781701 Description

Eric Stoner Soils (781701)

Objective:

The general objective is to define quantitatively the relationships between soil reflectance and physiochemical properties of soils of significance to agriculture and engineering. Selection of soil samples with a wide rangeof important soil characteristics by statistical stratification of continental United States climatic zones permits the evaluation of climatic and genetic effects on the relationships between multispectral reflectance and these soil properties. A further objective is to define the relationships sufficiently to design further research to quantify the contributions which different soil components make to the multispectral characteristics of specific soils.

Method:

Because of the need to provide a uniform moisture condition for spectroradiometric analysis of the prepared soil samples, a procedure was chosen which creates a one-tenth bar soil moisturetension on all the soil samples (3,5). Two asbestos tension tables were constructed and a 100 cm column of water was established to create a soil moisture tension for up to 56 soil samples at one time. Sample holders were designed and constructed of plastic rings 2 cm deep by 10 cm in diameter with 60 mesh brass strainer cloth stretched taut and fastened in a countersunk groove in one end. Sample holders were painted with non-reflecting black paint to reduce unwanted reflection external to the target of interest. After saturation of the soil filled, leveled sample holders for about four hours, the samples were placed on the tension tables for 24 hours in order to reach equilibrium. The one-tenth bar moisture tension was desirable mainly for the ease with which large numbers of samples could be prepared at uniform moisture characteristics. Shortly after placement of each sample holder on the sample table of the reflectometer for spectral readings, a portion of the sample was transferred to a moisture tin, weighed, dried in a forced air oven at 105 C, weighed again, and moisture content reported as percentage of oven dry weight.

Quantification of Soil Properties

Modern soil classification systems emphasize the importance of information about the quantitative compositions of soils. In order to differentiate among soil groups, it is necessary to rely on laboratory measurements of selected soil properties. Physical, chemical, and engineering determinations of most soil properties follow well established procedures of laboratory analyses. Certain of these soil properties are selected as diagnostic criteria in the soil classification process, based on their importance in understanding the genesis of the soil. By a procedure of empirical correlation, critical limits between sets of soils are established, designed to reflect the influence of the soil forming factors of climate, parent material, relief, biological activity, and time.

Quantitative measurements of soil spectral properties have become available as a diagnostic tool for the soil scientist with the advent of such instruments as the Exotech Model 20C spectroradiometer. However, the climatic and genetic effects on the relationships between measured spectral properties and specific chemical, physical, and biological properties of the soil are not well understood. Whereas soil color is used as diagnostic criterion in the U.S. Soil Taxonomy (7), the determination of soil color by comparison with a color chart continues to be a rather nonquantitative and subject procedure. Spectral characterization of soil "color" by means of quantitative spectroradiometric measurements may add to the precision with which soils can be differentiated. With this increased precision of soil spectral characterization, the relationships with the more important diagnostic soil characteristics or qualities that are not so easily and accurately observed may be better understood.

EXPERIMENTAL APPROACH

Stratification and Sampling

Approximately 250 soils, representing a statistical sampling of the more than 10,000 soil series in the United States were selected for this investigation. Selections were made from a list of the more than 1300 Benchmark soil series representing those soils with a large geographic extent and whose broad range of characteristics renders these soils so widely applicable for study. Stratification of soil sampling was based on series type location within climatic zones. Climatic strata included the frigid, mesic, thermic, and hyperthermic soil temperature regimes as defined by the U.S. Soil Taxonomy (2,6,7) as well as the perhumid, humid, subhumid, semiarid, and arid moisture regions as identified by Thornthwaite's 1948 Moisture Index (8). A random selection procedure was used within each stratified climatic zone to select a number of soils series approximately in proportion to the geographic extent of that region. Resulting sample distribution by climatic region for the soils actually received is shown in Table 1. Considerations were also made to include soils which represent the major parent material categories and the ten soils orders of the U.S. Soil Taxonomy (7). Table 2 presents the distribution of the Benchmark soil series on-hand according to soil parent material. As can be seen in Table 3, the distribution to Benchmark soils used for this study is very similar to the areal extent of the nine soil orders found in the continental United States (Oxisols being absent in the contiguous states).

