Plant Nutrients Flashcards
How many elements known to be essential
17
Photosynthesis
- Light Energy used, H split off of water
- H combined w/ C and O to make CO2 (diffused through leaf stomata)
- Results in CHO + other organic _______?___________
Macronutrients
Needed to supply plant so large amounts are needed:
- N
- P
- K
Secondary Nutrients
- Ca
- Mg
- S
Micronutrients
Minuscule amounts needed but so critical if below amount needed then it can cause major problems:
- B
- Cl
- Cu
- Fe
- Mn
- Ni
- Zn
Mechanisms of Nutrient Uptake
- Nutrients reach root surfaces by three mechanisms
- Absorption of Nutrients into roots
- Absorption through leaves
Nutrients reach root surfaces by three mechanisms
- Mass flow
- Diffusion
- Interception
- all three in constant operation but shift in priority as move through growing season
- root hairs primarily responsible for the uptake
Mass flow
movement of nutrients in water flowing towards the root
Diffusion
movement down a concentration gradient from high to low
Interception
roots explore new soil areas containing unused soil nutrients
Absorption of nutrients into roots
Mechanism not well understood (hard to see below ground)
- 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
Absorption through leaves
Leaf Stomata
- Exchange of H20, )2, CO2
- Some soluble elements can be absorbed in small amounts
* Mostly micronutrients
* Marcos typically need in too high quantities to foliage needs
Soil N gains and transformations
- N is the key nutrient in plant growth management
- Most Soil N isn’t in a form that can be absorbed
- Unique Nutrient
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 and are more succulent plants
- N deficiency= poor plant yields
Most soil N isn’t in a form that can be absorbed
-Most immobile in organic matter
-N2 gas in the atmosphere
-Must be fixed bu soil bacteria
first
Unique Nutrient
-Can be absorbed soluble organic form
-NH4, NO3
-Soluble, mobile, easily
leached
-can be easily denitrified by
soil microbes
2 forms of N available to plants
- NH4
- NO3
N deficiency symptoms
- poor
- spindly
- stunted growth
NH4 & NO3 are not necessarily interchangeable
- NH4 saves the plant energy (easier for plant to use)
- NO3 is more stable in the soil
NH4
Ammonium
NO3
Nitrate
Fixation of N gas (N2)
- Primary source of soil N
- Taken by soil microbes, converted to NH4
- Wide variation in how much N is fixed
Wide variation in how much N is fixed due to:
- soil
- fertilizers used
- crops
In very productive soil and high amounts of N plants don’t have a relationship with
N fixing bacteria, no nodules form on the roots
Mineralization of N
-Release of N from decomposition of organic materials
-Conversion of organic N to NH4 form
-Soil OM contains ~5% N
-Only small % of OM
decomposes each year
Nitrification of Ammonium
- oxidation of ammonium to nitrate by bacteria and other organisms
- Rapid microbial transformation (1-2 days)
- Most is complete w/in 1-2 weeks
- Some absorbed, some absorbed quickly
- Slowed by anaerobic conditions, dry, cold, toxic chemicals
Other Fixation reactions involving Soil N
immobilization
immobilization
soluble N held in plant materials or microbes
in immobilization N…..
- is not available to plants
- can be fixated to clay particles
- can be consumed by decomposing microbes and held until they die
N losses from the system
- leaching of soil N
- nitrification inhibitors
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
- losses from crop covered soils usually low
- losses from heavily fertilized, wet soils high
Leaching rates _____ as _______ increase, when plant growth rates aren’t quick enough to keep up with N production
increase
percolation rates
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 and can evaporate slowly
- DCD, ATC stable, easy to handle, can be applied as coatings to granules
What effect does Nitrification inhibitors have and what options does it allow producers?
Completely altering ecosystem, lost of N-fixing microbes which eliminate the process to nitrify in the soil, reliant on the addition because we have eliminated natural bacteria populations from the ecosystems
N losses from the system
- leaching of soil N
- nitrification inhibitors
- Gaseous losses of soil N
N losses from the system
- leaching of soil N
- nitrification inhibitors
- Gaseous losses of soil N
Gaseous losses of soil N
Denitrification: change by bacteria of NH4 to N gas
- biological process
- can be most extensive gaseous N loss (esp. with poorly aerated/wet soils)
- rapid process
- substantial N loss can occur in
N losses from the system
- leaching of soil N
- nitrification inhibitors
- Gaseous losses of soil N
- Ammonia Volatilization
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
N loss is most extensive under the following conditions:
- high pH, calcareous soils
- fertilizer left on soil surface
- high temperatures
- Low CEC soils
Materials supplying N
- Ammonia and Aqueous N
- Solid fertilizers
- Ammonium Sulfate
- UAN
- Organic Wastes
- Controlled-Release N fertilizers
Materials supplying N
- Ammonia and Aqueous N
- Solid fertilizers
- Ammonium Sulfate
- UAN
- Organic Wastes
- Controlled-Release N fertilizers
Ammonia and 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); 1st usable fertilizer product of this process, other N fertilizers require more processing
Ammonia and 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); 1st usable fertilizer product of this process, other N fertilizers require more processing
Anhydrous Ammonia
- 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)
when using Anhydrous Ammonia
-keeo
when using Anhydrous Ammonia
- 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
Materials supplying N
- Ammonia and Aqueous N
- Solid fertilizers
- Ammonium Sulfate
- Organic Wastes
- Controlled-Release N fertilizers
Solid fertilizers
Uera
Ammonium Sulfate
Solid fertilizers
Uera
Ammonium Sulfate
UNA
Solid fertilizers
Uera
Ammonium Sulfate
UNA
Solid fertilizers: Uera
- synthetic, organic fertilizer
- cheaper per lb than any other solid N fertilizer
- 45% N
- Must be converted in the soil to NH4
- readily soluble and leachable
- stabilized and 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
Solid fertilizers: Uera
- synthetic, organic fertilizer
- cheaper per lb than any other solid N fertilizer
- 45% N
- Must be converted in the soil to NH4
- readily soluble and leachable
- stabilized and 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
Solid fertilizers: Ammonium Sulfate
- 21% N
- high cost
- less popular
- commonly used in rice
- Ammonium is all available to plant
- sulfate keeps it from being denitrified quickly
- Strongest acidic N fertilizer
Solid fertilizers: Ammonium Sulfate
- 21% N
- high cost
- less popular
- commonly used in rice
- Ammonium is all available to plant
- sulfate keeps it from being denitrified quickly
- Strongest acidic N fertilizer
Solid fertilizers: UAN
- Urea-Ammonium Nitrate solution
- 28% N or 32% N
Organic Wastes
- considered controlled-release fertilizers
- nutrient concentration is low
- depends on decomposition rates
- may carry undesirables (wees seed, diseases, soluble salts, etc.)
