Soil surveys: A window to the subsurface

Soils and underlying parent materials form a continuous system we must understand and manage in total. Numerous concerns (e.g., water quality, on-site waste disposal, landfill placement, and nutrient or pesticide movement) require an integrated knowledge and understanding of soil, the soil-to-substratum transition, and the deeper substratum. Soil C-horizons can exceed the thickness of the overlying A and B-horizons and contain unique morphological properties. The subsolum including C-horizons receives less descriptive emphasis than upper soil horizons. Soil scientists map and classify soils mainly on A and B-horizon properties. Soil forming and hydrologic processes that impart morphological features, however, extend considerably below these horizons. Precise adherence to Soil Taxonomy places an arbitrary constraint on field observations at 2 m. Soil scientists routinely observe C and R horizons and deeper underlying substrata in gravel pits, road cuts, barrow pits, foundation excavations, and drill cores, but provide less documentation than for upper horizons. Parent material and stratigraphy need more consideration in soil map unit design and delineation. Field observations by soil scientists below 2 m are crucial for understanding the subsolum (i.e., the morphology of, and relationships of solum to substratum). Soil surveys can convey concise and more descriptive soil-to-substrata information with little added effort or resources. Soil surveys can accomplish this end by use of block diagrams, parent material maps, and geomorphic maps that include both pedostratigraphic and lithostratigraphic detail. Soil surveys must develop soil and map unit descriptions linked to measured sections and named stratigraphic units, and describe and analyze soils and parent materials to greater depths (\u3e2 m). We use case examples to demonstrate these concepts. Soil-to-substrata documentation and presentation conveys crucial information to soil survey users. Soil-to-substrata relationships identified and recorded during a soil survey create a knowledge window to the subsurface

Emergent Imaging and Geospatial Technologies for Soil Investigations

Soil survey investigations and inventories form the scientific basis for a wide spectrum of agronomic and environmental management programs. Soil data and information help formulate resource conservation policies of federal, state, and local governments that seek to sustain our agricultural production system while enhancing environmental quality on both public and private lands. The dual challenges of increasing agricultural production and ensuring environmental integrity require electronically available soil inventory data with both spatial and attribute quality. Meeting this societal need in part depends on development and evaluation of new methods for updating and maintaining soil inventories for sophisticated applications, and implementing an effective framework to conceptualize and communicate tacit knowledge from soil scientists to numerous stakeholders

Distribution and properties of soft weathered bedrock at ≤ 1m depth in the contiguous United States

The weathered bedrock zone is increasingly recognized as an important part of ecological and hydrologic systems, but its distribution is poorly known in the contiguous United States. We used spatial and laboratory characterization data from the United States Department of Agriculture (USDA)-Natural Resources Conservation Service to assess the distribution and soil-like properties of soft weathered bedrock (saprock and saprolite) within the 48 contiguous United States. Because USDA soil inventories generally do not extend below 2m, and because the upper 1m is clearly involved in ecosystem function and vadose zone hydrology, we restricted our inquiry to soft weathered bedrock within 1m of the land surface. Soft weathered bedrock within 1m of the land surface is widespread throughout the contiguous United States, underlying at least 6% of the land area. In-depth analysis of three states showed that soft weathered bedrock at the ≤ 1-m depth underlies 22% of the total land area in California, 33% in Wyoming, and 18% in North Carolina. Soft weathered bedrock hosts pedogenic activity, as indicated by morphological features such as roots, clay films, and iron (Fe)-/manganese (Mn)-oxide concretions recorded in pedon descriptions in the database. The physical and chemical properties of soft weathered bedrock are often similar to those of the overlying soil, suggesting that in many respects soft weathered bedrock behaves like soil. It supplies water and nutrients to plants whose roots penetrate into it and it modulates through flow runoff to streams. For a more complete understanding of soft weathered bedrock, systematic data are needed on its thickness across landscapes and a consistent terminology for its various forms needs to be adopted and widely used

INFLUENCE OF A MYCORRHIZAL FUNGUS AND/OR RHIZOBIUM ON GROWTH AND BIOMASS PARTITIONING OF SUBTERRANEAN CLOVER EXPOSED TO OZONE

The influence of soilborne symbionts such as rhizobia or mycorrhizal fungi on plant response to ozone (O3) has not been well defined. Leguminous plants in the field are infected by both types of organisms, which influence plant nutrition and growth. We studied the effects of infection with Rhizobium leguminosarum biovar trifolii and/or Gigaspora margarita on response of subterranean clover (Trifolium subterraneum L. cv Mt. Barker) to O3. Exposures were conducted in greenhouse CSTR chambers using four O3 concentrations [charcoal-filtered (CF), 50, 100, or 150 ppb; 6 h day-1, 5 day wk-1 for 12 weeks] as main plots (replicated). Four inoculum types were subplot treatments, i.e., inoculated with one, both, or neither microorganisms. At 2-wk intervals, plants were exposed to 14CO2 and harvested 24 h later for determination of biomass and 14C content of shoots and roots. Ozone at 100 or 150 ppb suppressed clover growth during the experiment. Inoculation with G. margarita alone suppressed clover growth by the last two harvests, whereas R. leguminosarum alone enhanced growth during this time period. When both symbionts were present, the plants grew similarly to the noninoculated controls. Shoot/root ratios were increased by 100 or 150 ppb O3 compared to that for CF-treated plants. Shoot/root ratios were greater for all inoculated plants compared to noninoculated controls. Under low O3 stress (CF or 50 ppb), plants inoculated with both R. leguminosarum and G. margarita transported a greater proportion of recent photosynthate (14C) to roots than did noninoculated plants; we attribute this to metabolic requirements of the microorganisms. At the highest level of O3 stress (150 ppb), this did not occur, probably because little photosynthate was available and the shoots retained most of it for repair of injury. Statistically significant interactions occurred between O3 and inoculum types for shoot and total biomass. When averaged across harvests, 50 ppb O3 suppressed biomass in the plants inoculated with G. margarita alone. Apparently, the mycorrhizal fungus is such a significant C drain that even a small amount of O3 stress suppresses plant growth under these conditions

Methane fluxes in permafrost habitats of the Lena Delta: effects of microbial community structure and organic matter quality

For the understanding and assessment of recent and future carbon dynamics of arctic permafrost soils the processes of CH4 production and oxidation, the community structure and the quality of DOM were studied in two soils of a polygonal tundra. Activities of methanogens and methanotrophs differed significantly in their rates and distribution patterns among the two investigated profiles. Community structure analysis showed similarities between both soils for esterlinked PLFAs and differences in the fraction of unsaponifiable PLFAs and PLELs. Furthermore, a shift of the overall composition of the microbiota with depth at both sites was indicated by an increasing portion of iso- and anteiso-branched fatty acids related to the amount of straight chain fatty acids. Although permafrost soils represent a large carbon pool, it was shown, that the reduced quality of organic matter leads to a substrate limitation of the microbial metabolism. It can be concluded from our and previous findings firstly that microbial communities in the active layer of an Arctic polygon tundra are composed by members of all three domains of life, with a total biomass comparable to temperate soil ecosystems. And secondly that these microorganisms are well adapted to the extreme temperature gradient of their environment