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5B

Indicator vegetation

Mallee with mixed understorey that includes a tamma (Allocasuarina corniculata), sword sedge, miscellaneous myrtaceous plants and some native halophytes

Where are you in the landscape? A slight bowl just below the ridge

Surface clues Gravel

Other clues The gravel pit provides an indication of the soil profile shown above Your conclusion

Landscape and soil(s)

Deep sandy gravel (page 38); 70 cm gravelly loamy sand with increasing gravel with depth over reticulite. This merges into duplex sandy gravel (page 39) as you walk to 5C

5C

Indicator vegetation

Capped mallee (E.pileata). The dense bluebush understorey has probably taken over from other understorey plants, but it is a good indicator of a shallow alkaline duplex soil

Where are you in the landscape? Spur (watershed divide)

Surface clues Occasional lime nodule and gravel stones

Your conclusion Landscape and soil(s)

Shallow sandy duplex soil (page 47). Profile 0–10 cm gravelly loamy sand pH 5.3; 10–15cm grey brown sandy clay loam pH 6.2; 15+ cm yellow-brown light clay

Note how the soil has gradually changed from tamma gravel to gravelly duplex as you walked from 5B. A few metres to the east there is a sudden increase in slope that was once a breakaway, but the soil returns to a lateritic gravel

Allocasuarina corniculata E. neutra mallee

5C

5B

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Tarin Rock case study

This case study features landscapes and soils of an area at Tarin Rock, 22 km from Lake Grace. The area (see Figure 39) has a dissected landscape and variable soils due to variations in the mineralogy of the underlying gneiss that is crossed by faults and mafic dykes.

Figure 39 Case study location

Figure 40 shows two major waterways that follow east-west trending faults and then merge.

There are also numerous north/north-west and south/south-east trending ridges and waterways that have resulted from differential erosion of composition rock bands in the basement gneiss. Numbers indicate stops that you can locate with your car odometer or GPS. The yellow arrows in subsequent maps indicate the direction in which the photographs were taken.

Figure 40 West-facing relief map of the case study area, with stops shown in yellow

0.0 km Start at the corner of Tarin Rock Road and Tarin Rock North Road and drive north.

0.9 km—Stop 1 GPS zone 50 615533/6339879. Stop just past the farm entrance and cross to the east side of the road. Note the bluebush understorey that commonly volunteers on degraded road verges with alkaline soils. The soil is a hard-setting grey shallow alkaline loamy duplex (page 53) with 15 cm loamy duplex (pH 5.8 CaCl2) over clay (pH 6.8) and lime nodules at depth.

Study area

2 3 1

4

7 6

5

9 8 Holden

Road

N

Hills Road

Tarin Rock North Road Tarin Rock Road

11

13 12

14

Start

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Figure 41 Stop 1: East view showing a hard-setting loamy duplex slope with a mafic ridge in the distance (left); pallid zone rock and lime nodules exposed in the gully (right)

1.3 km—Stop 2 615695/6340313. Mallees give way to red morrel trees at the change of slope. The soil here is an unusual alkaline shallow sandy duplex due to aeolian sand that has been blown from the trunk valley. The soil profile is 10 cm fine grey sand (pH 5) over yellow heavy sandy clay (pH 7.8). Roadside sand heaps indicate that the topsoil is very susceptible to wind erosion.

Figure 42 Stop 2: Soil profile showing the sudden change in texture and pH from topsoil to subsoil (left);

wind-blown sand on the road verge that has been colonised by bluebush (right)

2.5 km—Stop 3 616113/6341409. This is an area of low sand dunes (deep-grey brown to yellow loamy sand between the two waterways supporting York gum-intergrade type remnant vegetation.

Figure 43 Stop 3: Low sand dunes 10 cm

pH 7.8 pH 5

With pH indicator

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3.5 km—Stop 4 615937/6342369. This is a shallow sandy duplex plain supporting low mallee heath remnant vegetation. The shallow sandy duplex soils (page 47) are of two types:

1. Shallow sandy duplex (most common). This has 15 cm of grey-brown loamy sand (pH 4.6) over yellow light clay with orange and grey mottles. The shrub understorey has a diverse range of myrtaceaous plants and grevilleas, which usually indicates a soil that allows deeper root growth than the following soil type.

