D.C. Reicosky, Morris, MN

Key Words: no-till, CO₂ emissions, sustainability, soil carbon, soil organic matter, carbon credits

Agriculture has contributed to water contamination from sedimentation and the greenhouse effect with tillage-induced carbon dioxide (CO₂) losses. Improved tillage management techniques have shown that scientific agriculture can also be a solution to these environmental issues in general and specifically to mitigating the greenhouse effect (Lal et. al., 1998). Improved agricultural practices such as direct seeding or conservation tillage have the potential to sequester more carbon (C) in the soil than farming emits through land use and fossil fuel combustion. Thus, a combination of the economic benefits of enhanced soil management through reduced labor requirements, time savings, reduced machinery and fuel savings with direct seeding, combined with the environmental benefits listed above has universal appeal. Indirect measures of social benefits as society enjoys a higher quality of life from environmental quality enhancement will be difficult to quantify. Conservation agriculture, working in harmony with nature using direct seeding techniques that increase soil C, can be of benefit to society and can be viewed as both "feeding and greening the world" for global sustainability.

Conservation agriculture can enhance the harmony between man and the environment by offsetting some CO₂ emissions and will be a small, but significant player in storing or sequestering C. Preliminary assessments indicate that soil C sequestration can be a tool to partially offset C emissions from burning fossil fuels. We in agriculture play a significant role because of the large amount of soil C in the C cycle within agricultural production systems. The limited use of crop rotations combined with the intensive tillage decreases soil quality and soil organic matter as a result of C loss. Any operation that removes or incorporates crop residue contributes to the decline of soil C through direct loss or increased biological oxidation. The drive to maximize profit in food and fiber production has created environmental problems that have slowly crept up on conventional agriculture that now requires new knowledge, research and innovation to overcome these concerns for sustainable production.

High levels of fossil fuel combustion and deforestation have transformed large pools of fossil C from coal and oil into atmospheric CO₂. Conservation and increased fuel efficiency are important players in reducing CO₂ emissions from the use of fossil fuels. International strategies aimed at reducing CO₂ in the atmosphere include soil C sequestration, tree planting, and ocean sequestration of C. Other technological strategies to reduce C inputs include developing energy efficient fuels, and efforts to develop and implement non-C energy sources, such as hydrogen fuel cells. All of these efforts combined can reduce CO₂ concentrations in the atmosphere and help to alleviate global warming.

Over the past 150 years, the amount of CO₂ in the atmosphere has increased by 30%. Many scientists believe there is a direct relationship between increased levels of greenhouse gasses, especially CO₂ in the atmosphere and rising global temperatures. One proposed method to reduce atmospheric CO₂ buildup is to increase the global storage of C in soils. Additional benefits to this solution are the potential for simultaneous enhancement in agricultural production and ecosystem services for enhanced environmental quality. Soil C sequestration through conservation agriculture may be one of the most economical ways to reduce C emissions to buy time to help society develop cleaner fuels and produce in harmony with nature. Soil organic C is a valuable resource and is a renewable resource from which we can gain many environmental benefits by increasing its levels. Society needs to look at agriculture as part of the solution to an increasing concern, namely global climate change. Conservation agriculture can play a major role in enhancing soil C and environmental quality in our production systems.

Based on the soil C losses with intensive agriculture, reversing the decreasing soil C trend with less tillage intensity should be beneficial to sustainable agriculture and the global population by gaining better control of the global C balance. The literature holds considerable evidence that intensive tillage decreases soil C and supports increased adoption of new and improved forms of conservation tillage or no-till (direct seeding) to preserve or increase storage of soil organic matter (Lal et al., 1998). Better control of the C balance will lead to better harmony between man and nature. The environmental and economic benefits of conservation agriculture and direct seeding demand their consideration in the development of improved soil C storage practices for sustainable production.