             Table 1.  Distribution of soils by climatic region

             __________________________________________________

                                           Number of Benchmark
                 Climatic Region              Soil Series

             __________________________________________________

              1.  Perhumic Mesic                    6
              2.  Humid Frigid                     18
              3.  Humid Mesic                      37
              4.  Humid Thermic                    30
              5.  Humid Hyperthermic                6
              6.  Subhumid Frigid                  21
              7.  Subhumid Mesic                   23
              8.  Subhumid Thermic                 18
              9.  Subhumid Hyperthermic             2
             10.  Semiarid Frigid                   9
             11.  Semiarid Mesic                   24
             12.  Semiarid Thermic                 10
             13.  Semiarid Hyperthermic             5
             14.  Arid Frigid                       2
             15.  Arid Mesic                       16
             16.  Arid Thermic                     12
             17.  Arid Hyperthermic                 1
                                                  ___
                                                  240 total
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             Table 2.  Distribution of soils by parent material
      
       _________________________________________________________

           Parent Material                          Number of
                                              Benchmark Soil Series
       _________________________________________________________

      Rocks weathered in place                           
           Igneous                                       10
           Sedimentary                                   27
           Metamorphic                                    1
           Soft rock residuum                             5

     Transported materials
          Alluvium (general)                            38
               Calcareous                               11
               Non-calcareous                           15
          Colluvium                                      3
          Lacustrine                                     4
          Marine sediments                              16
          Loess                                         29
          Other eolian sediments                         8
          Glacial drift
               Till                                     29
               Calcareous till                           5
               Glaciofluvial deposits                    4
               Glacial outwash                           4
               Glaciolacustrine materials                2

      Organic materials                                  2
      Loamy sediments                                   17
      Silty sediments                                    4
      Calcareous silt loam                               3
      Marsh deposits                                     1
      Pedisediments                                      2
                                                       ___
                                                       240 total
      
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                Table 3.  Distribution of soils by Soil Order.

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                              Benchmark Soils    United States Extent

                            Number     Percent         Percent
       _________________________________________________________
       
          Mollisol             73        30.4            24.6
          Alfisol              40        16.7            13.4
          Entisol              39        16.2             7.9
          Aridisol             25        10.4            11.5
          Ultisol              22         9.2            12.9
          Inceptisol           18         7.5            18.2
          Spodosol             15         6.2             5.1
          Vertisol              4         1.7             1.0
          Histosol              4         1.7             0.5
                                 ___
                          total  240
       
       _________________________________________________________

Acquisition of Soil Samples

The Soil Survey Investigation Division of the Soil Conservation Service (USDA) cooperated with LARS in the collection of field samples from 39 states. Duplicate field samples were collected for all Benchmark soil series requested: one sample from a site near the type location for the current official series, and one sample from a site located from one to 32 kilometers from the first site and in a different mapping delineation. Soil Conservation Service field survey personnel were responsible for sample collection of Benchmark soils in their locality. Of the original list of approximately 250 Benchmark soils requested, the Soil Conservation Service has collected, properly identified, and forwarded 240 Benchmark soils, or 480 duplicate soil samples to LARS. This excellent response of over 95 percent of the requested samples forms an outstanding collection of soil samples for detailed chemical, physical, and spectral analysis. All samples conform to the central concept of each individual soil series as each soil would be identified and mapped by an experienced soil surveyor in the field.

Preparation of Soils for Analysis

After receipt of the soil samples and initial data logging, samples were dried, crushed, and sieved to remove all particles larger than 2 mm diameter. Cardboard containers were used to store subsamples of each soil sample for chemical, physical, spectral, and engineering determinations.

