NUTRIENT CYCLING - SOIL CLASSIFICATION

Soils and their fertility are important in determining the distribution of vegetation. To understand the ways in which nutrients cycle in rainforests we need some understanding of the different soil classification schemes used in the literature. These notes provide a brief introductory background to the description and classification of soils. Also see the lecture supplements in your Practical Manual.

Soil development

- eluviation ----> horizons

Soil profile

= set of horizons between undifferentiated parent material and the surface litter = SOLUM

Horizons may be subdivided as:

• O - sometimes given as A_o
• A - zone of eluviation
• B - zone of illuviation
• C = slightly weathered parent material, essentially unaltered by processes acting above.
• R = regolith - top layer of unconsolidated material that covers crustal rocks.

Produced by:-

1. shattering of parent rock due to expansions and contractions resulting from changing temperatures over long periods of geological time.
2. deposition of wind-blown material = LOESS, aeolian.
3. deposition of water-borne ALLUVIUM.
4. deposition of debris from surrounding hillsides that has worked down the slope = COLLUVIUM.

If soil hasn't developed in situ (i.e. loess, alluvium or colluvium),
D = underlying rock, which may be unrelated to the soil.

The thickness and complexity of a soil profile is related to time, climate and vegetation.
i.e. SOIL PROFILES ARE OFTEN MORE DEPENDENT ON CLIMATE AND VEGETATION THAN ON ROCK TYPE.

SOIL CLASSIFICATION

1. GREAT SOIL GROUPS

• system developed in Russia by Dokuchaiev.
• widely used, some Russian names.
• recognizes:

(a) ZONAL SOILS

• formation controlled by climate.
• fully developed soils of a given climatic zone tend to be very similar, i.e. characteristics are acquired from the environment rather than parent material.
• easily mapped on a global scale - relates to biomes.

{Soil maps are based on vegetation maps because soil profiles haven't been described for all areas.}

THERE ARE SIX MAJOR CLASSES OF ZONAL SOILS:

1. Tundra soils

2. Podzolic soils

3. Latosols and laterites
Laterites are widespread in Australia, reflecting past climates. It is thought that they result from a fluctuating water-table, with oxidation of Fe, and strong leaching to produce a kaolin clay layer.

4. Transition and Prairie soils

5. Chernozems

6. Desert soils

(b) AZONAL SOILS

• formation doesn't follow a regional pattern.
• many, or all, of the soil characteristics are inherited from the parent material, e.g. alluvial soils.

(c) INTRAZONAL SOILS

• possess some inherited and some acquired characteristics.

AUSTRALIAN SOIL CLASSIFICATION SCHEMES

Prescott (1931) introduced the Great Soil Groups for Australian soils.

• named many new groups not described elsewhere.
• This system has been used in Australia almost exclusively since,
  with some modifications based on more recent experience.

Stephens (1962) made the most important modifications of Prescott's groupings.

• based groupings on morphological features.
• divided profiles on basis of differentiation.

Solum differentiated:-

1. PEDALFERS - no CaCO₃ accumulated in profile because of leaching, hence acid with Al and Fe (podzols, lateritic soils).
2. PEDOCALS - CaCO₃ accumulation because soil not completely flushed through by percolating water because it is pulled back from above by evaporation.
   - i.e. found in dry, hot climates - Chernozems, prairie soils, desert soils.

Stace et al. (1968) contributed further modifications.

• present groupings in order of profile development.
• list profile descriptions.
• based on Russian system, widely used in Australian literature.
• no key, so description of profiles can be highly subjective.
• classes are heterogeneous and unwieldy.

2. NORTHCOTE'S (1971-->1979) SYSTEM

• developed a dichotomous hierarchical key to Australian soils.
• based on profile descriptions (physical features) = PROFILE FORM.
  (the overall visual impact of physical soil properties are used
  to distinguish between groups at each step in the key.)
• developed for soil mapping.
• alphanumeric - doesn't describe or name soil classes.
• simple, unambiguous; suitable for field work.

Disadvantages are:

• nomenclature is sometimes confusing.
• emphasis on A₁ and A₂ horizons can lead to difficulty with disturbed soils.

