Wetland soil taxonomy

Taxonomy is a narrower term than classification. Classification includes taxonomy, but it also includes the grouping of soils according to limitations that affect specific practical purposes, such as the soil limitations affecting the foundations of buildings. Taxonomy is the part of classification that is concerned primarily with relationships.Our study focus on comparison between United State and Vietnam Soil Taxonomy, also aim to comprehend the classification systems in the both two nations.

VNU University of Science

Wetland soil taxonomy in Vietnam and the US

Instructor: Associated Professor Nguyen Thi Loan, Faculty of Environmental Science, VNU University of Science

Group 1: Students: Do Thi Ngoc Bich Phan Thi Thuy Dung -Hoang Thi Giang - Tran Thu Trang - Trinh Thi Thu Trang

I. Introduction

Taxonomy is a narrower term than classification Classification includes taxonomy, but it also includes the grouping of soils according to limitations that affect specific practical purposes, such as the soil limitations affecting the foundations of buildings Taxonomy is the part of classification that is concerned primarily with relationships Our study focus on comparison between United State and Vietnam Soil Taxonomy, also aim to comprehend the classification systems in the both two nations

II. Study Methodology

The knowledge we obtained and the document that we studied was from monograph books, science reports from US Department of Agriculture/ Department of Land Management, articles and other references…

III. Results and Discussion

1 Comparison of soil taxonomy in VN and US

1.1 The US Soil Taxonomy:

There are 7 categories in the US soil taxonomy:

Order (12 orders): This category is based largely on soil forming processes as

indicated by the presence or absence of major diagnostic horizons A given order includes soils whose properties suggest that they are not dissimilar in their genesis They are thought to have been formed by the same general genetic processes

Suborder (63 suborders): Suborders are subdivisions of orders that emphasize

gentic homogeneity The presence or absence of properties associated with wetness, climatic environment, major parent material, and vegetation

Great Group (319 great groups): Great groups are subdivisions of suborders

according to similar kind, arrangement, and diagnostic horizons The emphasis is

on the presence or absence of specific diagnostic features, base status, soil temperature, and soil moisture regimes

Subgroup (2484 subgroups) Subgroups are subdivisions of the great groups The

central concept of a great group makes up one group (Typic) Other subgroups may have characteristics that are intergrades between those of the central concept and those of the orders, suborders, or great groups Extra gradation is used to identify critical properties common in soils in several orders, suborders, and great groups

Family (8000 families): Families are sound in soils with a subgroup having

similar physical and chemical properties affecting their response to management and especially to the penetration of plant roots Differences in texture, mineralogy, temperature, and soil depth are bases for family differentiation

Series (approximate 19000 series in the U.S.): Its differentiating characteristics

are based primarily on the kind an arrangement of horizons, color, texture, structure, consistence, reaction of horizons, chemical, and mineralogical properties

of the horizons

Phases: Based on these differences are detailed mechanical components, surface,

erosion rate, slope, or some other characteristic

1.1 The classification of soil in Vietnam

In Vietnam taxonomy, we divided soil into Order => Suborder => Group.

At the level of order, soil classification has only 13 orders The basic of Vietnam soil classification is composition characteristic.

1.2 Comparison between Soil taxonomy categories in VN and in the US:

- VN classify soil in 3 categories while in US taxonomy, there are 7 categories

- Vietnam soil taxonomy is mainly based on composition characteristic of soil while in the US taxonomy, in each categories, they based on many other criteria

1.3 Reasons for the differences :

• US taxonomy establishment:

Implemented long time ago with big budget and many experts Consult: self-established

Scale: whole territory

• Vietnam taxonomy establishment:

Newly implemented

Consult: from three giant taxonomy systems: Xoviet Union’s, FAO’s, US

Scale: small area or provinces

2 Wetland soil in the US taxonomy and Vietnam taxonomy:

In both two systems, we can find wetland in the areas of Histosols order and some other orders The orders with yellow marks indicates order that ave wetland areas

Histosol Histosols

Alisols

2.1 Histosols

Histosols are organic soils produced by the deposition and accumulation of dead plant remains The central concept of Histosols is that of soils forming in organic soil materials, that formed almost exclusively in wetlands, whereas the other orders are mineral soils The root element "histos" was used to indicate that these soils are composed largely of plant tissue (at least 20-30% in most of upper parts, Soil Survey Staff 1975, p 72)

