Genesis and classification of gypsiferous soils of the Middle Euphrates Floodplain, Syria

Ž .Geoderma 87 1998 67–85

Genesis and classification of gypsiferous soils ofthe Middle Euphrates Floodplain, Syria

N. Florea a,), Kh. Al-Joumaa b

a Research Institute for Soil Science and Agrochemistry, Bucharest, Romaniab UniÕersity of Aleppo, Agriculture Faculty of Deir-es-Zor, Aleppo, Syria

Received 21 September 1996; accepted 27 February 1998

Abstract

The Gypsisols and Gypsic Solonchaks of the Middle Euphrates Floodplain from Syria aredescribed and characterised. These soils are developed on alluvial fans and glacises consisting ofgypsiferous water-deposited sediments transported from the neighbouring higher areas. The profileof these Gypsisols is better developed than that of the upland Gypsisols. The main characteristicsof the studied Gypsisols and Gypsic Solonchaks are presented. There are good correlationsbetween CaCO content, humus content or CEC on the one hand and clay content on the other3

hand. The pedogenetic processes are very slightly expressed and consist mainly of a lowbioaccumulation reflected in an ochric A horizon and a slight migration of gypsum andaccumulation of gypsum in a subsurface gypsic or petrogypsic horizon. Due to gypsum migration,

Ž .higher contents of CaCO are found in the upper horizons ‘residual’ accumulation . In poorly3

drained areas, with shallow ground water, the soluble salts accumulate in the upper soil horizon,generating Gypsic Solonchaks. Careful observations of field morphology are needed to identifysecondary gypsum to diagnose a gypsic horizon in the case of soils developed in stratifiedgypsiferous parent materials. It would be helpful if Soil Taxonomy would provide a Fluventicsubgroup and also some subgroups depending on the content and depth of the gypsum in the soil.Providing of a Saligypsid great group instead of Gypsic and Petrogypsic subgroups of differentSalids is questioned. The Gypsisols from the Middle Euphrates Floodplain are successfullycultivated by using ground water saturated with gypsum. q 1998 Elsevier Science B.V. All rightsreserved.

Keywords: gypsiferous soils ; soil genesis ; soil classification ; Syria

) Corresponding author. Fax: q40-1-2225979; E-mail: [email protected]

0016-7061r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved.Ž .PII: S0016-7061 98 00066-4

( )N. Florea, Kh. Al-JoumaarGeoderma 87 1998 67–8568

1. Introduction

In a previous paper the characteristics of the Gypsisols and other soilsdeveloped from gypsum deposits on the upland in the Syrian desert have been

Ž .studied Florea and Al-Joumaa, 1993 . Here we describe the characteristics ofthe main soils developed in the gypsiferous alluvial materials on the EuphratesFloodplain.

The general features of the gypsiferous soils are described in the first paperŽ .Florea and Al-Joumaa, 1993 . Since then a new Gypsid soil suborder has been

Žintroduced replacing the former great group of Gypsiorthids Soil Survey Staff,.1994, 1996 .

2. Materials and methods

The data of this paper are based on the results of a detailed soil survey carriedout on the Middle Euphrates Floodplain. From the dozens of soil profiles studiedin the field a few were selected for laboratory analysis. Selected analytical dataare presented in Tables 1–3.

Soils were described, classified and analysed according to the World SoilŽ .Resources Report no. 60 of FAO-UNESCO 1988 . The soil analyses were

carried out in the laboratories of the Research Institute for Soil Science andAgrochemistry, Bucharest, and at the former General Administration for the

Ž . ŽDevelopment of the Euphrates Basin, Raqqa GADEB , in Syria Final Pedolog-.ical Report, 1978, Middle Euphrates Basin .

Due to the high content of gypsum, the laboratory analyses of gypsiferoussoils present some special problems. The particle size analyses take a very longtime because of the previous removing of salts, gypsum and carbonates. For thedetermination of exchangeable bases, soil samples are percolated with ammo-nium acetate at pH 7 and only K and Na are determined in the percolate.Exchangeable Ca and Mg cannot be determined directly; their sum was calcu-

Žlated by subtracting from the CEC the exchangeable K and Na corrected, if the.case, with the soluble K and Na determined in a 1:5 soil:water extract . The

values for CEC are obtained by the ammonium acetate method at pH 7.The gypsum content is determined by complete dissolution in water, its

precipitation in acetone and the conductometric measurement of gypsum.Wilting point and field capacity were calculated from the suction curves

Ž .determined with a porous pressure plate according to the Richards methodusing sieved samples.

The studied soil profiles were also classified according to the Soil TaxonomyŽ .Soil Survey Staff, 1996 .

( )N. Florea, Kh. Al-JoumaarGeoderma 87 1998 67–85 69

3. Results and discussion

The Euphrates Floodplain in Syria has many parts in which very welldeveloped and extensive glacis outwash deposits and alluvial fans are formed byrun-off waters or small streams. These landforms consist of relatively recentwater-deposited sediments and are very rich in gypsum. To the south, thesediments are derived from the neighbouring upland where the prevalent rock isgypsum alternating with limestone and marls. To the north, they are derivedfrom the lower terraces of the Euphrates, which contain here and there gypsifer-ous sediments. The alluvial fans form a separate depositional landscape betweenthe Euphrates Floodplain and the neighbouring highlands.

The mean annual temperature is 18.48C, the average rainfall is 231 mm, andthe mean annual evapotranspiration is 1028 mm. The soils have, generally, anaridic soil moisture regime, with about 930 mm annual water deficit.