Divisions (Primary Profile Forms) = 4 based on texture
Subdivisions = 11
Sections = 54
Classes = 271
Principal Profile Forms = 855

Divisions are:-

1. O = organic,
2. U = uniform,
3. G = gradational,
4. D = duplex.

Gradational soils

• each successive horizon passes gradually from the one above to the one below.
• boundaries usually diffuse or gradual.
• mineral soils showing increasingly more clay with depth.
• texture difference between consecutive horizons < 1½ texture groups.

Duplex/Texture Contrast soils

• mineral soils with a texture contrast 1½ texture groups between A and B horizons.
• usually have a sharp boundary, i.e. bottom of A₂ to top of B 10 cm.

• developed in 1960's, leading to the U.S. Soil Survey Manual (1975).
• developed for making and interpreting soil surveys.
• rapidly becoming a de facto international classification.
• hierarchical
  - order ---> suborder ---> great group --->subgroup --->family---> series.
• completely new nomenclature devised from classical Greek and Latin roots;
  therefore avoiding long-established but loosely used names.

Disadvantages:

• Classes are somewhat disjoint - intermediate soil types not easily catered for.
• Based on U.S. soils - not all possible classes have been described.
• Requires laboratory analyses - based on some methods not used in Australia.
• Uses soil moisture and temperature at high levels in the classification. Australian soil scientists disagree with this because these features are easily affected by seasonal and year-to-year variation.

{See lecture supplement for table of U.S. Soil Orders and approximate Great Soil Group equivalents.}

Moore et al. gives approximate correlations between the classifications of Stace et al., Northcote, U.S. Soil Taxonomy and World Soil Map (FAO-UNESCO hybrid of the Great Soil Groups and US Soil Taxonomy).

Refer to Australian Soil Key.

• developed by a committee convened by Ray Isbell (CSIRO Davies Laboratory), since 1985.
• first approximation "published" in 1989, second 1992, 3rd 1993, published by CSIRO in 1996.
• new scheme because overseas' schemes (US Soil Taxonomy or FAO- UNESCO) are based mostly on northern hemisphere temperate zone soils, and experience has shown that these aren't the most appropriate for Australian soils.
• all terms used in the classification are consistent with those defined in the Australian Soils and Land Survey Field Handbook (McDonald et al. 1990).

ROCKS OF THE WET TROPICS

1. Metamorphics
• formed 360 m y BP as sediments compressed on floor of ancient ocean. Sediments fused into a layered and folded block of mixed composition extending for hundreds of kilometres along the coast and for a hundred kilometres inland.
2. Granites
• formed about 200 to 300 m y BP from the injection of magma (molten rock) into the overlying rocks. Magma is rich in quartz and cools slowly, deep below the surface, forming coarsely crystalline, light-grey to pink rock which is only exposed where the overlying rock has eroded.
3. Volcanics
• formed when lava erupted onto the land surface and cooled quickly. Some light pink and grey volcanic rocks which are rich in quartz and have the texture of porcelain formed in the southern and western parts about 250 m y BP. More recently (about 1 to 3 m y BP) basalt lava, which contains no quartz, erupted and flowed over the Atherton Tableland and other parts of the Wet Tropics. The basalt, often containing bubbles, formed a layer of black, finely crystalline rock which weathered to bright red soils.

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General
• Black C.A., Evans D.D., White J.L., Ensminger L.E. & Clark F.E. (Eds) (1965) Methods of Soil Analysis, Part 1. Physical and Mineralogical Properties, Including Statistics of Measurement and Sampling. American Society of Agronomy, Madison, Wisconsin. [631.4 BLA]
• Black C.A., Evans D.D., White J.L., Ensminger L.E. & Clark F.E. (Eds) (1965) Methods of Soil Analysis, Part 2. Chemical and Microbiological Properties. American Society of Agronomy, Madison, Wisconsin. [631.4 BLA]
• Buckman H.O. & Brady N.C. (1969) The Nature and Properties of Soils. 7th ed. Macmillan, Toronto. [631.4 BUC]
• Rayment G.E. & Higginson F.R. (1992) Australian Laboratory Handbook of Soil and Water Chemical Methods. Australian Soil and Land Survey Handbooks v. 3. Inkata Press, Melbourne.
• Soil Survey Staff (1975) Soil Taxonomy - a Basic System of Soil Classification for Making and Interpreting Soil Surveys. U.S. Department of Agriculture, Washington, D.C.
• United States Department of Agriculture (1951) Soil Survey Manual. Agriculture handbook No. 18. U.S. Goverment Printing Office, Washington, D.C. [631.4773 UNI]




