Introduction

 

Management and use of soil for crop and grassland production can have a profound impact on sustainability and long-term preservation of soil quality.  Misuse or mismanagement of this valuable resource will strongly influence air, water, and environmental quality.  Soil is an extremely complex and dynamic system of physical, chemical, and biological properties and processes.  While the primary expectation of this resource is to provide nutrients and water to support plant and animal productivity, it is also being used for recycling of biosolids, manures and other byproducts and removing impurities to benefit water and air quality.  Soil management practices need to be developed to provide sufficient food and fiber yet maintain environmental sustainability and conserve the quality of soil, water, and air resources.  This National Program is organized around five major components: 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 soil physical, chemical, and biological properties.  Research is needed to develop practices and approaches to prevent soil degradation and to remediate soils where degradation has already occurred.  

 

Equipment traffic, repeated grazing, and natural consolidation that can limit root growth and movement of water, air, and nutrients normally cause compaction in agricultural soils.  Compacted soil layers have been shown to limit yield and reduce overall productivity of many Southeastern U.S. soils.  Repeated conventional tillage on these soils can cause root-impeding layers to move closer to the soil surface, reducing soil water storage and availability to crops during periods of drought common to this region.  Researchers at Auburn, Alabama, have developed a Alazer-distance sensor@ device that can move across an area and quantify the depth and compaction of hardpan layers develop by tillage operations.  Livestock grazing also has been shown to negatively impact surface soil compaction and thereby the rate of water infiltration.  Scientists at El Reno, Oklahoma, compared the effects of various livestock grazing schemes with respect to infiltration/runoff on winter wheat and native grass watersheds.  Results showed that only the top 5 cm of the surface soil was impacted by grazing.  Runoff was initiated sooner with greater runoff rates in grazed compared to ungrazed winter wheat watersheds.  Sandy soils in the Coastal Plain region of the U.S. are susceptible to nutrient losses through leaching and often contain compacted layers that restrict root growth.  To sustain yield and to promote root growth that can utilize nutrients and prevent fertilizers from leaching, subsoil layers occasionally must be deep tilled.  Researchers at Florence, South Carolina, demonstrated that for each 10 atmospheres increase in soil strength, corn yield decreased 20 to 50 bushels per acre.  Knowing the status of soil strength and compaction will allow producers to decide when deep tillage of hardpan soils is appropriate.

Soil erosion is still considered to be a major cause of soil degradation in the U.S. and around the world.  About 1.5 to 2.0 billion tons of soil is lost by soil erosion annually.  Erosion can degrade soil quality and sustainability of agricultural soils, and introduce sediment, nutrients, pesticides and pathogens into surface waters.  Soil erosion occurs about 17 times faster than soil formation, and about 90 percent of all U.S. cropland is losing soil above the sustainable rate.  Recent annual costs of soil erosion in the U.S. have been estimated to be between 30 to 40 billion dollars.  It is no surprise that the USDA Natural Resources Conservation Service (NRCS) has dedicated over 2 billion dollars annually to the Conservation Reserve Program (CRP) to eliminate highly erodible lands from agricultural production.  Researchers at Tifton, Georgia, demonstrated that, under worst-case conditions in the Coastal Plain cotton systems, no-till/para-till/rye system had nearly nine times less soil loss and three times more infiltration than conventional tillage systems.  At Oxford, Mississippi, scientists in a collaborative project with ARS scientists at Lubbock, Texas, and scientists at Ohio State University and Louisiana State University demonstrated that ferrihydrite, an iron oxide sludge byproduct, can effectively reduced soil erodibility and phosphorus levels in soil solutions, with potential for improving water quality of runoff from agricultural fields.  Researchers at Oxford, Mississippi also released the Revised Universal Soil Loss Equation (RUSLE2) to the NRCS and the general public via a website at the National Sedimentation Laboratory and plan to incorporate this latest version of RUSLE2 into the watershed planning tool AGNPS.  

 

Mismanagement of alternative nutrient sources such as biosolids, manure, and byproducts can deteriorate soil quality, primarily by buildup of excess nutrients, heavy metals, and other toxic trace elements to higher concentrations than the ordinary soil=s background levels.  The challenge is to devise more effective and economically feasible management practices that prevent further soil degradation and provide relatively rapid remediation of the contaminated soils.  Scientists at Beltsville, Maryland, developed a series of methodologies based on plant species that can remediate soils contaminated with heavy metals such as Ni, Zn, Pb, and Cd.  These plants (hyperaccumulator plants) can take up large amounts of metals into their tissues without causing harm to the plant.  The heavy metal-enriched biomass can be used as an ore source.  In collaborative work with the U.S. Environmental Protection Agency and the University of Washington, ARS scientists at Beltsville, Maryland, have recently demonstrated that lead contaminated soils that pose a health risk to children through inadvertent soil ingestion, can be inexpensively remediated.  In a field experiment, these scientists were able to show that soil lead could be inactivated using different phosphate sources and high-iron biosolids.  Three years after application of the soil amendments, human feeding trials showed that lead bioavailability was reduced by 69 percent compared to the untreated field soil.

