BRASSICA COVER CROPS ALTER WEED CO-OCCURENCES AND SOIL MICROBIAL COMPOSITION

Abstract

Farmers utilize cover crops to manage weeds, amend nutrients, improve resiliency against pest and disease, and build soil health. One limitation to adoption is that we cannot predict well enough how different cover crop species affect weed management or soil health. Brassica cover crops are a well-studied group because of their potential for agriculturally and ecologically significant weed control. The functions of soil microbiomes could contribute to underlying mechanisms behind these weed responses. Two properties of brassica cover crops have substantial and differing effects on the soil microbiome and weed community: glucosinolate and carbon release through root exudation and biomass breakdown. Glucosinolates break down into biocidal isothiocyanates that have been found to effectively control weeds and soil pathogens. Carbon from cover crop biomass and root exudates also stimulate microbial activity and create more diverse resource pools, resulting in more diverse weed and microbial communities. This thesis assesses whether the soil microbiome differed under cover crop treatments (Chapter 1), and if differing weed and microbial responses could distinguish between carbon and glucosinolate as driving mechanisms (Chapter 2).