Introduction

The thin layer of soil at the surface of the earth functions as a central resource to sustain life.  Soil management determines plant productivity, which in turn supports animal productivity.  Soils also remove impurities to benefit water and air quality.  It is imperative that a balance be reached between the shortterm use of the soil and the longterm sustainability of this critical resource.  Protecting, preserving, and enhancing the soil resource is a key element of this National Program.  Soil management practices need to be developed to overcome limitations to productivity while maintaining or enhancing environmental quality.  Tools need to be developed to determine the effectiveness and sustainability of soil management practices.  An overall understanding of soil physical, chemical, and biological properties and processes will allow management of the soil resource to ensure sustainable food, feed, and fiber production.  Research within this National Program is conducted in five component areas: Soil Conservation and Restoration, Nutrient Management, Soil Water, Soil Biology, and Productive and Sustainable Soil Management Systems.

Significant Accomplishments by Component:

Soil Conservation and Restoration

Soil degradation, through human activities and natural forces, has reduced the productivity of our soils and damaged adjacent ecosystems.  Soil degradation can result from accelerated soil erosion, loss of vegetative cover, oxidation of soil organic matter, and impairment of other soil physical, chemical, and biological properties.  Worldwide, erosion by water, wind, tillage, and irrigation remains a major cause of soil degradation and a primary environmental concern.  Lowcost and environmentallyfriendly methods of controlling soil erosion are needed to improve the longterm sustainability, productivity, and profitability of agriculture.  An interagency working group including Agricultural Research Service (ARS) scientists from the National Sedimentation Laboratory Oxford, Mississippi, developed design criteria for a new conservation practice for erosion control through the use of vegetative barriers (narrow strips of stiffstemmed grass).  A National Practice Standard for Vegetative Barriers was adopted and placed into the National Resource Conservation Service (NRCS) National Handbook of Conservation Practices in March 2001.  Vegetative barriers can now be used in farm conservation plans to reduce sheet and concentratedflow erosion, prevent gully development in notill systems, control runoff, stabilize steep slopes, and improve water quality by trapping sediment and other contaminants.  Scientists at the ARS Cropping Systems and Water Quality Research Unit (CSWQR), Columbia, Missouri, demonstrated that vegetative barriers reduced sediment loss by 98 percent during normal surface runoff.  However, excess runoff events can cause portions of the vegetative barrier to be washed away, particularily in areas of the landscape where runoff is concentrated causing previously trapped sediment to be eroded off the watershed.

Equipment traffic, grazing animals, and natural consolidation can cause soil compaction, thereby restricting root growth and movement of water, air, and chemicals.  Methods to determine the effects of soil compaction on crop yields and management practices to correct soil compaction are needed.  Scientists at the ARS Central Plains Resources Management Research Unit (CPRM), Akron, Colorado, have found that the Least Limiting Water Range (LLWR) can be used to evaluate changes in soil physical quality caused by compaction, and to predict compaction effects on crop yield.  In dryland cropping systems, LLWR is a good indicator of soil physical quality and crop response to the soil environment.  In irrigated systems, LLWR can improve irrigation water management by helping the producer maintain soil water content within a nonlimiting range.  Scientists from the ARS Northwest Irrigation and Soils Research Laboratory, Kimberly, Idaho, demonstrated that paratill (deep tillage without soil inversion) subsoiling breaks up compacted layers, improves water infiltration, and results in improved yield and quality of potatoes, dry beans, and small grains.  Although soil strength was consistently decreased by subsoiling, yield responses were variable for these crops, and compaction reduction was inadequate to avoid annual subsoiling.

Poor land management can cause accelerated soil acidification and buildup of excess salts, toxic trace elements, and nutrients in soil.  Effective and economically feasible management practices are needed to prevent soil degradation and to remediate degraded soils.  Certain plant species can take up large amounts of metals into their tissues (hyperaccumulator plants) without causing harm to the plant.  Growing these plants on contaminated soils or soils with a high natural content of the element of interest can result in remediation of a contaminated site and production of biomass that may be useful as an ore source.  Scientists from Beltsville, Maryland, conducted a field test of the agronomic management practices needed for profitable mining of nickel by plants (phytomining).  Biomass with 2.0 percent nickel on a dry matter basis and yields over 15 tons per hectare was obtained.  The biomass could be burned to generate energy and nickel could be recovered from the ash using existing technologies.  Growth of nickel hyperaccumulator plants in high nickel content soils of the Northwestern United States could provide producers with a new source of revenue.  This phytomining agricultural technology can also help meet U.S. strategic needs for nickel since all nickel mines in the United States have closed.

