Ustic Ultisoils in Belize

Presented by Richard Yudin

First described by Lietzke & Whiteside, 1981

I chose to describe some soils in Belize because thelandscape is superficially similar to the Pinelands that once dominated my area of Broward County in South Florida.

This is a USGS photo of Fire-dominated Pine forest in Everglades National Park.Elsewhere in South Florida fire has been eliminated as a natural vegetation control, so any remaining Pine forest here is usually choked by an unnaturally lush understory.

These “Palmettos” are Acoelorraphe wrightsii, also found in Florida

Taken near Cow Pen, Belize, latitude 16˚ 30’ N, 88˚ 30’ W. They still have Panthers here, but call them “Mountain Lions”

More similarities: buttonwoods and sandpaper bush are part of theunderstory, and oaks can be found in wetter areas that seldom burn.

However below the surface there are major differences:

In South Florida the Slash Pines grow on “rockland” limestone, and on sandy soils that sometimes have a “Spodic” horizon, but in Broward County our pines grow mostly on shallow sands over calcareous material as shown in this picture ( on a “Margate” soil ).

In Belize similar “Savanna” vegetation grows on sandy clays, with some illuviated horizons above secondary elluviated layers.

This unweathered Belizean pineland soilwas revealed by a recent cave-in of the bank of a roadsidedrain some way north of the fire site shown.

The lower light-coloured elluviated horizon is very deep, with prominent soft red inclusions that rapidly harden and turn brownon exposure to air

The spade is 40 incheslong (about one meter) sothe gully is about 14 feetdeep. The light-colouredlowest layer goes deeper than the streambed.

The reddish concretionscontinue down to about

ten feet from the surface.

The stones in the foreground are fill from the road on the east side of the gully.

I decided not to work at this site because the soil was very wet and crumbling, & I was afraid the steep bank might collapse on me !

Another gully in the same area, several years older andmore weathered. Included to show the fate of the iron concretions. After exposure to air they become hard lumps of Plinthic material and form an “erosion pavement”.

The cobbles in the bed of the gully do not belong to the native soil, they are part of the fillused to make the road I amstanding on to take the photo.

Note the pine seedlings !

A new drain in a citrus farm to the west starts insimilar soil, moves into an old wetland, the dark patch midway, & back to the same formation.

DC B

I will attempt to describe the soil horizons at the first gully & those at points B, C & D

The nearer hills are limestone, the further ones metamorphic rock with frequent quartz veins, but very poor in minerals. According to Lietzke & Whiteside, these soils are formed of material eroded from the latter.

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The soils examined are located in the Independence district of Belize. Soil A’s location is marked by the yellow star, soils B,C & D in the red circle. The red star marks the location of the erosion pavement shown in slide 8

The local Geology: Our locationis inside the black circle – thestreams are not drawn correctlyRed: granite, Orange: Pleistocene metamorphic,Yellow: similar coastal sedimentGreen: recent sedimentsBlues are limestones & c.

O

According to the USDA Soil Taxonomy system, they are “Ultisols” – having argillic horizons, in this case only low-activity clays.

These are very ancient soils, the Mayan or Coxcomb mountains to the west have some of the oldest rocks in all of Central America.

The little guy in the background was sunning himself on a sandbank in the Swazey river nearby – You never know when you’ll meet another Gator !

These soils formed on a level low-lying plateau between the Dolomitic limestone foothills and the mangrove-lined seacoast, where offshore coral reefs fringe the deep fault of the Gulf of Honduras.

The non-hydric soils belong to the “Udic” suborder, having developed under a humid tropical climate, with mean temperatures above 20˚ Centigrade, winter minimum temperatures never below 15˚ C., and which once had sufficient rainfall for plant development every month.

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Rainfall in Banana zone of Belize

The effects of global warming in the humid tropics: total rainfall Is not changing much, but there are sharper wet and dry seasons.

This could increase SOM oxidation, and also surface erosion !

1940’s data from Wright et al., 1990’s from IWMI website

In recent years the actual rainfallpattern has changed, and the areanow has very dry summers. So theyare no longer “ perudic.”

Lying along the coastal plainwell below the Tropic of Capricorn,they can be described as“Isohyperthermic.”

This is why these soils can no longer be considered “Perudic”

Common characteristics for this catena:

All these soils are on High Upland terrain, gently sloping ±2% westwards. Permeability is very low

Available water is limited by the depth of the rooting zone, effectively the O and A horizons where the fragipan is not present, and the latter where it exists.

