Here we explain differences between regions where trends are observed and where scientific evidence exists to explain the trends.
Switch to no-till
In cool, wet climates, practicing no-till may reduce soil temperature and hinder drainage, resulting in lower yield. In dry regions like the Rocky Mountains and the Great Plains, no-till may conserve moisture but yield gains remain limited and the overall plant biomass production tends to be lower than in the Corn Belt and the Southeast. The total carbon sequestration potential is most likely related to overall primary productivity.
Switch to conservation till
Results show wide ranges in values, and differences between regions may be related to the use of the term “conservation tillage” to describe a wide span of different practices that sit between full tillage and no till.
Eliminate summer fallow
Some lower values in the Rocky Mountains are because of water deficits in this region. In such cases, summer fallow may still be useful for water conservation purposes as there is not enough moisture to support crop growth every year. Therefore, elimination of summer fallow can result in lower total plant growth (and thus lower C sequestration).
Use winter cover crops
The difference in estimates is likely due to higher primary productivity in the California systems tested. Note that the upper range of values for both regions is similar, since the total winter vegetation productivity in the southeast and in California can be comparable.
Diversify annual crop rotations
As this includes a wide range of different crop variations, we see a wide range in outcomes that are not clearly distinguished by region. Note that diversifying by shifting from continuous corn to corn-soybean shows no soil C sequestration potential, because of lower total crop residue in that system. Diversifying in other cropping systems tends to have better results in capturing soil C.
Convert cropland to pasture
Due to higher temperatures, more moisture, and a longer growing season, the southeast has much higher primary productivity than the northern plains, and thus has higher rates of carbon sequestration when converting to perennials such as pasture.
Set aside cropland
The lower soil carbon sequestration value in the Rocky Mountains is due to much lower primary productivity in these dryland systems.
Reduce N application by 15%
The lower potential in the Rocky Mountain region is because of lower baseline N2O emissions in these systems.