unit 8: plant nutrients chapter 9. objectives knowledge of essential elements for plant growth ...
TRANSCRIPT
Objectives Knowledge of essential elements for plant
growth Mechanisms by which plant roots contact,
absorb nutrients Methods of N cycling and N loss Materials used in N fertilizers Understanding of the behaviors of nutrients
in the soils Fertilizer applications Importance of micronutrients in plant
development
Essential Elements
17 elements known to be essential C, H, O Photosynthesis
Light energy used, H split off of water H combined w/ C & O to make CO2
(diffused through leaf stomata) Results in CHO + other organic
molecules
Essential Elements
Macronutrients N, P, K
Secondary Nutrients Ca, Mg, S
Micronutrients B, Cl, Cu, Fe, Mn, Mo, Ni, Zn
Others as needed
Mechanisms of Nutrient Uptake
Nutrients reach root surfaces by three mechanisms
Mass flow – movement of nutrients in water flowing toward the root
Diffusion – movement down a concentration gradient from high - low
Interception – roots explore new soil areas containing unused soil nutrients
All three in constant operation Root hairs primarily responsible for the
uptake
Mechanisms of Nutrient Uptake
Absorption of Nutrients into Roots Mechanism not well understood
Movement through cell wall easy Movement into cytoplasm much harder Nutrient must go through passageway, or
bond w/ carrier to get through cell membrane
Some actively pulled into cell Electrical balance also involved
Mechanisms of Nutrient Uptake
Absorption through Leaves Leaf stomata
Exchange of H20, O2, & CO2
Some soluble elements can be absorbed in small amounts Mostly micronutrients Macros typically need in too high quantities to
foliar feed
Soil Nitrogen Gains & Transformations
N is the key nutrient in plant growth management Most commonly deficient nutrient,
controlling factor in plant growth Constituent of: proteins, chlorophyll,
nucleic acids Plants w/ sufficient N have thinner cell
walls & are more succulent plants N deficiency = poor plant yields
Soil Nitrogen Gains & Transformations
Much soil N isn’t in a form that can be absorbed Most immobile in organic matter N2 gas in the atmosphere
Must be fixed by soil bacteria first
Unique nutrient Can be absorbed soluble organic form NH4, NO3
Soluble, mobile, easily leached Can be easily denitrified by soil microbes
Soil Nitrogen Gains & Transformations
Deficiency symptoms: poor, spindly, stunted growth
NH4 & NO3 are not necessarily interchangeable NH4 saves the plant energy NO3 is more stable in the soil
Fixation of N Gas Primary source of soil N Taken by soil microbes, converted to NH4
Soil Nitrogen Gains & Transformations
Wide variation in how much N is fixed due to: soil, fertilizers used, crops, etc.
Mineralization of N Release of N from decomposition of
organic materials Mineralization – conversion of organic N
to NH4 form Soil organic matter contains ~5%N Only small % of organic matter decomposes
each yr
Soil Nitrogen Gains & Transformations
Nitrification of Ammonium Nitrification – oxidation of ammonium to
nitrate by bacteria, other organisms Rapid microbial transformation (usually 1-
2d) Most is complete w/in 1-2 wks
Some absorbed, some adsorbed quickly Slowed by anaerobic conditions, dry,
cold, toxic chemicals
Soil Nitrogen Gains & Transformations
Other Fixation Reactions Involving Soil N Immobilization – soluble N held in plant
materials or microbes N not available to plants N can be fixated to clay particles N can be consumed by decomposing
microbes and held until they die
Nitrogen Losses from the System
Leaching of Soil N NO3 – readily leached form of N, toxic to
young mammals Nitrate lost due to negative charge Ammonium held due to positive charge Leaching rates increase as percolation rates
increase, when plant growth rates aren’t quick enough to keep up w/ N production
Losses from crop covered soils usually low
Nitrogen Losses from the System Losses from heavily fertilized, wet soils high
Nitrification Inhibitors Chemicals used to inhibit nitrification
N-Serve, DCD, ATC Inhibit the first step of nitrification, slow the
release of N to the soil N-Serve more volatile & can evaporate slowly DCD, ATC – stable, easy to handle, can be
applied as coatings to granules What is the effect of all this? What options does it allow producers?