True soil conservation is C management. By properly managing the C in our agricultural ecosystems, we can have less erosion, less pollution, clean water, fresh air, healthy soil, natural fertility, higher productivity, C credits, beautiful landscapes, and sustainability. Dynamic soil quality encompasses those properties that can change over relatively short time periods (e.g. soil organic matter, labile soil organic matter fractions, soil structure components, and macro porosity) in response to human use and management and that are strongly influenced by agronomic practices. Soil organic matter is both inherent, as total soil organic matter is related particle size distribution, and dynamic, as it is related to ongoing inputs organic matter to the soil. A dynamic part of soil C cycling is directly related to the "biological C" cycle.

The "biological C" cycle is of the utmost importance in conservation agriculture and is differentiated from the "fossil C" cycle. Fossil C sequestration entails the capture and engineered storage of C content of fossil fuels prior to its release to the atmosphere. Biological C sequestration entails removal of C from the atmosphere by plants. Fossil fuels (fossil C) are very old geologically, as much as 2 million years. Biofuels (bio-C) are very young geologically and can very from 1 to 10 years in age and as a result can be effectively managed for improved C cycling. One example of biological C cycling is the agricultural production of biomass for fuel. The major strength of biofuels is the potential to reduce net CO₂ emissions to the atmosphere. Enhanced C management in conservation agriculture, may make it possible to take CO₂ released from the fossil C cycle and transfer it to the biological C cycle to enhance food, fiber and bio-fuel production as well as enhancing environmental quality.

The main benefit of conservation agriculture or direct seeding is the immediate impact on soil organic matter and soil C interactions (Reicosky, 2001). Soil organic matter is so valuable for what it does in the soil, it can be referred to as "black gold" because of its vital role in physical, chemical and biological properties and processes within the soil system. Agricultural policies are needed to encourage farmers to improve soil quality by storing C that also will lead to enhanced air quality, water quality and increased productivity as well as mitigating the greenhouse effect. Soil C is one of our most valuable resources and may serve as a "second crop" if global C trading systems becomes a reality. While technical discussions related to C trading are continuing, there are several other secondary benefits of soil C impacting environmental quality that should be considered. In agricultural production systems, many decisions are made based on farmer experience and economic considerations. However, the recent emphasis on environmental concerns requires a balance between economic and environmental factors that have caused soil organic matter management decisions to rise to a high-level priority.

Agricultural soils typically contain 1 to 4 % C on mass basis. The relatively small amounts of C could be considered analogous to a catalyst or to the tip of the iceberg where a small amount visible has a big impact. Soil C performs many important beneficial functions with respect to environmental enhancement. Farmers are the primary soil managers who each have a tremendous responsibility to maintain soil organic matter for environmental benefit of the global population. Thus, farmers who use conservation agriculture or direct seeding techniques are helping to maintain environmental quality for all of society. Quality food production and economic and environmentally-friendly management practices that are socially acceptable will lead to sustainable production and be mutually beneficial to farmers and all of society. Enhanced soil C management is a win-win strategy (Lal et al., 1998). Agriculture wins with improved food and fiber production systems and sustainability. Society wins because of the enhanced environmental quality.

Removing CO₂ from the atmosphere is only one significant benefit of enhanced C storage in soils. Soil organic C represents a key indicator for soil quality, both for agricultural functions (production and economy) and for environmental functions (C sequestration and air and water quality). Soil organic matter is the main determinant of biological activity because it is the primary energy source. The amount, diversity and activity of soil fauna and microorganisms are directly related to SOM content and quality. Organic matter and the biological activity that it generates, have a major influence on the physical, chemical and biological properties of the soils. Soil aggregation and stability of soil structure increases with increasing organic C.

The main contribution of conservation agricultural management techniques, which are successful in providing a net C sink in soils, includes conservation agriculture or no till (direct seeding) that minimizes or eliminates manipulation of the soil for crop production. It also includes the practice of conservation or mulch tillage, which leaves most crop residues on the soil surface. These procedures generally protect the soil, increase infiltration, reduce soil erosion, improve water use efficiency, and increase C concentrations in the topsoil. Conservation tillage can also reduce the amount of fossil fuel consumed in intensive tillage and by other farm operations and thus decrease the rate of CO₂ buildup in the atmosphere. Cover crops, such as clover for nitrogen accumulation and small grains, capture CO₂ through photosynthesis for soil protection and improvement between periods of regular crop production. Cover crops improve C sequestration by enhancing soil structure, adding nitrogen to the soil, and adding organic matter to the soil. Diverse crop rotation is a sequence of several different crops grown in regularly recurring succession on the same area of land. The more diverse crop rotations provide long-term stability in crop production systems by minimizing pest and disease problems. Diverse rotations mimic the diversity of natural ecosystems more closely than intensive mono-cropping practices. Varying the type of crops grown can increase the quality and level of soil C. However, effectiveness of crop rotation depends on the type of crops grown, rotation duration, intensity of tillage, soil type and climate conditions.

