Project Overview
The release of carbon dioxide (CO2) and nitrous oxide (N2O) from agricultural soils is one of the primary sources of anthropogenic greenhouse gas emissions contributing to global climate change. Due to the complexity of the biogeochemical processes associated with soil CO2 and N2O release, it can be difficult to predict how changes in agricultural management practices may impact an agroecosystem’s overall GHG emissions.
This study, conducted at Michigan State University’s Kellogg Biological Center (South Gull Lake, MI), examined the effects of cover crops on soil CO2 and N2O emissions after the first year of organic-transition corn across topographically diverse agricultural landscapes.
Farmer Takeaways
- Agricultural CO2 and N2O emissions are most directly associated with plant performance, which itself is influenced by topographic soil characteristics (soil temperature, soil moisture, and soil structure).
- Plants tend to perform worse on slopes than at either summits or depressions.
- Reducing cover crop residue fragment size via cutting prior to incorporation may lower CO2 emissions marginally, but additional research is needed to understand the magnitude and consistency of emissions reductions possible with this practice for organic-transitioning agricultural systems.
Project Objectives and Approach
Examine topographical effects on cover crop contribution to soil CO2 and N2O emissions after the first year of an organic-transitioning corn/soybean/wheat system
- For the topographical component of the experiment, a split-plot arrangement was established, with topographic position as the whole-plot factor and cover crop type as the sub-plot factor.
- Topographic positions included: (1) depression, (2) slope, and (3) summit.
- Cover crop types included: (1) no cover control, (2) cereal rye, (3) mixture of cold-susceptible/winter kill (WK) species, including oat, winter pea, and radish, and (4) mixture of cold-tolerant/winter-hardy (WH) species, including annual ryegrass, Dwarf Essex rapeseed, and crimson clover.
- Static flux chambers were installed in each sub-plot, and a total of 12 CO2/N2O flux measurements were recorded throughout the experimental period (one in winter at chamber installation, post-corn harvest; 6 during spring, between March and May when cereal rye and winter-hardy (WH) cover crops were growing; and 5 in early summer, after chisel ploughing and soybean planting).
- Soil samples were collected from each subplot at the time of each GHG measurement and analyzed for soil moisture, pH, and inorganic nitrogen (NH4 and NO3).
- Cover crop and weed biomass were measured from each sub-plot immediately prior to chisel ploughing.
Evaluate the impact of cover crop fragment size at incorporation on soil CO2 and N2O fluxes
- For the residue size component of the experiment, a split-plot arrangement was established, with aboveground residue processing treatment as the whole-plot factor, and cover crop type as the sub-plot factor.
- Aboveground residue processing treatments included: (1) incorporation of intact/whole-plant cover crop residue (residue size ~15-25cm), and (2) incorporation of cut/fragmented cover crop residue (residue size ~1-7cm).
- Cover crop types included: (1) no cover control, (2) cereal rye, (3) mixture of cold-susceptible species, and (4) mixture of cold-tolerant species.
- Data was collected in the same manner as the topographical experiment.
Key Findings
CO2 and N2O emissions are strongly correlated with plant performance/aboveground plant biomass, which are impacted by topographic soil characteristics (temperature, moisture, and structure)
- CO2 and N2O emissions were positively correlated with soil temperature within each topographical position (depression, slope, and summit), indicating that at each respective location, higher soil temperatures corresponded with greater greenhouse gas emissions.
- Despite the observation that slopes had higher soil temperatures than either summits or depressions, both CO2 and N2O emissions were lower for slopes than for the other topographical positions (although only CO2 was statistically significant).
- This could be due in part to worse cover crop performance on slopes, driven by low soil organic matter, lower soil moisture, and poor soil structure (soils more susceptible to erosion and nutrient/water runoff). Aboveground plant biomass was consistently lower on slopes than for summits or depressions.
Cover crop type may have a smaller impact on soil CO2/N2O emissions than topographic position, which itself is linked to soil characteristics and plant growth/performance
- There was only a significant difference between cover crop treatments at the summit topographical position.
- CO2 emissions were lowest in cereal rye plots, possibly due to poor cereal rye performance.
- CO2 emissions were highest in winter-hardy (WH) plots, possibly due to WH’s longer growing season (interseeded with corn; growing season June through May) and associated biodiversity benefits (improved soil structure, water flow, and nutrient cycling).
- N2O emission results were not statistically significant between cover crop treatments nor topographical positions, aligning with previous studies that highlight the high variability of N2O in agroecosystems.
Residue fragment size marginally impacted CO2 and N2O emissions, with smaller residue fragments resulting in lower CO2 emissions for some cover crop treatments than when maintained intact.
- Of the four cover crop treatments, only winter-kill (WK) resulted in significantly lower CO2 emissions when cover crop residues were cut into smaller fragments during incorporation.
Resources
Nguyen, L.T.T., and A.N. Kravchenko. 2021. Effects of cover crops on soil CO2 and N2O emissions across topographically diverse agricultural landscapes in corn-soybean-wheat organic transition. European Journal of Agronomy 122:126189.
Read MoreLocation
MichiganCollaborators
Alexandra Kravchenko, Michigan State University
Region
Midwest
Topic
Soil Health, Climate Solutions, Transitioning to Organic
Category
Grain and Field Crops
Year Published
2021