The vegetation is sparse. Species of Artemisia, Artiplex, Salsola, Stipa,Lactuca, Poa, Anabassis, Gladiolus, Alhagi, Acacia are common native plants.

Ž . Ž .Gypsisols Haplic and Petric FAO-UNESCO, 1988 are common. Most ofŽ .them are cultivated of long ago under irrigation like the associated Fluvisols of

the floodplain. Small areas of Gypsic Solonchaks also occur. According to SoilŽ .Taxonomy these soils belong to the Gypsids Haplogypsids, Petrogypsids and

Ž .Salids Gypsic Haplosalids, Petrogypsic Haplosalids, Gypsic Aquisalids .These soils very rich in gypsum cover large areas in the Middle Euphrates

Ž .Floodplain between Tabqa and Madan Jedid, Raqqa district . They occur at thecontact between the alluvial plain and the next terrace or upland, or as alluvialfans within the alluvial deposits of the Euphrates Floodplain. In the Euphratesfloodplain they comprise about 10–25% of the area, but in some places they arethe dominant soils.

3.1. Soil morphological features

From a morphological point of view the Gypsisols formed in gypsiferousŽwater-deposited sediments have a better developed profiles AqAC about

. Ž .45–55 cm than the upland Gypsisol profiles AqAC about 17–32 cm . This isa consequence of their long cultivation under irrigation.

The A horizon is 45–55 cm thick. It has brown, yellowish brown or lightŽ .yellowish brown colour 7.5YR 5r4, 10YR 5.5r4 when moist and yellowish

Žbrown, very pale brown or reddish yellow to pink colour 7.5YR 7r5, 10YR.6.5r5 when dry. Commonly it is a silt loam, loam or sandy loam with very few

gypsum fragments. Cultivation has often disturbed the structure in the firstcentimetres. Below it is subangular blocky or, sometimes, massive. It is slightlyplastic and slightly sticky when wet, friable when moist, rather hard when dry. Itis very strongly effervescent with HCl and has diffuse carbonates and gypsum aspowder and sand. It is porous and has common fine roots. The A horizon passesclearly or gradually to an AC or Bk horizon extending down to 45–55 cm,

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8570Table 1

Ž .Analytical data of some soils developed in gypsum alluvial deposits of the Middle Euphrates Floodplain depositional landscape

Ž .Horizon Depth Particle size distribution % CaCO CaSO P ECe Ratio3 4Ž . Ž . Ž .cm % 2H O dSrm2 22–0.2 0.2–0.05 0.05–0.02 0.02–0.002 -0.002 F.Silt F.Silt

mm mm mm mm mm C.Sand C.Silt

( ) ( )a E. Ratla, Haplic Gypsisol Xeric Haplogypsid

Ap 0–15 0.9 3.2 12.6 26.2 57.1 22.3 13.9 3.2 3.94 2.08CAy 35–50 2.5 7.0 16.0 20.1 54.4 15.9 43.7 3.4 2.29 1.262 Cy 70–90 3.0 33.0 24.4 27.9 11.7 16.3 20.3 4.5 0.74 1.143 C 120–140 1.7 8.2 26.3 16.3 47.5 21.5 17.0 14.4 3.21 0.62

160–180 0.9 5.0 25.6 18.2 50.3 18.5 23.9 15.1 5.12 0.71

( ) ( )b S. Madan Jedid, Petric Gypsisol Xeric PetrogypsidAp 0–10 32.0 48.0 9.5 3.0 7.5 8.3 11.4 3.2 0.20 0.32A 12–25 31.3 33.7 8.2 8.9 17.9 14.2 10.7 3.4 0.24 1.092 Cy 25–40 38.0 21.7 13.2 8.8 18.3 4.5 74.0 3.5 0.61 0.66Cym 50–60 48.1 18.2 10.0 11.8 11.9 2.9 78.3 3.5 0.55 1.183 Cy 80–90 48.9 8.5 25.3 7.1 12.0 4.9 73.4 3.5 3.47 0.24

( ) ( )c W. Khatuniye, Petric Gypsisol Xeric PetrogypsidAp 0–10 1.2 1.4 59.0 12.9 25.5 12.1 34.4 2.9 42.1 0.222 ACy 25–35 0.6 0.9 83.8 4.4 10.3 4.4 53.8 3.6 93.1 0.053 Cym 60–70 0.2 0.3 93.8 1.9 3.8 5.2 72.1 3.5 713.0 0.02

130–140 1.5 0.3 95.5 1.3 1.4 4.6 72.1 318.0 0.014

( ) ( )d E. Kasret Sheikh al Juma, Haplic Gypsisol Xeric HaplogypsidAp 0–15 0.5 17.8 21.6 32.2 27.9 17.5 2.4 2.8 1.21 1.49Bk 40–55 0.9 25.2 27.5 19.7 26.7 16.8 5.6 3.4 1.09 0.72Cy 70–85 1.6 25.6 27.9 19.3 25.6 13.3 21.9 3.1 1.09 0.692 C 105–120 1.8 32.5 25.8 20.9 19.0 10.8 35.7 3.7 0.79 0.81

150–165 0.8 29.3 30.2 20.9 18.8 10.0 36.8 6.8 1.03 0.69

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( ) ( )e NE Ratla, Sali-Haplic Gypsisol Xeric Haplogypsid

