Transcript Unit 4: Nutrients - Kaskaskia College

Unit 4: Nutrients
Chapter 7
Unit 4: Nutrients
 Unit 4 Objectives:
 Understanding of essential plant
nutrients and their roles
 Nutrient action in the soil
 Knowledge of soil testing and
interpreting nutrient needs
 Soil pH and how it affects nutrient
availability
 Deficiency symptoms
Unit 4: Nutrients
 Essential Nutrients and their Roles
 Chemical elements needed by plants for
normal growth and development called
nutrients
 16 essential elements divided into
groups
 Nonmineral elements
 C, H, O
 H & O supplied from carbon dioxide and water
through photosynthesis
 Primary Minerals
 N, P, K
Unit 4: Nutrients
 Secondary Minerals
 Ca, Mg, S
 Micronutrients
 B, Cl, Cu, Fe, Mn, Mo, Zn
 Mineral nutrients supplied by the soil
through nutrient uptake
 Sugars produced by photosynthesis are
responsible for most plant growth
Unit 4: Nutrients
 Fertilizers
 Added to soil to help supply needed
macro- and/or micronutrients
 N
 One of the most abundant and mobile
nutrients
 Part of every plant cell
 Soils may contain ~5000 lbs./ac.
 78% of Earth’s atmosphere
Unit 4: Nutrients
 Part of chlorophyll
 What do we observe when N is lacking?
 Starts at the tips of lower leaves
 Slower growth
 Spindly stalks and stems
 Manufactured most commonly into what
form?
 How is it made?
 What else can be manufactured?
Unit 4: Nutrients
 N and the Environment
 Very mobile
 Very susceptible to many physical, chemical,
and biological processes
 Significant losses are possible
 Where does it go?
 Leaching, erosion, denitrification,
volatilization
 >50% of all N supplied to the soil may
never be used by the crop
 Nitrification
 Regardless of how N is applied to the soil, it
ends up in Nitrate form
Unit 4: Nutrients
 Process converts ammonium from organic
matter or fertilizers to nitrate
 Only ammonium not converted is trapped
by soil clays
 Performed by soil bacteria
 Once converted to nitrate, becomes part of soil
solution
 Leaching
 Nitrates held only slightly by soil colloids
and humus (why?)
 Move w/ soil water
 Ammonium is held tightly in the soil (why?)
Unit 4: Nutrients
Nitrate losses during the growing season in
medium and fine-textured soils estimated at
<5% (greater in coarse-textured soils)
 Erosion
 Nitrates primarily lost in runoff water
 Ammonium and organic forms of N lost in
sediment
 Denitrification
 Occurs only under anaerobic conditions
 Bacteria convert nitrate back to N gas
 Estimated losses of 15-30% of total applied
N from an area flooded for just 3-5d
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Unit 4: Nutrients
 Losses from well-drained soils usually small
 Volatilization
 Occurs when urea converted to ammonium
carbonate when applied to warm moist soils
 Breaks down into ammonia gas
 Lost into atmosphere if this occurs on the
soil surface
 Usually <10%, but can be great if urea is
topdressed, then followed by 3+d of warm
dry conditions
 Incorporation or injection will eliminate this
loss
Unit 4: Nutrients
 Nitrogen Cycle
 Must be pulled from the atmosphere to be used
by plants
 Fertilizer plants
 N fixation by green plants
 N can take many forms from atmosphere to
soil to plant and back
 Nitrogen Fixation
 Elemental N removed from the atmosphere by
soil bacteria called rhizobia
 Live on nodes of legume plant roots
 Can provide more N to the soil than they
use
Unit 4: Nutrients
 Organic Matter (Humus)
 Decomposition/decay of plants into soil organic
matter
 Rate of decomposition & amount of N released
depends on C:N ratio
 <25:1 – plant/animal residues are quickly
converted to large amounts of N that can be
used by growing plants
 Conversion process called mineralization
 >25:1 – N is immobilized in the soil,
decomposition is slow, bacteria rob N from
the soil, N deficiencies can occur
Unit 4: Nutrients
 Material that has completely decomposed
called humus
 C:N ratio of ~12:1
 Controls the release of N in soil
 Humus contains ~5% N
 Soil w/ 1% organic matter will have ~1000
lbs. N/ac. (only ~2% is available annually)
 P
 Very immobile
 Only moves if soil particles move
 Lost via plant removal and erosion
Unit 4: Nutrients
 Must be near plant roots to be used
 Soil Reactions
 Soil P amounts closely related to pH
 Maximum availability at slightly acid pH
 P will form insoluble compounds w/ other
elements under higher or lower pH’s
 P Sources
 DAP & Triplesuperphosphate are main fertilizer
sources
 DAP generally used in dry bulk fertilizers
 TSP available in bags/bulk
Unit 4: Nutrients
 Other sources include:
 Animal manure, sludge, plant residues, etc.