Sustainable agriculture requires a knowledge of the spatial distribution of nonpoint source pollutants such as salts and trace elements.  A number of practical, fieldscale salinity assessment techniques, based on rapidly measuring the salinity of a soil with both direct contact fourelectrode sensors and noninvasive electromagnetic sensors,  have been developed by ARS scientists from the U.S. Salinity Laboratory (USSL), Riverside, California.  Predictions of salt loading at field scales and larger have been reliably ascertained using a geographic information system (GIS), spatial statistics, noninvasive mobile salinity measurement equipment, and a model of salt movement in soil.  This GISlinked salt transport modeling approach provides a means of preparing regional scale maps showing predicted areas of salt accumulation in soil and drainage water.  These maps can be used as an information tool to ameliorate the future detrimental impact of salinity on soil and water resources.

Nutrient Management

Fertilizer useefficiency is commonly less than 50 percent in many agricultural systems.  Application of excessive amounts of fertilizer or manure is one reason agriculture is the largest nonpoint source of pollution to surface and ground water.  Economic use of renewable nutrient sources and improved nutrient use efficiency in agricultural systems are problems that must be addressed to reduce input costs and protect the environment.  Dryland corn and millet producers spend about a third of their production input dollars on fertilizer nitrogen.  Scientists at CPRM Akron, Colorado, developed a decision tool that gives producers the optimum nitrogen application rate based on different commodity prices and fertilizer costs.  As fertilizer costs go up, a substantial reduction in the optimum nitrogen rate results.  Use of this decision tool could save producers a minimum of 10 pounds of nitrogen per acre.

Nitrogen is one of the most important elements required to produce food and to supply protein.  Worldwide demand for nitrogen will increase with increasing population.  Additional information will be needed about nitrogen sources and nitrogen management so that human food needs can be met while protecting the environment.  A book edited by ARS scientists from Ft. Collins, Colorado and Ames, Iowa, "Nitrogen in the Environment: Sources, Problems, and Management," provides a holistic perspective and comprehensive treatment of nitrogen management on a national and international scale.

Research has demonstrated the value of sitespecific nitrogen management.  Scientists at the ARS Northern Plains Agricultural Research Laboratory, Sidney, Montana, compared variable rate and uniform rate fertilization methods to see if sitespecific farming and remote sensing could improve production efficiency.  Variable rate fertilization with nitrogen, phosphorus, and potassium increased sugar beet production an average of five tons per hectare without decreasing the percentage of sugar or increasing impurities.  This represents a gross production increase of approximately $170$200 per hectare.  The research also demonstrated that sugar beet yields could be predicted more than 2 months prior to harvest using remote imagery.  Beltsville, Maryland, researchers have shown that sitespecific nitrogen management can be accomplished by identifying the spatial variation in leaf chlorophyll concentration and applying appropriate amounts of nitrogen fertilizer to optimize crop growth and yield.  Reflectance spectra of corn leaves and canopies with a wide range of leaf chlorophyll concentrations were converted to spectral vegetation indices that were linearly related to leaf chlorophyll concentrations.  This technique holds promise as a valuable decision aid for managing nitrogen applications.

As plant residue decomposes in soil, most of the carbon is released back into the atmosphere as carbon dioxide, but a small fraction of the carbon is transformed into stabilized organic matter which may persist in the soil for a few years to several hundred years.  ARS scientists from the National Soil Tilth Laboratory (NSTL), Ames, Iowa,  have identified two distinct phases of stabilized organic matter: (1) an old, highly stable phase of soil organic matter that exists as discrete high density metalhumic particles and (2) a relatively young and biologically available phase existing as dense coatings on surfaces of soil clay minerals.  About 20 percent of the total soil organic carbon in a typical soil is in the old, highly stable phase, suggesting that soils can be a long term sink for carbon storage.

Soil Water

Water is the most limiting soil factor for crop growth and yield in most agricultural soils, accounting for approximately 80 percent of crop yield variability.  Soil water, directly or indirectly, affects most soil physical, chemical, and biological properties and processes.  It also functions as a transport medium for chemicals and microorganisms into, through, and below the soil profile.  Most crop production problems associated with soil water relate to its supply and availability; infiltration adequacy and timing; and prevention, elimination, or mitigation of soil water excesses.  Research is needed to develop soil management practices that will provide the optimum amount and distribution of soil water for plant growth.