2. Alkaline shallow sandy duplex. This has 10 cm of yellow-grey hard-setting loamy sand over dense cream with orange mottled clay (pH 7.1). Vegetation is

characteristic mallee-melaleuca with the occasional salmon gum.

Figure 44 Stop 4: Broad sandy duplex plain (top); understorey vegetation types (above). The vegetation may appear the same to a casual observer but there are many shrub species on the left and mostly melaleucas on the right.

After you leave Stop 4, a shallow gravel pit indicates a marked change of slope and soil type to mafic gravelly soils.

4.1 km—Stop 5 615728/6343045. This is a mafic ironstone spur. Note the remnant

Grevillea insignis shrubs that are common on this mafic shallow gravel. Mallee with dryandra understorey is on the other side of the road.

Figure 45 Stop 5: Shallow gravel

Pallid zone dam Patches due to cutworm damage

Davesia sp. Melaleucas Mallee with mixed species understorey

Mallee-melaleuca

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From Stop 5 you continue along a mafic rise with tamma vegetation on loamy and shallow gravel rises. The hollows have mallee-melaleuca red-brown loamy duplex soils.

In Figure 46 the aerial photograph has been rotated to face north.

Mafic gravels Red-brown

loams Shallow sandy

loamy duplex Yellow sandy

gravels Grey sandy

gravels Deep sand

(white) Deep sandy

duplex

Figure 46 Northern view of the case study area with broad soil types between stops

6.1 km—Stop 6 615154/6344918. A shallow gravel pit on your right adjoins a slight

breakaway. The loamy gravel topsoil has been removed from the profile shown in Figure 47 to reveal the underlying clay that retains the banded pattern of the parent mafic gneiss.

Figure 47 Stop 6: Mafic gravelly duplex profile

Turn left on to Holden Road.

6.7 km—Stop 7 614807/6345407. Stop just after the T-junction sign.

10

2 3 1

4 7

6

5 9

8

N

11

12 14

13

A

B

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Figure 48 Stop 7: Upslope (top) and downslope (above) views

This is the centre of a large north-west south-east trending band of mafic gneiss. At this stop, the surrounding mafic ironstone ridges have been eroded and soils have formed on

underlying layers. View 7A shows a breakaway face, below which is pallid-type clay with kaolinised rock fragments. Down the slope in view 7B are mafic loamy duplex soils formed on underlying mafic gneiss that merge into paler shallow duplexes from more quartz-rich gneiss.

After Stop 7 you travel over a mafic ironstone ridge with silver mallets and down a mafic mallee loamy duplex slope that merges into shallow sandy and loamy duplex soils. Note the pale dam and the differences between the accompanying salmon gums and upslope silver mallets. From the dam, variable soils occur in the dissected land surface until you reach a patch of wandoos (deep sandy duplex soil) that marks a change to much sandier soils.

8.6 km—Stop 8 613000/ 6345966. This is a coarse yellow sandy slope with dense rock sheoak and Acacia lasiocalyx vegetation. A soak dam in a hollow on the right collects water that seeps through the sand.

Figure 49 Stop 8: Acacia lasiocalyx (left); sand pit (right)

7A

7B

Mallet ironstone id

Gravel pit

Soil formed on kaolinised rock

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9.4 km—Stop 9 612206/ 6346204. Stop at the dam and look south at the grey sandy slope.

This is a good example of a sandy landscape view with grey deep sandy duplex soil at the dam, grey sand over gravel/deep grey sand on the slope and grey sandy gravel/sand over gravel on the ridge.

Figure 50 Stop 9: Views in July (top) and September (above). Better wheat growth areas are due to extra nitrogen fertiliser from seeding overlaps. Fan-leaf hakea is common on this soil.

Driving upslope from here the depth of sand to gravel becomes shallower and you will see a typical grey sandy laterite heath. This includes woolly banksia, woolly bush, roadside tea tree, cauliflower hakea, chittick, and fan-leaf hakea (see page 28). As you approach the ridge, note another change to yellow sandy gravel soil and associated vegetation.

