Organic Farming Sequesters Atmospheric Carbon and Nutrients in Soils

Paul Hepperly, The New Farm® Research Manager
The Rodale Institute®

Executive Summary

Organic farming may be one of the most powerful tools in the fight against global warming. Findings from The Rodale Institute’s 23-year Farming Systems Trial® (FST) comparing organic and conventional cropping systems show organic/regenerative agriculture systems reduce carbon dioxide, a major greenhouse gases-positioning organic farming as a major player in efforts to slow climate change from runaway greenhouse gases increases.

Besides being a significant underutilized carbon sink, organic systems use about one third less fossil fuel energy than that used in the conventional corn/soybean cropping systems. According to studies of the FST in collaboration with Dr. David Pimentel of Cornell University, this translates to less greenhouse gases emissions as farmers shift to organic production. The ability of organic agriculture to be both a significant carbon sink and to be less dependent on fossil fuel inputs has long-term implications for global agriculture and its role in air quality policies and programs.

Since 1981, data from the Farming Systems Trial has revealed that soil under organic agriculture management can accumulate about 1,000 pounds of carbon per acre foot of soil each year. This accumulation is equal to about 3,500 pounds of carbon dioxide per acre taken from the air and sequestered into soil organic matter. When multiplied over the 160 million acres of corn and soybeans grown nationally, a potential for 580 billion pounds of excess carbon dioxide per year can be sequestered when farmers transition to organic grain systems.

It is believed that agricultural soil has a significant potential to capture and retain or sequester carbon dioxide. The 1995 Kyoto Protocol references this potential without emphasizing its capacity nor the importance of organic agriculture management for this purpose. Since then, researchers have moved forward strongly with investigations to support agriculture’s real potential to sequester carbon. The Rodale Institute® findings have taken this one step further by measuring carbon content and studying the positive impacts of carbon sequestration in organically-farmed soils.

The Rodale Institute’s 23-year findings show that organic grain production systems increase soil carbon 15 to 28%. Moreover, soil nitrogen in the organic systems increased 8 to 15%. The conventional system showed no significant increases in either soil carbon or nitrogen in the same time period. Soil carbon and nitrogen are major determinants of soil productivity.

Why does the soil carbon level increase in organic systems but not in conventional systems when crop biomass is so similar? We believe the answer lies in the different decay rates of soil organic matter under different management systems. In the conventional system the application of soluble nitrogen fertilizers stimulates more rapid and complete decay of organic matter sending carbon into the atmosphere instead of retaining it in the soil as the organic systems do.

Additionally, soil microbial activity, specifically the work of mychorrhiza fungi, plays an important role in helping conserve and slow down the decay of organic matter. Collaborative studies in our Farming Systems Trial® with the United States Department of Agriculture Research Service (ARS) researchers, led by Dr. David Douds, show that mychorriza fungi are more prevalent in the FST organic systems. These fungi work to conserve organic matter by aggregating organic matter with clay and minerals. In soil aggregates, carbon is more resistant to degradation than in free form and therefore more likely to be conserved. Support for this work comes from United States Department of Agriculture researchers at the Sustainable Agriculture Laboratory in Beltsville, Maryland. Their findings demonstrate that mychorrizal fungi produce a potent glue-like substance called glomalin that is crucial for maximizing soil aggregation. We believe that glomalin is an important component for carbon soil retention and encourage increased investigation of this mechanism in carbon sequestration.

Increasing soil organic matter for the soil’s carbon bank is a principle goal of organic agriculture. Organic agriculture relies on the carbon bank and stimulated soil microbial communities to increase soil fertility, improve plant health, and support competitive crop yields. This approach utilizes the natural carbon cycle to reduce the use of purchased synthetic inputs, increase energy resource efficiency, improve economic returns for farmers, and reduce toxic effects of fertilizers and pesticides on human health and the environment.

US Secretary of Agriculture, Ann Veneman, puts it this way, “The technologies and practices that reduce greenhouse gases emissions and increase carbon sequestration also address conservation objectives, such as improving water and air quality and enhancing wildlife habitat. This is good for the environment and good for agriculture.”