Ap 0–20 2.0 2.9 42.0 16.2 36.9 20.8 37.0 3.6 14.5 0.39A 30–40 1.4 2.1 28.5 21.1 46.9 21.2 38.2 13.8 13.6 0.742 Cy 60–80 1.7 4.7 5.2 33.9 54.5 15.2 62.3 13.6 1.11 6.52

90–110 2.1 8.7 15.6 24.3 49.3 17.6 67.7 12.3 1.79 1.56C 120–130 0.9 7.4 20.3 21.2 50.2 28.0 24.8 16.8 2.74 1.04

( ) ( )f E. Madan Jedid, Sali-Haplic Gypsisol Xeric HaplogypsidAp 0–20 0.4 4.2 20.9 27.6 46.9 24.0 21.1 11.2 4.98 1.32CA 40–50 0.2 3.7 25.6 26.0 44.6 18.5 22.6 11.1 7.11 1.022 Cy 70–90 0.9 4.7 33.2 44.5 16.7 15.7 42.3 14.5 7.06 1.343 C 140–160 0.1 2.9 22.8 39.0 32.5 19.7 36.6 16.6 7.86 1.714 C 220–240 0.4 3.0 8.4 36.0 52.2 18.3 37.4 14.9 2.80 4.29

( ) ( )g South Experimental Granada Farm, Gypsic Solonchak Petrogypsic HaplosalidAz 0–15 0.3 1.0 65.8 10.6 22.3 12.4 33.3 62.0 65.8 0.162 Cyz 40–50 0.3 0.1 96.7 0.7 2.2 10.7 64.5 28.5 967.0 0.01

100–120 0.1 0.1 91.6 2.8 5.4 3.3 75.3 13.5 916.0 0.03C 150–160 0.1 0.7 88.1 4.3 6.8 12.3 62.1 15.0 126.0 0.053 C 190–200 1.2 3.8 77.4 6.4 11.2 18.4 65.3 16.3 20.4 0.084 C 230–240 6.0 37.1 34.7 7.8 14.4 19.2 70.4 14.6 0.94 0.22

( )P1, Experimental Granada Farm, Petric Gypsisol Xeric PetrogypsidAp 0–15 4.8 8.1 27.0 29.1 31.0 20.7 12.2 2.8 3.33 1.08A 20–29 4.8 9.1 20.0 27.9 38.2 21.4 6.7 2.7 2.20 1.4ACy 30–45 4.9 6.9 22.1 18.1 48.0 13.2 49.0 2.8 3.20 0.82Cy 50–60 5.7 6.6 28.9 23.7 35.1 5.9 69.7 3.1 4.38 0.82Cmy 70–80 2.9 5.2 24.7 17.8 49.5 5.1 71.8 2.8 4.75 0.722 C 100–110 1.8 4.4 24.5 30.7 38.6 7.1 63.2 4.2 5.54 1.25

150–160 0.9 0.9 20.1 38.8 39.3 11.3 69.0 8.0 22.3 1.93

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Ž .Table 1 continued

Ž .Horizon Depth Particle size distribution % CaCO CaSO P ECe Ratio3 4Ž . Ž . Ž .cm % 2H O dSrm2 22–0.2 0.2–0.05 0.05–0.02 0.02–0.002 -0.002 F.Silt F.Silt

mm mm mm mm mm C.Sand C.Silt

( )P13, 0.5 km N. of Kasret Srur, SaliHaplic Gypsisol Xeric Haplogypsid

Ap 0–20 1.8 6.4 37.3 13.9 40.6 24.1 44.5 2.8 5.83 0.37ACy 30–45 0.5 3.7 34.1 13.8 47.9 19.5 59.3 4.7 9.22 0.42 Cyz 60–75 0.0 3.4 23.6 27.0 46.0 20.9 59.6 6.9 6.94 1.14

85–100 0.4 3.3 28.8 25.5 42.0 20.5 60.6 6.8 8.73 0.89125–140 1.2 4.1 27.0 29.2 38.5 17.8 58.0 6.0 6.59 1.08

3 C 170–185 0.4 2.6 21.8 27.1 48.1 18.3 58.1 6.3 54.5 1.24

( )P21, S. of Abu Hammad, Gypsic Solonchack Gypsic AquisalidAp 0–20 1.7 4.4 15.2 25.0 53.7 22.1 2.1 41.0 3.45 1.64A 30–40 1.6 4.3 10.9 22.4 60.8 32.6 2.4 20.4 2.53 2.06Cy 45–60 1.9 3.6 8.7 19.9 65.9 22.7 25.3 16.4 2.42 2.292Cy 75–90 5.5 17.6 13.0 23.9 40.0 23.1 23.8 14.7 0.74 1.843 C 150–165 7.8 23.9 28.8 13.3 26.2 20.9 24.5 6.9 1.21 0.46

200–215 3.2 27.2 22.7 21.6 25.3 22.7 22.6 7.4 0.83 0.95


Ž .where the gypsic horizon Cy occurs. Locally the Cy horizon occurs directlyunder the A horizon.

The Cy horizon, generally at a depth of 45r55 to 90r100 cm, is yellowishŽ .brown or reddish yellow 10YR 6r6, 7.5YR 6r6 when moist. Rarely there are

Ž .small very pale brown or white lighter mottles. The texture is silt loam toloam. It has a subangular blocky structure or is structureless. Consistency isslightly plastic and slightly sticky when wet, firm when moist, and hard whendry. It is strongly to very strongly effervescent with HCl. The carbonates andgypsum are diffuse. Crystals, veins and nests of gypsum are distributed locally.The horizon is little porous to porous, has few roots, and a gradual lowerboundary.