10.2 km—Stop 10 611477/6346409. Stop at the corner of Holden and Hills roads. From here you can see the soil in the paddock grade from yellow shallow gravel to sandier soils

downslope and associated native vegetation. The grey green foliage of ‘Red toothbrush’

(Grevillea hookeriana) with prickly Proteaceae-rich heath is characteristic of yellow sandy gravels. Compass bush (Allocasuarina pinaster) (see page 30) that is also present here is more common on very sandy gravels in contrast to tamma and black tamma that prefer more iron rich and/or loamy gravels.

Although the soil at the corner is stony and shallow, you can see in Figure 51 that crop growth is markedly better than on grey sandy gravels further downslope (due to better nitrogen nutrition). The mallee at this stop is silver mallee (E. falcata), the mallee equivalent of silver mallet.

Fan-leaf hakea Hakea brownii Christmas tree

Pines planted in pale deep sand hollow

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Figure 51 Stop 10: Roadside vegetation, soil type and wheat growth downslope.

Drive down Hills Road and note the change back to grey sandy lateritic soils with a pine plantation on deep sand to the right. For the next 6 km the road crosses a landscape that has mafic soils on the top of ridges and less mafic soils on slopes and valleys. When the road turns sharp left note the large mafic breakaway and, at the right turn, a roaded catchment that changes from red-brown loamy duplex (mallee with broombush understorey) upslope, to shallow hard-setting grey loamy duplex (mallee sparse understorey) near the dam.

After the dam, you drive up a long shallow gravel slope and over the ridge that has a relatively narrow band of loamy gravel. From here, the soil gradually becomes lighter until it has changed to coarse grey sandy gravel where the reserve on the right ends. Note the compass bush.

16.4 km—Stop 11 611181/634094. The roadside mallee vegetation at this stop could be deceiving at a casual glance but the understorey is typical of a sandy gravel soil (and the mallee is a species common on light soils—ridge-fruited mallee (E. incrassata).

Figure 52 Stop 11: Roadside vegetation

Turn left at the junction with Tarin Rock Road. The road follows a waterway with shallow sandy and loamy duplex soils that support salmon gum-York gum-mallee roadside vegetation.

Turn left on to the unnamed road.

Grey sandy gravel Yellow sand over gravel Yellow shallow gravel Red toothbrush grevillea

Hakea multilineata

Kite leaf poison Hakea incrassata

Roadside tea tree Flame grevillea

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18.4 km—Stop 12 612504/634045. This is a grey deep sandy duplex slope. Note the soil heaps on the road verge deposited by wind erosion and the road that is now below the surrounding soil surface.

Figure 53 Near Stop 13

19.6 km—Stop 13 612919/6341566. You have stopped on a narrow mafic gravel ridge.

Figure 54 Stop 14: North-east view

The ridge continues to your right where it intersects lines of mafic gneiss. At these points the resulting rock is more erosion-resistant, and as the landscape gradually eroded, it remained as a line of mafic hills. North and south of this point you will see lighter soils formed from more quartz-rich rocks. Turn around, return to the Tarin Rock Road and turn left.

22.1 km—Stop 13 613316/6339776. Note the sign 8CN on the gate. This is a typical mafic red-brown heavy soil ridge that supports salmon gum.

Return to the junction of Tarin Rock and Tarin Rock North roads.

24.2 km End

Degraded road verge vegetation; occasional roadside tea tree, melaleuca and dense weeds

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Karlgarin case study

This case study features an area east of Karlgarin on the lower slope of a valley that joins the salt lake system from Hyden. In contrast to areas further south, igneous rock outcrops are common on uplands with well-defined waterways, and soils in the broad trunk valleys have more yellow-brown to red-brown heavy soils.

Figure 55 Case study location

Yellow numbers below indicate stops that you can locate with your car odometer or GPS.

Arrows in subsequent maps indicate the direction in which photos were taken.

Figure 56 Aerial photograph of the study area with landscape relief, and stops indicated in yellow

Figure 57 shows radiometrics imagery draped on a relief map of the study area. Due to different image processing, the colours differ from those shown in the field trip radiometrics map.

