Classification of the soil at CIMMYT s experimental station in the Yaqui Valley near Ciudad Obregón, Sonora, Mexico

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1 Classification of the soil at CIMMYT s experimental station in the Yaqui Valley near Ciudad Obregón, Sonora, Mexico Nele Verhulst 1,2, Jozef Deckers 2, Bram Govaerts 1 Summary The soil at the experimental station is classified as a Hyposodic Vertisol (Calcaric, Chromic) in World Reference Base (IUSS Working Group WRB, 2007) and as a fine, smectitic Chromic Haplotorrert in Soil Taxonomy (Soil Survey Staff, 2003). A. Description of the soil profiles In the spring of 2008, profile pits of 2 m depth were dug in Block 810 and Block 710 of the experimental station. A description of the profiles was made in the field and samples were taken for laboratory analysis of chemical and physical properties. In both profiles, two main layers can be distinguished in the soil profile: a dark clayey layer of approximately 1 m on top of an almost unaltered, light colored, silty layer (Figure 1, 2, 3). The clay layer contains clay minerals that swell when wet and shrink when dry, causing cracking of the soil when it dries out. The shrinking and swelling of these clays results in the development of two specific structural characteristics: slickensides: polished and grooved ped surfaces that are produced by aggregates sliding one past another (Figure 4) wedge shaped structural aggregates (Figure 3, 5) Since these structural properties are found in a sufficiently thick clay layer and the soil has cracks that open and close periodically, it is classified as a Vertisol in both the World Reference Base (the FAO system; IUSS Working Group WRB, 2007) and Soil Taxonomy (the USDA system; Soil Survey Staff, 2003). The complete descriptions of both profiles can be found in Annex 1 and 2. B. World Reference Base Classification As described above, the soil is placed in the Reference Soil Group (the first level of World Reference Base [WRB] classification) of the Vertisols. For the second level of WRB classification, qualifiers are used as prefix and suffix. Prefix qualifiers are typically associated to the Reference Soil Group and the intergrades to other Reference Soil Groups. All other qualifiers are listed as suffix qualifiers between brackets following the Reference Soil Group name. The following prefix qualifier applies: Hyposodic: The exchangeable Na on the exchange complex is 6 percent or more in a layer, 20 cm or more thick, within 100 cm of the soil surface. 1 International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6 641, Mexico, D.F., Mexico; 2 Katholieke Universiteit Leuven, Department of Earth and Environmental Sciences; Celestijnenlaan 200 E, 3001 Leuven, Belgium; 1

2 The following suffix qualifiers apply: Calcaric: The soil has material that contains 2 percent or more calcium carbonate equivalent between 20 and 50 cm from the soil surface. Chromic: There is a subsurface layer, 30 cm or more thick, within 150 cm of the soil surface that has a Munsell hue redder than 7.5 YR or that has both, a hue of 7.5 YR and a chroma, moist, of more than 4 (in other words, the soil has a slightly reddish color). Consequently, the soil is classified as a Hyposodic Vertisol (Calcaric, Chromic). C. Soil Taxonomy Classification The first level of classification in Soil Taxonomy is the Soil Order. As explained above, the soil is placed in the Order of the Vertisols. Because of the moisture conditions in the Yaqui Valley, the soil is classified in the Suborder of the Torrerts (the prefix torr refers to the to the torric moisture regime [L. torridus = hot and dry], the ert refers to the Vertisol Order). At the next level (Great Group), the soil does not qualify for any specific category, so it is named Haplotorrert ( haplo refers to showing no special characteristics). The subgroup level is intended to show relations between soils in a given great group or properties which are not characteristics or typical of any other kind of soil. Because of the color, the soil is classified as a Chromic Haplotorrert. The family level intends to be useful for making major interpretations concerning use for growing plants or for engineering purposes. The first part of the family name is the name of a particle size class, used to characterize the grain size composition of the soil. In both profiles, the control section used to determine the particle size class ( cm layer in Block 710 and cm layer in Block 810) has less than 60 percent (by weight) clay in the fine earth fraction, placing the soil in the category fine. The second part of the family name is the mineralogy class. The swell shrink characteristics of the soil indicate a montmorillonite mineralogy. Since montmorillonite belongs to the smectite group, the soil is put in the category smectitic. Other information that can be included in the family name is soil temperature class, but the necessary data were not available. Consequently, the soil is classified as a fine, smectitic Chromic Haplotorrert. Figure 1. Location of the soil profile in Block 710 in CIMMYT s experimental station in Ciudad Obregón. 2