ŽThe C horizon continues to depths greater than 200 cm, is brownish or.reddish yellow, light brownish yellow, yellow, very pale brown, light brown to

Ž .pink 10YR 6.5–7.5r4, 6r6 or 7.5YR 6.5–7r4, 6r6–7r5 with commonŽ .lighter mottles 10YR 8r2–4 . The texture is sandy loam, silt loam or loam. It

Ž .has no structure massive, sometimes single grains , is strongly effervescentwith HCl and has diffuse carbonates, efflorescence of carbonates and crystalsand nests of gypsum. This part of the profile is porous to little porous.

Sometimes a 20–30 cm thick cemented horizon is observed within the CyŽ .horizon petrogypsic horizon .

Examined with a stereomicroscope, the soil material of the upper part of theŽ .Gypsisols shows isolated gypsum granules about 0.05 mm ø and agglomerates

Ž .0.1–0.3 mm of gypsum granules coated with soil plasma skins. One can seealso recent depositions of gypsum or soluble salts in the voids and cracks. Thequantity of agglomerates decreases with depth.

3.2. Soil physical and chemical properties

The content of gypsum and carbonates in these soils is very high, oftenreaching 20–45% in the A horizons or even 58–68% in the case of clayey soilsand 36–46% or even 60–85% in C horizons. Consequently the silicate content

Ž .is lower than in many other soils Tables 1–3 , frequently representing only20–50% in the lower part of the profiles.

The content of silicate material and also its particle size distribution vary bothhorizontally and vertically in the same profile. The particle size distribution

Ž . Žvaries from very coarse 30–49% coarse sand to fine clay up to more than.65% . The dominant field textures of these soils however seems to be loam to

silt loams due to the high content of gypsum powder, the prevalent form inwhich the gypsum occurs.

The vertical heterogeneity of the parental material is reflected by the high andirregular variation along the soil texture profile as well as by the fine siltrcoarse

Ž .silt and coarse siltrfine sand ratios Table 1 .Ž .All soil samples have CaCO ; the CaCO content equivalent varies from 33 3

to 12% in the case of sandy and silty soils, from 10 to 17% for medium textured

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Table 2Ž .Analytical data of some soils developed in gypsum alluvial deposits of the Middle Euphrates Floodplain depositional landscape

Depth Water Org. Total C:N Total Available Available Exchange cations CEC ESPŽ . Ž . Ž . Ž .cm pH matter N P O P O K O cmolrkg cmolrkg %2 5 2 5 2

Ž . Ž . Ž . Ž . Ž . Ž . 2q 2q q q1:2.5 C=1.72 % % ppm ppm Ca qMg K NaŽ .%

( ) ( )a E. Ratla, Haplic Gypsisol Xeric Haplogypsid

0–15 8.1 1.25 0.085 10.4 0.159 128 509 18.7 0.9 0.1 19.7 0.635–50 8.1 0.52 0.034 10.3 0.096 127 193 13.0 0.4 0.1 13.5 0.970–90 8.0 0.13 0.008 10.9 0.092 130 361 17.4 0.7 0.2 18.3 1.3120–140 8.1 – – – – 171 361 – – – – –160–180 8.3 – – – – – – – – – – –

( ) ( )b S. Madan Jedid, Petric Gypsisol Xeric Petrogypsid0–10 8.1 0.40 0.030 9.3 0.075 233 108 10.1 0.2 0.2 10.5 1.512–25 7.7 1.10 – – – 295 199 12.8 0.4 0.2 13.3 1.225–40 7.7 0.20 0.010 8.8 0.037 119 78 9.4 0.1 0.2 9.7 2.150–60 7.7 – – – – 101 84 9.0 0.1 0.1 9.2 1.180–90 7.6 0.20 – – 0.043 135 102 7.9 0.2 0.1 8.2 1.3

( ) ( )c W. Khatuniye, Petric Gypsisol Xeric Petrogypsid0–10 8.4 1.10 0.052 13.5 0.089 140 375 19.2 0.7 0.1 20.0 -125–35 8.5 0.75 0.046 11.0 0.076 150 145 13.6 0.3 0.1 14.0 -160–70 8.1 0.29 0.020 9.8 0.036 70 95 6.7 0.2 0.1 7.0 -1130–140 8.1 – – – – – – – – – – –

( ) ( )d E. Kasret Sheikh al Juma, Haplic Gypsisol Xeric Haplogypsid0–15 8.0 0.76 0.040 13.1 0.110 203 274 15.6 0.4 0.2 16.3 1.540–55 7.9 0.25 0.040 13.0 0.160 168 312 17.9 0.5 0.3 18.7 1.4

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70–85 7.9 0.32 0.020 12.7 0.130 108 216 15.8 0.4 0.2 16.3 1.0105–120 7.9 – – – – – – 13.6 0.4 0.2 14.1 1.1150–165 8.0 – – – – – – 14.4 0.3 0.2 14.9 1.0

