Building Sustainable Soil Systems

Past management of nature to meet the food and fiber needs of increasing populations has taxed the resiliency of natural processes to maintain global balances of energy and matter. Increasing farm sustainability is not simply a matter of substituting one product for another, but of moving away from product-focused methods toward process-focused management. The sustainability of the soil resource is only slightly related to fertilizer and other inputs. Instead, sustainability is almost entirely related to management of soil and cropping systems. Intrinsic soil factors like slope, texture, and local rainfall, along with soil management-related factors like forage-based rotations, soil organic matter content, aggregate stability, and tillage practices have a much greater influence on the sustainability of any given farm than does the type or amount of any conventional or non-conventional soil amendment (Doran et al., 1994).
Since the late 1950’s, conventional wisdom has popularized the notion that improved inputs such as crop varieties, synthetic nitrogen fertilizers, herbicides for weed control, and pesticides for insect and disease control have replaced management as a necessary means for maintaining and even increasing crop yields (Bullock, 1992). The past generation of soil managers has focused primarily on the chemical properties of soils (i.e. proper soil pH and “nutrient sufficiency”) to promote maximum crop yields, often neglecting soil physical and biological parameters (Larson and Pierce, 1991). Monoculture production of cash grain crops and reliance on chemical fertilizers and pesticides to maintain grain yields are related to declining soil productivity and increased environmental contamination (Fraser et al., 1988). Soil research has concentrated on soil chemical and physical factors, with comparative neglect of biological factors. Consequently, there is relatively limited understanding of how best to capitalize on the dynamics and potentials of soil biology so as to enhance the regenerative capacity of soil systems for agriculture.
More agronomic research and empirical experience for biologically based agriculture are called for as a primary means for sustainable crop yields, economic returns, and a diversified rural economy. Motivation for shifting from chemically intensive management to alternative practices includes: concern for protecting human and animal health from the potential hazards of pesticides; concern for protecting air, water, and soil resources; and, a need to lower production costs (Fraser et al., 1988).
Soil erosion is a major environmental threat to the sustainability and productive capacity of agriculture. During the last 100 years, nearly one-third of the world’s arable land has been lost by erosion and continues to be lost at a rate of more than 10 million hectares per year (Pimental et al., 1995). Erosion usually results in decreased primary productivity, which in turn adversely affects C storage in soil because of the reduced quantity of organic C returned to the soil as plant residues. Thus the use of management practices that prevent or reduce soil erosion may be the best strategy to maintain, or possibly increase, the world’s soil C storage (Gregorich et al., 1998).
Soil degradation by water and wind erosion and depletion of organic matter, with related consequences such as loss of nutrients, are among the main factors affecting the quantity and quality of land and thus the long-term sustainability of agriculture in the Southern Region (Cannell and Hawes, 1994). Extensive land clearing and intensive tillage for cotton, tobacco and corn in the last 200 years has made these consequences all-too-common in Southern states and clearly increased organic matter loss from soils (Rasmussen and Collins, 1991).
Sustainable systems should favor less tillage in order to conserve soil, water and energy (Conway, 1996). The increased adoption of conservation tillage is generally viewed as a way to enhance environmental quality. It is considered to be an important "best management practice" (BMP) for reducing nonpoint-source pollution from agricultural fields. The proper incorporation of sound, sustainable principles for crop production in conjunction with conservation tillage, at present, offer the only solution for continued row crop production on large acreages in the southeast. It is essential that farmers in Southern states adopt practices that conserve soil water and afford minimum soil disturbance and maximum soil cover, especially during the period of April through July, when intensive rainfall can severely erode soil left loose and bare by tillage for warm-season crops. Leaving crop residues on the soil surface protects it from the erosive forces of heavy rains, particularly on highly erodible Southeastern soils (Tyler et al., 1994).
