Announcements
• Tuesday, March 10th, extra credit movies due
• Final date for LEAD summaries: Sunday, March 8th
(final LEAD weekend)
• Topic for today: Soil and agriculture
Soil and agriculture
• Dishing the dirt on soil
– Soil properties and formation
– Erosion: Mechanisms and consequences
• How to feed the planet
• I’m Dr. Andy Bach.
• I teach ENVS 327 The Soil Environment (winters)
– Lecture based Prereq ENVS 203 or GEOL 211
– Development of modern agriculture
– Organic farming
– Genetically modified crops
• ENVS 427 Soil Landscapes (spring- field based)
What is soil?
What is soil?
• - not dirt!
• soil is in situ
• (forms in place)
• the surfical geology is
altered by a number of
unique soil processes
Soil takes time to form- thousands of years- but it also
changes seasonally.
What is soil?
• - a natural body consisting of layers or
horizons of mineral and/or organic
constituents of variable thicknesses, which
differ from the parent material in their
morphological, physical, chemical, and
mineralogical properties and their biological
characteristics
•
Soil is a resource
• Agriculture – nutrient availability,
moisture, productivity, recoverability,
erosivity.
- tillage, grazing, forestry
(Birkeland, 1999).
1
Soil is a resource
• Agriculture
• Building substrate – engineering properties
- not as critical anymore with
effectiveness/low cost of earthmoving
- can dictate how land can/should be developed
- GEOL 318 Engineering Geology
Soil is a resource
• Agriculture
• Building substrate
• Ecosystem services
• Mining – for top soil, aggregate, minerals,
peat
Soil is a resource
•
•
•
•
•
•
Soil is a resource
• Agriculture
• Building substrate
• Ecosystem services:
– critical part of most terrestrial ecosystems,
especially vegetation and in-soil ecosystem
– the carbon cycle, moisture cycle, nitrogen cycle
oxygen cycle, mineral cycle
– buffers precipitation-runoff processes
– Filters contaminants
– Relationships to ecosystem type and productivity
Soil is a resource
• Agriculture
• Building substrate
• Ecosystem services
• Mining
• Aesthetics -
Soil Composition
Agriculture
Building substrate
65 ka
Ecosystem services
738 ka
Mining
Aesthetics
~ 1,000 ka?
Sherwin Grade roadcut on US 395 near Mammoth, CA
Archeological /environmental information
- stratigraphic deposition
• Geomorphosites (natural heritage) are landforms and
landscapes important for Earth and climate history
knowledge.
2
Soil composition
Soil Properties and fertility
• Mineral grains
– Sand: 0.063 mm – 2 mm = coarse = drainage/no nutrients
– Silt: 0.002 mm – 0.063 mm
– Clay: ~0.0005 mm - 0.002 mm = fine = poor draingage/nutrients
• Organic matter (humus)
• Living organisms (bacteria, fungi, animals)
• Typical organic-matter concentration: ~ 5%
Typical soil
~5%
• Pores allow air and water to move
• through and be available to plant roots
~45%
~50%
Soil Texture
- fine fraction - particles < 2 mm diameter
– refers to amount of sand-silt and clay size particles
•
•
•
•
•
•
•
Property
Water infiltration
Aeration
Workability
Water-holding capacity
Nutrient-holding capacity
pH
Salt content
Soil components
Sand
Sand
Sand
Clay, humus
Clay, humus
Indicates fertility
retards plant growth
Best soil texture for agriculture:
~40% sand, 40% silt, 20% clay → loam
Soil Horizons- vertical organization
USDA terminology
• Soil horizons:
– O Horizon (organic)
Sand is 2-0.05 mm
- low nutrient
- drains well
- spherical shape
Silt is 0.05-0.002 mm
Clay is <0.002 mm
- high nutrient
- poor drainage
-shaped like
paper
Soil development
• Top soil formation very slow average~ 1 cm per 100 y
• Steps:
1: Weathering
2: Organic-matter addition
and decomposition
• Chemical weathering → clays
Geologic materials react with a
atmosphere and biosphere to be
transformed into soil
– A Horizon (top soil)
– E Horizon (eluviation)
– B Horizon (sub soil)
– C Horizon (parent material)
Soil properties vary
among biomes.
Grasslands:
A – thick
E and B – thin
Forest:
A – moderately thin
E and B – thick
Desert:
All horizons thin
3
Soil development is highly controlled by climate/vegetation.
Fig. 9.10, p. 237
Aridisols
Gelisols
In the USA soil data collection and mapping are accomplished
largely by the USDA – Natural Conservation Service
Mollisols
Mollisols
Spodosols
Oxisols
Alfisols
Ultisols
Thickness of
Weathering and
Soil profiles
US
Equator
North Pole
Climate
Dominated
Soil
Orders
Soil Maps and
Soil Data
Need water as a solute, and higher temperature for Energy
Soil Erosion
- natural process where wind or water dislodges and transports material
across the landscape
- erosion can be altered by human activity
- accelerated erosion is faster than the natural rate
- erosion control reduces the erosion rate
- anywhere a soil exists, the natural rate of erosion is slow
- i.e. soil formation rate is faster than erosion rate
Most counties have a ‘Cooperative Office’ with soil experts
that are knowledgeable of local soil issues, especially
agriculture
Soil Surveys –atlases of soil and environmental data Google it
Impacts of Soil Erosion
- physical loss of soil
- loss of plants
- decreased productivity (O- and A-horizons lost first)
- Need for more fertilizers
- declining water quality from runoff (turbidity and chemicals)
- increased sediment load changes fluvial characteristics,
especially flooding
- reservoirs, harbors, and sewers fill with sediment
- eutrophication (especially N, P from fertilizers)
- toxicity of pesticides, herbicides etc.
.
Using soil sustainably
• Reduce erosion (terraces, wind breaks,
reduce tilling, soil cover crops)
• Low till farming encourages natural
processes – increases productivity
• Reduce nutrient loss (crop rotation,
natural fertilization)
• Reduce sprawl
Conventional
Conservation till
4