Growing season carbon dynamics differ in intermediate wheatgrass monoculture versus biculture with red clover

Authors: WIESNER, SUSANNE - University Of Wisconsin; Duff, Alison; Niemann, Kristine; DESAI, ANKUR - University Of Wisconsin; CREWS, TIMOTHY - The Land Institute; PICASSO RISSO, VALENTIN - University Of Wisconsin; Riday, Heathcliffe; STOY, PAUL - University Of Wisconsin

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2022
Publication Date: 8/15/2022
Citation: Wiesner, S., Duff, A., Niemann, K.M., Desai, A.R., Crews, T., Picasso Risso, V., Riday, H., Stoy, P.C. 2022. Growing season carbon dynamics differ in intermediate wheatgrass monoculture versus biculture with red clover. Agricultural and Forest Meteorology. 323(15). https://doi.org/10.1016/j.agrformet.2022.109062.
DOI: https://doi.org/10.1016/j.agrformet.2022.109062

Interpretive Summary: Perennial crops can improve the ecological and economic sustainability of agroecosystems because of their potential to provide diverse ecosystem services. Adding a legume in combination with perennial grass forages may provide added benefits, including reducing the need for fertilizer inputs and increasing biomass production. Intermediate wheatgrass (IWG; Thinopyrum intermedium) is a stress-tolerant grain and forage species and can be grown in bicultures with legumes like red clover (Trifolium pretense L.) for symbiotic nitrogen fixation. We compared ecosystem services production, including carbon accumulation and grain yields, in the IWG monoculture and the IWG-red clover biculture. Using a combination of eddy covariance data (carbon dioxide, methane, and meteorological measurements), collected biomass samples, and harvest and manure estimates, we found that IWG bicultures had greater forage and grain biomass. Over the course of this two-year study, IWG monocultures were larger carbon sinks (–542 to –593 g C m-2 yr-1) compared to bicultures (–456 to –520 g C m-2 yr-1). Grain and forage harvest resulted in carbon loss from both systems which was not recovered until 30 days post-harvest. Carbon loss was greater for bicultures (by 20 g carbon m-2 month-1). Our estimates suggested that the IWG monoculture accumulated more carbon (319 ±85.6 C m-2), whereas the biculture was on average carbon neutral (5 g ±128.9 C m-2), when biomass removal and manure additions were taken into account. Our study demonstrates the complexities of quantifying carbon budgets in dynamic agricultural systems over short time scales, and the importance of assessing crop multifunctionality within a site’s ecological and economic context.

Technical Abstract: Perennial crops can improve the ecological and economic sustainability of agroecosystems because of their potential to provide diverse ecosystem services including carbon storage. Intermediate wheatgrass (IWG; Thinopyrum intermedium) is a stress-tolerant grain and forage species that can be grown in bicultures with legumes for symbiotic nitrogen fixation that provide additional ecosystem services but also compete with IWG for resources and may diminish field-scale carbon uptake. An eddy covariance (EC) tower was installed in December 2018 in an IWG field in Wisconsin – in which half of the field was frost seeded with red clover (Trifolium pratense L.) – to investigate how perennial grain bicultures and monocultures differ in carbon accumulation compared to monocultures. Using a combination of spatially-partitioned carbon and energy fluxes, collected biomass samples, and harvest and manure estimates, we found that IWG monocultures were larger carbon sinks (–538 to –580 g C m-2 yr-1) compared to bicultures (–458 to –520 g C m-2 yr-1), due to greater photosynthetic activity during the growing season and following harvests in August each year. In contrast, evapotranspiration rates were greater in bicultures compared to monocultures (by 0.3–1.4 kg H2O m-2 day-1), specifically during summer. Grain and forage harvest resulted in carbon loss which was not recovered until 30 days post-harvest. Carbon loss was greater for bicultures (by 20 g C m-2 month-1). Net ecosystem carbon balance (NECB) estimates suggested that the IWG monoculture accumulated more carbon (306 ± 88 C m-2), whereas the biculture was on average carbon neutral (7 g ± 131 C m-2), when biomass removal and manure additions were accounted for. Our study demonstrates the complexities of quantifying carbon budgets in dynamic agricultural systems over short time scales, and the importance of assessing crop multifunctionality within a site’s ecological and economic context.