Spectral Measurements

The Exotech Model 20C was used in an indoor configuration with a bidirectional reflectance factor reflectometer (1,4) in order to obtain spectral readings in the 0.52-2.3 um wavelength range. The illumination source was a 1000 watt tungsten iodine coiled filament lamp which transfers a highly collimated beam by means of a paraboloidal mirror to the sample-viewing plane. Detector height above the sample was 2.4 m, and a 3/4 field of view required that the sample holder be approximately 10 cm in diameter.

Soil Measurements

Other measurements made of the soil are listed in Table 4.

 
Table 4.  Soil characteristics and descriptions that may be 
included in the data base.
 
       Taxonomic                             Site
      Information                       Characteristics
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Order                                   Soil series name
Suborder                                Horizon designation
Great group                             Moisture regime
Subgroup name                           Drainage class
Particle size class                     Slope
Contrasting particle size class         Erosion phase
Mineralogy class                        Physiographic position
Temperature regime                      Parent material
Other modifiers                         Soil evaluation
                                        Natural vegetation or crop
                                           Site location
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      Physical                                 Chemical
  Characteristics                          Characteristics
_________________________________________________________
 
Soil moisture tension                      Organic carbon
Water content                              Extractable bases:
Munsell color (moist)                        calcium
Textural class designation                   magnesium
USDA particle size distribution:             sodium
   sand content                              potassium
   silt content                            extractable acidity
   clay content                            cation exchange capacity
   very coarse sand                        base saturation
   coarse sand                             Iron oxide
   medium sand                             Aluminum oxide
   fine sand                               Manganese dioxide
   very fine sand
   coarse silt                             Available phosphorus
   fine silt                               Available potassium
Erosion factor
Wind erodibility group
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_________________________________________________________
                      Engineering
                    Characteristics
_________________________________________________________
     Liquid limit                    Compression index
     Plastic limit                   ASTM particle size distribution:
     Plasticity index                medium sand
     Activity                        fine sand
     Liquidity index                 fines
     Shrinkage limit                 Specific gravity
     Shrinkage ratio                 AASHO soil classification
     Volumetric shrinkage            Unified soil classification
     Linar shrinkage
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Additional Information

Additional information about the experiment including detailed chemical, physical, and spectral soil properties can be found in reference 9.

References

1. DeWitt, D. P. and B. F. Robinson. 1976. Description and evaluation of a bidirectional reflectance factor reflectometer. Information Note 091576, Laboratory for Applications of remote Sensing, Purdue University, West Lafayette, IN.

2. FAO-UNESCO. 1975. Soil map of the world, Vol. II: North America. United Nations Educational, Scientific, and Cultural Organization, Paris.

3. Jamison, V. C. and I. F. Reed. 1949. Durable asbestos tension tables. Soil Science 67:311-318.

4. Leamer, R. W., V. I. Meyers and L. F. Silva. 1973. A spectroradiometer for field use. Rev. Sci. Instrum. 44:611-614.

5. Leamer, R. W. and B. Shaw. 1946. A simple apparatus for measuring noncapillary prorsity on an extensive scale. J. Amer. Soc. Agron. 33:1103-1108.

6. Smith, Guy D., Ranklin Newhall and Luther H. Robinson. 1964. Soil temperature regimes, their characteristics and predicatability. SCS-TP- 144. Soil Conservation Service. U.S. Dept. of Agriculture Washington, D.C.

7. Soil Survey staff. 1975. Soil taxonomy -- a basic system of soil classification for making and interpreting soil survey. Soil Conservation Service. U.S. Dept. of Agric. Agriculture Handbook No. 436, Washington, D.C.

8. Thornthwaite, C. W. 1948. An approach toward a rational classification of climate. Geograph. Rev. 38:55-94.

9. Stoner, E. R., M. F. Baumgardner, L. L. Biehl, and B. F. Robinson. 1980. Atlas of Soil Reflectance Properties. Research Bulletin 962. Agriculture Experiment Station, Purdue University, West Lafayette, Indiana.

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