 Mineral Apatite – main source for P fertilizer
manufacturing
 Mined in: FL, NC, WY, MT, TN
 K
 Second most-used nutrient
 Also relatively immobile
 Most common deficiency symptom is
scorching or browning along leaf margins or
lower/bottom leaves
Unit 4: Nutrients
 Soil Reactions
 Found in greatest quantity in the soil, available
amounts are relatively small
 Most tied up w/ other soil minerals
 Considerable amounts trapped between clay
particles
 K Sources
 Most K is mined from deposits found from
ancient seas
 Largest deposit in Saskatchewan, CAN
 Muriate of Potash most common source of K
fertilizer
Unit 4: Nutrients
 Secondary & Micronutrients
 Just as important for plant growth, but
needed in much smaller amounts
 S
 Most present in organic form
 Becomes available upon decomposition of
organic matter
 Mineralized to sulfate form
 Subject to leaching and immobilization by
microbes
Unit 4: Nutrients
 May be supplied from atmosphere by rain
 May be present in some lower-grade
fertilizers as an impurity
 Gypsum can be used to increase soil S
levels
 Plants absorb in sulfate form
 Constituent of amino acids, proteins,
vitamins, enzymes
 Also contribute to distinct odors
 Mustard, onion, garlic
 Required for N fixation
Unit 4: Nutrients
 Ca
 Supplied by soil minerals, organic matter,
fertilizer, lime
 Primary ion on CE sites
 Essential part of plant cell wall structure
 Helps w/ transport/retention of other
nutrients
 Provides strength
 Critical balance w/ Mg and K
 Abundance of one can cause deficiencies of the
other two
Unit 4: Nutrients
 Mg
 Sources
 Soil minerals, organic matter, fertilizers,
dolomitic limestone
 Held on CE sites like Ca, K
 Part of chlorophyll and essential for
photosynthesis
 Activates many plant enzymes
 Relatively mobile in the plant
 Can be translocated from older to younger
plant parts to prevent deficiencies
Unit 4: Nutrients
 Micronutrients
 Most apt to limit crop growth under several
conditions
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Highly leached acid sandy soils
Muck soils
Soils high in pH or lime
Soils heavily cropped and fertilized w/
macronutrients
 Fe
 Essential for chlorophyll synthesis
 Part of many plant organic compounds
 Antagonist w/ Mn
Unit 4: Nutrients
 Cu
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Essential for growth
Activates many enzymes
Deficiencies interrupt protein synthesis
Excess Cu can cause Fe deficiency
 Mn
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Absorbed in ionic form
Believed to activate many enzymes
Antagonist w/ Fe
Availability closely related to soil pH
 Deficiencies can occur in slightly
acid/alkaline soils
Unit 4: Nutrients
 Zn
 Controls synthesis of indoleacetic acid which
dramatically regulates plant growth
 Also active in enzyme activity
 Mo
 Important for enzymatic activity, N fixation
 Inadequate Mo can cause N deficiencies
 Required in minute amounts
 B
 Regulates the metabolism of CHO in plants
 Needs vary w/ crop, and high levels may
damage B sensitive crops
Unit 4: Nutrients
 Nutrient Availability & Plant Uptake
 Nutrients must be available in the soil in
forms the plant can absorb to be effective
 Absorption occurs when plant roots come
into contact w/ soil solutions that contain
these nutrients
 Nutrients held by soil particles
 Although large amounts of nutrients may
be found in the soil, small quantities are
actually available
Unit 4: Nutrients
 Unavailable nutrients may be found in the
following forms:
 Insoluble chemical compounds – P and micros
 Unweathered or Undecomposed soil minerals –
most all nutrients can be in this form
 Organic Matter or Plant Residues – mostly N or
S
 Trapped by Soil Particles – lots of K, some
ammonium
 Greatly affected by soil pH
Unit 4: Nutrients
 Nutrient Interactions
 How one nutrient may help/hinder the uptake
of another
 Conditions may affect
 Nutrients may also vary
 Examples:
 Ammonium-potassium: ammonium can
interfere w/ K uptake, can create K
deficiencies in some crops
 K-Mg: K can reduce uptake of Mg at high
rates, can result in Mg deficiencies
Unit 4: Nutrients
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P-N: P uptake increased in presence of N
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P-Zn: high P can reduce uptake of Zn
 Soil pH
 Acid/base balance of the soil
 Highly acid/alkaline soils can negatively affect
nutrient uptake and/or production
 Causes of Acid Soils
 High losses of Ca, Mg, K from erosion, leaching,
and crop removal
 Conversion of ammonium to nitrate results in
soil acids
Unit 4: Nutrients
 Adjusting Soil pH
 Can be easily adjusted to any desired range
 Adjustments should only be made based on
soil test results
 What would we apply to adjust soil pH
up/down?