3 (a) (b) Figure 2. The soil profiles in (a) Block 710 and (b) Block 810 in CIMMYT s experimental station in the Figure 3. Schematic outline of the soil profile in Block 710 in CIMMYT s experimental station in the 3

4 Figure 4. Example of slickensides (coin with 21 mm diameter used for scale reference) Figure 5. Examples of wedge shaped structures (coin with 21 mm diameter used for scale reference) 4

5 Annex 1: Soil profile description Block 810 General information Region Yaqui Valley, State of Sonora, Mexico Location CIMMYT research station, Dr Norman E Borlaugh, km 12, entre 800 y 900 Valle del Yaqui, CP 85000, Cd Obregón, Sonora, block 810 Coordinates N, W Elevation site 38 m asl Date 31/03/2008 Land system Geological formation Lacustrine/fluvial alluvial deposits Parent material Alluvium Physiography Lifted coastal lagoon Macrorelief Slopes <2% Microrelief Flat Land use/ Vegetation Wheat based cropping systems. Natural vegetation would be subtropical dry savanna woodland Climate Arid subtropical Moisture regime Moisture condition Moist Ground water level More than 10 m deep Drainage class Well drained Permeability Medium to slow Internal drainage Good Altered drainage conditions Yes, major drainage ditches; whole area under furrow irrigation Water erosion Surface features Sheet erosion (class 1), mainly at the beginning of the furrow Root distribution Effective soil depth Human influence Soil fauna Surface cracking Other features No roots due to absence of crop 120 cm Whole area was shaped into furrows for irrigation Few earthworms with galleries down to 160 cm None, due to plowed sandy top layer and moist condition of the soil profile 5

6 Soil characteristics Depth Horizon Description (cm) 0 15 Ap1 7.5 YR 4/2 grayish brown (moist) and 7.5 YR 5/2 grayish brown (dry); clay; weak coarse subangular blocky; dry slightly hard; moist friable; slightly sticky; slightly plastic; many medium (2 5 mm) interstitial pores; very few rock fragments (1 cm); slightly calcareous; abrupt, smooth boundary Ap2 7.5 YR 4/2 grayish brown (moist) and 7.5 YR 3/2 brownish black (dry); clay; strong coarse subangular blocky; dry hard; moist very friable; very sticky; very plastic; many fine (1 2 mm) interstitial pores; very few rock fragments (1 cm); slightly calcareous; clear, wavy boundary (B)i 5 YR 3/3 dark reddish brown (moist) and 5 YR 3/4 yellowish red (dry); clay; strong medium angular blocky; slickensides; shear planes tilted with an angle of 30 compared to horizontal axis; dry hard; moist firm; moderately sticky; moderately plastic; many fine (1 2 mm) interstitial pores; slightly calcareous; gradual, wavy boundary BC 5 YR 3/4 yellowish red (moist and dry); clay; strong very coarse angular blocky; dry hard; moist friable; very sticky; very plastic; common fine (1 2 mm) interstitial pores; many fine (1 2 mm) interstitial pores; very few moderately calcareous weathered rock fragments (5 7 mm, angular, 7.5 YR 8/2); slightly calcareous; gradual, wavy boundary C1 7.5 YR 5/4 brown (moist) and 7.5 YR 6/4 light brown (dry); clay; weak very coarse angular blocky; dry soft; moist very friable; non sticky; non plastic; many very fine (<1 mm) tubular pores; very few soft carbonate concretions of 0.5 cm; moderately calcareous; clear, wavy boundary C2 7.5 YR 5/4 brown (moist) and 7.5 YR 6/4 light brown (dry); sandy clay loam; weak very coarse subangular blocky; dry loose; moist loose; non sticky; non plastic; very few very fine (<1 mm) tubular pores; non calcareous; 6