 They are essentially the Peat, Bog, Half Bog, and Muck soils of classifications Obviously, the preservation of organic matter in these soils is associated with the predominance of saturated conditions These soils are of biogenic origin (along with marls) and are the most fertile soils worldwide Histosols form only under conditions of continuous to near continuous saturation or waterlogging The general rule is that a soil without permafrost is classified as a Histosol if half or more of the upper 80 cm is organic Having organic soil materials that meet one or more of the following:

a Overlie cindery, fragmental, or pumiceous materials and/or fill their interstices and directly below these materials have either a densic, lithic, or paralithic contact; or

b When added with the underlying cindery, fragmental, or pumiceous materials, total 40 cm or more between the soil surface and a depth of 50 cm; or

c Constitute two-thirds or more of the total thickness of the soil to a densic, lithic,

or paralithic contact and have no mineral horizons or have mineral horizons with a total thickness of 10 cm or less; or

d Are saturated with water for 30 or more cumulative days during normal years (or are artificially drained), have an upper boundary within 40 cm of the soil surface, and have a total thickness of either:

(1) 60 cm or more if three-fourths or more of their volume consists of moss fibers or if their bulk density, moist, is less than 0.1 g/cm3; or

(2) 40 cm or more if they consist either of sapric or hemic materials, or of fibric materials with less than three-fourths (by volume) moss fibers and a bulk density, moist, of 0.1 g/cm3 or more.

 Other Histosols that have more thickness of sapric soil materials than any other kind of organic soil materials either:

1 In the organic parts of the subsurface tier if there is no continuous mineral layer 40 cm or more thick that has its upper boundary within the subsurface tier; or

2 In the combined thickness of the organic parts of the surface and subsurface tiers if there is a continuous mineral layer 40 cm or more thick that has its upper boundary within the subsurface tier.

 Histosols in US are divided into 5 suborders: Folists, Wassists, Fibrists, Saprists, and Hemists

 Folists(“free drained” histosols’ found in cool mountainous regions): Histosols that are not saturated with water for long periods of time during the year

 Wassists: Histosols that are submerged for more than 21 hours every day

 Fibrists(fibers compose >2/3 of the mass; Sphagnum bogs): Histosols that are primarily made up of only slightly decomposed organic materials, often called peat

 Saprists(fibers compose <1/3 of the mass; mucks): Histosols that are primarily made up of highly decomposed organic materials, often called muck

 Hemists(fibers compose 1/3; peats): Histosols that are primarily made up of moderately decomposed organic materials

These dominant suborders of histosols in US were located as in figure 1 below:

Figure 1: Distribution of histosols’ dominant suborders in US

 There are two main histosols areas in Việt Nam: U Minh Thuong (kiengiang) national park and VồDơi Nature reserve (camau);

The two suborders: Thionic histosols and Fibric Histosols

• Thionic Histosol:is formed in low-lying terrain by plants thrive, after death they accumulate in the plant material layer thickness> 50 cm

Thionic histosols is flooded 40-50cm in rain season lasting 5-6 months/year with pH (water) equals to 5.4 and clay percentage is 17.7%

Figure 2: A tidal marsh Histosol The inset shows the fibric (peaty) organic material that contains recognizable roots and rhizomes of marsh grasses that died perhaps centuries ago, the anaerobic conditions having preserved the tissues from extensive decay The soil core (held horizontally for the photograph) gives some idea of the soil profile, the surface layer being at the right and the deepest layer at the left The water level is usually at or possibly above the soil surface (Photos courtesy of R Weil)

2.2 Comparisons of histosol in Vietnam and the U.S

2.2.1 Similarrities:

Histosols soil in VN and US have some similarities:

• Histosols are soils forming in organic soil materials

• Properties: they are rich in organic matter and the accumulation of peat

• Distribution in the wet and low-lying areas

2.2.2 Differences:

• In US, wetland soil appears in two suborders: Hemists and Saprists:

1) Hemists

Hemists are the Histosols that:

1 Are saturated with water for 30 or more cumulative days during normal years (unless artificially drained);

2 Do not have more thickness of fibric soil materials and do not have more thickness of sapric soil materials than any other kind of organic soil material either In the organic parts of the subsurface tier if there is no continuous mineral layer 40 cm or more thick that has its upper boundary within the subsurface tier;

3 Have a sulfuric horizon that has its upper boundary within 50 cm of the soil surface, or sulfidic materials within 100 cm of the soil surface