Study area

3

2 1 4

7 6

5

9 8

Walton Road

N

Medcalfe Rock Road

Karlgarin Road South Pederah Road.East

11 13

12

14 10

15

N

A B

5A 5B

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Figure 57 Radiometrics image with landscape relief and stops (yellow)

The following key explains the colours shown in Figure 57:

• turquoise: lateritic sands and gravels with paler areas having more clay in the profile

• grey-white: grey duplex and granitic soils

• yellow-orange: yellow-brown to red-brown duplex and clay soils.

0.0 km—Stop 1 GPS zone 50 665750/6395611. Start at the corner of Pederah Road East and Karlgarin Road South. To the south (upslope) you will notice some low granite outcrops.

The soils on this slope are mixed sandy duplex and gravelly duplex soils. The view to the east shows soils more typical of the south of Lake Grace, but much less common here.

Figure 58 Views 1A and 1B at stop 1

3

2 1 7 4

6

5

9 8

Walton Road

N

Medcalfe Rock Road

Karlgarin Road South Pederah Road East

11 13

12

14 10

15

View 1A

View 1B

A B

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Note the dense melaleuca-mallee scrub and the lime nodules that are typical in this poorly structured alkaline shallow sandy duplex soil (see page 47).

0.3 km—Stop 2 666532/6395587. The landscape is more sloping with a gravelly sandy duplex soil (yellow gravelly sand over clay) that grades to a sandy duplex at the waterway.

Note the tamma-mallee vegetation on the roadside here.

Figure 59 Stop 2: Looking west (upslope)

1.1 km—Stop 3 667017/6395583. The broad valley is typical of this area with salmon gum calcareous duplex soils with yellowish subsoils (see salmon gum grey valley soils page 52).

Note the lime fragments exposed in the drain that has been excavated to reduce waterlogging.

The bare patches are gilgai (‘crabhole’) hollows where seed failed to germinate due to waterlogging. Gilgai have a cracking clay subsoil with better structure than the grey calcareous duplex soils in the south of the district. Gilgai mounds have heavier soil in the hollows than the edges that cause ponding in wet seasons.

Figure 60 Stop 3: Looking back upslope

2.1 km—Stop 4 667828/6395569. See the saline waterways at the break of slope. Note how the waterways flank the sides of the flat valley, and that they are saline while the valley is still non-saline.

Seepages are common at changes of slope in this district where they result from subsurface water that travels downslope through sandy soils overlying restricting layers such as rock or

Waterlogging-affected gilgai

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silcrete. When seeps first appeared they were fresh, but over the years evaporation has made them saline.

Note how the soil changes quickly upslope to a sandy gravel and also the revegetation on the south side of the road to reduce severity of the seepage.

2.6 km—Stop 5 668255/6395565. Stop at the gate next to the large salmon gum adjoining the roaded catchment. Soils at this stop are typical of a dissected landscape in this area.

View 5A in Figure 61 shows a change in the roaded catchment soil type from granitic grey shallow duplex to mafic red-brown loamy duplex. On the other side of the road, salmon gum and York gum trees indicate even heavier red-brown soils that have formed from dolerite.

In the upslope View 5B you can see gritty sandy soils formed from coarse-grained granite.

Figure 61 Stop 5: Looking back upslope

From Stop 5 continue upslope and note the shallow soils over granite that supports mixed roadside vegetation, including tamma, tea tree, and acacia heath.

Turn left down Medcalfe Rock Road. The road goes up a small rise (a concealed breakaway). Note the sandy soils at the base of the slope.

3.8 km—Stop 6 669034/6396223. You are now on undulating yellow sandplain and gravel soils (see yellow sandy earth page 42). These soils are common on uplands east and north of Hyden, and correspond with the turquoise in Figure 57.

View 5A

View 5B

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Note the vegetation and soil changes along the road:

• tamma and dryandra on stony gravel

• grevilleas on deeper yellow sand over gravel

• native pines (Callitris tuberculata and C. canescens) on yellow sandy earth soils.

Figure 62 Stop 6: Soil and vegetation types

4.6 km—Stop 7 669044/6396931. This is a pallid zone-silcrete dam in the waterway in a deep sandy duplex soil that supports mallee-heath.

