The current debates over solutions to global warming have been concentrating on the combustion side of the carbon cycle. I believe the biological side of the carbon cycle (photosynthesis and mineralization) has a greater potential for practical solutions. This paper discusses the potential of the biological side to reduce CO2 concentrations in the atmosphere.
We have approximately 340 million acres of land in the U.S., which is still being tilled to grow field crops. Current and past tillage practices have mineralized much of the stored organic matter (humus) in these soils, releasing billions of tons of CO2 into the atmosphere. This oxidation of humus, along with the increased combustion of fossil fuel (old buried humus), has surely contributed to the increasing concentration of CO2 in the atmosphere over the past 50 years. With CO2 concentrations at historical highs and still rising, it's time for society to take action. We cannot afford to bet the planet that these historic levels won't cause major environmental problems.
With the U.S. signing of the Global Warming Treaty in Kyoto, Japan, carbon suddenly has an economic value. The two prevalent solutions being proposed to comply with this Treaty are: (1) taxing fossil fuel at a cost high enough to reduce consumption, or (2) purchasing carbon credits from Russia or other countries with low per capita fuel usage. Neither of these solutions will be effective without severely impacting our strong economy.
I feel that using our humus-depleted cropland as a biological sink for some of the excess CO2 would be a much more practical solution. Our soils are more than a sink, they are a gigantic bathtub, which is probably less than half full of their original humus level. Recent data indicates that many of these soils can recover to near their original level of humus within 25 years, if they are not tilled and good carbon sequestering crops are grown under good management.
To reward farmers for taking carbon out of the atmosphere and retaining it in their soil, and to offset the additional risk and initial extra cost to grow field crops without tillage, I recommend a FSA payment or tax credit to farmers in proportion to the amount of carbon they can add to their soil humus pool. Based on the history of many long term no-till fields, as well as limited USDA-ARS (Agricultural Research Service) data, it appears that 5 to 10% of the organic carbon left in humus depleted fields after harvest, can be retained as humus in the absence of broadcast (full width) tillage. Table 1 illustrates the approximate amount of organic carbon in the grain, stems and roots of the five major crops, using the 1997 average yields for the U.S.
There is considerable variability between crops and environments on the amount of carbon sequestered and retained. ARS could use existing information and begin gathering additional data to develop carbon retention models on which payments would be based.
Models would also be developed and payments made for humus added to the soil by various cover crops, as well as, from applications of manure, sludge, landscape waste and other sources. At this point, the quantities retained are not as important as reversing the current trend of soil humus depletion.
The carbon payments should stay with the land and would be redeemable, at least in part, if and when broadcast tillage is resumed. It makes no sense to pay farmers to sequester and store carbon and then allow them, or other farmers, to till the soil sending most of the recently stored carbon back to the atmosphere without retribution.
We have spenders and savers in all phases of society. If we did not have the Federal Reserve to balance interest charges and payments between spenders and savers of money, our banking system would be in chaos. If we don't have some retribution for the spenders of the carbon society has paid to store; the carbon banking system would be exploited making it ineffective.
Before an incentive can be provided for soil carbon storage we must assign a value to soil humus, which is approximately 50% carbon. Considering just the nutritional components of humus, its valued conservatively at around $200/ton or 10¢ / lb. This does not consider the intrinsic value of humus in improving soil, water and air quality and long term productivity. Using $200/ton value for humus would place a value of 5¢ / lb. for soil organic carbon (SOC). Table II estimates the potential payment to farmers using average yields of the five major crops and 5¢ / lb. C estimated to be stored. If farmers received 5¢ / lb. for C they could sequester and retain in their soil, most landowners and farmers would soon change their farming system and find innovative ways of improving their ability to store carbon.
This voluntary program should be relatively easy to administer. Farmers would turn in their crop acres and yields as they are doing now for Federal Crop Insurance. Under this program they would also turn in their yearly tillage practices. Remote sensing technology is currently available as a check, or at least as a threat to check, on the accuracy of these tillage reports.
This carbon credit or payment could be financed with a maximum of 1 cent per gallon tax on liquid fossil fuel and an equivalent tax per pound of carbon on coal and natural gas. If just 50% of the major crop acres participated, the 1-cent/gal equivalent tax would pay for the program with ample money left over to research better sequestration methods. I believe the vast majority of carbon fuel consumers will support this modest tax if the benefits are properly understood and compared to other alternatives. If a 1-cent per gallon tax is politically unacceptable, the program could be financed with other funding currently budgeted for global warming issues.
I believe we should establish a national goal of adding 1% organic matter to the topsoil (seven inches) of our cropland by the year 2025. The only practical way this can be accomplished without severely limiting production is to provide positive incentives to grow field crops without mixing the soil profile with tillage.
Adding 1% organic matter to the top seven inches of our 340 million acres of cropland would take about 2 billion tons of carbon out of the atmosphere and sink it into our topsoil. Besides reducing greenhouse gases, attaining this goal would dramatically improve the quality of our soil and our water, improve production and water use efficiency, reduce sedimentation of our lakes, streams and oceans, and provide sustainability to food production. The fuel saved by not tilling this land for the next 25 years would also reduce carbon emissions by over 60 million tons.
Improving soil humus may not have the pioneering glamour associated with putting a space station in orbit, but it will cost much less and have a much greater probability of sustaining our species. It's time we concentrate on improving the knowledge base and the care of our own house; this delicate little planet called EARTH.