Transcript 9-7-plant nutr & soi..

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TODAY
Questions from Dr. Florin’s “omnivore's
dilemma” lecture?
I have more Huitlacoche soup – cheap - any
takers?
Today: Ecology of Agriculture
Agricultural management
 Photosynthesis
 Plant nutrition
 Soil Water
 Soil Nutrients
Soils
© T. M. Whitmore
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Plant ecology and agriculture
All Plants need
Solar energy (sunlight) for photosynthesis
Carbon & Oxygen: from CO2 in the
atmosphere
Water: taken from soil moisture
Major mineral nutrients in soils (N, P, & K):
 Nitrogen (N): only after it is “fixed” or
freed from the air or from
decomposition of organic matter
 Phosphorus (P) and
 Potassium (K) are most important
© T. M. Whitmore
 about 10 more minor ones
Plant ecology and agriculture II
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Humans cannot much alter atmosphere or
solar energy (but see below)
Plants get all water and mineral nutrients via
roots in the soil
Mineral nutrients are dissolved in soil water
Thus, soil moisture levels and soil fertility
(i.e., levels of available N, P, K, etc.) are the
major management issues for agriculture
© T. M. Whitmore
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Other Management Issues
Micro-environment & climate management
Clearing
Shading
Tillage
Mulches
Space management
Pest and disease management
Weeds
In-field pests & diseases
Pests in storage
© T. M. Whitmore
Photosynthesis
• Joining together of carbon dioxide with water to
make plant material (carbohydrates) and oxygen,
using the sun's energy
Basic photosynthetic pathway:
6CO2 + 12 H2O --> C6H12O6 + 6O2 + 6H2O
From Atm
Plant material
from soil moisture via roots Respired back to atm
Energy to carry out the reaction comes from
light absorbed by chlorophyll
There are three types of photosynthesis: C3,
C4, and CAM.
 The type of photosynthesis utilized by a
species reflects its adaptation to different
environments.
© T. M. Whitmore
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Types of Photosynthesis
C3 Photosynthesis:
Most plants use C3 photosynthesis
C3 plants are more efficient under cool and
moist conditions and under normal light
C4 Photosynthesis:
C4 plants can photosynthesize faster under
high heat and light conditions than C3
plants
C4 plants include some tropical crop plants
(e.g., corn & sorghums)
CAM photosynthesis:
Better water use efficiency than C3 plants
under arid conditions;
CAM plants include many succulents such as
© T. M. Whitmore
cactuses and agaves
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Soil water
Plants need H2O & nutrients for growth
Water + nutrients = soil solution
 Soil solution provides plants with
essential elements
Plants use H2O from soil & transpire it
through leaves  lose H2O
 If not replenished, plants become
stressed
© T. M. Whitmore
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Soil moisture management
Rain: surface & infiltration management
Runoff barriers to slow flow => more
infiltration
Irrigation
Runoff irrigation
Permanent
 Surface sources - rivers, lakes, etc
 Sub-surface sources - natural artesian
wells; dug wells
© T. M. Whitmore
© B.L. Turner II
Semi-terrace (meteplantli) temporal cultivation in C Mexico
Hill slope temporal
cultivation
(with ridges) in Mexico
© B.L. Turner II
Plant Nutrients from Soil I
• Nitrogen (N) dissolved in soil water - from
decomposition of proteins in plant material
Biological function of N
 Base pairs for RNA/DNA, Hormones,
chemical defenses, etc
Almost all comes from humus (decomposed
organic matter)
Fertilizer also a major source
 ammonium NH4+ Or nitrate NO3Much also from N2 fixing bacteria
(Rhizobium spp) & others
© T. M. Whitmore
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Plant Nutrients from Soil II
Phosphorus (P)
Biological functions of P
 ATP/ADP energy transport and storage
compounds
 Sugar phosphates form the "rails" of the
nucleic acids DNA and RNA (which Ncontaining bases forming the "rungs")
 Etc.
From decomposition of soil organic matter
(humus)
And/or from phosphate fertilizers
© T. M. Whitmore
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Plant Nutrients from Soil III
Potassium (K)
Biological functions of K
 Not a constituent of any plant structures
or compounds – but - essential in nearly
all processes: Photosynthesis, Protein
synthesis, water regulation, etc., etc.
 activates at least sixty enzymes involved
in plant growth
From decomposition of organic matter and
feldspar (or fertilizer)
© T. M. Whitmore
Nodules hosting rhizobium
Clover roots magnified
(each nodule is 2-4 mm in dia)
Plant Nutrients from Soil IV
• Neither P nor K are very soluble (thus not as
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likely to leach out, but also not easy to get in
solution to plant roots)
N, P, & K are the primary components of
commercial fertilizers
Other major nutrients
Calcium (Ca) from soil minerals (e.g.,
limestone soils)
Magnesium (Mg) from soil minerals
Sulfur (S) (essential to protein’s amino
acids) from organic decomposition and some
minerals
© T. M. Whitmore
Soils
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4 major parts to soils
Organic matter
 Dead material
 Partly decomposed (humus)
 Live
Inorganic matter — sand, silt, and clay
Moisture
Air
© T. M. Whitmore
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Soils
Quality for agriculture depends on many
factors – but stored nutrients (N, P, K, etc.)