These are wet Histosols in which the organic materials are moderately decomposed The botanic origin of much of the organic material cannot be readily determined The fiber content of much of the organic material is between one-sixth and two-thirds after rubbing between the thumb and fingers The bulk density commonly is between 0.1 and 0.2 g/cm3 Ground water is at or very close

to the surface of these soils much of the time unless artificial drainage has been provided The level of ground water may fluctuate but seldom drops much below the bottom of the surface tier Hemists occur from the Equator to latitudes with a cryic temperature regime, that means soils in this temperature regime have a mean annual temperature higher than 0°C but lower than 8°C They are in closed depressions and in broad flat areas, such as coastal plains and outwash plains Most Hemists are under natural vegetation and are used as woodland, rangeland,

or wildlife habitat Some large areas of Hemists are cleared, drained, and used as cropland

2/ Saprists

Saprists are the Histosols that:

1 Are saturated with water for 30 or more cumulative days during normal years (unless artificially drained); and

2 Have more thickness of sapric soil materials than any other kind of organic soil materials either These are the wet Histosols in which the organic materials are well decomposed The botanic origin of the organic material is difficult to determine in most of these soils The fiber content is less than one-sixth after rubbing between the thumb and fingers Most of these soils have a bulk density of more than 0.2 g/cm3 Saprists occur in areas where the ground water table tend to fluctuate within the soils or in areas where the soils were aerobic during drier periods in the past They consist of the residue that remains after the aerobic decomposition of organic matter When drained, fibric and hemic materials commonly decompose to form sapric materials If the organic materials are deep and are drained either artificially or naturally, the Fibrists and Hemists are converted after some decades to Saprists

3/ Comparison:

Now we come to compare 2 suborders of histosols order The reason to compare 2 suborders is that these suborders have a similar capability of decomposing organic material

Table 1: Comparision of wetland soil in US and Vietnam

OM

decompositio

n

Moderately decomposed

Moderately decomposed Mainly Melaleuca (câytràm)

Profile

- Mineral layer: 0-40 cm -Half-decomposed dead plant:

0-30cm

- Sulfuric horizon: 40-100 cm

- Peat and dead plant layer:

30-100 cm

- Alum accumulation Clay

layer: 100-150 cm

Forming

condition

Cryic temperature regime Low-lying areas where

vegetation thrive

Ex: Minesota, Alaska

Ex: U Minh Thuong (KienGiang) national park and VồDơi Nature reserve (Ca Mau)

2.3 Other oders in US taxonomy and VN taxonomy that have wetland.

2.3.1 In the US:

Another order that contains wetland: Order Alfisols - Suborder Aqualfs - Great Groups JAJ Epiaqualfs They have episaturation condition: The soil is saturated with water in one or more layers within 200 cm of the mineral soil surface and also has one or more unsaturated layers with an upper boundary above 200 cm depth, below the saturated layer(s)

1) Epiaqualfs

a Have episaturation and a frigid, mesic, isomesic, or warmer temperature regime;

b Do not have a glossic, kandic, or natric horizon or a duripan;

c Do not have a fragipan with an upper boundary within 100 cm of the mineral soil surface;

d Do not have an abrupt textural change between the albic and argillic horizons if the saturated hydraulic conductivity of the argillic horizon is moderately low or lower;

e Do not have one or more layers, at least 25 cm thick (cumulative) within 100 cm of the mineral soil surface, that have 50 percent or more (by volume) recognizable bioturbation, such as filled animal burrows, wormholes, or casts; and

f Have, in all horizons at a depth between 30 and 150 cm from the mineral soil surface, less than 50 percent (by volume) plinthite

Typic Epiaqualfs are the Epiaqualfs that:

a Do not have, in any horizons between the A or Ap horizon and a depth

of 75 cm below the mineral soil surface, in 50 percent or more of the matrix, one or a combination of the following: either

• Hue of 7.5YR or redder; and (1) If peds are present, either chroma of 2 or more on 50 percent or more of s or no redox depletions with chroma of 2 or less in ped interiors; or (2) If peds are absent, chroma of 2 or more in 50 percent or more of the matrix;

• Hue of 10YR or yellower and:

(1) Both a color value of 3 or more (moist) and chroma of 3 or more (moist and dry); or (2) Chroma of 2 or more (both moist and dry) and no redox concentrations;

b Do not have, throughout one or more horizons with a total thickness of 18 cm or more within 75 cm of the mineral soil surface, any of the following:

• A fine-earth fraction with both a bulk density of 1.0 g/cm3 or less, measured at 33 kPa water retention, and Al plus 1/2 Fe percentages (by ammonium oxalate) totaling more than 1.0