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TSSH Part 623

Dynamic Soil Properties

Collecting and using dynamic soil property data to assess soil quality in NRCS conservation activities (623.00)

The soil survey program has four legislated core mission functions:

  • Make an inventory of the soil resources of the United States;
  • keep the soil survey relevant to ever-changing needs;
  • interpret the information and make it available in useful form; and
  • promote the soil survey and provide technical assistance in its uses for a wide range of community planning and resource development issues related to nonfarm and farm uses.

Collecting and using dynamic soil property (DSP) data in NRCS conservation planning touches to varying degrees upon each of these four mission functions. It is important that the soil survey define, document, and interpret how soil properties and their interpretations change in relation to various land uses and management systems.

To date, the soil survey program has done an outstanding job of providing the Nation with soil maps and descriptions of the dominant and minor soil components within the polygons of a soil map unit. For many soils, one or more soil profiles have been sampled for laboratory analysis and have had what is called a “complete characterization” suite of analyses performed. While our current laboratory database is the best in the world, each dataset represents the given soil under whatever use and management was present at the time of sampling. Sample sites were and are typically selected by the soil mapper because they represent the dominant scenario of soil properties and land use. The dataset is a snapshot in time and reflects the use and management at that site.

As time has passed, soil scientists have become increasingly aware that some soil properties can vary significantly for a given soil under different vegetation, vegetative condition, and management systems. These varying properties can have a dramatic effect on interpretations needed for conservation planning, environmental analysis, monitoring, planning, and decision making. Some of these properties are: soil erodibility factors, such as structure and soil organic matter (for wind erosion and water erosion); runoff vs. throughflow (hydrologic soil groups); available water capacity; depth to restrictions that limit the penetration of roots, water, and air; pH and base status; organic matter content; and ability to hold and supply nutrients and to hold and break down pesticides. Recently, we have become aware of the need to know how much carbon a soil can sequester and sustainably retain under different use and management scenarios. Soils data need to reflect what is known about the real world if we are to make better decisions regarding carbon sequestration, energy production, and other concerns.

These properties that vary with use and management have been called use-dependent, temporal, or dynamic soil properties. Changes in dynamic soil properties can be driven by natural factors, by use and management, or by their combined impacts. Two primary kinds of change are trend and fluctuation. Trend changes, such as a decrease in soil organic matter, are important considerations for long-term soil resource management. Fluctuations, such as seasonal variations in the depth to the water table, are important for short-term management decisions. The soil survey can provide information about both kinds of change.

Collecting and delivering data and interpretations for NRCS conservation planning activities will provide the information needed to maintain high-quality soils, a productive landscape, and a healthy environment. Dynamic soil property data and interpretations will help to meet the following customer needs:

  1. Provide soil survey data through eFOTG that contain the most appropriate information tailored for the land manager’s system to support USDA programs and planning activities and guide the selection of conservation practices
  2. Provide information and procedures for soil resource inventory for farm planning to assess current conditions or the soil’s quality and estimate benefits of recommended conservation systems and practices
  3. Determine and quantify soil properties of sustainable land management systems and provide data documenting unsustainable practices from the perspective of soil quality, soil function, and ecosystem services
  4. Provide information for use by decision makers to help identify and protect lands at risk of irreversible change (e.g., erosion, contamination)
  5. Provide products to educate the public on how soils change in response to human activity and on the importance of soil to society

As an example, the resource soil scientist can assist the field office planner by reviewing the published soil survey information for the cooperator’s land, learning of the cooperator’s requests, assisting in the field resource inventory, determining soil-related concerns, and recommending or evaluating planned practices and their ability to ameliorate the concerns. Typically, in conventionally tilled fields, organic matter has been depleted, structure has deteriorated, tillage pans have formed, and acidification or salinization may have occurred. The soil scientist can determine whether the conservation practices that will address these issues have been included in the plan. At present, RUSLE2 K factors cannot be altered (except within RUSLE2 for areas that have frozen soils in the winter). Organic matter, structure, and water permeability affect the K value. Even where data (such as K value) cannot be changed, conservation practices that improve the ability of the soil to resist erosion can be implemented. Soil properties, derived properties, interpretations, and conservation practice recommendations need to be based on the best available information.

If the opportunity exists to collect dynamic soil properties data according to the DSP data collection protocols (more intensive data collection than brief observations to document the need for selected conservation practices), it is recommended that the resource soil scientist coordinate measurements/sampling plans with the appropriate MLRA Soil Survey Office Leader and build the collection into a project plan. Doing so will help to ensure that the data collected will be documented in standardized databases and will become available for future use.

Any findings should be documented for the plan. Any data collected should be entered in pedon PC, entered in NASIS, and transmitted to the State Soil Scientist in order to enrich the database and provide information that may be needed in any update activities.