( ) ( )e NE Ratla, SaliHaplic Gypsisol Xeric Haplogypsid0–20 8.2 1.32 0.089 10.0 0.149 161 385 14.6 0.6 0.4 15.6 2.630–40 7.9 1.27 0.085 10.1 0.164 186 315 15.0 0.6 0.5 16.1 3.160–80 7.9 0.67 0.043 10.5 0.104 113 277 11.9 0.5 0.3 12.7 2.790–110 8.0 0.23 0.017 9.1 0.090 64 193 10.7 0.3 0.3 11.2 2.3120–130 8.1 – – – – – – – – 0.4 15.1 2.8

( ) ( )f E. Madan Jedid, SaliHaplic Gypsisol Xeric Haplogypsid0–20 8.0 1.74 0.115 10.2 0.176 485 1096 19.1 1.4 0.5 21.0 2.340–50 7.9 0.79 0.053 10.1 0.123 499 337 16.3 0.6 0.6 17.4 3.270–90 7.9 0.42 0.029 9.8 0.125 472 157 14.6 0.3 0.5 15.4 3.5140–160 8.2 – – – – – – – – 0.4 18.4 1.9220–240 8.3 – – – – – – – – 0.4 22.0 2.0

( ) ( )g South of Experimental Granada Farm, Gypsic Solonchak Petrogypsic Haplosalid0–15 8.0 0.88 0.055 10.8 0.109 296 636 17.0 0.4 0.1 17.5 -140–50 8.4 0.19 0.014 9.2 0.038 38 60 5.8 0.1 0.1 6.0 -1100–120 8.6 – – – – – – 5.7 0.2 0.1 6.0 -1150–160 8.5 – – – – – – 8.6 0.2 0.1 9.0 -1190–200 8.4 – – – – – – 11.0 0.3 0.1 11.4 -1230–240 8.3 – – – – – – – – – – –

( )3P1, Experimental Granada Farm, Petric Gypsisol Xeric Petrogypsid0–15 7.9 1.08 0.095 7.7 0.137 240 601 22.0 0.220–29 7.8 0.84 0.051 11.1 0.132 227 516 24.0 0.230–45 7.9 0.54 0.034 10.7 0.080 209 337 20.0 0.250–60 8.0 0.36 – – 0.039 176 179 12.0 0.2

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Ž .Table 2 continued

Depth Water Org. Total C:N Total Available Available Exchange cations CEC ESPŽ . Ž . Ž . Ž .cm pH matter N P O P O K O cmolrkg cmolrkg %2 5 2 5 2

Ž . Ž . Ž . Ž . Ž . Ž . 2q 2q q q1:2.5 C=1.72 % % ppm ppm Ca qMg K NaŽ .%

70–80 8.1 0.30 – – 0.034 188 145 14.0 0.7100–110 8.0 0.15 0.012 9.0 – 135 159 16.0 2.1150–160 8.2 0.12 – – – – – 15.0 14.0

( )P13, 0.5 km N. of Kasret Srur, SaliHaplic Gypsisol Xeric Haplogypsid0–20 7.9 1.77 0.112 10.7 0.151 320 403 16.0 0.830–45 8.2 0.94 0.066 9.6 0.131 133 417 11.0 4.160–75 8.2 0.41 0.030 9.3 0.121 147 653 12.0 4.385–100 8.3 0.35 – – – 121 797 13.0 3.9125–140 8.3 – – – – – – 13.0 3.1170–185 8.2 – – – – – – 14.0 2.7

( )P21, S. of Abu Hammad, Gypsic Solonchak Gypsic Aquisalid0–20 7.9 1.47 0.085 11.7 0.110 202 614 17.5 1.6 7.4 26.5 28.030–40 8.0 0.83 0.041 13.6 0.110 83 482 15.9 1.0 4.6 21.6 21.545–60 8.2 0.35 0.033 7.4 0.060 89 310 21.5 0.7 4.4 26.4 16.575–90 8.2 – – – – 73 310 14.9 0.7 3.1 18.6 16.5150–165 7.9 – – – – – – – – 1.0 15.7 6.1200–215 7.8 – – – – – – – – 1.1 18.6 6.1


soils and from 15 to 26% for fine textured soils. The first soil horizon hasgenerally 12–24% CaCO and these values are commonly the highest values in3

the soil profiles. Its content decreases irregularly with depth.Ž .The gypsum content ranges from 2 to 44% frequently 10–20% in the A

Ž .horizon, 22–78% in the Cy horizon and 25–75% in the C horizon Table 1 .The petrogypsic horizon often has 72–78% of gypsum. In general, high values

Žof gypsum content are associated with low values of CaCO content CaCO s3 3

23.12y0.174 gypsum or gypsums75.04y2.117 CaCO , for C horizon, R23

.being 0.368 .In general these soils do not have soluble salt accumulations; the ECe

Ž . Žsaturation extract electroconductivity is 2.8–4.5 dSrm in the A horizon the.lower limit of the gypsum saturation solution being 2.4–2.8 dSrm and

increases in some cases to 7–15 dSrm below 100 cm depth. Nevertheless, inpoorly drained conditions, the soluble salts from the ground water can accumu-late in soil and the ECe can increase to more than 40–60 dSrm in the upper

Ž .horizon of the Gypsic Solonchaks Table 1 .Soil pH has dominantly values of 7.9–8.2. Gypsisols rich in coarse sand have

lower values of 7.6–7.8 and salt affected soils with an ECe of 16–18 dSrmŽ .Table 2 have higher values of 8.3–8.6.

Ž . Ž .The organic matter content Table 2 , rather low in the A horizon 0.9–1.8% ,Ž . Žbecomes very low in the ArC horizon 0.5–0.9% , and the C horizon 0.2–

. Ž .0.4% . Also the total N content is low 0.040–0.110% . The C:N ratio is 9–13,reflecting a good rate of organic matter mineralization.

