Contrasting Physiological and Environmental Controls of Evapotranspiration over Kernza Perennial Crop, Annual Crops, and C4 and Mixed C3/C4 Grasslands

This work is licensed under a Creative Commons Attribution 4.0 International License.Perennial grain crops have been suggested as a more sustainable alternative to annual crops. Yet their water use and how they are impacted by environmental conditions have been seldom compared to those of annual crops and grasslands. Here, we identify the dominant mechanisms driving evapotranspiration (ET), and how they change with environmental conditions in a perennial Kernza crop (US-KLS), an annual crop field (US-ARM), a C4 grassland (US-KON), and a mixed C3/C4 grassland (US-KFS) in the Central US. More specifically, we have utilized the omega (Ω) decoupling factor, which reflects the dominant mechanisms responsible for the evapotranspiration (ET) of the canopy. Our results showed that the US-ARM site was the most coupled with the lowest decoupling values. We also observed differences in coupling mechanism variables, showing more sensitivity to the water fluctuation variables as opposed to the radiative flux variables. All of the sites showed their lowest Ω value in 2012, the year of the severe drought in the Central US. The 2012 results further indicate the dependence on the water fluctuation variables. This was especially true with the perennial Kernza crop, which displayed much higher soil moisture values. In this regard, we believe that the ability of perennial Kernza to resist water stress and retain higher soil moisture values is both a result of its deeper roots, in addition to its higher Ω value. Through the analysis of both the site comparison and the comparison of the differences in years, we conclude that the perennial Kernza crop (US-KLS) is more similar in its microclimate effects to the C4 (US-KON) and mixed C3/C4 (US-KFS) grassland sites as opposed to its annual counterpart (US-ARM). This has implications for the role of perennial agriculture for addressing agricultural resilience under changing climate conditions

Evaluating Methods to Account for Soil Organic Carbon Stock Changes in Agricultural Lands

Soil organic carbon (SOC) sequestration has essential implications for climate change mitigation, land health, and sustainable community development. However, land management strategies that encourage SOC sequestration are often underprioritized in carbon offset programs. We hypothesize that this is due to difficulties regarding accounting for soil carbon stock changes in response to land management choices. Field measurements are expensive and not often accessible to those in non-Annex I countries. Therefore, estimation methods using empirical or mathematical models are often utilized, but there are large discrepancies in estimates of changes in SOC stocks when applying different methodologies. We first focused on two of the estimation methods set out in the Intergovernmental Panel on Climate Change (IPCC) Tiered accounting approach in order to understand how well they performed against observed SOC changes in two U.S. field studies. This was accomplished by applying the tiered methodologies (Tier 1 & 3) to two published studies in the United States. Tier 3 was represented by the process-based models: COMET Farm and COMET Planner. We hypothesized that COMET Farm would produce estimates closest to the observed field measurements. However, we found that Tier 1 performed just as well as COMET Farm. To assure that land management strategies are being taken to sequester SOC, IPCC Tier 1 estimation methodology use should not be discouraged in situations where resources or land information is sparse. Next, we surveyed past and present participants in the Clean Development Mechanism (CDM) and Climate, Community and Biodiversity/Verified Carbon Standard (CCB/VCS) restoration and carbon offset programs to understand their approach for accounting for changes in soil carbon stocks. The survey invitations revealed communication issues between project leaders and developers. Several email invites came back with error messages stating that those addresses were no longer in existence. Therefore, we believe that this may lead to issues with project verification. This also suggests that collaboration is not occurring between projects. Finally, based on survey responses that were collected, soil carbon sequestration accounting does not seem to be prioritized in the CDM or the CCB/VCS. More research should be done to understand this prioritization given to accounting for soil carbon sequestration in carbon offset programs

Contrasting Physiological and Environmental Controls of Evapotranspiration over Kernza Perennial Crop, Annual Crops, and C4 and Mixed C3/C4 Grasslands

Perennial grain crops have been suggested as a more sustainable alternative to annual crops. Yet their water use and how they are impacted by environmental conditions have been seldom compared to those of annual crops and grasslands. Here, we identify the dominant mechanisms driving evapotranspiration (ET), and how they change with environmental conditions in a perennial Kernza crop (US-KLS), an annual crop field (US-ARM), a C4 grassland (US-KON), and a mixed C3/C4 grassland (US-KFS) in the Central US. More specifically, we have utilized the omega (Ω) decoupling factor, which reflects the dominant mechanisms responsible for the evapotranspiration (ET) of the canopy. Our results showed that the US-ARM site was the most coupled with the lowest decoupling values. We also observed differences in coupling mechanism variables, showing more sensitivity to the water fluctuation variables as opposed to the radiative flux variables. All of the sites showed their lowest Ω value in 2012, the year of the severe drought in the Central US. The 2012 results further indicate the dependence on the water fluctuation variables. This was especially true with the perennial Kernza crop, which displayed much higher soil moisture values. In this regard, we believe that the ability of perennial Kernza to resist water stress and retain higher soil moisture values is both a result of its deeper roots, in addition to its higher Ω value. Through the analysis of both the site comparison and the comparison of the differences in years, we conclude that the perennial Kernza crop (US-KLS) is more similar in its microclimate effects to the C4 (US-KON) and mixed C3/C4 (US-KFS) grassland sites as opposed to its annual counterpart (US-ARM). This has implications for the role of perennial agriculture for addressing agricultural resilience under changing climate conditions