PESKY WEEDS AND PATCHY RESOURCES: UNDERSTANDING THE ROLE OF SOIL SPATIAL HETEROGENEITY AND ROOT FORAGING IN INTERSPECIFIC COMPETITION

Improving the capacity of crop roots to compete for soil resources will reduce the need for irrigation and fertilizer, while increasing crop competitiveness against weeds. Root foraging encompasses the morphological and physiological plastic responses utilized by roots to exploit heterogeneously distributed resources. Soils are extremely heterogeneous environments. However, it is not yet clear how agricultural management influences the heterogeneous distribution of resource within the soil, and how that in turn influences belowground competition. Recent crop breeding efforts have aimed to enhance root foraging, but foraging responses are not always predictable under competitive environments. The goal of this project is to compare root foraging strategies among maize varieties (Zea mays) and common weeds, and evaluate how spatially heterogeneous resources influence root foraging and maize-weed competition.We will use a series of greenhouse experiments to characterize root foraging of maize and weeds, with and without competition. We will also conduct a field experiment to determine the effects of cover crop residue spatial heterogeneity on the distribution and availability of soil resources, root foraging and mycorrhizae colonization, and weed-crop competition. We will utilize a novel approach to directly study the mechanisms influencing competition by using 15N enrichment combined with high pressure dye injection. 15N enriched red clover residue will allow us to directly trace the flow of N from resources of specific sizes and location within the soil. A high pressure dye injection system will be used to stain roots and facilitate identification to species.Improved understanding of the effects of soil resource heterogeneity and root foraging plasticity on weed-crop competition will enhance our capacity to adapt crops to low-input environments, and reduce our reliance on herbicides and synthetic fertilizers. Long-term outcomes include increased awareness among researchers of the role that soil heterogeneity plays in mediating belowground competition, as well as increased appreciation among breeders of the importance of considering belowground competitiveness when selecting for root traits. An additional outcome is a deeper understanding of how nutrient placement (N banding, manure injection, zonal cover cropping) influences crop N uptake and weed competition. Results from the proposed research will be disseminated through presentations at academic and scientific meetings, publications in scientific journals, and extension presentations and bulletins.