Ž .The total P O content 0.075–0.160% , as well as the available P content2 5Ž .140–320 ppm are high due, probably, to the long fertilisation. Also, the

Ž .available K content is high 150–1000 ppm .Ž .The cationic exchange capacity CEC in the A horizon is between 10 and 26

Ž . Ž .cmol q rkg, and decreases to 7–18 cmol q rkg in the C horizon dependingŽ .on the soil texture Table 2 . The CEC values are, in general, too high related to

the clay and organic matter content of soils, probably due to the fact that thegypsum retains some ammonium during the percolation of soil samples withammonium acetate. This assumption is suggested by the existence of highestdiscrepancies in the case of samples that are very rich in gypsum.

The predominant exchangeable cations are Ca2q and Mg2q; Kq and Naq arefound in low proportion, except Na in Aquisalids where the Naq increasesŽ . Ž .Table 2 . Exchangeable sodium percentage ESP is less than 3.5, frequently

Žless than 1, but can increase to high values in the Gypsic Solonchak Gypsic.Aquisalid because of the water movement toward the soil surface. These saline

soils very rich in gypsum, have however low ESP values due to the presence ofgypsum, and the leaching of the soluble salts takes place without alkalization.

In spite of the low silicate content of these soils, there are rather good directcorrelations between CaCO content, humus content or CEC on the one hand3

Ž .and clay content on the other hand Fig. 1 . Correlations are highest for A


Fig. 1. The correlation between CaCO content, organic matter content or CEC and clay content.3


Table 3Some physical properties of the soil developed in gypsum alluvial deposits of Middle EuphratesFloodplaina

Depth PD BD P AP WP FC AWC K FI3 3Ž . Ž . Ž .cm kgrdm kgrdm %vrv %vrv %vrv % % mrday mrday

( )a E. Ratla0–15 2.64 1.21 55 14 18.3 31.1 12.835–50 2.68 1.20 55 11 20.5 34.6 14.1120–130 2.66 1.15 56 15 20.1 34.1 14.0( )b S. Madan Jedid0–10 2.69 1.40 48 20 6.7 14.3 7.6 0.3825–45 2.68 1.20 55 11 20.7 34.8 14.180–90 2.64 1.25 53 9 20.5 33.4 12.9( )c W. Khatuniye0–10 2.67 1.31 51 9 19.0 30.4 11.4 0.4825–35 2.64 1.35 49 6 19.6 30.2 10.660–70 2.46 1.29 51 9 20.5 30.5 10.0( )d E. Kasret Sheikh al Juma0–15 2.64 1.31 50 15 12.3 23.5 11.240–55 2.61 1.34 49 13 13.2 23.9 10.770–80 2.67 1.38 48 10 14.8 25.0 10.2( )e NE Ratla10–20 2.66 1.12 58 20 17.5 31.5 14.0 0.3030–40 2.64 1.14 57 17 16.6 33.0 16.460–80 2.68 1.15 57 15 17.5 34.6 17.190–100 2.69 1.17 56 19 16.5 28.8 12.3 0.16( )f E. Madan Jedid0–20 2.67 1.16 57 16 17.3 33.3 16.0 0.1740–50 2.68 1.17 56 17 18.2 27.9 12.970–90 2.67 1.17 56 16 20.7 32.4 11.7 0.11( )g S. of Exp. Granada Farm5–15 2.57 1.30 49 6 19.7 31.4 11.7 0.3240–50 2.60 1.35 48 3 20.0 32.1 12.1100–110 2.69 1.40 48 1 21.0 33.7 12.7P1 Experimental Granada Farm5–10 2.67 1.09 60 28 16.4 27.0 10.6 0.74 0.6340–45 2.69 1.06 61 29 16.0 29.0 13.0 0.62 0.4375–80 2.32 1.13 51 11 19.1 34.0 14.9 0.27 0.23125–130 2.34 1.17 50 11 20.5 31.7 11.2 1.05 0.95P13 N Kasret Srur15–20 2.46 1.08 56 21 16.7 30.6 13.9 1.73 1.5170–75 2.50 1.08 57 23 15.2 29.0 13.8 2.07 1.81115–120 2.45 1.06 57 24 15.9 30.2 14.3 1.82 1.56P21 S. of Abu Hammad0–20 2.63 1.26 52 6 15.0 35.2 20.2 0.1845–60 2.65 1.32 50 4 15.0 34.8 19.8 0.23100–160 2.65 1.48 44 3 8.0 27.6 19.6 0.59

aPD particle density; BD bulk density; P total porosity; AP air porosity; WP wilting point; FCfield capacity; AWC available water capacity; K infiltration rate; FI final intake rate.


horizons; the difference between A horizon and C horizon curves for CEC is dueevidently to the humus content.

Ž .The physical properties of the Gypsisols are relatively favourable Table 3 .The soil particle density varies between 2.63 and 2.69 grcm3, rarely 2.32–2.61grcm3. Bulk density ranges between 1.06 and 1.40 grcm3 and the total porosity

Ž .between 48 and 61% frequently 51–57% .The moisture content at wilting point is 12–21%, at field capacity it is

Ž23–35% and the available water capacity is 11–17% excepting for the coarse.textured soils where these values are 7, 14 and 7% respectively . The available

water capacity estimated in mm water depth is 75–80 for a soil layer of 50 cm,of which 38–40 mm are easily available.