Livestock grazing may increase soil bulk density and compaction, thus reducing water infiltration.  Scientists at the ARS Grazinglands Research Laboratory, El Reno, Oklahoma,  conducted research to study the effects of varying grazing schemes on infiltration and runoff.  Grazed areas initiated runoff sooner and produced greater flows than areas not grazed, but varying the timing and intensity of grazing did not effect surface runoff on native grass watersheds.  Only the top 50 mm of the soil was compacted by grazing, indicating that hoof effects are superficial and should not persist.

Soil and crop management practices can impact water infiltration and movement through the soil profile.  ARS scientists at the Soil and Water Conservation Research Unit, Pendleton, Oregon, found that the shallowest tillage produced both the greatest earthworm populations and the greatest water infiltration rates.  These results suggest that the presence of earthworms, even at the low population numbers found in the semiarid Pacific Northwest, might be important to improved water infiltration and reduced erosion under reduced or no tillage cropping systems.  Scientists at Beltsville, Maryland, using realtime measurements of soil water content, demonstrated that nearly 60 percent of all measured infiltration events were indicative of preferential flow, and that on average preferential flow occurred more readily in notill than in plowtill soil, thus possibly increasing chances for groundwater contamination.

Understanding the variability of hydrologic processes at field and watershed scales will be critical in the development of improved strategies for sustaining agricultural production and improving water quality.  Scientists from Beltsville, Maryland, developed a protocol based on groundpenetrating radar mapping of soil structures and remote sensing to accurately identify the location of environmentally sensitive source areas where water and agricultural chemicals converge.  Soil hydraulic properties are needed to predict the transport of chemicals from the soil surface to groundwater, but these properties are generally not readily available.  Scientists from USSL, Riverside, California, have developed a decision support tool, Rosetta, to predict hydraulic properties from readily available soil survey type data.  These tools will allow agencies, such as NRCS and the Environmental Protection Agency, to identify areas most at risk for transport of nutrients, trace elements, and organic contaminants from the soil surface to groundwater.

Soil Biology

The living portion of the soil consists of plant roots and remarkably diverse organisms.  Over 10,000 species of microorganisms can exist in a single gram of soil.  A greater understanding of the role of these organisms in soil physical, chemical, and biological properties and processes will be needed to manage this resource for the benefit of agricultural and other land uses.  Research will be needed to understand the basic ecology of soil organisms; to determine interactions between soil management practices and soil organisms; to manage soil organisms for control of plant diseases, plant pests, and weeds; and to employ soil organisms in the degradation of pesticides and other synthetic and natural toxins.

The successful production of leguminous crops depends on the establishment of an effective symbiosis between the plant and nitrogenfixing bacteria (rhizobia).  ARS scientists have made significant progress in identifying rhizobia that have significantly increased the productivity of field crop and forage legumes.  ARS scientists at the Soil, Plant and Nutrient Research Unit, Ft. Collins, Colorado, have developed an improved rhizobium for soybeans that has resulted in significant yield increases in the Midwestern United States.  ARS scientists from the Appalachian Farming Systems Research Center, Beaver, West Virginia,  have developed a field level sampling technique that has allowed them to capture over 300 strains of indigenous rhizobia that can survive the adverse soil conditions of the Appalachian Region.  These rhizobia can be used to improve forage establishment, growth, and persistence in the Appalachian Region, and as a germplasm resource to characterize the genetic determinants of resistance to soil acidity.

Arbuscular mycorrhizal fungi are beneficial soil fungi that colonize plant roots and contribute to plant nutrient uptake, improve soil properties, and impart disease resistance to plants.  Scientists from Beltsville, Maryland,  have shown that glycoprotein exudates from mycorrhizal hyphae can stabilize soil aggregates and contribute to storage of carbon in soils, thus improving soil quality and contributing to a reduction in atmospheric carbon dioxide.  ARS scientists from the Microbial Biophysics and Biochemistry Research Unit, Wyndmoor, Pennsylvania, are conducting research on physiological and biochemical interactions between roots and mycorrhizal fungi so they can understand why arbuscular mycorrhizal fungi are unable to complete their life cycle in the absence of a host plant.  This research should eventually allow them to produce large quantities of sterile inoculum without a host plant, for applications in agriculture and horticulture.