7 Table 1. Chemical properties for the soil profile in Block 810 in CIMMYT s experimental station in the Depth Horizon OM Total CaCO 3 ph P Exchangeable cations CEC N 1:2 Olsen K Ca Mg Na (cm) (%) (%) (%) H 2 O ppm (meq/100g) (meq/100g) 0 15 Ap Ap (B)i BC C C2 0.1 t OM: Organic matter content determined with the Walkley Black method; Total N: Total nitrogen content determined with the Kjeldahl method; CaCO 3 : Carbonates determined by digestion with 0.5 N HCl; Exchangeable cations and Cation Exchange Capacity (CEC) were determined with the ammonium acetate method at ph 7. Table 2. Physical properties for the soil profile in Block 810 in CIMMYT s experimental station in the Depth Horizon Particle size fractions Texture class Gravel Bulk Ksat Sand Silt Clay density (cm) (%) (%) (%) (%) (g/cm³) (mm/h) 0 15 Ap clay Ap clay (B)i clay BC clay C clay C sandy clay loam Soil was sieved at 2 mm to separate the gravel from the fine earth. Particle size fractions were determined with the hydrometer method and texture class with the USDA texture triangle; Bulk density was measured by taking four undisturbed cores per horizon at field capacity; Ksat: hydraulic conductivity at saturation was measured in the field with a double ring infiltrometer. 7

8 Annex 2: Soil profile description Block 710 General information Region Yaqui Valley, State of Sonora, Mexico Location CIMMYT research station, Dr Norman E Borlaugh, km 12, entre 800 y 900 Valle del Yaqui, CP 85000, Cd Obregón, Sonora, block 710 Coordinates N, W Elevation site 38 m asl Date 31/03/2008 Land system Geological formation Lacustrine/fluvial alluvial deposits Parent material Alluvium Physiography Lifted coastal lagoon Macrorelief Slopes <2% Microrelief Flat Land use/ Vegetation Wheat based cropping systems. Natural vegetation would be subtropical dry savanna woodland Climate Arid subtropical Moisture regime Moisture condition Slightly moist (irrigation within 5 m) Ground water level More than 10 m deep Drainage class Well drained Permeability Medium to slow Internal drainage Good Altered drainage conditions Yes, major drainage ditches; whole area under furrow irrigation Water erosion Surface features Sheet erosion (class 1), mainly at the beginning of the furrow Root distribution Effective soil depth Human influence Soil fauna Surface cracking Other features 40 % from 0 to 80 cm; 20 % from 80 to 110 cm; 10 % from 110 to 160 cm; 5 % from cm 110 cm Whole area was leveled and shaped into furrows for irrigation Few earthworms with galleries down to 160 cm None, due to plowed sandy top layer 8