Nitrogen Losses from the System
Gaseous Losses of Soil N Denitrification – change by bacteria of
NH4 to N gas Biological process Can be most extensive gaseous N loss
Especially w/ poorly aerated/wet soils Rapid process
Substantial N loss can occur in <1d ~10-20% normal ~40-60% in extreme conditions, 100% in
wetlands
Nitrogen Losses from the System Three reasons large amounts of N lost:
Lack of adequate free O in the soil Energy source of organic matter for the
bacteria Warm, slightly acidic soils
Ammonia Volatilization Occur when ammonium is in alkaline
environment Chemical process Losses occur from surface applications of
ammonium/urea Can be ~30%, normally <10%
Nitrogen Losses from the System
Most extensive under following conditions: High pH, calcareous soils Fertilizer left on soil surface High temps Low CEC soils
Materials Supplying Nitrogen
Ammonia & Aqueous N Anhydrous Ammonia (NH3)
Most common N fertilizer >90% of all N fertilizers made up of some form
of ammonia 82% N Manufactured from atmospheric N using
natural gas to supply H (Haber Process) First usable fertilizer product of this process Other N fertilizers require more processing
Materials Supplying Nitrogen Applied w/ chisels to ~5” Pressured liquid in the tank, gas at
atmospheric pressure Least expensive N fertilizer (per unit N) Very dangerous to handle
Burns Blindness Inhalation risks Safety precautions
Wear proper safety equipment (gloves, goggles)
Materials Supplying Nitrogen Keep away from flames Keep away from ammonia clouds Have water available Store in proper tanks, don’t overfill Paint tanks white to reflect heat Inspect tanks regularly for leaks/problems
Solid Fertilizers Urea
Synthetic, organic fertilizer Cheaper per lb than any other solid N fertilizer 45% N Must be converted in the soil to NH4
Materials Supplying Nitrogen Readily soluble & leachable Stabilized & can be stored when converted in
the soil to NH4 Popular
Cheapest solid N source Soluble in water Convenient for application in sprinkler,
spray, solution Ammonium Sulfate
21% N High cost Less popular
Materials Supplying Nitrogen Commonly used in rice
Ammonium is all available to plant Sulfate keeps it from being denitrified
quickly Why is this so important for them?
Strongest acidic N fertilizer UAN
Urea-Ammonium Nitrate solution 28% N or 32% N
Materials Supplying Nitrogen Organic Wastes
Considered controlled-release fertilizers Nutrient concentration is low Depends on decomposition rates May carry undesirables
Weed seed, diseases, soluble salts, etc.
Materials Supplying Nitrogen
Controlled-Release N Fertilizers Standard N fertilizer crop use rates ~40-
70% Rest is leached, denitrified, etc.
Slow-release N fertilizers used to control proportion of fertilizers available at one time
More efficient use of N means more cost savings & less pollution
Materials Supplying Nitrogen Slow-release N products most commonly used in
turf grass Urea-Formaldehydes
Varying rates of urea & formaldehyde Greater urea, more available N
Environmental conditions must favor microbe activity to release N Losses may be ~20%
Polymer-coated N Soluble form of N (urea) diffuses through
polymer membrane Reliable, consistent control of N release
Soil Phosphorus
Traditionally, second-most prescribed nutrient in the soil K has now passed in use
Essential part of nucleoproteins in cell nuclei Carry DNA
Main component of cell energy currency (ATP)
Soil Phosphorus
Roles in: Cell division Root growth Plant maturation Energy transformation w/in cells Fruit/seed production Animal/human nutrition
Growth of bones & teeth
Soil Phosphorus
Young plants absorb soil P readily Most critical for plants to have available
P sources early in development Wheat from tillering to flowering Corn ~3 wks into growing season
The P Problem
Soil forms of P very low solubilityP applied through fertilizer often
combines w/ substances to reduce solubility
Most P supplied to plants by diffusion in the soil
Diffusion rates extremely slow (.02 - .1 mm/hr)
Major problem to keep P soluble & available to the plants in soils
