SST3005 – Fundamentals of Soil Science
PJJ, PPL / UPM
LAB 11 SOIL CLASSIFICATION
Learning outcomes Student will be able to 1.
describe the Soil Taxonomy classification
2.
classify soil using Soil Taxonomy
Introduction Soils are different from one place to another because the geologic parent materials in which soils form vary across the landscape. Furthermore, different parent materials have been in place and subject to pedogenic processes for different lengths of time. Pedogenic processes also vary from one location to another depending on climate, soil organisms and topography. Parent material, time, climate, organisms and topography are considered the five factors of soil formation and these five factors control those processes directly responsible for soil formation. The degree of soil horizon development is the direct result of one or more of the following pedogenic processes: 1) accumulation of organic matter; 2) leaching of soluble salts, carbonates and bases; 3) reduction, solution and transfer of Fe; and 4) formation and translocation of colloidal material, especially, clay.
Materials 1. Soil Taxonomy : A Basic System of Soil Classification for Making and Interpreting Soil Surveys. 2nd Edition, 1999, Soil Survey Staff. USDA. (Go to http://soils.usda.gov/technical/classification/taxonomy/ to download a full text in pdf).
SST3005 – Fundamentals of Soil Science
PJJ, PPL / UPM
2. Paramananthan. S. 2000. Soils of Malaysia : Their characteristics and Identification. Vol. 1. Academy of Sciences Malaysia. (For data on soils of Malaysia)
Activities Examine the soil profile description in Appendix 2. Try to figure out the possible Soil Order with reference to Table 11.2 in Appendix 1.. Take a few minutes to examine the soil description for the Bungor series in this example. Try to figure out why it is classified in the Ultisol soil order?
Appendix 1 SOIL CLASSIFICATION The classification system used in the Malaysia is the system used in the US called Soil Taxonomy. (For a full text on the system, go to: http:// soils.usda.gov/technical/classification/taxonomy/). Soil Taxonomy uses measurable soil properties as the basis for classification. There are six categories of increasing specificity in Soil Taxonomy, from order, the most general category, to series, the most specific. Table 11.1 lists and describes these six categories. There are 12 soil orders (see Table 11.2 for a list and major features of each) and over 260 soil series in Peninsula Malaysia alone. In this system, the series name of a soil is given, followed by family and subgroup. The subgroup includes great group and the latter also indicates both suborder and order. For example, there is the series Bungor (clayey, kaolinitic, isohyperthermic subactive Typic Paleudult). Bungor is the soil series name. clayey, kaolinitic, isohyperthermic, subactive is the family. Typic Paleudult is the subgroup. The great group is Paleudult. The latter includes suborder, Udult, and indicates order, Ultisols, in abbreviation. Although this and any other subgroup name may seem only a string of nonsense syllables, each part (Typic, Pale-, ud- and -ult) has a well-defined meaning and gives qualitative or semi-quantitative information about the Bungor series soil. The family name includes similar information. Continuing with the Bungor example, the trailing -ults means that this soil belongs to the Order, Ultisol (see Table 11.2). The ud- indicates the moisture regime of this soil (Udic, meaning that there is usually adequate moisture throughout the year). Thus, the Bungor is a fertile soil that typically does not suffer from drought. The Pale- part
SST3005 – Fundamentals of Soil Science
PJJ, PPL / UPM
of the great group name indicates that this soil has an old or excessive development. The Typic indicates that this Paleudult is typical of Paleudults. Since this is an introductory course, however, we won’t go any further into classification than the most general category, Order. Soils are classified so that we can more easily remember their significant characteristics, assemble knowledge about them, see relationships among different soils and to the environment and understand their behavior and response to management. First through classification and then through use of soil maps, we can apply our knowledge of soils to specific fields and other tracts of land. Most of Malaysian soils are from seven of the 12 orders, namely Alfisols, Entisols, Inceptisols, Histosols, Spodosols, Ultisols and Oxisols. Although soil classification entails laboratory characterization, field description of soils is essential for classification. Table 11.1. Categories in Soil Taxonomy. Classification Level Order Suborder
Great Group
Subgroup
Description Most general category. All soils belong to one of 12 orders. Differentiate soils within an order due to effects of soil moisture, soil temperature and chemical or textural features. Types and number of suborders vary with different orders. Differentiate soils within a suborder due to existence of particular horizons or other features. Types and number of great groups vary with different suborders. Each great group divided into subgroups that are either typical of the great group or that are intergrades to other great groups, suborders or orders. Also, extragrades that are neither typical nor intergrades.
Family
Differentiate soils within a subgroup on the basis of soil properties that are important to plant growth or engineering applications. Such properties include texture, mineralogy, pH and so forth.