Figure 63 Stop 7 Vegetation change from laterite to deep sandy duplex downslope

Turn right and go up the track to the clump of mallees at the end.

5.5 km—Stop 8 669618/6397048. The mallee here is wandoo mallee (E. capillosa var.

polyclada). This mallee is common north of here on grey shallow duplex soils over pallid zone and/or silcrete rock, and is usually found below breakaways. Note the shallow gritty sand soils over pale rock. The rock is silcrete, a silica-cemented rock that is often found above pallid zone in the eastern and north-eastern wheatbelt. Contour banks downslope indicate that water erosion has been a problem on these shallow soils.

C. tubercalata C. canescens Dryandra Tamma

Sandy gravel

Flame grevillea

Deep yellow sand Yellow-orange sandy earth Tamma

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Figure 64 Stop 8: View downslope

Return down Medcalfe Rock Road and turn right. As you drive, note that the landscape changes from shallow rocky soil to gravelly, then back to shallow rocky at the ridge before reaching a gravel pit on your left.

7.6 km—Stop 9 669041/6398619. The gravel pit and sand pit on the corner of Medcalfe Rock and Walton roads give good cross-sections of lateritic sandplain soils from here and further north. Note that the depth of the gravel pit has been limited by silcrete (soil

classification: shallow gravel page 37).

Turn right (east) and travel down Walton Road until you reach the red-brown soil rise supporting salmon gums and red morrel.

8.6 km—Stop 10 669862/6398739. The soil here is a mafic rise with a red-brown alkaline (pH 6.9–7.1 CaCl2) loamy gravel that grades to an alkaline clay with lime nodules at depth.

This soil is intermixed with red-brown loamy duplex soils (page 50), and is an example of an intergrade soil where gravel has been overprinted by invading myrtaceous vegetation.

Figure 65 Stop 10

Return back the way you came and cross Medcalfe Rock Road.

10.2 km—Stop 11 668372/6398778. Coarse quartz-rich granite upslope has weathered to form deep coarse sand at this stop. Note the pale deep sand profile in the gully and remnant vegetation typical of deep sands (particularly the tea trees).

Silcrete

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Figure 66 Stop 11: View from the paddock

After leaving Stop 11, you travel down a slope with mixed mainly sandy surfaced soils to shallow alkaline sandy duplex soils supporting salmon gum in the main valley.

Turn left at the T-junction on to Karlgarin Road South that traverses the edge of the main valley.

12.9 km—Stop 12 665814/6398697. This stop is on the footslope of a granitic spur where it joins the main valley. The soil is an intergrade grey shallow sandy duplex supporting a shrub- heath mix of tamma, melaleuca, and quondong. The soil profile is:

• 0–12 cm sand (pH 6)

• 12–20 cm pale sand with large gravel pebbles

• > 20 cm orange and grey mottled sandy clay loam (pH 5.9).

Figure 67 Stop 12: Looking back upslope

This area is susceptible to winter waterlogging. Note the patch of introduced perennial paspalum grass.

Waterlogging-affected gilgai

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13.8 km—Stop 13 665807/6397179. Note that you at the confluence of the main valley and a tributary. The shallow sand over grey clay pH 6.9 (see shallow sandy duplex page 47) has saline patches. Remnant vegetation is mallee-melaleuca scrub that has been invaded by blue bush and native saltbush.

Figure 68 Stop 13

After leaving Stop 13, you will travel on a gentle slope that is a rise between two waterways.

Note the change in understorey from melaleucas and halophytes to a variable heath with perennial grasses and mixed shrubs. The soil varies from sandy duplex to duplex gravel.

15.4 km—Stop 14 665764/6396032. This is a minor waterway with a gully that gives you a cross-section of a mallee duplex soil profile. The soil profile is:

• 0–15 cm: grey-brown loamy sand with bleached layer at the base

• Next 30 cm: massive cream sandy loam (pH 6.7) overlying structured sandy clay (pH 6.8).

Figure 69 Stop 14: Soil profile exposed in the gully

The yellow colour and low granite outcrops indicate a slightly better structured soil than a grey duplex.

Poorly structured subsoil

More friable underlying subsoil Sandy topsoil

Bleached layer

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Cross Pederah Road East.