Tropics

• Craswell E.T. & Isbell R.F. (Eds) (1985) International Workshop on Soils Research in the Tropics. ACIAR and Inkata Press, Mt Waverley, Victoria.
• Food & Fertilizer Technology Centre (1985) Soil Taxonomy: Review and Use in the Asian and Pacific Region. FFTC Book Series No. 29, Taiwan.
• Golley F.B. (1986) Chemical plant-soil relationships in tropical forests. J. Trop. Ecol. 2, 219-29.
• Kalpage F.S.C.P. (1974) Tropical Soils: Classification, Fertility and Management. Macmillan, Delhi. [631.4913 KAL]
• Lal R. (1987) Tropical Ecology and Physical Edaphology. John Wiley & Sons, New York. [574.52623 LAL]
• Landon J.R. (ed.) (1984) Booker Tropical Soil Manual. A Handbook for Soil Survey and Agricultural Land Evaluation in the Tropics and Subtropics. Pitman Press, Bath. [631.49113 BOO]
• Lathwell D.J. & Grove L. (1986) Soil-plant relationship in the tropics. Ann. Rev. Ecol. Syst.17, 1-16. [574.5 P11]
• Richter D.D. & Babbar L.I. (1991) Soil diversity in the tropics. Adv. Ecol. Res. 21, 315-89.
• Sanchez P.A. (1989) Soils. In: Tropical Rainforest Ecosystems: Biogeographical and Ecological Studies (Ed. by H. Lieth and M.J.A. Werger), pp. 73-88. Ecosystems of the World 14B, Elsevier, Amsterdam.
• Stark N. (1978) Man, tropical forests, and the biological life of a soil. Biotropica 10, 1-10.
• Theng B.K.G. (1991) Soil science in the tropics - the next 75 years. Soil Science 151, 76-90.




Australia

• Division of Soils, CSIRO (1983) Soils: an Australian Viewpoint. CSIRO, Melbourne/ Academic Press, London. [631.4994 SOI]
• Isbell R.F. (1992) A brief history of national soil classification in Australia since the 1920's. Aust. J. Soil Res. 30, 825-42.
• Isbell R.F. (1996) The Australian Soil Classification. (Australian Soil And Landsurvey Handbook Series, v. 4). CSIRO, Australia.
• Leeper G.W. & Uren N.C. (1993) Soil Science - An Introduction, 5th edition. Melbourne University Press, Melbourne.
• Lindsay A.M. (1985) Are Australian soils different? Proc. Ecol. Soc. Aust. 14, 83-97. [574.50994 P1]
• McDonald R.C. & Isbell R.F. (1990) Soil profile. In: Australian Soil and Land Survey: Field Handbook, 2nd edition. (Ed. by R.C. McDonald, R.F. Isbell, J.G. Speight, J. Walker & M.S. Hopkins), pp. 103-152. Inkata Press, Melbourne.
• Northcote K.H. (1979) A Factual Key for the Recognition of Australian Soils, 4th ed. Rellim, Adelaide. [631.4794 NOR]
• Stace H.C.T., Hubble G.D., Brewer R., Northcote K.H., Sleeman J.R., Mulcahy M.J. & Hallsworth, E.G. (1968) A Handbook of Australian Soils. Rellim, Adelaide. [631.4994 STA]
• Stephens C.G. (1962) A Manual of Australian Soils, 3rd ed. CSIRO, Melbourne. [631.4994 STE]

Page last revised October 2002/ Bob Congdon