Organic Farming Sequesters Atmospheric Carbon and Nutrients in Soils

Background, Findings, and The Next Steps

An analysis of gases trapped within glacier ice shows that 18,000 years ago, during the last ice age, atmospheric concentrations of carbon dioxide were 60% lower than those found in the atmosphere today. This low concentration of carbon dioxide was associated with a 4° C (about 10° F) drop in average temperature. Presently, global atmospheric carbon dioxide levels are 25% higher than in the late 1800’s. If emissions continue at current levels, carbon dioxide in the atmosphere may double or even quadruple within the next 100- 300 years.

In 1938, G. Callendar published findings suggesting that the burning of fossil fuels, such as coal, oil and natural gases, would likely increase world temperatures. Since 1958, continuous carbon dioxide measurements on Mount Mauna Loa in Hawaii confirm that carbon dioxide is increasing in the atmosphere at a rate of about 1.3 parts per million (ppm) per year. Atmospheric scientists believe that although several other gases contribute to the greenhouse effect in the Earth’s atmosphere, carbon dioxide is responsible for over 80% of potential warming. NASA scientist James Hansen tracked temperature changes in relation to past carbon dioxide levels and he correlated the 25% increase in carbon dioxide over the last 100 years with a 0.7° C warming of the atmosphere. A number of models have predicted that at current rates of carbon dioxide emission, the Earth will warm 2.5° C in the next 100 years at current rates of carbon dioxide emission.

According to climatic change models, agriculture could be seriously affected by global warming. It is estimated that 20% of potential food crop production is lost each year due to unfavorable weather patterns (drought, flood, severe heat and cold, strong storms, etc.). The deterioration of weather patterns in North America could have devastating effects on world supplies of basic food grains such as wheat and corn. Climate change modelers predict that higher temperatures will generate more extreme weather events, such as severe droughts and torrential rains. A shift of 1 to 2° C in summer temperatures at pollination season can cause a loss of pollen viability, resulting in male sterility of many plant species such as oats and tomatoes.

As global temperatures rise, the glaciers and polar icecaps will melt, leading to major island- and coastal-flooding. About 50% of the United States population lives within 50 miles of a coastline. As coastlines move inland, uncontrolled carbon dioxide levels will directly affect coastal dwellers. If greenhouse gases continue to increase in the next several hundred years, the rise of global temperature is estimated at 7° C, or almost 15° F, and the sea level would rise over 2 meters, or in excess of 6 feet.

Soil Organic Matter-Key to Sequestration

Normal seasonal carbon dioxide fluctuations in the atmosphere demonstrate that plant growth governs major amounts of carbon dioxide, enough to change atmospheric concentration by up to 10 ppm. By increasing plant production, we can reduce carbon dioxide concentrations in the atmosphere. Carbon dioxide levels are minimized in summer when vegetation is lush, and maximized in winter when plants die or go dormant. The fluctuation of carbon dioxide from season to season (about 10 ppm) is about 7 times greater than the yearly average increase in atmospheric carbon from fossil fuel burning and deforestation (1.3 ppm). Plants serve as sinks for atmospheric carbon dioxide. Carbon stored in vegetation, soil, or the ocean, which is not readily released as carbon dioxide, is said to be sequestered. To balance the global carbon budget, we need to increase carbon sequestration and reduce carbon emissions. While carbon can cycle in and out of soil or biomass material, there are methods for building up what are called soil “humic” substances (also known as organic matter) that can remain as stable carbon compounds for thousands of years.

Before forests and grasslands were converted to field agriculture, soil organic matter generally composed 6 to 10% of the soil mass, well over the 1 to 3% levels typical of today’s agricultural field systems. The conversion of natural grasslands and forests around the globe works to elevate atmospheric carbon dioxide levels significantly. Building soil organic matter by better nurturing our forest and agricultural lands can capture this excess atmospheric carbon dioxide, and preserve more natural landscapes.