17.4 km—Stop 15 665718/6394157. You are now on a mafic gravel ridge in a loamy gravel soil patch (loamy gravel page 36). Note the dense tammas and the blue mallets (E. gardneri) with their distinctive dull blue-green leaves. Blue mallet is at the limit of its range and it is more common in similar situations in the west of the district.

Figure 70 Stop 15

Case study ends

Tamma

Blue mallet Black tamma

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Glossary

Adamellite Form of granite with roughly equal calcium and potassium-bearing minerals Alluvium Material transported and deposited by flowing water such as rivers

Bleached layer Subsurface soil that is white, near white or much paler than adjacent soil layers, caused by leaching of soil minerals

Breakaway Landform found on the edge of a plateau or plateau remnant, where a relatively flat lateritic upland ends abruptly in a low scarp above a debris slope

Colluvium Materials transported and deposited by gravity Craton Large stable mass of the Earth’s crust

Crystalline rock Igneous or metamorphic rock consisting of interlocking crystals, e.g. granite or gneiss

Dispersion or clay dispersion Complete breakdown of aggregates into sand, silt and clay-sized particles when wet. Usually occurs slowly, often taking hours to complete. The dispersed clay can block pores, reducing rainfall infiltration and gas exchange. A characteristic sign of dispersion is muddy or cloudy water, the cloudiness being dispersed clay in suspension

Dolerite Medium-grained basic igneous rock that has crystallised near the surface, typically occurring as a dyke, sill or plug

Diorite Granular intermediate igneous rock consisting essentially of felspar and hornblende

Duplex soil Soil with a sudden increase in texture between the topsoil and subsoil of 1.5 or more texture groups, e.g. a sand over a clay loam or clay, or a loam over clay

Dyke Sheet-like body of igneous rock cutting across the bedding or structural planes of the host rock. Typically appears on the surface as relatively narrow, linear features

Effective rooting depth Refers to the rooting depth of the soil in which plants may have an unimpeded path until an obstruction, such as a dense layer of clay or rock, is encountered. Only approximate, as good subsoil structure may allow more root penetration

Erosion Wearing away of the land surface and removal of soil by running water, rain, wind, frost or other geological agents

Fault Fracture in rock along which there has been movement

Felsic (acidic) rock Crystalline rock with a high content of silica and light-coloured minerals, e.g.

granite (c.f. mafic)

Ferricrete Layer of material strongly cemented by iron and which looks like rock, or a dense ironstone gravel layer

Gabbro Coarse-grained mafic igneous rock similar to dolerite

Gilgai surface relief Gilgais are irregular small depressions (20–60 cm deep) and mounds separated by level or gently sloping land. They are caused by soils with

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(or crabhole country) shrink-swell properties

Gneiss Distinctly foliated, generally coarse-grained igneous rocks formed through high grade regional metamorphism. Gneisses and banded granites are often confused (Lane P 2004)

Granite Coarse-grained igneous rock consisting essentially of quartz (20–40%), feldspar and very commonly mica

Gravel Any coarse mineral material or fragments from 2 to 60 mm in diameter.

Could be ironstone, quartz, other rock fragment or any concretions or nodules

Horizons Term used to describe individual layers in a soil profile. Each horizon has morphological properties different from those above and below it

Igneous rocks Rocks which have formed by crystallisation from a molten magma. They include a range of rocks which vary in composition and grain size Indurated layer Layer of material hardened by cementation or pressure

Intrusive rock

Landscape

Magma that has not reached the rock surface before cooling Land area characterised by processes of erosion, weathering,

sedimentation, and movements in the Earth’s crust. Includes all identifiable and measurable features such as climate, geology, soils and land use Laterite Typically consists of sand or gravel on top of a ferruginous duricrust where

iron oxides have accumulated. Often overlies mottled clay and then a pallid zone (white clay on acidic laterites) from which the leaching has occurred Lineament Major linear topographic feature of regional extent of structural or volcanic

origin, e.g. a fault system

Lime (or calcium carbonate) Usually found in heavier soils that are alkaline. Can be present as soft segregations or nodules, or be finely mixed through the soil. Presence of lime can be detected with a simple test using dilute acid (1M hydrochloric).