Management practices and amendments can be used to stimulate soil microbial populations for control of pathogen and weed pests.  ARS scientists from the Nematology Laboratory, Beltsville, Maryland, demonstrated that good quality compost, especially biomineral compost, has the capacity to suppress root rots caused by various disease agents including "red stele" of strawberry.  Significant control of this strawberry disease by biomineral compost provides a sound basis for development of a rotational cropping system for strawberry production that does not depend on methyl bromide.  Scientists from CSWQR, Columbia, Missouri, found that soils with high organic matter content and a history of minimal tillage, low agrichemical inputs, regular inputs of organic amendments, and diverse cropping systems exhibited high soil enzymatic activity, which correlated with suppression of weed seedling growth by indigenous soil microorganisms.  Maintaining soil quality and weed suppressive activity will reduce herbicide use, improve surface water quality, and improve the soil resource.

Scientists from Stoneville, Mississippi, found that atrazine degradation was rapid in fields that received two or more atrazine applications in the past 6years, while atrazine degradation was slow in fields that had received limited or no exposure to this herbicide.  Rapid adaptation of soil microorganisms for atrazine degradation may reduce the risk of water pollution, however, it also may limit the efficacy of invasive weed control.  Scientists from Urbana, Illinois, found that atrazine can be used as a nitrogen source by some soil microorganisms, and that microbial degradation of atrazine in some organisms and in soil  may be, in part, prevented by the presence of nitrogen fertilizers.  Therefore, it may be necessary to consider soil nitrogen levels when predicting the fate of atrazine.  Scientists from Urbana, Illinois, also demonstrated that soil pH can have a profound effect on both persistence and mobility of some herbicides in the environment by controlling the ionization state of the herbicide.  Herbicides in their unionized (neutral) form are preferentially taken up by bacteria, while ionized (charged) forms of a herbicide are more readily bound to soil surfaces.

Productive and Sustainable Soil Management Systems

Sustainable soil management practices that will optimize land use, protect the environment, and be readily adopted by producers must be developed using a systems approach that will integrate principles of soil biology, chemistry, and physics.  Research in this area will include developing environmentally sound, economically viable, and innovative crop rotation and residue management strategies; providing sitespecific soil management practices to optimize soil biological, chemical, and physical properties and processes; and developing soil quality tools to assess the sustainability of land management practices.   

ARS scientists are developing tillage and residue best management practices that meet the soil, climate, and crop requirements in different regions of the country.  A 13 year study of tillage and residue management by scientists from the ARS Soil and Water Management Research Unit, St. Paul, Minnesota, showed that residue management was a more important determinant of corn yield than tillage system, with important water conservation benefits in moderately dry years, but not in normal or excessively dry years.  In the Pacific Northwest, large quantities of residue from previous cereal crops are a major barrier to adoption of conservation tillage systems.  Scientists from Pullman,Washington, determined that cultivars of wheat and barley differ in their rate of straw decomposition, thus giving producers the option of selecting cultivars with more rapidly decomposing straw.  The type of tillage tool used by a producer influences the amount of crop residue left on the soil surface.  Scientists from the ARS Soil Dynamics Research Unit, Auburn, Alabama, found that chiseltype implements retain much greater amounts of crop residues on the soil surface independent of tillage depth.  Disctype implements bury larger amounts of crop residues, and the amount buried increases with tillage depth.

Soils with physical limitations to germination and root development require limited soil disturbance (conservation tillage).  Scientists at Stoneville, Mississippi, demonstrated that deep tillage (subsoiling) in the fall increased soybean yields by 2042 percent and net returns by 4398 percent when compared to conventional (disked) production systems on two high clay content soils of the lower Mississippi River Valley.  In dryland production systems in the Southwest, scientists at the ARS Conservation and Production Research Laboratory, Bushland, Texas, found that subsoil tillage reduced soil compaction, but did not increase water infiltration which was controlled by surface soil crusting.  Therefore the greater expense of subsoil tillage was not offset by increased soil moisture storage.   Rowzone strip tillage improved plant establishment and early season growth on high clay content soils with surface crusting problems at the ARS Grassland, Soil and Water Research Laboratory, in Temple, Texas.  The strip tillage modification of notillage systems can be sustainable on soils previously considered inappropriate for any type of conservation tillage practices, thus increasing adoption of conservation tillage on difficult clay soils.  All of these investigations should provide sitespecific best management practices for producers and action agencies such as NRCS.