Fri May 21, 2010 06:44 AM CDT
Carbon Connections - 2 05/21 06:20 Calculator Shows Little Impact on Global Warming DTN Staff Agronomist makes an estimate of his farm's impact on the environment. He sees room for improvement, but is pleasantly surprised his farm is sequestering more carbon than it produces. By Daniel Davidson DTN Agronomist OMAHA (DTN) -- There is a lot of talk about carbon footprints in industry, manufacturing and farming. With concerns over greenhouse gas emissions and global warming, we have to be aware of our carbon footprint and make an effort to reduce it. The question is, do I use more carbon in my farming operation from field activities, transportation costs and inputs purchased than the carbon I put back in the soil? Crops, especially high biomass crops like corn or perennial switchgrass, capture a lot of carbon from the atmosphere. Soil experts call this carbon sequestration. Historically, agriculture's carbon budget has been in the red. Extensive tillage released carbon from the soil, and those multiple tillage passes required inefficient, smoke-belching machines. Today farmers can reduce or eliminate tillage, cut the number of field passes and sequester more carbon while reducing the carbon expended when farming. But first, each farmer needs to know where he or she stands. CURRENT CARBON STATUS In the 1990s, my father farmed with a 50-50 corn-soybean rotation, drilling soybeans into disked cornstalks and no-tilling corn into soybean stubble. My brother and I took over nine years ago, and converted to a 100 percent no-till corn and soybean rotation. We sold all the tillage equipment except for a plow to plow the garden. Our passes include fertilizing, planting, harvesting and two for spraying. I soon realized soybean profits were meager, and we converted to continuous no-till corn. I already knew the switch greatly increased soil organic matter. In nine years, organic matter has nearly doubled from 1.5 percent to just under 3.0 percent. Higher organic matter means more carbon being sequestered though growing continuous no-till corn is a challenge. Ample crop residue immobilizes nitrogen and can interfere with planting and seed germination. To remedy that, I apply a residue digester, which requires another field pass. We bale about 30 percent of the corn residue on about 30 percent of the acres and recently ran a vertical tillage tool across the field to process the stalks. So, while my organic matter and soil quality is increasing, it requires carbon expenditures to achieve that. OUR CARBON FOOTPRINT To test our carbon footprint, I used the web-based Fieldprint Calculator ( to evaluate a single field. I selected a 155-acre field that has been in no-till corn for five years, hasn't had a cover crop and yielded 155 bushels per acre in 2009. I entered data on state, crop, season, soil slope and type, tillage practices, rotation and conservation practices, fertilizer use and pesticide passes. I learned, based on that field at least, that our operation has a significantly smaller carbon footprint than the Nebraska state average, and that our state's farms have a smaller footprint than the national average. As hoped, our farm's no-till continuous corn creates a carbon budget in the black -- we sequester more carbon that we expend. Our land use index was 49, similar to the state and national averages, meaning we have only mediocre average production. However, if corn production could be increased to 250 bushels, the index would drop to 30 as our resource efficiency increases. Achieving that yield in this field is impossible at the moment, but the calculator allows you to examine such "what if" scenarios. While we do not use terraces, contour farming or buffer strips on this field, we had a soil loss index value of 15, lower than the state's 33 and the nation's 50. Our energy use index was 7, compared to 46 for the state and 50 for the national average. We were spending 6003 BTUs of energy per bushel of corn produced. According to the calculator, this field has no impact on the environment: our Climate Impact Index score was zero compared to 47 for the state and 50 for the nation. We are sequestering 6.778 pounds of carbon dioxide per bushel produced of corn produced. Our carbon budget is in the black. CONCLUSIONS AND ADVICE I am proud of what we have accomplished, even though it was driven by improving our bottom line and not sequestering more carbon. Still, are there things I can do to improve our footprint? The results do need to be taken with a grain of salt. This calculator, while simple and easy to use, is really designed to look more at the sustainability of a farm than to specifically look at its carbon footprint. It doesn't take into full consideration the carbon used to make and apply the inputs we use. It also doesn't account for other greenhouse gases, such as nitrous oxide and methane that can be released as nitrogen fertilizer breaks down in the soil. It did ask about fertilizer rates and whether nitrogen stabilizers were used but using them didn't make a significant difference. The results I discuss here are also based on one example field. In other fields we performed some vertical tillage to deal with the results of a wet harvest and to reduce the amount of residue. I would need to account for the fuel used and the carbon released during that tillage for a whole-farm score. I know there is other room for improvement. We still run '80s vintage tractors that aren't as fuel efficient as modern machines and we pull smaller implements that take us longer to complete the job. I also did not account for baling that 30 percent of the corn residue on a third of the acres every year. That would change the carbon budget, but it sure makes growing continuous corn easier. On the plus side, we are starting to plant a rye cover crop on that acreage each fall to remediate that residue loss, reduce soil erosion potential and add some carbon back to the soil. Any further changes to lessen our footprint will have to pay off in profits. Yet it is interesting to see how field activities change your carbon footprint and allows you to set some realistic goals. Go to the website, complete the questionnaire and see where you stand. Daniel Davidson can be reached at (GH/ES/KM) Copyright 2010 DTN/The Progressive Farmer, A Telvent Brand. All rights reserved.