Drops of acid are placed on a clod of soil and if lime is present the soil effervesces immediately, releasing carbon dioxide as bubbles

Loam Medium-textured soil of approximate composition 10–25% clay, 25–50% silt and less than 50% sand

Map unit Representation of a soil, or group of soils, that occurs within an area. A soil- landscape area is a topographic unit (e.g. low hills and rises, or a level to gently undulating plain) that contains a series of common soil units. These units can be found on the corresponding soil-landscape map produced for the area

Mafic (basic) rock Rock with a major component of ferromagnesium (dark coloured) minerals.

(c.f. felsic)

Mesa Isolated table-top hill with steep sides

Metamorphic rocks Rocks which have been altered or deformed, by heat or pressure, deep in the Earth’s crust

Mottles Patches of different colours (often red, brown, orange or blue-grey spots) in a soil horizon

Orogen Zone of weakness in the Earth’s crust along which movement and deformation has taken place during a period of tectonic plate movement.

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The rocks of an orogen may include deformed and reworked older cratons as well as new volcanic and sedimentary rocks

Pallid zone White to pink kaolinitic clay formed in the lower part of the lateritic profile pH The pH of a soil measures its acidity or alkalinity—the concentration of

hydrogen ions in the soil. It affects nutrient availability to plants and extremes can lead to toxicity or deficiencies.

The pH is measured on a logarithmic scale (i.e. pH = negative logarithm of concentration of hydrogen ions). A soil with a pH of 5 contains 10 times as many hydrogen ions as a soil with a pH of 6.

Two systems are commonly used to measure pH, one in calcium chloride solution and the other in a soil:water suspension. As a rule, to convert from pHw to pHCa , subtract 0.8, although the difference can range between 0.6 and 1.2, and in extreme cases from 0 to 2

Soil reaction pHCa pHw

Strongly acid Less than 4.5 Less than 5.5

Acid 4.5–6.0 5.5–6.5

Near neutral 6.0–6.5 6.5–7.5

Alkaline 6.5–7.5 7.5–8.5

Strongly alkaline More than 7.5 More than 8.5

Plateau Level to rolling landform pattern of plains, rises or low hills standing above a cliff or escarpment

Profile Vertical exposure of soil extending from the surface to the decomposing rock or other underlying consolidated material

Quartz Mineral composed of silicon dioxide (main component of sand)

Regolith All material including the soil from bedrock to the surface

Reticulite Indurated (hardened) layer in a laterite profile, usually with residual root channels

Rooting condition Refers to the soil volume available for plant roots and the mechanical impedance to root development. Soil volume can be reduced by rock and gravel content, dense pans and clay layers

Salinity Presence of high concentrations of soluble salts in the soil. Estimated from the electrical conductivity of a mixture of soil and water

Saprolite, saprock Soft, more or less decomposed rock remaining in its original place

Sedimentary deposits Materials moved from their site of origin by the action of wind, water, gravity or ice and then deposited. When these materials become consolidated and hard, known as sedimentary rocks

Segregations Gravels or other accumulations of material which occur in the soil. Formed by concentration of some constituent by chemical or biological action.

‘Ferruginous’ describes concentrations of iron Silcrete Rock in-filled with cemented silica

Slope Incline either upward or downward from the horizontal

Sodicity Measure of exchangeable sodium in the soil. Soils that are sodic have a high percentage of cation exchange sites occupied by sodium ions.

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Adversely affects soil stability and increases likelihood of soil dispersion Texture Measure of the proportion of sand, silt and clay-sized particles in a soil Truncated laterite Lateritic profile where upper layers have been stripped by erosion. Soils on

truncated laterites often formed from mottled or pallid zone materials

Volcanic rock Either ejected material or lava flow

Waterlogging Excess water in root zone present either as a perched watertable or as water ponded on soil surface

Water repellence Condition which affects wetting pattern of soils, especially sandy soils, and results in an uneven wetting pattern in autumn

Weathering Physical and chemical disintegration, alteration, and decomposition of rocks and minerals at or near the Earth’s surface by atmospheric and biological agents

Water availability Amount of moisture in the soil that is available to be absorbed by plant roots

References

Related documents

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