Numerous studies have demonstrated significant changes in organic matter concentration with time as a function of crop rotation, tillage, fertilizer practices and other agronomic factors (Janzen 1992). Unfortunately, crop residues decompose rapidly in the warm, humid southeastern U.S., making year-round soil protection a challenge and compounding the threat of soil loss on the region’s highly erodible soils. However, Mitchell and Entry (1998) reported results from Alabama’s long-term ‘Old Rotation’ cotton experiment. Long-term planting of winter legumes with no other source of N applied resulted in higher soil organic C in the plow layer compared to continuous cotton with no winter cover crops. They concluded that after 100 years, the Old Rotation indicates that winter legumes and crop rotations result in larger amounts of both C and N in soil, which ultimately contribute to higher cotton and corn yields regardless of other practices. Other studies have reported that relatively short-term tillage and amendment management can significantly impact C, N, and P transformations and transfers within soil organic matter of a southeastern U.S. soil (Kingery et al., 1996).
Although maintenance of crop residues on the soil surface or the growing of cover crops are the best available means of controlling erosion, it has been recognized that the problems of southern reduced-tillage agriculture are unique to the region. Mild winters and prevalence of soil hardpans have required specific management to overcome the disease, pest, weed and root penetration problems that result from these regional characteristics. Recognition and accommodation of all the soil physical and fertility considerations are necessary to design and achieve successful cropping systems that limit soil erosion (Sojka et al., 1984).
Flue-cured tobacco quotas were cut by 35 percent over the 1998 and 1999 growing seasons (Beacham et al., 2000). The loss of demand for tobacco means a loss of jobs and income for southeastern farmers. For many communities, tobacco has not only been a source of economic prosperity, but is also a long established way of life. Specialty crops such as fruits and vegetables offer an economically viable alternative to tobacco production, particularly for smaller producers. However, production of these crops will require growers to subscribe to and implement an entirely new set of soil management practices. Extensive tillage, short rotations, extensive use of chemical inputs, fallow soils before and after cropping, aversion to organic matter additions to soil, and other conventional attitudes and practices will need to be replaced by more sustainable practices appropriate to high-value, intensively managed (in particular, soil water management) specialty crop enterprises.
Although better understanding and practices can serve immediate on-farm needs, they alone would unlikely achieve the desirable changes in farming systems. Policies and institutional arrangements profoundly influence agricultural research and practice, so effective soil health initiatives must also engage broader social and political considerations. This will require a greater balance in research and teaching to emphasize biology and ecology, enhanced linkages between research and extension, new inter-institutional partnerships and collaboration, and increased stakeholder involvement in policy formulation and implementation (Sherwood and Uphoff, 2000).
Many of the concepts addressed above are poorly understood and only narrowly described in traditional agricultural teaching programs. It is important for educators to fully understand the principles of sustainable soil management and to teach those principles to others, in particular, farmers. Participants in this project will learn about the components of sustainable soil management—soil quality (in particular, biological parameters), organic matter management, nutrient management, conservation tillage, long-term rotations, cover cropping, etc. They will learn how to integrate the various components in an integrated approach to soils management in sustainable farming systems.
Literature Cited
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Doran. J.W., M. Sarrantonio, and R. Janke. 1994. Strategies to promote soil quality and health. In C.E. Pankhurst, B.M. Doube, V.V.S.R. Gupta, and P.R. Grace (Eds.) Soil Biota: Management in sustainable Farming Systems. p. 230-237. CSIRO. Australia.
Fraser, D.G., J.W. Doran, W.W. Sahs, and G.W. Lesoing. 1988. Soil microbial populations and activities under conventional and organic management. Journal of Environmental Quality. 17: 585-590.
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Sojka, R.E., G.W. Langdale, and D.L. Karlen. 1984. Vegetative techniques for reducing water erosion of cropland in the southeastern United States. Advances in Agronomy. 37:155-181.
Tyler, D.D., M.G. Wagger, D.V. McCracken, W.L. Hargrove, and M.R. Carter. 1994. Role of CT in sustainable agriculture in the southern United States. CT in Temperate Agroecosystems. pp. 209-229. Lewis Publishers Inc. Boca Raton, FL.