in the longer term. This knowledge is exploited by management practices such as intercropping, where the focal crop is sown alongside another with potentially beneficial effects (e.g. nitrogen fixing legumes) [3]. Recent data (Rowntree & Price unpublished) suggests that certain rare weeds are compatible with barley (i.e. barley yield does not decrease with coexistence) and that temporal dynamics of coexisting plants can be important in regulating crop-no crop interactions [4]. This provides an opportunity to manage for yield and biodiversity simultaneously, and the potential to improve ecosystem sustaining factors such as soil function and resilience by increasing plant diversity.

The aims of this project are:
1) to assess management approaches that can sustain barley yields alongside rare arable weeds
2) to determine whether rare arable weed mixtures can be used to promote healthy soil function and increase resilience
3) to understand the temporal dynamics of crop-weed interactions and maximize complementarily

Methods and Approach: The student will use a combination of pot, mesocosm and field experiments to test the effect of specific species and mixtures of rare arable weeds on barley yield, soil function (including nutrient cycling and soil structure and community composition) and resistance to invasive species (e.g. blackgrass). Using novel approaches developed by Schofield et al. [3] There will be a focus on the timing of interactions, both at the individual plant level in terms of nutrient use and at the field scale in terms of examining the effectiveness of intercropping versus rotation approaches. Destructive (e.g. harvesting and nutrient analysis) and non-destructive methods (e.g. natural isotope, zymography) will be used to assess changes in nutrient cycling; meta-barcoding approaches will be used to examine changes in the biological soil community (microbial, micro and macro fauna) over time and different mixtures will be challenged with pernicious weeds to test for resistance to invasion. Plant abundance, biomass, seed production (yield) and nutrient content data will be collected at barley harvest.