Soil P doesn’t leach
The P Problem Mineral P
Available P critical Supply of P in soils is low Phosphates in soils not readily available
While there is lots of P in the soil, minutes fractions actually available
Original natural source of P – apatite (rock phosphate) Along with others, these can be used as
low-quality fertilizer sources
The P Problem Soluble phosphate often reacts w/ other
soil substances to form insoluble compounds Also readily adsorbs to other molecules Explains soil P buildup
Soil P most available at pH ~6.5 Phosphates in Anaerobic Soils
Phosphates more soluble than in aerated soils
Iron phosphates are soluble in flooded soils, less tie-up for P
The P Problem Works out good for rice growers
Organic Soil P Phosphatases used by plant roots &
some microbes to split P from organic residues – making it available for absorption
P in organic residues tends to more soluble, therefore, more useful to plants May comprise >50% of soluble soil P
Managing Soil P
Major pollutant of surface waters Not really discussed in depth in this unit
Mycorrihzae helps plants access soil P Fumigated soils, non-healthy microbe
population soils - < access to soil P - <growth
Soil pH influences Changes solubilities of Fe, Ca, Al, &
affects soil bacterial growth
The P Problem ~6.5 pH optimal for P availability
Phosphate fertilizer effectiveness Most efficient use when banded
What does this mean? What problems does this cause? Want to place ~2” away from root zone on
either side Only 10-30% of soil applied P is actually
used
The P Problem Excess P retained in the soil
Can cause Zn deficiency P pollution from runoff
Maximizing P efficiency Maintain soil pH 6-7 Promote healthy soil organic matter content Band P fertilizer for row crops, broadcast &
incorporate for non-row crops What’s wrong w/ this?
Materials Supplying P
U.S. is world’s largest producer Estimated our supply may run out in 20 yrs
at current usage Most comes from FL or western U.S.
Western Africa has 6x more supply than U.S.
Phosphate Ores & Deposits Rock phosphate mined, ground
Materials Supplying P Mixed w/ sulfuric acid to form
superphosphate 8-9% P, 48% gypsum
Mixed w/ phosphoric acid to form triple superphosphate 20-22% P (40-45% phosphate)
Mixed N-P Fertilizers Monoammonium & Diammonium
Phosphate fertilizers Apply N & P w/ same product These will be covered more in a later unit
Soil K
Ranks 2nd to N in plant use & fertilizer applied
Chemical compounds of K very soluble, but mineral form is not
Can see considerable soil amounts of K, but much of may not be available
Decomposition of plant residues provides much soluble K
Soil K
Roles of K Cell division Formation of CHO’s Movement of sugars Enzyme actions
>60 enzymes known to need K for activation Disease resistance Cell permeability Important for water balance
Soil K Forms of Soil K
Most K used by plants in exchangeable or soluble form Exchangeable K forms as micas & feldspars
weather, or as plant residues release Exchangeable soil K in root zone may be
small amount Often must supply 150-180 lb/ac
K Losses & Gains K may be taken up in excess amounts by
plants – Luxury Consumption
Soil K May be expensive waste of K fertilizer May inhibit Mg absorption May not increase crop yield
Soluble K losses Immobilized by microbes Leached Trapped in soil clay layers Eroded
Soil K K gains
Mineralization of organic matter K Can be used ~ as fast as water moves through
soils Held on cation sites in the soil
Soil K is relatively stable & not volatile w/ temp changes
Soil K Supplying K to Plants
K fertilizers usually very soluble May not be very mobile in the soil
Is held on cation sites, or will replace other ions on those sites
Needs to be supplied in the root zone to be most effective
Acidic soils often result in K deficiencies Abundance of soil Ca, Mg, or K may antagonize
uptake of one of the others Competition for plant absorption
Soil K KCl – cheapest K fertilizer source
Can choose sulfate or nitrate forms to add additional nutrients…but more costly