are key
Stored nutrients depend on
Soil forming factors
 Time
 Geology/Parent material
 Topography
 Climate
 Biota
© T. M. Whitmore
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Soil formation: Time & Weathering
Time
Centuries or even millennia
Weathering
Rocks  smaller rocks  component
minerals
Physical weathering
 Temperature changes produce stress &
break down parent material
 Water, wind, ice are abrasive
Chemical weathering
 H2O, O2, acids convert rocks to their
mineral components (sand, clay, silt) &
to soluble minerals for plant growth
© T. M. Whitmore
Physical
Weathering
temperature
roots
water
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Soil formation: Parent material
Igneous, metamorphic, or sedimentary rocks
serve as parent material
Rhyolite (igneous)  sandy soils
Slate (metamorphic)  clayey soils
Sandstone (sedimentary)  sandy soils
Shale (sedimentary)  clayey soils
Loess (Windblown sediments)  silty soils
© C.M.Erlien
rhyolite
slate
sandstone
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Soil formation: Topography
Hillslopes vs. toeslopes
Toeslope receives accumulation from
erosion
Eroded slopes will have less soil
development due to removal of materials
Physical properties of soils
Soils & erosion
 Erosion is natural
 Accelerated erosion is human induced
 Soils vary in their resistance to erosion
© C.M.Erlien
Soil formation: Topography
Hillslope
Soils differ depending on
their place in the
landscape
Toeslope
© C.M.Erlien
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Soil formation: Climate
Arid climates
Physical weathering (temperature
fluctuation & wind action) predominates
Warm, humid climates
Intense chemical & physical weathering
Soils with little organic matter, most
soluble nutrients leached, Fe & Al
accumulation
Cool, humid climates
Chemical & physical weathering
More organic matter & nutrients
© C.M.Erlien
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Soil formation: Biota
Vegetation
Roots & other veg. decompose, adding
organic matter to soil
Animal activity
Earthworms & rodents introduce o.m. to the
soil through burrowing activities
Arthropods (e.g., insects, spiders,
centipedes) aerate & mix soil, shred o.m.
Bacterial & fungal activity
• Break down plant materials
© C.M.Erlien
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Soil classification
Soils are classified according to chemical,
physical, biological properties
Moisture
Temperature
Color
Texture
Structure
Classification system is hierarchical
Several systems – here the USDA’s
“Seventh Approximation”
Some examples of some soil orders (top
level) for agriculture
© C.M.Erlien
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Tropical Soils
Lower fertility soils– require inputs of lime
and fertilizers to be productive for
agriculture
Ultisols: Dominant soils of SE U.S. – the
red clays
Oxisols: Intensely weathered soils of the
humid tropics
© C.M.Erlien
Ultisol
Oxisol
(this soil is from NC)
© T. M. Whitmore
© C.M.Erlien
© C.M.Erlien
Temperate climate soils: Mollisols
• Soils of grassland ecosystems
• Thick, dark surface horizon (result of
long-term addition of organic matter
derived from plant roots)
• Some of the most important and
productive agricultural soils in the world
(grains, corn, soybeans, etc.)
© C.M.Erlien
Mollisol
(great fertility)
Mollisol landscape (Iowa) – corn & soybean production
© C.M.Erlien
Mollisols in Guatemala
© T. M. Whitmore
Temperate climate soils: Histisols
• Very fibrous, moist, spongy
• Described as peat or muck
• Cranberries  grown on low-lying vines
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in bogs (a mixture of sand & peat soil)
Berries float  bogs are flooded in
order to harvest
© C.M.Erlien
Histisol soils
Cranberry bog
© C.M.Erlien
Cranberry harvesting
© C.M.Erlien
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Soil fertility & erosion management
Soil fertility management
Of the constraints to ag this is most
controllable by farmers
Natural systems – all nutrients are recycled
or replenished by natural forces (closecoupled recycling)
In agriculture -- humans remove
nutrients/energy from the system &
increase erosion => need
 organic soil amendments
 inorganic soil amendments
 erosion management
© T. M. Whitmore
Organic soil amendments
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Manures (including human waste)
Plant residues
Ash
Green manures
Organic mulches
Intercropping
N2 etc. from irrigation water
© T. M. Whitmore
© BL Turner
© R. Soriano and H. Losada
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Inorganic soil amendments
Silts (to replenish mineral-sourced nutrients
of soils)
Farmers can and do control flooding
Via irrigation
Mucks - e.g., from canals, rivers, lakes etc.
Chemical fertilizers- much more on this later
© T. M. Whitmore
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Erosion management
Slope alteration
Sloping terraces with barriers
Contour-flat terraces
Field-scale modifications
Splash erosion reduction
cover crops
Stubble
Tillage reduction
© T. M. Whitmore
© BL Turner
© BL Turner
Anthropogenic soils
• Terra preta do Indio (Indian black
earths)
• See web page for more info and
links
© T. M. Whitmore
Terra preta do Indio
Terra preta do Indio
Neighboring oxisol