Runoff potential is high, especially after fire destroyssurface OM. The sand fraction is transported downhill, and accumulates in undrained depressions.

The potential uses of all four soils are severely limiteddue to the low Infiltration rates and high water table.

Traditionally the Mayan settlers have avoided these soils and concentrated their shifting cultivation along river terraces or better-drained soils in the nearby foothills.

Soil A

the most easterly of those examined, still under natural savannavegetation.

C – 0-12” 7.5YR 4/2 loose medium gravelly sand and 10YR 8/1 extremely firm sandy loam, 5% distinct 2.5YR 6/8 coarse nodules, medium to coarse blocky fractured brittle blocky stucture, abrupt boundary, numerous roots in channels. Ggravel-sized materialis ≤ 5mm quartz. (Anthropogenic addition from road construction).

A – 12-18” 5YR 3/3 sandy clay, very friable coarse granular structure, many roots along top of layer, irregular clear wavy boundary Bw - 18-26” 7.5YR 5/6 friable coarse sandy clay, structureless, gradual boundary

Bg1 – 26-36” 2.5YR 7/1 friable sandy clay, irregular prismatic blocky structure, no apparent redox features. I would guess that the Bk2 - E2 boundary was originally the top of the seasonal water table.

Bg2 – 36”+, sandy clay, matrix 2.5YR 7/1, prismatic structure, 25% diffuse soft concretions 10YR 4/8, exposed surfaces have “halos” 7.5YR 6/8

Profile A

Soil Classification: Epipedon: OchricSubsurface horizon: Argillic ?Order: Ultisol

Properties & Interpretations: Infiltration Rate: LowHydraulic Conductivity: LowAvailable Water: LowSoil Wetness Class: Class 1 (25-50cm)

Soil Interpretations: Dwellings w/basement: SevereSeptic Tank: Severe

Local roads and streets: Moderate

Site Characteristics: Position of Site: UplandParent Material: FluvialSoil Slope: Nearly levelSurface Runoff: RapidErosion Potential: High

Top left – close-up of the upper fill material – note thesmall red concretions.

Lower right – close-up of thefreshly-exposed nodules in the “Bg2” horizon, stillsoft and friable.

Soil B

The highest pedon of the cleared & plantedarea to the west ofthe previous photos.

Note the strongerRedox features.

Soil exposed for threeDays, with heavy rainthe night before.

A1-6” 7.5YR 4/2 , friable sandy clay, pH 5.5, clear boundary. Many medium roots. The organic material is generally sapric. Note this is not an Ap horizon, the area has never been plowed, only burned over and then the remaining refuse was bulldozed.

E1 – 6-12” 10YR 4/1 friable sandy clay. Large irregular blocky structure, peds several inches across. Some roots between faces. Bg1– 12-17” 10YR 5/3 firm sandy clay, pH 6. Structure as above. The sand grains from this layer turned out to be coated after drying.

Bg2 – 17-22” 10YR 5/1 sandy clay, massive, clear boundary.

Btv1-22-33” 7.5YR 7/2 with 40% 7.5YR 6/8 very coarse nodules, coarse sandy clay, some small coated quartz gravel. Massive, gradual boundary.

Btv2 – 33”+ 2.5YR 7/1 sandy clay matrix, pH 6.5, massive, 50%+ diffuse soft concretions 10YR 4/8, seemingly increasing with depth, see cleared area of trench floor in blue circle.

Note: I was asked not to dig into banks or floor, but permitted to scrape.

Profile B

Soil Classification: Epipedon: HisticSubsurface horizon: ArgillicOrder: Ultisol

Properties & Interpretations: Infiltration Rate: LowHydraulic Conductivity: LowAvailable Water: ModerateSoil Wetness Class: Class 2 (25-50cm)

Soil Interpretations: Dwellings w/basement: SevereSeptic Tank: Severe

Local roads and streets: Moderate

Site Characteristics: Position of Site: UplandParent Material: FluvialSoil Slope: Nearly levelSurface Runoff: ModerateErosion Potential: High

Soil C

The intergrade betweenthe typic tropudultseen in the previousslide and the aquictropudult shown next.

The E horizon returns.

There is an ant’s nest airhole above B1h labelbelow the E layer. I am guessing this marks the seasonal highwater level.

The Airhole

→

A 0- 6”  10YR 2.5/1 friable mucky clay, coarse crumb structure, clear boundary. Numerous grass roots.