Agricultural and forest carbon sequestration will reduce the dangers that carbon dioxide currently presents to our atmosphere and world climatic patterns. These benefits will complement energy conservation and emission control efforts. Improved energy use is important because if all fossil fuel reserves were used in the next several hundred years, carbon dioxide in the atmosphere would increase 4 to 8 times present levels (currently the atmosphere holds 750 Gigatons of carbon, while known fossil fuel energy reserves hold 5,000 Gigatons of carbon.). Soil organic carbon, even at its present depleted level (1,580 Gigatons of carbon[C]), is still estimated to be almost double the quantity of all the carbon currently found in the atmosphere as carbon dioxide (800 Gigatons C), and about three times the amount found in all living organisms on the planet (500 Gigatons C).

Soil, agriculture, and forests are essential natural resources for sequestering runaway greenhouse gases helping to derail drastic climate changes. The amount of carbon in forests (610 Gigatons) is about 85% of the amount in the atmosphere. The 1998 Resources For the Future Climate Issue Brief #12 states, “Although it is well known that the world’s tropical forests are declining, it is less widely recognized that the world’s temperate and boreal forests have been expanding, albeit modestly…Nevertheless, overall, the size of the global forest carbon stock appears to be declining, thereby generating a net carbon source.”

The Rodale Institute Farming Systems Trial® Findings

Agriculture is, and always will be, a major tool in carbon sequestration. The Rodale Institute’s 23 year Farming Systems Trial® research provides real world experience and the starting point for understanding the potential for agriculture to reduce greenhouse gases. The FST® is the longest running agronomic experiment designed to compare organic and conventional farming methods and production systems.

Since 1981, The Rodale Institute® has continuously monitored soil carbon and nitrogen in its Farming Systems Trial® (FST). Carbon and nitrogen monitoring is just one component of a comprehensive battery of soil quality, economic and energy data that The Rodale Institute researchers gathered over the 23-year lifespan of the FST®. Researchers at The Rodale Institute believe that soil carbon and nitrogen findings are especially significant and dramatic. In the organic systems, soil carbon increased 15-28%, demonstrating the ability of the organic systems to sequester significant quantities of atmospheric carbon. Specifically, the FST organic manure system showed an average increase of soil carbon of about 1000 lbs per acre-foot of soil per year, or about 3,500 pounds of carbon dioxide per acre-ft per year sequestered. When multiplied over the 160 million acres of corn and soybeans that are produced nationally, a potential of an increase of 580 billion pounds of carbon dioxide per year would be sequestered by farmers switching from conventional chemically based farming systems to organic grain farming methods.

Additionally, in the organic systems, soil carbon has increased 15 to 28%. Over the 23 year lifespan of the FST, the conventional system showed no significant increases in either soil carbon or nitrogen. This demonstrates that organic farming methods increase stored carbon and retain other nutrients because organic soils hold these nutrients in place for uptake by plants. In the process, reduce nitrate and other nutrient runoff into streams and water aquifers. These findings can be beneficial to all farmers by helping them to increase crop yields while decreasing energy, fuel and irrigation costs.

We believe this is the longest scientifically replicated study that has been continuously monitored for soil quality including carbon and nitrogen levels. Certainly study is a first in terms of its duration and comparison of the carbon sink potential of organic and conventional agriculture soils. This study gives us a baseline for developing an ambitious scale of work to replicate and then accelerate the carbon sequestration potential of organic farming methodologies.

In addition to capturing more carbon as soil organic matter, organic agricultural production methods also emit less greenhouse gases through more efficient use of fuels. Energy analysis of The FST by Dr. David Pimentel from Cornell University show that organic systems use only 63% of the energy input used by the conventional corn and soybean production system. In all systems, yields of corn and soybean were not different, except in drought years, when organic systems yielded 25 to 75% more than the conventional system. The organic yield advantage in drought years is specifically related to the ability of higher-carbon organic soils to capture and deliver more water to crop plants. Dr. David Pimentel’s findings show that the biggest energetic input, by far, in the conventional corn and soybean system is nitrogen fertilizer for corn, followed by herbicides for both corn and soybean production.