Understanding the role of soil C and biodiversity in agricultural ecosystems has highlighted the value and importance of a range of processes that maintain and fulfill human needs. These basic needs are called "ecosystem services" that are the basis of our economic and social system. Ecosystem services are the processes by which the environment produces resources that we often take for granted. An ecosystem is a community of animals and plants interacting with one another and with their physical environment. Ecosystems include physical, chemical and biological components such as soils, water, and nutrients that support the biological organisms living within them. People are part of these ecosystems. Agricultural ecosystem services include production of food, fiber and biofuels, provisions of clean air and water, natural fertilization, nutrient cycling in soils, mitigation of climate, pollination, genetic resources, recreational, cultural and social benefits and many other fundamental life support services required for our existence. These services may be enhanced by increasing the amount of C stored in soils. Our agricultural ecosystems help moderate weather extremes and their impacts, mitigate natural droughts and floods, protect stream and river channels and coastal shores from erosion, control agricultural pests, maintained biodiversity, generate and preserve soils and renew their fertility, detoxify and decompose wastes, contribute to climate stability, purify the water and air, regulate disease carrying organisms, to name a few. Conservation agriculture through its impact on soil C is the best way to enhance ecosystem services. Recent analyses have estimated national and global economic benefits from ecosystem services of soil formation, nitrogen fixation, organic matter decomposition, pest bio-control, pollination and many others. Intensive agricultural management practices cause damage or loss of ecosystem services, in the form of changes in nutrient cycling, primary productivity, species diversity, species dominance, and population fluctuation in exchange for economic productivity (Smith et al., 2000). Soil C plays a critical role in the harmony of our ecosystems providing these services.

Increased soil organic matter is known to increase the water holding capacity along with increasing infiltration so that it has a tremendous effect on soil water management. Soils relatively high in C, particularly with crop residues on the soil surface, are very effective in increasing soil organic matter and reducing soil erosion loss. Under these situations, the crop residue acts as tiny dams that slow down the water runoff from the field allowing the water more time to soak into the soil. Worm channels, macropores and plant root holes left intact increase infiltration. Soil organic matter contributes to soil particle aggregation that makes it easier for the water to move through the soil and enables the plants to use less energy to establish to root systems. Intensive tillage breaks up soil aggregates and results in a dense soil making it more difficult for the plants to get nutrients and water required for their growth and production. Reducing or eliminating runoff that carries sediment from fields to rivers and streams will enhance environmental quality. It is important, therefore, that C loss from the soil system through historical land use of farming practices be restored to its natural potential using direct seeding and conservation tillage methods for sustainable production.

Conservation agriculture or no-till (direct seeding) saves time, saves money, and with the environmental benefits can be useful in saving the planet. Eco-efficient farming is economically competitive and environmentally friendly that maintains the sustainability of food and fiber production. This requires a certain level of environmental consciousness and a normal part of doing business in modern agriculture. We must reduce pollution and use our resources in line with the earth’s carrying capacity for sustainable production of food and fiber. The responsibility lies on the shoulders of the farmer to maintain a delicate balance between the economic implications of farming practices and the environmental consequences of using the wrong practices. This responsibility entails producing food and fiber to meet the increasing population while maintaining the environment for a high quality of life. The social value of an agricultural community is not just in food and fiber production, but producing in harmony with nature for better quality soil, water, air and biological diversity where C cycling is fundamental.