Ž .The infiltration rate K is good to high, 0.10–2.00 mrday depending on thesoil texture and structure. Final intake rate is somewhat lower than the infiltra-

Ž .tion rate Table 3 .Although the physical soil properties are good, these soils have a very

deficient moisture regime due to the climate aridity unless they are irrigated.Osmotic pressure takes some water also. A special problem is the extreme soilhardening when the soil material is dried, probably due to making fast the soilparticles by the gypsum precipitation from out soil solution; but by moisteningthe soil mass becomes again friable.

The volumetric distribution of the soil components shows a whole or unitaryimage for the main properties of the soil profile. This graphic representationattenuates the discrepancy between the content of silicate and the content of

Ž . Ž .CaCO and gypsum on a weight base of the soil Fig. 2 .3

3.3. Pedogenetic considerations

The Gypsisols have little evidences of the pedogenetic horizon development,except for an ochric A horizon and a Cy horizon. The soil genesis is particularly

Ž .characterised by the following features: a the parent material has been subjectedto a very slight amount of leaching as shown by the dissolution and precipitation

Ž .of gypsum; b a slight bioaccumulation of humus and nutrients in a rather thinA horizon, due to very low biomass production and a high rate of mineraliza-

Ž .tion; c a leaching of the soluble salts from the upper part of the soils except forthe soils situated in poorly drained areas where a surface salt accumulation can

Ž .take place; d a slight migration of gypsum and its accumulation in a subsurfaceŽ .horizon gypsic horizon , sometimes with a cementation of the soil material

Ž . Ž .petrogypsic horizon ; e a lack of CaCO migration due to the low rainfall on3

one hand and to the decrease of the CaCO solubility in the presence of gypsum3Ž .salt with common Ca ion on the other hand; the increased CaCO content of3

Žthe upper horizon can be a consequence of the gypsum migration ‘residual’.accumulation .

Ž .In addition the following topics can be mentioned: a the vertical variation ofŽ .the particle size reflects the variation of the sedimentary conditions; b the


Fig. 2. The volumetric distribution of the soil components for some Gypsisols.

fining of the soil texture towards the fan periphery or sometimes within the soilŽ .cover in the frame of the alluvial fan; c the interference of the processes of soil

Ž . Ž .erosion by wind or even run-off water; d the alkalization sodization of theGypsisols takes place in the case of the salt affected Gypsisols, but it is not a


problem from the reclamation point of view, because the presence of thegypsum prevents the soil alkalization during the leaching of the soluble salts.

3.4. Taxonomic remarks

ŽConcerning the new criteria for the gypsiferous soil classification FAO-UN-.ESCO, 1988; Soil Survey Staff, 1994, 1996 the following aspects need

Ž .attention: i The variation of the gypsum content with increasing depth is verymuch influenced by the parent material stratification. Because of this, the

Ž .requirement for a gypsic horizon Cy to have at least 5% gypsum more than theŽ .underlying C horizon FAO-UNESCO, 1988 does not fulfil for all profiles

developed in gypsiferous alluvial material, for example b, c, d, f, P1, P13 andP21 of Table 1. More or less similar questions of the gypsiferous soil classifica-

Ž . Ž .tion were discussed by Porta and Herrero 1988 , Herrero 1991 and Herrero etŽal., 1996. According to the new criteria of Soil Taxonomy Soil Survey Staff,

.1994, 1996 , the laboratory data alone may not be adequate to classify correctlythe soils developed in gypsiferous alluvial material, without careful examination

Ž .their morphology 1% more by volume secondary gypsum . From this point ofview the FAO criteria for a gypsic horizon should to be changed according tothe Keys to Soil Taxonomy.

It would be helpful if a Fluventic subgroup were to be provided within theŽgreat groups of Haplogypsids and Petrogypsids based on irregular variation

with increasing depth of the organic matter content andror soil material.stratification .

Also, it seems to be very useful to distinguish some subgroups according tothe depth at which the gypsum starts to be present in high quantity affecting theroot growth of some plants.

Considering that the gypsic horizon is more stable than the salic horizon, onecan question the inclusion of the Gypsic or Petrogypsic subgroups within Salidsas Saligypsid or Salidic subgroups in Haplogypsids or Petrogypsids.

3.5. Fertility and land use

Due to lack of rainfall and low content of humus and nutrients, the Gypsisolshave a low fertility. The high content of gypsum affects the mobility andavailability of P, K, Mg, Fe, Mo, Zn for plants.

The agricultural value of these Gypsisols is low and their use is generallylimited to grazing. However, in the Middle Euphrates Floodplain as they areirrigated, these soils are cultivated to a large extent. Problems however arise inthe irrigation systems due to the dissolution of the gypsum. Good results havebeen obtained by the farmers irrigating with ground water from the same area;as this water is saturated in CaSO , the dissolution of gypsum and its removal4

from the soil is avoided.


Under irrigation the most successful crops are Mexican wheat, black barley,cotton, sugar beet, potatoes, alfalfa, sorghum, tomato and sesame.

4. Conclusions and summary

ŽIn the Middle Euphrates Floodplain, between Tabqa and Madan Jedid Raqqa.district, Syria there are several alluvial fans and glacis outwash deposits

consisting of gypsiferous water-deposited sediments transported from the neigh-bouring higher areas. On these landforms and under the arid climatic conditionsGypsisols have developed. Most of the soils are cultivated like the neighbouringFluvisols. Gypsic Solonchaks occur also, but are smaller in extent.