 

Nutrient Management

 

Nutrient losses from over application of animal manures and/or inefficient use of fertilizers on cropland is considered to be a major nonpoint source of pollution to surface and ground water resources.  Management practices must be developed that optimize the use of fertilizers and recycling of animal manure nutrients in agriculture while protecting soil and water quality.  

 

A team of ARS scientists is conducting nationally coordinated research to develop predictions of manure nitrogen availability.  Common experimental design and research protocols used at seven locations around the country demonstrated that soil temperature and soil type have the greatest impact on nitrogen availability from a given manure.  This information can be integrated into a decision support tool for optimizing manure use by synchronizing N availability with nitrogen demand by crops.

 

Nitrogen status is critical for site-specific crop nutrient management.  Large-scale assessment of the within-field spatial variability of leaf chlorophyll concentration can provide guidance for applying the appropriate amounts of N fertilizer to optimize production while minimizing excess fertilizer loss to the environment.  Scientists at Beltsville, Maryland, in cooperation with NASA scientists evaluated the status of active and passive fluorescence sensing techniques for agricultural applications.  The fluorescence contribution to the apparent reflectance signal of plants under nitrogen stress was found to be an indicator of nitrogen status.  This information tool can be used for large-scale assessment of plant conditions for site-specific nutrient management and carbon sequestration levels.

  

Soils that have received animal manures over many years have excessive nutrients, especially phosphorous that can lead to high levels of phosphorous in runoff.  Management practices must be developed that optimize recycling of manure-derived nutrients while minimizing adverse environmental consequences of manure application.  Scientists at University Park, Pennsylvania, developed a remediation treatment, synthetic gypsum from flue gas desulfurization that reduced phosphorus in runoff while posing little or no environmental threat.  Amending high P soils with this specific coal combustion by-product decreases the solubility of soil phosphorus without reducing plant available phosphorus below optimum levels for crop production.  

Vegetative buffers are increasingly adopted to minimize losses of pesticides and nutrients to surface water resources.  Because of the substantial variability in the soil and topography within individual fields and watersheds, research is being conducted to specifically understand the linkage between vegetative buffer parameters and the optimum positioning of riparian/vegetative buffers in relation to drainage area and nutrient loss.  ARS scientists at Ames, Iowa, have developed a methodology using digital elevation data and Geographic Information Systems (GIS) to identify optimum placement of riparian buffers and constructed wetlands within a watershed for more effective interception of excess nutrients.  These techniques find combinations of slope, elevation and drainage area that indicate areas where riparian buffers would be most effective.  The developed methodology could provide guidance to the Natural Resource Conservation Service (NRCS) and farmers concerning optimal buffer/constructed wetland placement for protection of water quality.

 

Soil Water

 

Water is the driving force governing crop production and nutrient movement, fate, and efficiency in the field.  Understanding the complex interactions of soil physical properties and landscape positioning on soil water dynamics will be critical to conserving natural resources while sustaining US agricultural productivity.  Since over 70 percent of US agriculture is non-irrigated, water availability is often the most limiting factor controlling crop growth and yield.  The spatial and temporal variability of soil moisture content in the field also has been shown to be the major cause of crop yield variability.  Thus, to optimize farm production, the impact of soil water dynamics (availability and variability) will have to be accounted for and used to identify different management zones within a production field.  Scientists at Fort Collins, Colorado, developed an on-the-go TDR system integrated with differential global positioning system technology to make spatial measurements of soil moisture.

 

Another challenging issue facing agriculture is the availability of accurate estimation of the spatial and temporal dynamics of soil water over large areas.  This information is crucial for hydrologic studies, agricultural planning, and decision making for water resources managers.  A simple soil water budget model has been evaluated by scientists at El Reno, Oklahoma, for its ability to adequately predict daily surface soil water content from limited soils information, climatic, and remotely sensed data for tallgrass prairie sites in Oklahoma.  Results demonstrated that the model could adequately simulate daily values of soil water content when provided good estimates of antecedent soil water content from remotely sensed data.  Such a remote sensing/modeling approach will be a valuable tool for water resource managers to assess current and future soil water supplies, and could potentially benefit crop yield prediction models.

 

Sub-optimal soil moisture conditions are often the most significant factor responsible for reducing yield in US agriculture.  Scientists from Beltsville, Maryland, have developed a Soil Moisture Stress Indicator (SMSI) that represents a wide range in climatic conditions.  The SMSI was highly correlated with corn grain yield and can potentially be used by farmers and producers to determine when and where soil moisture stress may occur.  Soil properties also can be used to estimate water retention and conductivity characteristics of soil profiles.  Scientists from Beltsville, Maryland, in collaboration with NASA developed procedures that incorporate soil survey profile information into a predictive system.  The procedures developed are capable of predicting soil water retention and conductivity properties for the thousands of soil survey descriptions available in the US.