9 Soil characteristics Depth Horizon Description (cm) 0 15 Ap 5 YR 4/2 grayish brown (moist and dry); sandy clay; moderate coarse subangular blocky; dry soft; moist friable; non sticky; non plastic; many medium (2 5 mm) interstitial pores; many fine roots; at some places (3 dm²/8 m²) high concentrations of small gravel (50 µm 0.5 cm) and gravel ( cm); slightly calcareous; abrupt, smooth boundary (B) 5 YR 4/3 dull reddish brown (moist and dry); clay; strong very coarse prismatic breaking into coarse angular blocky; dry hard; moist firm; slightly sticky; slightly plastic; many medium (2 5 mm) interstitial pores; many fine roots; slightly calcareous; gradual, wavy boundary (B)i 5 YR 4/3 dull reddish brown (moist and dry); clay; strong very coarse angular blocky breaking into strong coarse angular blocky with wedge shapes ( cm length and cm width); clear grooved slickensides; shear planes that are aligned towards a well rooted chimney; dry very hard; moist very firm; moderately sticky; slightly plastic; many medium (2 5 mm) interstitial pores; many fine roots; in lower part some enriched calcareous weathered rock fragments (5 7 mm, rounded, 7.5 YR 8/2); slightly calcareous; diffuse, wavy boundary BC 5 YR 4/6 reddish brown (moist and dry); clay; strong medium angular blocky; dry hard; moist firm; very sticky; very plastic; common fine (1 2 mm) interstitial pores; common fine roots; 12 to 15 % moderately calcareous weathered rock fragments (5 7 mm, rounded, 7.5 YR 8/2) in chimney (1/5 of soil profile); slightly calcareous; gradual, wavy boundary C1 7.5 YR 5/4 brown (moist) and 7.5 YR 6/4 light brown (dry); clay loam; structureless massive; dry soft; moist very friable; non sticky; non plastic; many very fine (<1 mm) tubular pores; few fine roots; very few (2/m²) stones of cm; moderately calcareous; abrupt, irregular boundary C2 7.5 YR 6/4 light brown (moist and dry); sandy clay loam; structureless massive; dry loose; moist loose; non sticky; non plastic; many very fine (<1 mm) tubular pores; very few fine roots; moderately calcareous; abrupt, irregular boundary C3 7.5 YR 5/4 brown (moist) and 7.5 YR 6/4 light brown (dry); clay; structureless massive; dry loose; moist loose; non sticky; non plastic; many very fine (<1 mm) tubular pores; very few fine roots; moderately calcareous; 9

10 Table 3. Chemical properties for the soil profile in Block 710 in CIMMYT s experimental station in the Depth Horizon OM Total CaCO 3 ph P Exchangeable cations CEC N 1:2 Olsen K Ca Mg Na (cm) (%) (%) (%) H 2 O ppm (meq/100g) (meq/100g) 0 15 Ap 0.8 t (B) 0.8 t (B)i 0.3 t BC C1 0.8 t C2 0.4 t C3 0.5 t OM: Organic matter content determined with the Walkley Black method; Total N: Total nitrogen content determined with the Kjeldahl method; CaCO 3 : Carbonates determined by digestion with 0.5 N HCl; Exchangeable cations and Cation Exchange Capacity (CEC) were determined with the ammonium acetate method at ph 7. Table 4. Physical properties for the soil profile in Block 710 in CIMMYT s experimental station in the Depth Horizon Particle size fractions Texture Gravel Bulk Ksat Sand Silt Clay class density (cm) (%) (%) (%) (%) (g/cm³) (mm/h) 0 15 Ap sandy clay (B) clay (B)i clay BC clay C clay loam C sandy clay loam C clay Soil was sieved at 2 mm to separate the gravel from the fine earth. Particle size fractions were determined with the hydrometer method and texture class with the USDA texture triangle. Bulk density was measured by taking four undisturbed cores per horizon at field capacity. Ksat: Saturated hydraulic conductivity measured in the field with a double ring infiltrometer. References IUSS Working Group WRB World Reference Base for Soil Resources 2006, first update World Soil Resources Reports No FAO, Rome, pp 128. Soil Survey Staff, Keys to Soil Taxonomy. United States Department of Agriculture, Natural Resources Conservation Service, Washington DC, pp 332. Acknowledgements N.V. received a PhD fellowship of the Research Foundation Flanders. We thank M. Ruiz Cano, J. Gutierrez Angulo, J. Sanchez Lopez, A. Zermeño, C. Rascon, B. Martínez Ortiz and H. González Juárez for technical assistance. The research was funded by the International Maize and Wheat Improvement Center (CIMMYT, Int.) and its strategic donors. Citation Verhulst, N., Deckers, J., Govaerts, B., Classification of the soil at CIMMYT s experimental station in the Yaqui Valley near Ciudad Obregón, Sonora, Mexico. CIMMYT Report, CIMMYT, Mexico D.F. 10