Profiles of the Gypsisols formed in these gypsiferous alluvial sediments arebetter developed than those of the upland Gypsisols. As a consequence of theiruse as arable land under irrigation, they are also richer in humus and nutrients.

Ž .The textures of these soils varies from sandy loams to clays Table 1 . Theparent material stratification is clearly shown by the irregular variation of thesoil texture and of the ratios between fine silt and coarse silt or coarse silt and

Ž .fine sand Table 1 .The CaCO content varies between 12 and 24% in the upper horizons and3

decreases irregularly with increasing depth. The gypsum content is between 2Ž .and 44% frequently 10–20% in the A horizon and increases to 38–78% in Cy

Ž .gypsic horizon ; the underlying C horizon has 25–75% gypsum.The organic matter content is 0.9–1.8% in the A horizon. For the most part,

organic C decreases regularly with depth. The total N content is also lowŽ .0.040–0.115% . Amounts remain relatively high with depth in some of theprofiles thus supporting our view that a Fluventic subgroup for Gypsids is

Ž . Ž .needed. The total P O 0.075–0.160% and available P 140–320 ppm are2 5Ž . Ž .relatively high, as well as the available K 150–1000 ppm Table 2 .

Ž .Soil reaction is slightly to moderately alkaline pHs7.7–8.3 . The CEC,Ž . Ž10–26 cmol q rkg in the upper horizon, decreases a little with depth 7–18

Ž . .cmol q rkg . ECe is 2.8–4.5 dSrm and the ESP 1–3.5, except for the saltŽ .affected Gypsisols. The physical properties Table 3 are relatively favourable.

A special problem is the extreme soil hardening upon drying.Relatively good correlations are found between contents of CaCO , organic3

Ž .matter and CEC on the one hand and clay content on the other hand Fig. 1 .There is a relatively uniform volumetric distribution of non gypsic compo-

Ž .nents in some of these Gypsisols Fig. 2 .The genetic processes are only slightly expressed and consist mainly of a low

bioaccumulation reflected in an ochric A horizon and in a slight migration ofŽ .gypsum and its accumulation in a subsurface gypsic horizon Cy or even a

petrogypsic horizon. The migration of CaCO does not take place; the higher3


content of CaCO in the upper horizon is a consequence of the gypsum leaching3Ž .‘residual’ accumulation of CaCO . In areas with poor drainage conditions high3

salt concentrations occur at the soil surface. This may be a ground water effectŽ .in Gypsic Solonchaks . It is to underline that the reclamation of the salt affectedGypsisols is facilitated by the presence of gypsum that prevent the soil alkaliza-tion during the leaching of the soluble salts.

Based on the collected data about these Gypsisols formed in alluvial deposits,one can observe that a correct classification of Gypsids commonly will require acareful morphological observation in order to identify the secondary gypsumaccumulations. The studied soils would be better classified if a Fluventicsubgroup was provided within the great groups of the Haplogypsids andPetrogypsids. Also it would be helpful if subgroups were provided for differenti-ating amount and the depth of gypsum. This would allow to differentiate classesof soils according to different gypsum free rooting depths. Because of therelative stability of gypsum and soluble salts it would be better to recogniseSalidic subgroups of Gypsids rather then Gypsic Salids.

The use of the Gypsisols is limited to grazing unless they are irrigated.Nevertheless, the irrigation of these soils may cause problems due to the gypsumdissolution. However farmers have obtained good results by irrigating withground water that is saturated with CaSO , thus avoiding gypsum dissolution.4

Acknowledgements

The authors wish to gratefully thank Dr. Wiley D. Nettleton and an anony-mous referee for their review, suggestions and comments on earlier drafts of thearticle, as well as Dr. Rosa M. Poch and Prof. Dr. Juan Herrero, for their kindassistance.

References

FAO-UNESCO, 1988. Soil Map of the World. Revised legend, World Soil Resources, report 60,Rome, 119 pp.

Florea, N., Al-Joumaa, Kh., 1993. Soils developed from gypsum deposits on the upland in theSyrian desert, R.J. of Aleppo University, Agricultural Sciences Series, no. 20, pp. 103–124.

Herrero Iser, J., 1991. Morfologia y genesis de suelos sobre Yesos, Ministerio de Agricultura,Pesca y Alimentation, Madrid, 447 pp.

Herrero, J., Poch, Rosa, M., Porta, J., Boixadera, J., 1996. Soils with gypsum of the CentralCatalan Depression, Intern. Symp. on Soils with Gypsum, Leida, 87 pp.

Porta, J., Herrero, I., 1988. Micromorphologia de suelos con yeso. Anales de edafologia yŽ .agrobiologia T XLVII 1–2 , 179–197.


Soil Survey Staff, 1994. Keys to Soil Taxonomy, 6th edn., USDA, Soil Conservation Service,Washington, DC, 306 pp.

Soil Survey Staff, 1996. Keys to Soil Taxonomy, 7th edn., USDA, National Resources Conserva-tion, Conservation Service, Washington, DC, 644 pp.

ŽFinal Pedological Report, 1978, Middle Euphrates Basin, Romagrimex, Bucharest Manuscript,.G.A.D.E.B., Raqqa, Syria .

Documents

Genesis and classification of gypsiferous soils of the Middle Euphrates Floodplain, Syria