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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.

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unit 4 nutrients1
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 nutrients2
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
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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
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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
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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?
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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
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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?)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Unit 4: Nutrients
  • Micronutrients
    • Most apt to limit crop growth under several conditions
      • 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
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Unit 4: Nutrients
  • Cu
    • Essential for growth
    • Activates many enzymes
    • Deficiencies interrupt protein synthesis
    • Excess Cu can cause Fe deficiency
  • Mn
    • 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
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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
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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
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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
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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
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Unit 4: Nutrients
          • P-N: P uptake increased in presence of N
          • 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
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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
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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
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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
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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?
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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
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Unit 4: Nutrients
  • Tissue Testing
    • Rapid Tissue Testing
      • 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
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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)
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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
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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
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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
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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?)
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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
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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
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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 nutrients41
Unit 4: Nutrients
  • Unit 4 Assignment:
    • Chapter Review Questions pgs. 165-166
      • #’s 6-10, 12-15
      • Each question 2 points
      • Due next class!