Series
Several series per family. Name comes from some geographic feature near where series was first described and has no pedogenic significance.
SST3005 – Fundamentals of Soil Science
PJJ, PPL / UPM
Table 11.2 Twelve Soil Orders of Soil Taxonomy. Order
Formative Element
Brief Description
Entisols
Entrecent
Little profile development A horizon only. Either very young soil or pedogenesis retarded by environmental conditions.
Inceptisols
Inceptinception
Somewhat more profile development than in Entisols. Cambic horizon usually present.
Andisols
Andvolcanic ash
Weakly developed soils formed in volcanic debris. These soils have a melanic epipedon. More developed than Entisols.
Aridisols
Aridarid
Arid region soils. Profile development limited due to little water movement through soil. Salt or carbonate layers present.
Mollisols
Mollmollic horizon
Grassland soils with mollic epipedon. Usually with well-developed B horizon. These are highly fertile soils.
Vertisols
Vertinvert
Soils with a high content of shrink-swell clay and dry sufficiently long for deep cracks to develop. Pedoturbation limits development.
Alfisols
Alfforest soil
Forest soils with an E and argillic B horizon but no mollic epipedon or spodic horizon. Less acid and more fertile than Ultisols.
Spodosols
Spodspodic horizon
Sandy and acidic forest soils. Contain a dark spodic horizon beneath an E horizon.
Ultisols
Ultultimate
Forest soils similar to Alfisols but more weathered. Differentiated from Alfisols by low content of base cations.
Oxisols
Oxioxic horizon
Highly weathered soils of tropical regions. Exhibit an oxic horizon. Low fertility.
Histosols
Histtissue
Organic soils. Exhibit a histic epipedon. Minimum organic matter content > 20 % if clay content low or > 30 % if clay content high.
Gelisols
Gelgelid, cold
Cold soils. Exhibit permafrost within 1 m of the surface or evidence of cryoturbation and permafrost within 2 m of the surface.
SST3005 – Fundamentals of Soil Science
PJJ, PPL / UPM
Appendix 2 SOIL PROFILE DESCRIPTION Series : Bungor o
o
Location : 2 58.844 N; 101 42.722 E
Parent Material : Shale
Drainage : Well drained
Terrain : Undulating
Vegetation/Land Use : Grass Classification : Clayey, kaolinitic, isohyperthermic, subactive Typic Paleudult. PROFILE DESCRIPTION Ap 0 – 23 cm Yellow (10 YR 7/6) clay; fine, moderate subangular blocky structure; friable; many fine pores; many fine roots; few channels; diffuse boundary to. Bt1
23 – 50 cm
Yellowish brown (10 YR 5/4) clay; moderate, medium to fine subangular blocky structure; moderately friable; thin patchy cutans on ped faces; few fine roots; few channels; diffuse boundary to. Bt2
50 – 78 cm
Dark yellowish brown (10 YR 4/6) clay; weak to moderate, medium to large, subangular blocky structure; firm; thin patchy cutans on ped faces; very few fine roots; very few channels; diffuse boundary to. Bt3
78 – 107 cm
Dark yellowish brown (10 YR 4/6) clay; weak, medium to large, subangular blocky structure; firm; thin patchy cutans on ped faces; very few fine roots; diffuse boundary. Bt4
> 107 cm
Strong brown (7YR 5/6) clay; some fine reddish brown (5 YR 5/4) mottles; medium to large, weak subangular blocky structure; firm; thin patchy cutans on ped faces; no root.
SST3005 – Fundamentals of Soil Science
PJJ, PPL / UPM
Physico-chemical Analysis Physico-Chemical Data
Ap
Bt1
Bt2
Bt3
Bt4
pH (H2O)
4.71
4.55
4.37
4.42
4.64
Ca
0.50
0.21
0.21
0.27
0.24
Mg
0.12
0.05
0.03
0.04
0.03
K
0.12
0.10
0.07
0.06
0.12
Na
0.06
0.03
0.03
0.03
0.03
ECEC (cmolc /kg)
0.80
0.39
0.34
0.40
0.42
CEC (cmolc /kg)
7.20
6.60
6.40
6.90
7.00
N
0.14
0.07
0.06
0.05
0.04
O.C
1.46
0.78
0.61
0.49
0.35
9
10
11
11
11
Sand
42.36
34.12
31.97
26.97
25.57
Silt
11.62
11.56
9.54
10.97
11.34
Clay
45.91
54.17
58.34
61.96
63.02
Exchangeable cation (cmolc /kg)
Total (%)
Available P (mg /kg)
Granulometry (%)