Transcript PowerPoint: Soils for Small Farms

Introduction to
Soil Science in
Sustainable
Agriculture
Craig Cogger
WSU Puyallup
Sept. 19, 2002
Soil Components
Mineral Matter
Pore Space
Organic
Matter
The soil
ecosystem
Residue decomposition
Nutrient cycling
Aggregation and porosity
Enhance plant growth
Break down contaminants
•Water Movement
How quickly water moves
through soil
Water Holding Capacity
How much water a soil can hold
available for plant growth
Soil pores and
water movement
•Macropores:
Infiltration and
drainage
•Capillary pores: Available
water
•Micropores: Unavailable
water
Soil properties that
affect porosity
•Soil texture
•Soil structure
•Compaction and
disturbance
•Organic matter
Soil Particle Sizes
Sand
Silt
Clay
.05-2 mm
.002-.05 mm
<.002 mm
Coarse Fragments
>2 mm
Approximate
surface areas of 1
gram samples
Coarse sand
Half dollar
Fine clay
Basketball court
Hand texture technique
Soil Structure
Aggregation of sand, silt, and clay particles
Formation of soil
structure
• Growth of roots and movement of
organisms create pores and aggregates
• Soil organisms break down organic
residues, producing glues that
stabilize aggregates
• Fungi provide structural support to
aggregates
• Physical, chemical processes also
involved
Soil Structure
•Improves
•Promotes
•Promotes
macroporosity
aeration
infiltration
Major soil types
of the Puget
Sound area
Most local soils
formed from glacial
materials
•Glacial Till (Ice laid)
•Glacial Outwash (Meltwater)
•Lacustrine (Lakebed)
Glacial till soil
•Ablation till
•Not compacted
•Permeable to
water and roots
•Basal till
•Compact and
cemented
•Barrier to water
and roots
0 to 4”
gravelly sandy loam
4 to 10”, very
gravelly loamy sand
10” +
sand and gravel
Glacial outwash soil
Very low water and
nutrient holding
capacity
Glacial lacustrine
(lakebed) soil
Fine texture, high
water holding
capacity, hard to
work when wet or
very dry.
Soil fertility and
nutrient
management
Nutrient Management
•Meet crop nutrient needs
•Maintain soil quality
•Conserve resources
•Protect water quality --
reduce leaching and runoff
risk
Plant Nutrients
Major Nutrients
• Nitrogen
• Phosphorus
• Potassium
• Calcium
• Magnesium
• Sulfur
Micronutrients
• Boron
• Iron
• Manganese
• Zinc
• Copper
• Chloride
• Molybdenum
How nutrients become available
Mineral Matter
K
Ca
Organic Matter
Mg
-
N
S
Not
available
P
K+ NH4+ Ca++ SO4-soluble, available
Ca++
K+
- - - - - - clay
K+
-
Mg++
- -
-
OM
Nutrient Anion
Availability
Anion
Binding
Solubility
PO4-3
BO3-3
SO4-2
NO3-
strong
medium
v. weak
v. weak
low
medium
high
v. high
Nitrogen Cycle
Organic N
Plant residues,
Manure
NH4+
NO3 Leaching
Gases
Plants,
Microbes
Organic
Materials
•Little or no processing
•Low nutrient content
•Slow release of nutrients
•Plant, animal, or mineral sources
Organic Materials:
Slow release nutrients
• Plants
can only take up nutrients that
are in available form (simple, soluble
ions).
• Most nutrients in organic materials
are in complex organic molecules or
minerals, and are not immediately
available to plants.
Slow release
nutrients
• Biological
processes slowly release the
nutrients in organic amendment into
available forms.
• Rate of nutrient release depends on
the nature of the amendment and
environmental conditions.
Nutrient uptake
•The forms of nutrients
taken up by plants are the
same for all types of
fertilizer -- manufactured
or organic.
Organic materials:
Fertilizers vs. Soil
amendments
• Fertilizer
1. High nutrient content and availability.
2. Main benefit is nutrients.
3. Relatively small amounts applied.
• Soil
amendment
1. Low nutrient content and availability.
2. Main benefit is organic matter.
3. Large amounts applied.
Carbon:Nitrogen ratio
•Low C:N supplies
•High C:N ties up
immobilization
N to plants
N by biological
C:N ratio and N
availability
C:N
N availability
<10:1
High
10:1 to 20:1
Med - Low
20:1 to 30:1
Very Low
>30:1
Negative
High N Content
C:N < 10:1
•Rapid N availability
•Use as a fertilizer
•Over application leads
to excess
nutrient levels in soil -potentially harming crop and water
quality.
High N Content
Examples
•Poultry manure
•Packaged organic fertilizers
•Fresh dairy or goat manure
Moderate N Content
C:N 12:1 to 25:1
• Slow N availability
• Can add large amounts
without risk of
over-fertilization
• Use as a soil amendment
• Expect some N immobilization (tie-up)
shortly after application.
Moderate N Content
Examples
•Compost
•Yard debris
•Cover crop residues
•Dairy solids
Low N content
C:N > 30:1
•N immobilization
•Need to add N along
with organic
amendment
•Use as mulch or bulking agent for
compost
Low N content
Examples
•Straw
•Sawdust
•Paper waste
Soil Testing
Nutrients
Contaminants
Biological
Soil Quality
What is a soil
nutrient test?
•A chemical extraction of
“plant-available” nutrients.
•Used to predict nutrient
availability and fertilizer
need.
Soil Nutrient
Tests
•Standard agricultural tests (P, K,
Ca, Mg, B, pH, lime requirement)
•Nitrate tests
• Sampling Reference: UIdaho Bulletin
704. Soil Sampling
When to sample?
•Standard tests can be taken
at any time before
fertilization.
•It is best to be consistent
from year to year.
•Nitrate tests are taken at
specific times.
How often to sample?
•Sample each unit every 1
to 3 years, or at least
once every crop rotation.
How to sample
• Divide farm into units (based on
soil type, crop, management).
• Small, diverse farms will need to
group crops for sampling.
• Take 10 to 20 cores per unit (0 to
12 inch depth).
• Avoid unusual areas.
Sample handling
• Keep moist samples cool during
and after sampling.
• Refrigerate, freeze, or bring
directly to lab.
• OR, spread in thin layer and air
dry
• Send about 1 pint to lab, carefully
labeled.
Choosing a lab
• Does the lab routinely do ag tests?
• Do they use OSU or WSU test
methods?
• Do they give fertilizer
recommendations?
• What information do they need?
• How to send sample?
• Cost? Turn-around time?
• What does report look like?
Interpreting soil tests
• Nutrient status
Low, medium, high
• Fertilizer recommendation
• You will need to interpret for
organic fertilizers.
• You will need to interpret if one
test represents multiple crops.
• Reference: EC 1478. Soil Test
Interpretation Guide
Web Addresses
• WSU
Publications:
http://pubs.wsu.edu/
• OSU Publications:
http://eesc.orst.edu/
• UIdaho Publications:
http://info.ag.uidaho.edu/
• Organic nutrient management web site:
http://www.puyallup.wsu.edu/soilmgmt/