A/E 6-14” 2.5Y 4/1 firm sandy clay and 10YR 7/1 sandy clay, massive, clear boundary

Bt1 14-18” 2.5Y 4/1 firm sandy clay, gradual boundary. Showing signs of illuviation of organic matter

Bt2 18-23” 2.5Y 7/3 sandy clay, gradual boundary, massive.

Bt3 – 23-30” .5YR 7/2 with 30% 7.5YR 6/8 medium nodules, gradual boundary, massive.

Btg1 – 30-41” 2.5YR 7/2 sandy clay matrix, 40% diffuse soft concretions 7.5Yr 6/8, gradual boundary, massive.

Btg2 – 41”+, 2.5YR 7/1 sandy clay matrix, 50%+ diffuse soft concretions 10 YR 4/8, plinthic, massive.

Profile C

Soil Classification: Epipedon: HisticSubsurface horizon: ArgillicOrder: Ultisol

Properties & Interpretations: Infiltration Rate: LowHydraulic Conductivity: LowAvailable Water: LowSoil Wetness Class: Class 1 (<25cm)

Soil Interpretations: Dwellings w/basement: SevereSeptic Tank: Severe

Local roads and streets: Moderate

Site Characteristics: Position of Site: DepressionParent Material: FluvialSoil Slope: Nearly levelSurface Runoff: ModerateErosion Potential: High

Soil D

The hydric member of this soil family

I have never seen a“lasagna” pattern ofalternating muck andsandy clay layers before.This is not “CrossBedding” since thetextures are different.This variegation iscontinuous for severalhundred feet.

A – 0-10” 10YR 2.5/1 loose granular sapric clay. Abrupt boundary. Thin layer of weak fine grassy roots, no sign of turf formation.

A/E– 10-32” alternate layers of 10YR 2/1 muck & 10YR 7/1 soapy clay, structureless, clear boundary. The muck layers are too thin ( < 30mm ) to be designated as individual horizons.

Btg1 – 32-38” 2.5Y 5/3 plastic clay, massive, gradual boundary.Makes good ribbon and 7mm rod, I am guessing some silicate clay present. Btg2 – 38-42” 10YR 4/6– softer stickier clay, massive, gradual boundary. Hard to form ribbon, 5mm rod, possibly only non-adhesive kaolinitic clay ?

Btg3 – 42” + 5Y 4/2 sandy clay, some signs of structure formation.

Profile D

Soil Classification: Epipedon: HisticSubsurface horizon: ArgillicOrder: Ultisol

Properties & Interpretations: Infiltration Rate: LowHydraulic Conductivity: LowAvailable Water: LowSoil Wetness Class: Class 1 (<25cm)

Soil Interpretations: Dwellings w/basement: SevereSeptic Tank: Severe

Local roads and streets: Severe

Site Characteristics: Position of Site: DepressionParent Material: FluvialSoil Slope: Nearly levelSurface Runoff: PondedErosion Potential: High

What I learned:

1 – reduced coated sand grains may appear clear and uncoated when first exposed to air

2 – when there is no lab nearby, take test tubes to make a rough assessment of the particle sizes by mixing them in water, shaking thoroughly, and letting them settle out. Sieves are too bulky.

3 – Gardener’s pH kits using colour comparisons are not practical for clay soils because the liquid gets too cloudy, dipping litmus tape in a 1:1 soil/water solution is better.

4 - add insect repellent to Willie’s sheet on how to describe a soil, also water for washing off clay, a rag is not enough

5 – use a non-reflective measuring tape, the intervals come out better in digital photos !

References:

A.C.S.Wright, D.H.Romney, R.H.Arbuckle &V.E.Vial: “Land in British Honduras,” Her Majesty’s Stationery Office,London, 1959 ( in UF library ) – The first reconnaissance soil survey of the country done in 1952-54, commissioned by Britain’s Colonial Office, its soil descriptions do not use USDA terminology but go down to roughly “Family” level. The authors labelled the soils I have studied the “Puletan set.”

D.A.Lietzke & E.P.Whiteside; “Characterization and classification of some Belize soils,” Soil Science Society of America Journal, Vol. 45, pages 378-345 – a more detailed survey of a tract of land just south of my site down to Family level, done in 1968-69 but not published until 1981, this time using USDA Soil Taxonomy criteria.

Recent rainfall data from International Water Management Institute, online at “www.iwmi.cgiar.org/WAtlas/AtlasQuery.htm