Maize and Prairie Root Contributions to Soil CO₂ Emissions in the Field

Abstract

Increasing soil carbon content via agricultural practices not only enhances the production potential of the land, but also counteracts rising atmospheric CO2 levels. When predicting production systems’ effects on soil carbon, quantifying CO2 efflux derived from live roots is of particular importance as it is a through‐flux and does not signify depletion of soil carbon. This field study aimed to measure and compare soil CO2 emissions derived from roots in annual and perennial agroecosystems. We used periodic 48‐hour shading over two growing seasons to estimate root growth‐derived CO2 in continuously grown maize (CC) with grain and 50% stover harvested each year, unfertilized reconstructed tallgrass prairie (P), and the same prairie grown with spring nitrogen fertilization (PF), both which had biomass harvested post‐frost. In CC, P, and PF root‐derived CO2 contributed to 28, 31, and 30% of each crop's respective growing season cumulative CO2 emissions in 2012, and 19, 24, and 28% in 2013, respectively. Season‐cumulative root‐derived CO2 was not proportional to end‐of‐season belowground biomass (BGB): P had nearly twice the BGB of PF, but their cumulative root‐derived fluxes were not significantly different in either year. A significant proportion of soil CO2 emissions is derived from roots, making it a critical process to consider when comparing or modeling soil emissions of cropped or prairie soils. Using BGB alone may not be a useful proxy for estimating root contributions.

A solution for sampling position errors in maize and soybean root mass and length estimates

“…This problem exists because of the laborious nature of root measurements in the field that limits the number of root samples across space and time (Oikeh et al, 1999;Paez-Garcia et al, 2015). Furthermore, individual soil cores are extrapolated to unit areas by assuming root uniformity across sampling positions in row crops (Maeght et al, 2013;Nichols et al, 2016;Dietzel et al, 2017). Such an assumption may be valid when the objective is to compare different treatments, such as crop cultivars, but not valid when the objective is to quantify carbon budgets, root/shoot ratios, calibrate simulation crop models, or compare root estimates across different studies (Amos and Walters, 2006;Fan et al, 2016).…”

Corn stover harvest reduces soil CO2 fluxes but increases overall C losses

“…Even though grain yields were increased with stover removal in CT throughout the study (Table 4), as well as in NT and BC in 2010, the magnitude of increase suggests that additional root biomass C and rhizodeposited C in higher yielding plots are unlikely to offset losses from stover removal. This assumption is supported by research showing that increased root biomass does not always equate to increased soil respiration (Hirte, Leifeld, Abiven, Oberholzer, & Mayer, 2018;Nichols, Miguez, Sauer, & Dietzel, 2016).…”

Scaling approach to microbial interactions in soil across three bioenergy cropping systems

“…In a prairie restoration, nitrogen fertilization can be used to promote increased plant aboveground plant biomass . However, while nitrogen fertilization has increase aboveground productivity, it also decreases belowground root inputs into the soil community (Sainju et al, 2005;Dietzel et al, 2015;Nichols et al, 2016;Gebhardt et al, 2017). Nitrogen fertilization may influence fungal communities indirectly through local plant-microbe interactions.…”