The study of tillage has evolved into a science built on an understanding of the relationships between tillage and soil physical properties, crop growth, pests, soil erosion, and, most recently, C sequestration. The recognition of two processes associated with tillage has the potential to dramatically change future tillage research (Lobb et al., 2000). These processes are tillage translocation and tillage erosion (Lindstrom et al., 1992; Govers et al., 1994; Lobb et al., 1995; Poesen et al., 1997). Tillage translocation is the resultant displacement of soil by tillage tools expressed as a mass of soil moved forward or laterally relative to the direction of tillage. The translocation of soil by tillage varies greatly within landscapes as a result of several factors; these include the design and operation of tillage implements and the topographic and soil properties of landscapes. The consequence of this variation in translocation is net soil redistribution or "leveling" within landscapes resulting in tillage erosion. Typically, tillage results in the progressive down-slope movement of soil, causing severe soil loss on upper slope positions and accumulation in lower slope positions. Visual evidence of tillage erosion includes: loss of organic rich topsoil and exposure of subsoil at the summit of ridges and knolls, and undercutting of field boundaries (fencelines, hedgerows, terraces, etc.) on the down-slope side and burial on the up-slope side.

The moldboard plow was first identified as the major contributor to tillage erosion, but all tillage implements will contribute to this problem (Govers et al., 1994; Lobb and Kachanoski, 1999). Soil translocation from moldboard plow tillage operations has been identified as a cause of soil movement from specific landscape positions that can be greater than currently accepted soil loss tolerance levels (Lindstrom et al., 1992; Govers et al., 1994; Lobb et al., 1995; Poesen et al., 1997). Soil is not directly lost from the fields by tillage translocation, rather it is moved away from the convex slopes and deposited on concave slope positions. Lindstrom et al. (1992) showed that soil movement on a convex slope in southwestern Minnesota, USA could result in a sustained soil loss level of approximately 30 t ha^-1 yr^-1 from annual moldboard plowing. Lobb et al. (1995) estimated soil loss in southwestern Ontario, Canada, from a shoulder position to be 54 t ha^-1 yr^-1 from a tillage sequence of moldboard plowing, tandem disk and a C-tine cultivator. In this case, tillage erosion, as estimated through resident ¹³⁷Cesium, accounted for at least 70% of the total soil loss. Tillage speed increases nonlinearly the rate of tillage erosion.

The relationship between soil productivity and tillage erosion is complex. Soils are not the sole factors controlling crop yields. The degree to which crop yield losses are related to soils is a function of several interacting factors including soil physical, chemical and biological properties, landscape position, crop grown, management practices, and weather conditions before and during the growing season. Schumacher et al. (1999) used modeling procedures to show that tillage erosion caused soil loss from the shoulder position while soil loss from water erosion occurred primarily in the mid to lower backslope position. The decline in overall soil productivity was greater when both processes were combined compared to either process acting alone. Water erosion contributed to nearly all the decline in soil productivity in the backslope position when both tillage and water erosion processes were combined. While there are many other reasons for intensive tillage, tillage sets up the soil to be loose, open and very susceptible to high intensity rainfall and subsequent erosion. The net effect of soil translocation from the combined effects of tillage and water erosion was an increase in spatial variability of crop yield and a likely decline in overall soil productivity (Schumacher et al., 1999).

The increase in greenhouse gas concentrations in the atmosphere is a global problem that requires a global solution (Kimble et al., 2002; Lal, 2002). Concern about negative effects of climate warming resulting from increased levels of greenhouse gases in the atmosphere has led nations to establish goals and policies for reductions of these emissions. Initial targets for reductions are stated in the Kyoto protocol to the United Nations framework convention on climate change, which allows trading credits that represent verified emission reductions and removal of greenhouse gases from the atmospheres (United Nations framework convention on climate change secretariat, 1997). The emissions trading may make it possible to achieve reductions in net greenhouse gas emissions for far less cost than without trading (Dudek et al., 1997). Storing C in soils using conservation agriculture techniques can help offset greenhouse gas emissions while providing numerous environmental benefits such as increasing site productivity, increasing water infiltration, and maintaining soil flora and fauna diversity (Lal et al., 1998; Lal, 2002). Storing C in forests may also provide environmental benefits resulting from increased numbers of mature trees contributing to C sequestration (Row et al., 1996).

