OOS 19-5 - Distinguishing the influence of cover crop roots on nitrous oxide emissions from soil

Cover crops are touted as an agricultural management practice that can contribute to greenhouse gas emissions reductions and carbon sequestration on agricultural lands. As plant roots are a key interface of biogeochemical cycling in the soil, the form and function of cover crop root systems may have a strong influence on N2O emissions and warrant overcoming the methodological challenges of studying roots in soil. However, production of nitrous oxide (N2O) in soil is highly variable and strongly responsive to weather and management events, which compounds the challenges of systematic assessments of cover crops’ overall impact on greenhouse gas emissions.

We isolate root impacts on N2O emissions through in situ and ex situ measurements of cover crop root traits adjacent to chamber measurements of N2O emissions throughout the non-growing season in a cover crop field trial. We couple this work with a controlled lab experiment using microcosms with automated continuous measurements of N2O to distinguish the plant-soil mechanisms that drive emission differences observed in our field experiments. Through these studies, we demonstrate a novel approach of using lab-made minirhizotrons for imaging roots in the soil to capture root growth and morphology to associate with N2O fluxes. Our preliminary results indicate species diversification of cover crops may have non-additive effects on root trait expression and N2O emissions compared to sole cropped species. Our lab experiment shows distinct effects of cover crop species and species mixtures in amplifying pulses of N2O emissions that follow soil freezing and thaw (i.e., simulating common weather events in cold climates that lead to significant contributions of total N2O emissions). Through novel investigations of root-soil interactions with N2O fluxes, our research is intended to inform cover crop management and evaluate the role of plant diversification in meeting climate change mitigation goals.