Overview of Soil Propertiesfor Crop Production

By

J.G. Mexal

Department of Plant &

Environmental Sciences

New Mexico State University

Soil Properties

• Outline– Definition– Classification– Physical Properties– Chemical Properties

Soil Properties

Bottom Line

• Three most important characteristics: – Depth– Rock Content– Texture

• Water Storage = (Depth - Rock)Texture

Soil Properties

Soil Definition

• Agricultural: “dynamic natural body… composed of mineral and organic materials and living forms.”

• Engineering: “fragmented mineral material at or near the surface … plus the air, water, organic matter, and other substances….”

Soil Properties

Soil Definition

• Practical Definition: – Reservoir for water, oxygen, nutrients, and

beneficial organisms– Provides physical support for plants

Soil Properties

RoT Soil Composition

Minerals

Air

Water

OrganicMatter

~50%

~25%

~25%

1-5%

Soil Properties

Soil Classification

• Characteristics:– Texture– Structure– Horizon Development– Color

• Soils Maps Available

Soil Properties

Arid Climate

0

5

10

15

20

25

30

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0

20

40

60

80

100

120

140

160

180

Temperature

PET

Ppt

Deficit

Utilization

Recharge

Temperature (oC) PET or Ppt (mm)

Soil Properties Physical Properties• Soil Texture

– Particle Size Distribution (by weight)• Sand

• Silt

• Clay

– Soil Triangle

Soil Properties

Soil ClassificationClass Subclass Size (mm)

Very coarse 1.0 – 2.0

Coarse 0.5 – 1.0

Sand Medium 0.25 – 0.5

Fine 0.1 – 0.25

Very Fine 0.05 – 0.10

Silt 0.002 – 0.05

Clay < 0.002

Soil Properties

Particle Size vs Area

Soil Properties

Soil Triangle

Soil Properties Physical PropertiesTexture Feeling & Appearance

Dry Moist-Casts Moist-Ribbons

Sand Non-cohesive Crumbles No

Sandy Loam Gritty Fragile No

Loam Velvety/Gritty Not fragile Slight

Silt Loam Flour-like Not fragile Slight

Clay Loam Gritty-aggregates

Durable Yes

Clay Gritty-aggregates

VeryDurable

Yes

Compaction affects water availability Steinhardt et al. 1987

Soil Bulk Density (Mg/m3)

Moisture Content (kg H2O/kg soil)

Unavailable

Available

Readily available

Air space

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Saturation

-0.03 Mpa

-0.01 Mpa

-1.50 Mpa

Soil Properties

Bulk Density Affects Growth

0

20

40

60

80

100

1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9

-0.02 M Pa-0.033 M Pa-0.05 M Pa-0.067 M Pa

Soil Bulk Density (g/cm3)

Root Penetration (%)

Soil Bulk Density & Hypoxia Reduce Growth/ Gilman et al. 1987

12

51

38

>51

25

RootingDepth(cm)

2

4.1cm 3.2cm 1.8cm

1.8 g/cm31.7 g/cm3 +

low O2

Root Length (m)

Gleditsia

1426

36

1.2 g/cm3

Soil Bulk Density Affects Growth/ Alberty, et al. J. Env. Hort. 2:48:84

1.05 1.21 1.21 1.23 1.31Bulk Density (g/cm3)

Dry Weight (g)

Puddled 20 15 10 5

05

101520253035

Forsythia-shoot

Forsythia-root

Cornus-shoot

Cornus-root

Soil Properties Important Soil Properties• Physical

– Texture– Structure

• Chemical– pH– C.E.C.– W.H.C.– Organic Matter

Soil Properties

Physical Properties

• Structure– Natural organization of particles into units– “Peds”

• Platy

• Prismatic

• Columnar

• Blocky

• Granular