As interest in soil C sequestration grows and C trading markets are developed, it is important that appropriate policies be developed that will prevent the exploitation of soil organic C and at the same time replace the lost C and establish its value (Walsh, 2002). Policies are needed that will encourage the sequestration of C for all environmental benefits that will evolve (Kimble et al., 2002). Making C a commodity necessitates determining its market value and doing so with rational criteria. Both farmers and society will benefit from sequestering C. Enhanced soil quality benefits farmers, but farmers and society in general benefit from erosion control, reduced siltation of reservoirs and waterways, improved air and water quality, and biodegradation of pollutants and chemicals. Farmers need to be compensated for the societal benefits of C sequestration and the mechanisms that develop will allow for C trading and maintaining property rights. One important criterion in developing the system is the measurement and verification of the C options for sequestration that must be developed and the importance of making policymakers aware of these procedures and the technical difficulties. The use of the C credit market mechanisms is intended to help meet the challenge of climate change and future C constraints that enable sustainable development and at the lowest social cost. Carbon credit accounting systems must be transparent, consistent, comparable, complete, accurate, and verifiable (IPCC, 2000). Other attributes for a successful system include global participation and market liquidity, linking of different trading schemes, low transaction costs, and rewards for early actions to voluntarily reduce emissions before regulatory mandates are put in place. Characterizing the relationships between soil C and water quality, air quality and all the other environmental benefits should be an easy sell to get social acceptance of this type of agriculture. The largest impediment is the educational processes directed at the policymakers and food consuming public that require further enhancement.

A growing number of organizations around the world are implementing voluntary projects that are climate-beneficial as a means to improve efficiency and reduce operating costs and risk. Businesses and institutions throughout the world are realizing that the benefits of good environmental management far outweigh the cost, both now and in the future, of good corporate management that include strategies to reduce greenhouse gas emissions, risk exposure, costs and enhance overall competitive operations. Multinational organizations are participating in C energy credit trading markets in order to avoid future compliance costs and to protect their global franchise in the face of increasing concern over global warming (Walsh, 2002). In the evolution toward a global economy and as concerns over global environmental impacts increase, CO₂ emissions management will become a factor in the planning and operations of industrial and government entities all over the world, creating challenges and opportunities for those who are able to recognize and capitalize on them.

Conservation agricultural practices can help mitigate global warming by reducing C emissions from agricultural land and by sequestering C in the soil through regulatory, market incentive, and voluntary or educational means (Lal, 2002). Public policy can encourage adoption of these practices. For the present, there is a degree of uncertainty for investors and potential investors in forest related C sinks over the specific rules that will apply to implementation of the sinks provisions of the Kyoto Protocol. Investors and potential investors in C sinks need to be aware that there is uncertainty at the international level. Administration and transaction costs could play a key role in determining the success of any C credit trading system. Cost of these areas are expected to be minimized through improved techniques and services for measuring and reporting sequestered C, private sector consultants, economies of scale, and the emergence of market mechanisms and strategies such as C pooling or aggregating. There are risks involved in selling C credits in advance of any formalized international trading system and those participating in early trading need to clarify responsibilities and obligations. However, care should be taken in the design of these policies to ensure their success and to avoid unintended adverse economic and environmental consequences and to provide maximum social benefit.

While we learn more about soil C storage and its central role in environmental benefits, we must understand the secondary environmental benefits of conservation agriculture (no-till) and what they mean to sustainable production agriculture. Understanding these environmental benefits and getting the conservation practices implemented on the land will hasten the development of harmony between man and nature while increasing production of food and fiber. Increasing soil C storage can increase infiltration, increase fertility, decrease wind and water erosion, minimize compaction, enhance water quality, decrease C emissions, impede pesticide movement and enhance environmental quality. Increased levels of greenhouse gases in the atmosphere require nations to establish international and national goals and policies for reductions. Accepting the challenges of maintaining food security by incorporating C storage in conservation planning demonstrates concern for our global resources and our willingness to work in harmony with nature. This concern presents a positive role for conservation agriculture that will have a major impact on global sustainability and our future quality of life.

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