I have been thinking about carbon. This particular atom is profoundly important for organic life and the sustainability of life. In plants, carbon is about half of the total dry weight. Carbon dioxide is the precursor to organic carbon assimilation in plants; we know this as photosynthesis. This reaction, driven by solar radiation and the change in energy of electrons, is easily the most important chemical reaction on the planet’s surface. We call this the biosphere.
We have just concluded another year and its harvest. I live in Gratiot County, Michigan, largely a corn, wheat and soybean farming area. Anecdotally, most of the post-harvest fields are tilled using a residue harrow or cultivator; the grower is burying well over half of the plant residue into the surface soils.
Over winter, some of this residue decomposes, albeit slowly. Growers know the practice of residue incorporation and fall tillage helps prepare the field for the next growing season when time is short to get that crop in the ground.
I was talking with our state NRCS agronomist, my colleague, about this practice. We both know that much of our work in nutrient management centers on manufactured fertilizers and animal manures and the concentrations of nitrogen, phosphorus and potassium in them.
Our 590 Nutrient Management Standard is one of the most important conservation practice standards in our electronic field office technical guide (eFOTG). There is mention of carbon in the standard, but the reference is linked to soil organic matter.
We know there’s much discussion about climate change and particularly the role of carbon flow and flux. One metric is the increasing concentration of carbon dioxide in the atmosphere; as a gas, it exists for at least 100 years and absorbs solar radiation as a greenhouse gas.
Our goal is limiting and reducing this gas in the atmosphere. Agriculturally, we already have a suite of practices to accomplish this task. The soil as a carbon sink instead of a carbon source makes sense.
As you know, the conservation title of the U.S. Farm Bill appropriates money for growers transitioning towards improving and enhancing resources, especially soil and water resources. The title is based on resources that are in the public domain; soil and water resources are not limited or constrained by property or legal boundaries.
Putting all this together, I suggest we build a carbon management conservation practice, and fund it accordingly. Like the three-year fixed payment of the 590 Nutrient Management Standard, this new carbon management standard could also provide an incentive payment for growers.
The incentive is built upon the proven strategy of using the soil as a carbon sink instead of a carbon source. For instance, residue management is coupled with its fate on the crop field … figuring out how to incorporate as much of it as possible and yet address water and wind erosion is the challenge.
Here in Gratiot County, residue management might be some method of minimum tillage to meet the erosion standard and then planting a cover crop to capture carbon dioxide as plant growth. Yes, very little growth in winter, but in early spring the cover crop can begin fixing carbon as plant growth. Growers can use the cover crop for green manure – therefore another minimum tillage operation – or remove the biomass for feed or biofuel.
A large amount of research and anecdotal evidence points to the benefits of carbon sequestration, at least in the short term. The objective is storing carbon in the soil, with the outcome of increasing soil health or tilth, which results in increasing the nutrient capacity of the soil (increasing cation exchange capacity) and increasing the water-holding capacity (greater soil water available for plant transpiration). Another benefit is soil aggregation, with the desirable outcome of improving drainage.
I admit the link between carbon management and our other farming practices, including soil fertility and water and wind erosion, require a systems approach at farming. For growers as well, we must figure out a strategy that yields workable and practical recommendations for adjusting to the weather. A wet spring is difficult at best and adding another management operation, or two, is unworkable.
My point is that if we built a workable carbon management conservation practice, and funded it as an incentive payment for farmers in our Environmental Quality Incentive Program (EQIP), we move toward more soils as carbon sinks and fewer as carbon sources.
We already have a cover crop conservation practice. I believe it is underutilized, at least in the Midwest. The systems approach of using the 590 Nutrient Management Standard, a new carbon management standard and the existing cover crop standard might well help growers become more efficient, more profitable and address one of the huge issues of the day – carbon and its role in climate change.
This is all in the concept phase, I know. But I will be thinking more about this approach with my fellow colleagues at NRCS. Stay tuned. PD
Mike Gangwer
Agricultural Scientist
USDA-NRCS