Soil Biology  

 

Soil microbial communities are poorly understood, yet critically important to soil health.  Research will be needed to provide a better understanding of the dynamics of soil microbial communities and their relationship to soil quality.  Specifically, it is important to know how: agricultural management practices influence soil organisms; to enhance beneficial interactions between and among roots and soil biota; to manage soil organisms to control plant diseases, plant pests, and weeds; and to promote soil organisms for more efficient degradation of pesticides and other harmful and toxic compounds.  Forage legumes have a low presence in the grasslands of humid, temperate regions in the eastern US, in part because of acidic soils.  Researchers at Beaver, West Virginia, developed resistant strains of rhizobia that can survive the acidic soil conditions of the Appalachian Region.  The technique is based on an understanding of rhizobial responses to ions that characterize acidic soils, since a soil reservoir of free-living rhizobia is essential for the initiation of nitrogen-fixing nodules in legumes.

 

Management/farming practices that use high levels of fertilizers, pesticides, and fungicides, have contributed, to a certain extent to the depletion of soil beneficial organisms such as arbuscular mycorrhizal (AM) fungi.  AM fungi colonize, or invade plant root cells, establishing a symbiotic relationship which increases crop yield with lower input of fertilizer and pesticides.  The challenge is how to efficiently replenish the soil with these valuable microorganisms since AM fungi require the presence of roots for development.  Scientists at Wyndmoor, Pennsylvania, have developed methodology that allows growth of the fungus in the absence of the host.  This technique allows the production of inoculum from germinating spores more reliably and in a shorter period of time than once feasible.  Other ARS scientists are exploring the role of AM fungi in carbon sequestration and in stabilization of soil aggregates.  In collaborative work with scientists from the University of Montana, scientists from Beltsville, Maryland, demonstrated that ecosystem warming can increase carbon allocation to AM fungi, which in turn increases fungal exudates that stabilize soil aggregates. These changes, if widespread, could have important consequences for soil carbon storage and soil erosion under global warming.

 

Inhibition of soil microorganisms by herbicides has been reported in the literature, but the precise mechanisms of inhibition and development of microbial resistance to herbicides have seldom been clearly explained.  Scientists from Urbana, Illinois, examined the ecology of nitrification and herbicide biodegradation in the presence of mixtures of herbicides containing one or more components with anti-microbial properties.  They observed evidence for development of resistance of soil bacteria over time to certain inhibitory herbicides.  These findings demonstrate the possibility of microbial adaptation to the presence of herbicides within a single growing season, thus providing explanation for non-recurring persistence of some herbicides when first added as a component of a mixture, and may lead to management strategies for limiting herbicide carryover damage to crops in rotations.      

 

Productive and Sustainable Soil Management Systems

 

Because of the increasing economic and environmental concerns associated with current agricultural practices, there is a need for developing new management systems that are more sustainable and are easily adoptable by producers.  Improving or maintaining soil quality, protecting the environments, and land productivity are perhaps the most critical component to be considered in developing sustainable management practices.  Such practices, protocols or recommendations, however, are successful when they can be used to effectively manage and conserve soil and water resources while maintaining or increasing farm profitability.  There is a need for developing more comprehensive soil quality indices/tools for assessing the sustainability of land management practices.

 

ARS scientists from Ames, Iowa, in cooperation with scientists at the University of California, Davis, evaluated information from the Sustainable Agricultural Farming Systems (SAFS) study and from on-farm studies investigating the use of supplemental carbon management practices (i.e. cover crops, manure, and/or compost addition) within the San Joaquin Valley.  They were able to use a representative minimum data set (MDS) of carefully chosen soil quality indicators to provide a decision tool that could be used to select the most efficient sustainable management practices. Using this soil quality indices concept for the on-farm study demonstrated that soil organic matter and its associated benefits could be obtained in this region despite the very high temperature, intensive tillage, and need for irrigation.  This new MDS approach for soil indices should provide a more comprehensive and quantitative tool to evaluate sustainability of soil management practices.

 

Within the past seven years, ARS scientists at Beltsville, Maryland, have established a Farming Systems Project (FSP), evaluating ecological and economic sustainability of five regionally-appropriate field cropping systems.  The five cropping systems (one synthetic no-till, one conventional till, and three organic) were designed by a team of extension agents, scientists, and farmers.  A 7-year database has been developed that provides the basis for assessing the sustainability of the systems and is a valuable information tool for crop modelers.  Cover crops are becoming the essential component of sustainable farming systems because they provide additional nitrogen, reduce fertilizer need, and suppress weeds, and minimizing herbicide use.  ARS scientists at Beltsville, Maryland, evaluated over 20 species of cover crops for incorporation into the vegetable production systems and orchard management at two diverse climatic locations: tropical (Florida) and warm and arid (California).  Results demonstrated a possible reduction of nearly 50 percent in nitrogen and herbicide use in these systems.