SOIL ORDER : ULTISOLS
(Latin : ultimus means last, highly leached, clay accumulation in B horizon)
Soil Properties
Ultisols predominantly covered 5.6% of world land area (730.106 ha) or 10.6% of tropical
area (520.106 ha) (Lal, 1997). This soil have low in basic cation saturation, strongly
weathered but less than Oxisols, well-drained, highly leached and acidic, and contain an
argilic or kandic horizon (Lal, 1997). But, according to Miller et.al., 1990 that Ultisols often
have an umbric epipedon (dark-colored A and strongly acidic). However, the common
feature of Ultisols is the existing of argilic horizon. Argilic horizon has a high clay
accumulation (Bt), which is moderate to strongly acidic, often a surface horizon dark with
humus (A), and typically a leached layer (E). The high clay content in this soil may be due
to (1) sedimentation; (2) illuviation; and (3) lithological discontinuities. Intensive
weathering forms the clayey B and often reddish in color. Reddish color is caused by iron
in the soil as sesquioxide in oxidation status. Basic cation saturation must have less than
35%. Soil has low pH (less than 5.5) and in nutrients, although the nutrients content is
higher than in Oxisols. Furthermore, Landon (1984) explained that the following
possibilities will be happened when pH value less than 5.5: (i) phosphate ions combine
with iron and Al to form compounds which are not readily available for plants, (ii) All
nutrients except Molybdenum (Mo) become more available with increasing acidity,
deficiencies are therefore rare (iii) Al ions are released from clay lattices and become
established on the clay complex. Soils with low pH should be tested for exchangeable Al
as a measure of potential Al toxicity, (iv) Bacterial activity is reduced and nitrification of
organic matter is significantly retarded. The mineralogy indicates strong weathering
where kaolinite clays is more dominant than the other clays (montmorillonite, illite,
vermiculllite). Ultisols have generally good physical properties (well-drained, moderate
permeability), but have severe problems in nutrient balance.
Soil Taxonomy
Order : Ultisols
Suborders :
Aquults (Latin, aqua = water) : seasonally saturated with water
Humults (Latin, humus =earth) : high-humus surface accumulation
Udults (Latin, udus = humid) : adequate water most of year
Ustults (Latin, ustus = burnt) : dry many months
Xerults (Latin, xeros =dry)
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Character of soil in those suborders explained in detail as follows:
1. AQUULTS
Saturated water in several times during a year can lead to many features: mottling,
iron-manganese’s concretion with diameter more than 2 mm; Chroma in moist is less
than 2 or less at Ap horizon.
1.1. Plinthaquults (plinthite)
1.2. Fragiaquults (fragipan)
1.3. Albaquults (albic horizon)
1.4. Paleaquults (paleos, old = excessive development, usually very old)
1.5. Ochraquults (ochric epipedon)
1.6. Umbraquults (umbric or molic epipedon)
2. HUMULTS
1.1. Sombrihumults (sombric horizon)
1.2. Palehumults (paleos, old = excessive development, usually very old. Argilic
horizon contains weatherable mineral less than 10% in 20 to 200 micron of fraction
at 50 cm soil depth)
1.3. Haplohumult (other humults)
3. UDULTS
1.1. Fragiudults (fragipan on or under argilic horizon)
1.2. Plinthaudults (plinthite)
1.3. Paleudults
1.4. Rhodudults (value in epipedon is less than 4; argilic horizon with value is less
than 5)
1.5. Hapludults (other udults)
4. USTULTS
1.1. Plinthustults (phlinthite)
1.2. Paleustults
1.3. Rhodustults (value in epipedon is less than 4; argilic horizon with value is less
than 5)
1.4. Haplustult (other ustults)
5. XERULTS
5.1. Palexerult
5.2. Haploxerults (other xerults)
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Soil-Plant Relationship in Plantation Forestry
Some general soil-related constraints to intensive use of soils in the tropics based
on soil characteristics, moisture regime and interaction with predominant climatic factors
are identified in the following table.
Soil-related constraints for plantation forestry in the tropics (Stewards et.al., 1991 cit. Lal,
1997).
Soil Order
Inherent
P
Erosion Compaction/Crusting Trafficability
soil
availability
fertility
Oxisol
3
3
2
2
1
Ultisols
3
3
2
2
1
Inceptisols
1
1
3
2
2
Entisols
1
1
3
2
2
Alfisols
2
1
3
3
3
Aridisols
2
1
3
3
1
Vertisols
2
2
3
3
3
Note: 3 represents severe constraint; 2 moderate constraint; and 1 slight constraint
Sanchez and Salinaz (1981), Stewards et.al. (1991) and others have shown that
Oxisols and Ultisols have generally favorable soil physical properties, but are highly acidic
(pH range of 4.5 to 5.5), may contain toxic concentration of Al and Mn, are low in available
P, and are low in major plant nutrients (e.g. N, P, K, Ca, Mg). Thus, tree growth in these
soils is often correlated with the nutrient availability. Improper land use and soil
mismanagement can cause fertility depletion and structural degradation. For example,
severe erosion in many plots of teak plantation in Java and areas in outside Java is
happened which caused lost of organic matter layer. With proper land use and judicious
soil and management, afforestation and rehabilitation of degraded land as well as
plantation building, can restore soil quality and enhanced productivity.
Significant soil physical properties which influence seedling establishment and tree
growth are : (i) soil structure, (ii) soil water, (iii) soil temperature, (iv) aeration. As
mentioned above, soil physical properties in Ultisol, favor the tree growth. Soil
mismanagement such as continues cultivation and operating of logger in harvesting can
lead to structural degradation, compaction, low rate of permeability, increasing erosion.
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