UMN Extension Strategic Farming: Let’s talk crops! discusses whether we can and why we should want to store carbon in production ag systems -…

University of Minnesota Extension

Carbon is the one of earths most common and important elements and is one of lifes building blocks. Jodi DeJong-Hughes shared with the audience that carbon makes up approximately 58% of soil organic matter and that soils with higher carbon content tend to be darker in color and more resilient to precipitation extremes, improving both water infiltration and retention. Minnesota, Wisconsin and Iowa have soils with some of the highest organic matter content in the lower 48 states and consequently some of the most productive soils in the world. We can help to conceptualize carbon storage by thinking about it as a bank account, with additions and withdrawals of carbon. Both aboveground and below-ground crop biomass left in the field after harvest can be considered deposits, as can manure and cover crop biomass, while soil erosion, crop harvest (grain, chopping, baling), tillage, burning residue, and microbial respiration can all be considered withdrawals, says DeJong-Hughes.

Carbon dioxide (CO2) is important for capturing the suns energy to create the temperate environment that sustains life on Earth. Too much CO2 in the atmosphere traps too much heat, contributing to global climate change and an increased probability of extreme weather events such as flooding, droughts, hurricanes and wildfires occurring. Under pressure from shareholders and consumers alike, boards of directors of publicly-traded companies are seeking ways for companies to become carbon neutral. Carbon-neutrality can be obtained by companies finding ways to streamline their own operations or purchasing carbon credits from others that can remove CO2 from the air. This has led to the development of carbon markets where companies can pay farmers to adopt production practices that capture (or sequester) carbon.

Ten percent of all CO2 emissions in the US are due to agriculture, with tillage and other soil management strategies accounting for 55% of the total. At the request of the Minnesota Corn Growers Association, Jodi DeJong-Hughes and Anna Cates have developed a program called Carbon Smart to help familiarize Minnesota crop producers with how carbon cycles through our agronomic cropping systems, the benefits to soil health and resiliency that increasing soil organic matter can provide and the promise and pitfalls associated with entering into a carbon program.

DeJong-Hughes and Cates suggest that increasing soil organic matter by changing practices such as reducing tillage intensity or adding a cover crop is slower in fields that already have higher soil organic matter contents. Says DeJong-Hughes, If a crop producer is interested in enrolling in a carbon program, they might be better able to document carbon sequestration in fields that do not have as much soil organic matter to begin with.

Signing up for one of these carbon markets may seem like a no-brainer for farmers that were already interested in adopting an additional conservation practice; it would, after all, be another potential source of income from cropland. But DeJong-Hughes and Cates urged the audience to temper expectations due to the realities associated with latitude. The further north the farm, there is a trend toward less rainfall and cooler temperatures. Cates added, Full-season crops in Minnesota will therefore have a shorter growing season to pull CO2 out of the air for growth and development than full-season crops further south, and so will tend to sequester less carbon than crops produced further south.

From both a research and a carbon markets perspective, it is important to be able to properly claim that carbon sequestration has indeed taken place. Without baseline measurements of soil organic carbon before implementing conservation practices, we are not able to claim that carbon sequestration has taken place. Soil disturbance through tillage, planting, incorporating fertilizer or other field work redistributes both soil microbes and soil aggregates, providing them access to different residue and soil components that the microbes can use for growth and development. This disturbance leads to a burst of CO2 loss from the soil, explains Dr. Cates. Without having baseline measurements of soil organic carbon before implementing practices intended to capture carbon, we cannot be sure whether carbon is continuing to be lost, whether carbon content is staying stable over time or whether carbon is actually being sequestered after adopting conservation practices. This is also one of the reasons that most carbon markets require soil sample collection before practice adoption and at specific intervals after adoption so that they are selling actual carbon credits.

Cates and DeJong-Hughes answered many audience questions, including: which practices if adopted can sequester the most carbon?; will farmers enrolled in carbon programs be penalized for poor cover crop growth?; if a farmer switches to a no-till system and ends up needing to till, will all of the positive benefits to soil health be erased?; what is more valuable, organic matter that provides easily mineralizable nutrients or organic matter that is more stable?; is it more important to take select land out of production or just implement more carbon sequestration practices across more of the landscape?; how does fertilizer nitrogen (N) placement affect denitrification to N20, a potent greenhouse gas?; how much are carbon markets paying brokerage firms versus farmers?; how long is the typical farmer carbon agreement?; will adding grazing livestock to a field increase carbon sequestration compared to not?

For those that missed this session, it is now available to view on YouTube at: https://youtu.be/460hSVYxJns. For more information and to register to attend other weekly session through the end of March, visit z.umn.edu/strategic-farming.

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UMN Extension Strategic Farming: Let's talk crops! discusses whether we can and why we should want to store carbon in production ag systems -...