Managing Soils for Healthy Plants

1
Soil Science and Nutrients
Tim Griffin Sustainable Agriculture John
Jemison Water Quality
2
What is Soil?
3
Soil Formed from Weathering of Parent Material

• Freezing and thawing
• Wetting and drying
• Microbial action
• Plant roots
• Formed from
• Residual Parent Material
• Transported Parent Material

4
Fluvioglacial profile Glacial till overlain
by sediments deposited by water This soil is
common in many areas in northern Maine
5
Defining Soil Texture

• Proportions of Sand, Silt, and Clay in the
  Soil
• Sand, Silt, and Clay are just different
  particles sizes
• Clays smallest lt2 uM
• Sands gt 2mm

6
Textural Triangle
7
Soil Texture and Soil Water

• Finer Textured Soils
• Slower infiltration and slower drainage
• Greater potential for Runoff
• Coarser Textured Soils
• Faster infiltration and drainage
• Greater potential for Leaching
• More OM holds more water

8
Soil Texture and Nutrients

• More surface area more reaction sites
• Surface for P to sorb to
• Fairly strong bond
• Sand 1 m2/g
• Clay 400-500 m2/g

9
(No Transcript)
10
Categories of Soil Organic Matter

• Living
• Dead
• Very Dead

11
Sources of Soil Organic Matter

• New and decomposed plant material
• Live and dead microbes
• Other organic amendments

12
SOM
Rapid
Humus

• Plants, manure
• Energy for microbes

• Stable
• Cements crumbs
• Holds water

13
Quality Soil
14
Measuring Soil Quality

• Soil organic matter content
• Nutrient holding capacity (CEC)
• Water holding capacity
• Density
• Aggregation or tilth

15
Soil Structure

• How soil particles stick together
• Descriptive terms given for structure
• crumb, granular, blocky, platy
• granular - surface soils blocky - subsoils
• Interaction with soil texture
• Can be a sign of poor soil management

16
Effects of Soil Structure

• Water entry (infiltration)
• Rooting medium
• Preventing structural problems
• Dont over till
• No traffic when wet
• Increase organic matter

17
Cation Exchange Capacity

• Measures nutrient holding capacity of soil
• Analogous to a pantry
• more shelves means more storage
• large CEC means lots of nutrient reserve
• Affected by soil texture / organic matter
• CEC gt 6 meq/100g - adequate reserve
• Manure and organic matter build CEC

18
Sources of Negative Charge
Broken Edge
Substitution
OH O- Al OH O-
H K
OH O- Al OH O-
Clay
OH O- Mg OH O-
19
Sources of Negative Charge
H Ca2 K K Mg2 H
O- COO- O- COO- O- COO- O- COO-
The CEC of humus is 300 meq/100g
Humus
20
pH Dependent Charge
pH 5.2
pH 6.8
O- COO- O- COO- O- COO- O- COO-
O- COOH OH COO- OH COOH O- COOH
Humus
Humus
21
Charge of Solute on Solute Movement
Exception to the Rule P
SWC 7-29a
22
Erosion and Consequences
23
Types of Erosion

• Splash Raindrop energy dislodges soil
• Sheet Thin layer of soil eroding
• Rill Small channels have formed in soil
• Gully Large channels formed in soil
• Saltation Soil bounces along from wind
• Suspension Dust carried by big storms

24

• Sediment in Water
• Nutrients in Water
• Loss of SOM

25
Vegetative and Residue Cover

• Protects the soil surface
• Slows runoff velocity
• Higher infiltration rates
• Holds soil particles

26
Hydrologic Cycle
27
Hydrologically Sensitive Area

• Near a public water supply
• In a watershed that is sensitive to a
  specific nutrient
• Critical management zone

28
Soil Drainage and Water Management

• Soils and water holding capacity
• Moderate textured soils hold most water
• more organic material - higher WHC
• Highly structured clay soils exception
• macropores transmit large amounts water

29
Soil Moisture Benchmarks

• Field capacity
• Permanent Wilt
• Saturation
• How to affect these values