 What are the recommended pH ranges for
some common crops? (See pg. 155)
 Lime Sources
 Most economical source is ag lime
Unit 4: Nutrients
 Dolomitic – contains Mg
 When might we use this?
 Calcitic – contains only Ca
 Functions
 “Sweetens” the soil (most plants don’t prefer
acid soils)
 Improves availability of plant nutrients
 Increases effectiveness of applied N, P, K
 Increases microbe activity, especially for N
fixation and decomposers
 Improves plant growth and yields
Unit 4: Nutrients
 Soil Testing
 Most accurate method for determining
fertilizer needs
 Measures soil pH and available nutrients
 Most fertilization problems associated
w/: lack of/improper use of N, P, K, and
lime
Unit 4: Nutrients
 Collecting the Sample
 Must be a representative sample
 Take a large composite sample
 Mix for one representative sample
 Each sample shouldn’t represent >10 ac.
 How do we collect a sample?
 What are some new technologies being
used?
Unit 4: Nutrients
 Foliar Symptoms
 Vary w/ plant species
 What other things can produce foliar
symptoms?
 Suspicion of nutrient deficiencies should
be confirmed w/ other diagnostic
methods
Unit 4: Nutrients
 Tissue Testing
 Rapid Tissue Testing
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Green tissue collected for analysis
Chemicals used to test for present elements
Accuracy may be sacrificed for speed
Dry tissue testing more accurate
 Dry Tissue Testing
 Uses dry leaves or plants
 Entire leaf ground up and tested for selected
nutrients
 Should be very accurate
Unit 4: Nutrients
 More expensive and time-consuming
compared to Rapid Testing or Soil Analysis
 Plant part sampled and stage of
development critical to interpretation of
results
 Choosing the Fertilizer Source
 Many fertilizers available to supply
needed nutrients
 If fertilizer supplies only one nutrient –
called straight material (urea, muriate of
potash)
Unit 4: Nutrients
 If contain each of 3 primary nutrients –
called complete or mixed fertilizer
 Can be purchased bag or bulk
 How do we determine N, P, K amounts in
a fertilizer?
 What forms are they in?
 Solid or Liquid Fertilizer?
 Performance is equal if equal amounts are
applied
 Makes little difference to the plant
Unit 4: Nutrients
 Selection should be made based on:
 Availability
 Economics
 Other factors
 Fertilizer Placement
 Soil characteristics, crop, nature of
fertilizer material should be considered
when determining method of application
 Things to consider:
 Provide adequate nutrient quantities in the
root zone
Unit 4: Nutrients
 Irregular distribution can lower
effectiveness of fertilizer
 Early seedling stimulation usually
advantageous – fertilizer should be placed
near seedling roots
 Rate and distance of fertilizer movement
depend on the soil, can be carried up in dry
conditions, or down in wet conditions
 Fertilization in dry conditions may do more
harm than good to the plant
 N, K more readily soluble than P and should
not be placed in as high a concentration
near plant roots
Unit 4: Nutrients
 Reduction in soil moisture increases salt
concentration and can result in crop injury
 P should be placed in the root zone due to
immobility
 Banding fertilizers can reduce rates by 50%
compared to broadcast
 Slows conversion of P to unavailable forms
 Foliar Fertilization
 Feed plants through leaves, stems, etc.
 Should only be used in a supplementary role
 Can only apply in small amounts (why?)
Unit 4: Nutrients
 Can be expensive
 Most appropriate to supplement micros
 Other Fertilization Sources
 Animal Manures
 Nutrient concentration is generally low, but
some quantities of all nutrients are present
 Nutrient content may be variable
 What might affect this?
 General Rules of Thumb:
 ~16T on manure produced/hd/yr regardless of
species
Unit 4: Nutrients
 Adding superphosphate to manure can reduce
ammonia volatilization
 Not appropriate for intensive livestock
operations (why?)
 Hydroponic Requirements
 What is hydroponics?
 Can be especially effective for some
vegetables (spinach, tomatoes)
 Bath plant roots in nutrient solution
 Must be changed weekly due to plant
depletion
Unit 4: Nutrients
 Avoid problems w/ weeds, soil textures,
diseases
 Must balance all chemical and physical
conditions properly to work
 All essential plant nutrients must be
supplied in solutions
 Imbalances of elements can cause serious
problems
Unit 4: Nutrients
 Unit 4 Assignment:
 Chapter Review Questions pgs. 165-166
 #’s 6-10, 12-15
 Each question 2 points
 Due next class!