Managing Soil K Hay harvesting removes much K from
the soil each year Highest K requirement during vegetative
growth
Soil K K Management keys
Maximize efficient use of added K Minimize luxury consumption
Split applications – especially in sandy soils Maximize use of natural K (organic matter
sources) Maintain soil pH 6-6.5 – reduces leaching
losses
Soil K Materials Supplying K
Potash Most potash imported from Canada Muriate of potash (KCl) – principle source
60% potash Potassium sulfate – 2nd most used K fertilizer Potassium-magnesium sulfate – provides 3
nutrients Potassium nitrate – adds N w/ K
Soil Ca
Occurs in many minerals, more plentiful in soils than any other plant nutrient
Ca deficiency is rare due to wide range of Ca sources in soils
Mobility of Ca Taken up as Ca Strongly adsorbed to cations
Large amounts may be leached simply due to large supply in the soil
Soil Ca Mass flow usually supplies enough Ca to
root zone Only absorbed through root tips
Plant Need for Ca Dividing cells – forms Ca pectate which
cements cells together Physical integrity & normal cell function Deficiencies
Deformation of new leaves/necrotic appearance
Death of buds
Soil Ca Used more than Mg, less than K Needs to be supplemented in
greenhouses Ca deficiency common due to not enough
fertilization w/ higher Ca sources Ca Fertilizers
Limestone Usually only used on soils if they’ve
become acidic Can use gypsum if pH raise not needed
Soil Mg Mobility of Mg
Most soluble/exchangeable forms supplied in the soil
Reacts similar to Ca Lower total leaching loss, less present
Plant Need for Mg Most supplied to the roots by mass flow 1/5 of Mg used by plants for chlorophyll Stabilizes ribosome structure Enzyme activator
Soil Mg Readily mobile in the soil Deficiency symptoms
Interveinal chlorosis of older leaves Hypomagnesia (grass tetany)
Can occur in livestock grazing soils low in Mg
Mg can be tied up by heavy applications of K and/or ammonium fertilizers
Soil S
Constituent in 2 of the 20 amino acidsEssential part of proteinsAlso found in vitamins, oilsMuch overlookedFactors increasing need for S fertilizers
Lower amounts of sulfate added incidentally w/ other nutrients
Lower pollution from sulfur oxides into air Higher plant yields, greater demands on
soils
Soil S
Sources of S Availability of soil S hard to determine –
major portions come from organic matter Depends on decomposition, climate, temp,
etc. Rainfall
Can be toxic to fish, if S is too high S also supplied as part of other fertilizers
Rare need to supply S separately, but the need has been observed
Soil S Characteristics of Soil S
Decomposition can release much S Exists in many chemical forms,
depending on the soil Easily leached
Why? Waterlogged soils can cause soil S
sources to convert to sulfide – toxic gas to plants
Acidifies the soil
Soil S Managing Soil S
Reduced air pollution, purer fertilizers, better understanding = reduced incidental S additions
Some increased reports of S deficiencies Sulfur Fertilizers or Amendments
Select ammonium sulfate or potassium sulfate fertilizers
Gypsum Others can be recommended
Soil B
Essential for: Cell wall formation, sugar movement,
pollination
Deficiencies: Terminal bud death Reduced flowering, retention of flowers Reduced pollen germination Less fruiting
Soil B Soil Chemistry of B
Forms a weak acid Deficiencies common in high rainfall
areas Various borates (forms) may exist in
different soils Sources for B
Primary rocks & minerals Combined in soil organic matter Adsorbed in soil clays Boric acid
Soil B Boron Deficiency & Amendments
Deficiency in grapes greatly reduces yield
Cost to supplement relatively inexpensive If over-supplemented can be toxic
Fine line between adequate & excess amounts Supplemental B supplied by borax
Very soluble 11% B
Soil Cl
Found in soil as Cl- Very soluble, mobile Not very reactive in the soil Will it be held in the soil?
Osmotic role – maintains/equalizes cell charges
Unique Features of Cl Cycles easily Supplied by manures, KCl, rainfall, etc.