Organic farming also makes economic sense. In addition to reducing input costs, economic analysis by Dr. James Hanson of the University of Maryland has shown that organic systems in the FST are competitive in returns with conventional corn and soybean farming, even without organic price premiums. Real world organic price premiums allow farmers to take advantage of certified organic production systems to achieve economically viable returns without massive governmental subsidies.

How can low input organic systems be competitive in productivity with a high input chemically based conventional system? USDA scientist, David Douds, in collaboration with scientists at The Rodale Institute®, has shown that in the organically managed systems, the biological support system of mycorrhiza fungi is much more robust and the fungi are more prevalent, active, and diverse. Synthetic chemical fertilizers and pesticides inhibit mycorrhizae. In organic production systems, increased mycorrhiza fungal activity allows plants to increase their access to soil resources, thereby stimulating plants to increase their nutrient uptake, water absorption, and their ability to suppress certain plant pathogens.

The process and ability of mycorrhiza to sequester carbon has perhaps an even greater significance. Mycorrhiza fungi produce a novel glue-like substance called glomalin. Glomalin stimulates increased aggregation of soil particles. Soil particle aggregation results in an increased ability for soil to retain carbon. The role of mycorrhiza and glomalin in soil carbon retention requires further investigation. Other biological mechanisms that will result in a greater ability of soil to sequester carbon naturally and to improve soil properties require further investigation as well.

Benefits Beyond Carbon Sequestration

The presence of sequestered carbon in The Rodale Institute’s FST® organic field trials is an indicator of healthy soil because healthy soil is abundant in carbonaceous matter, in particular the organic material humus. It is humus that enables healthy soils to retain water during periods of drought; as well as retaining mobile nutrients found in soils such as phosphates and nitrates, that would otherwise be lost as runoff to streams and aquifers.

These trials are illustrative of both economic benefit as well as environmental protection working hand in hand. The economic benefits are realized by farmers and landowners who see reduced costs for fertilizer, energy fuels and irrigation, and increased crop yields at the same time. It is also economically beneficial to the agricultural business economy, and an environmental benefit to all of us, that specific soil management and tillage practices can help to sequester or retain carbon in the soil--carbon that would otherwise be lost to the atmosphere as a component of greenhouse gases.

In summary, organic farming can reduce the output of carbon dioxide by 37-50%, reduce costs for the farmer, and increase our planet’s ability to positively absorb and utilize greenhouse gases. These methods maximize benefits for the individual farmer as well as for society as a whole. It is a winning strategy with multiple benefits and virtually no risk. These proven approaches mitigate current environmental damages and promote a cleaner and safer world for future generations.

The Next Steps

In recent months, staff from The Rodale Institute® met with officials of the Pennsylvania Departments of Agriculture and Environmental Protection. Together, we are working on a Statement of Cooperation that will provide a platform for future research and education on how organic farming can provide significant economic and environmental benefits. With 22 years of data from the FST® field trials in place, we will explore ways to promulgate and systematize the knowledge that has been gathered. In recent years, other researchers around the world have also begun to investigate and document the potential for soil carbon and nutrient sequestration. It is important to move forward quickly to lead the research in this field.

First, we propose to review the current body of scientific literature to determine if there are ways to accelerate the formation of organic material in soil, and to determine if it is possible to predict the rate of carbon and nutrient sequestration. Additionally, we would like to determine if there may be important opportunities for sequestration in manufactured soils with expanded applications on abandoned mine and conservation program lands.

Second, we propose the development of protocols whereby landowners could adopt organic soil management practices and quantify sequestration potential. Ultimately, this could enable landowners to participate in carbon and nutrient trading markets, which would provide a financial incentive to adopt organic soil management practices.

Third, we propose to expand the knowledge base on soil carbon sinks through communication and collaboration with other scientific, educational, research and agricultural institutions.

This is emerging as a new field from the perspective of many in the agricultural and soil management communities. While the data from the field trials is a matter of record, much needs to be done before we know how to transfer this knowledge for use in broader markets and applications. Nonetheless, what has been demonstrated is significant and shows promise in helping to reduce the build-up of greenhouse gases while promoting greater use of organic agriculture.


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