7/27/2019 Soil Moab 08p2
1/26
Desert Soils - Part 2
7/27/2019 Soil Moab 08p2
2/26
Soil Formation in a Moist
Environment
Water,Clay particles,Organic matter,
Salts
Water
Water,
Salts
7/27/2019 Soil Moab 08p2
3/26
Water transportssalts, clays, and
organic materialsin the soil profile
7/27/2019 Soil Moab 08p2
4/26
Soil Formation in an Arid
Environment
Na+
Na+
K+
Na+
Mg++
Ca++Ca++ Ca++Ca++ SO4=
Na+K+ Na+Na+
H2O
H2OH2O
H2O
H2O
H2O
H2O
H2O
HCO3-
SO4=
SO4=
Cl-
Cl-
Cl-
Cl-
H2OH2O H2O
H
H2OH2ONa+
H2O
CO3=
HCO3-
7/27/2019 Soil Moab 08p2
5/26
Water Transports Salts
7/27/2019 Soil Moab 08p2
6/26
Caliche
A layer of cemented Ca or Mg carbonates
7/27/2019 Soil Moab 08p2
7/26
Soil Horizons
Soil horizons or layers are formed by: Addition of organic materials
Movementof salts, clays, organic materialsilluviation (leaching)
eluviation (deposition)
Loss of salts (leaching)
Transformations
7/27/2019 Soil Moab 08p2
8/26
Soil Horizons
7/27/2019 Soil Moab 08p2
9/26
Arid Soil Horizons
7/27/2019 Soil Moab 08p2
10/26
Properties of Desert Soils
Shallow limited rainfall and soil development
Low organic matter content*
High pH
accumulation of carbonates
Caliche
cemented soil layers High levels of soluble salts
limited leaching
high evapotranspiration
7/27/2019 Soil Moab 08p2
11/26
Soil Organic Matter Content
Highorganicmatter
soils
Loworganicmatter
soils
slow plant growth in arid climate
rapid decomposition in warm soils
rapid decomposition in
well-drained soils
rapid decomposition in tilled soils
7/27/2019 Soil Moab 08p2
12/26
Soil Organic Matter
Organic wetland soil Well-drained mineral soils
7/27/2019 Soil Moab 08p2
13/26
Soil Biota & Aerobic Respiration
C6
H12
O6
+ 6 O2
6 H2
O + 6 CO2
Oxygen (gas)
Organic material
Carbon dioxide (gas)
Water
Soil microbes
7/27/2019 Soil Moab 08p2
14/26
7/27/2019 Soil Moab 08p2
15/26
Acidity
O H
H
H+ (Acid)
OH- (Base)
7/27/2019 Soil Moab 08p2
16/26
The pH Scale
Neutral
Range of AlkalinityRange of Acidity
0 2 4 6 8 10 12 14
Plant Growth
Each pH unit is 10 times more acid or alkalinethan the next unit
7/27/2019 Soil Moab 08p2
17/26
Soil pH
Most arid western soils
Optimum for most plants
0 2 4 6 8 10 12 14
7/27/2019 Soil Moab 08p2
18/26
Alkalinity in Arid Soils
Na+
Na+Na+
Mg++
Ca++
Ca++
Ca++Ca++Na+Na+
H2
O
H2OH2O
H2OH
2
O
H2O
H2O
H2O
HCO3-
H2OH
2O
H2O
H
H2OH2ONa+
H2O
CO3=
HCO3-
HCO3--
CO3=
CO3= HCO3
-Ca++
Ca++ Ca++
CO
7/27/2019 Soil Moab 08p2
19/26
Alkalinity in Arid Soils
Calcium bicarbonate
Ca++
HCO3- + H2
OCa++
OH-
(moderatelystrong base)
CO2
High pH (8
HCO3-
H2O
OH-
CO2
i l l i
7/27/2019 Soil Moab 08p2
20/26
Essential Plant Nutrients
C - Carbon
H - Hydrogen
O Oxygen
* Cations-Anions
MacroN Nitrogen-
P Phosphorus-
K Potassium*S Sulfur -
Ca Calcium*Mg Magnesium*
MicroFe Iron*
Mn Manganese*Cu Copper*Zn Zinc*B Boron-
Cl - Chloride
Mo - Molybdenum
Essential: A plant can not complete its life cycle withoutthese nutrients
7/27/2019 Soil Moab 08p2
21/26
Soil pH
Alters nutrient availability
Affects microbial activity
Can affect disease susceptibility
Controls organic matter solubility
7/27/2019 Soil Moab 08p2
22/26
Effects of pH on Nutrient Availability
The thicker the bar, the more available the nutrient
4.0
5.0
9.0
8.0
7.0
6.0
8.5
7.5
6.5
5.5
4.5
4.0
5.0
9.0
8.0
7.0
6.0
8.5
7.5
6.5
5.5
4.5
pH pH
7/27/2019 Soil Moab 08p2
23/26
Salt-Affected Soils
Saline - excess salts
good structure
moderate pH
Sodic - excess Na
poor structure
high pH (>8.5)Saline-sodicexcess salts
excess Na
good structure
high pH
7/27/2019 Soil Moab 08p2
24/26
Tests for Soil Salts
SAR - sodium adsorption ratio (SAR>13=sodic soil ESP - exchangeable sodium percentage
(ESP>15=sodic soil) measures of the amount of sodium
used to identify sodic soils EC - electrical conductivity
measures all soil salts used to identify saline soils
7/27/2019 Soil Moab 08p2
25/26
Salts Affect Soil Structure
Na+- -
-
--
- -- -Na
+
Na+
- - -----
--
Na+Na+
Na+
Na+ Na+Ca
++
- - ---
--
--
- - ---
--
--
Ca
++
- - ---- -- -
Na+ Na+- - ---
--
--
A little sodium makes particles repel one another.
A lot of sodium or a little calcium
makes particles attract one another.
7/27/2019 Soil Moab 08p2
26/26
Salts Affect Soil Structure
0
10
20
30
40
50
0.5 1.0 1.5 2.0 2.5 3.0
Electrical conductivity (dS/m)
ES
P
Unstablesoil
Stablesoil
Top Related