Soil Cl Can accumulate to toxic amounts
Especially in soils high in soluble salts Some diseases linked to Cl deficiencies
(stripe rust, take-all root rot, leaf rust) Cl Amendments
Deficiencies rarely seen in the field Cl typically supplied incidentally w/ other
fertilizers
Soil Cu
Essential for many enzymesVery low solubility
Solubility related to soil pH
Strongly adsorbed to soil clays Problem Soils & Susceptible Plants
Deficiencies: Common in organic soils
Bonds strongly to organic substances & won’t become soluble
Soil Cu Sandy soils Calcareous soil – pH 8-8.4 High competition w/ other metals
Less common than other micro deficiencies
Symptoms of deficiency Yellowing of younger leaves Off-color (bluish/green) Small dead spots Leaf curling
Soil Cu Sensitive plants:
Alfalfa Rice Wheat Oats, etc.
Cu Amendments & Their Use Successful, when applied Often only need supplement few ppm/ac CuSO4
Can be applied as foliar treatment
Soil Fe
Important part of energy-providing reactions
Much Fe association w/ chloroplasts
Very low solubility Difficult to keep Fe soluble for plants to
absorb
Very low amounts needed for plants
Soil Fe Fe in Soil Solution – Chelates &
Availability pH has dominant effect of iron solubility
Very soluble at pH – 3 Solubility decreases by factor of 1000/pH
unit rise At normal pH – soluble iron very low
Fe needs mostly provided by soil organic matter, stays bonded to something else to keep it soluble
Soil Fe Some supplied in chelate form
Keep metals in a mobile/soluble form Move to plant roots by diffusion or mass
action
Problem Soils, Susceptible Plants, & Fe Amendments Deficiencies common in calcareous soils High P levels also antagonize Fe
Soil Fe Fe deficiency symptoms:
Interveinal chlorosis Soluble chelate supplementation will
often correct deficiencies Foliar sprays
May need to be repeated Soil applications have longer residual, but
much slower acting Keep organic matter high
Soil Mn
Involved in enzyme systemsSolubility increases w/ pH increasesOrganic matter decomposition aids Mn
solubility Toxicity, Problem Soils, & Deficiency
Symptoms Toxic concentrations more common than any
other micro Soils may naturally have high Mn Conditions can cause Mn toxicity easily
Soil Mn High Mn soils may show toxicities at pH
just below 6, excessive water, or even at high pH’s
Somewhat common in Hawaii Treatment w/ lime & gypsum
Deficiency symptoms – chlorosis of younger leaves
Soil Mo
Exists & needed in minute amountsImportant for enzyme function & N
fixationStrongly adsorbed, yet soluble Problem Soils & Susceptible Plants
Deficiencies common in acid/sandy soils Susceptible crops:
Soybeans, alfalfa, corn, tomatoes, etc.
Soil Mo Toxicities usually only show up in grazing
animals Known to happen on soils w/ high organic
matter & neutral/alkaline pH Problem related to imbalances of Cu & Mo Stunted growth, bone deformation
Feed, inject Cu will often correct
Mo Amendments Foliar sprays Lime acidic soils
Soil Zn
Essential for enzyme systems Zn in the Soil Solution
Quite immobile in the soil (+ charge) Can become deficient in flooded soils
Problem Soils & Susceptible Plants Deficiencies:
Occur in basic soils, limed soils, cropping w/ high Zn demand crops (corn, fruits, etc.)
Most expected at high soil pH
Soil Zn Cotton responds to Zn supplementation
in SW US Symptoms:
Interveinal chlorosis in young & old leaves Reduced stem elongation Bunched leaves Small, thick leaves Early defoliation
Soil Zn
Zn Amendments ZnSO4 most commonly used to cure
deficiencies Foliar application for treatment Soil application if problem is anticipated
Ni & Other Beneficial Elements May not be essential for all plants, but
may be essential for one plant Co
Essential for microbes involved w/ N fixation Can be deficient in high Ca soils, sandy,
leached soils Si
Very abundant in the environment Can be deficient in very weathered soils Appears to strengthen cell walls
Ni & Other Beneficial Elements Na
Essential for desert species to maintain turgor
Growers usually reluctant to add Why?
V (Vanadium) Essential for algae, microbes May substitute for Mo in enzyme activation
Ni & Other Beneficial Elements Ni
Raised to essential status in 1983 Scientists still argue over its roles Suspected roles in plant metabolism
Enzyme activator No fertilizer w/ Ni currently available Soybeans have demonstrated a positive
response to Ni treatment