Controlled-Release N Fertilizers
- Standard N fertilize 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 saving & less pollution
Controlled-Release N Fertilizers
- Standard N fertilize 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 saving & less pollution
- slow release N products most commonly used in turf grass
Controlled-Release N Fertilizers: Urea-Formaldehyde
- varying rates of urea & formaldehyde (greater urea, more available N
- Environmental conditions must favor microbe activity to release N (losses may be ~20%)
Controlled-Release N Fertilizers: Polymer-coated N
- soluble form of N (urea) diffuses through polymer membrane
- reliable, consistent control of N release
Soil Phosphorus
- Traditionally, 2nd 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
- cell division
- root growth
- plant maturation
- energy transformation w/in cells
- Fruit/seed production
- Animal/human nutrition (growth of bones and teeth)
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 weeks into growing season
- Wheat from tillering to flowering
Problems with P
- soil forms of P very low solubility
- P applied through fertilizer often combines w/ substances to reduce solubility
- major problem to keep P soluble and available to the plants in the soils
- soil P doesn’t leach
Most P supplied to plants by ________ in the soil
diffusion
-diffusion rares extremely slow (.02-.1mm/hr)
The P Problem:
- Mineral P
- Phosphates in Anaerobic soils
- Organic Soil P
The P Problem: Mineral P
- available P critical: supply P in soils is low, P in soils not readily available
- While there is lots of P in the soil, minute fractions actually available
- Original natural source of P: apatite (rock phosphate), along with others, these can be used as low-quality fertilizers sources
- Soluble P often reacts w/ other soil substances to form insoluble compounds (also readily absorbs other molecules, explains soil P buildup
- Soil P most available at pH ~6.5
The P Problem: Phosphates in anaerobic soils
- phosphates more soluble than in aerated soils
- iron phosphates are soluble in flooded soils, less tie-up for P
- works out well for rice growers
The P Problem: Organic soil P
- phosphates used by plant roots and some microbes to split P from organic residues-making it available for absorption
- P in organic residues tends to be more soluble therefore, more useful to plants (may comprise >50% of soluble soil P)
- the more favorable conditions are for microbe decomposition, > available soil P
Managing Soil P
- major pollutant of surface waters
- Mycorrihzae helps plants access soil P (fumigated soils, non-healthy microbe population soils
P Problem
-~6.5 pH optimal for P availability
Phosphate fertilizer effectiveness
- most efficient use when banded (row of plants and then right next to it a row of P application)
- only 10-30% of soil applied P is actually used
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 and incorporate for non-row crops
Places supplying P
- U.S is world’s largest producer (estimated our supply may run out in 20 years at current usage, most comes from FL or western US)
- Western Africa has 6x more supply than U.S
Materials supplying P: Phosphate ores and deposits
- rock phosphate mined, ground
- mixed w/ sulfuric acid to form superphosphate (8-9% P, 48% gypsum)
- Mixed w/ phosphoric acid to from tripled superphosphate (20-22% O (40-45% phosphate)
Materials supplying P: Mixed N-P fertilizers
-Monoammonium and Diammonium Phosphate fertilizers (apply N and P with same product)
Soil K ranks _____ to N in plant use and fertilizer applied
2nd
Soil K
Chemical compounds of K very soluble, but mineral form is not
- can see considerable soil amounts of K, but much of it may not be available - Decomposition of plant residues provides much soluble K
Roles of soil 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
Forms of Soil K
- Most K used by plants in exchangeable or soluble from
- 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 150-180lb/ar)
K losses and Gains
- K may be taken up in excess amounts by plants (Luxury Consumption)
- 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
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 ______ and ________ with temperature changes
stable and not volatile
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)
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
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
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 with 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
- 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 and normal cell function
Symptoms as Ca deficiencies
- deformation of new leaves/necrotic appearance
- death of buds
Ca is used more than _____ and less than ____
-Mg, K
Ca needs ….
to be supplemented in greenhouses
-Ca deficiency common due to not enough fertilization with higher Ca Sources
Ca fertilizers
- Limestone
- Usually only used on soils if they’ve become acidic
- can use gypsum if pH raise not needed
Mobility of Mg
- Readily mobile in the soil
- 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
Symptoms of Mg deficiency
-interveinal chlorosis of older leaves
Soil Mg
- 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
Mg fertilizers
- Dolomitic limestone (Ca w/Mg)
- Can also use Mg salts
Soil S
- Constituent in 2 of the 20 amino acids
- essential part of proteins
- Also found in vitamins, oils
- Much overlooked
Factors increasing need for S fertilizers
- Lower amounts of sulfate added incidentally with other nutrients
- Lower pollution from sulfur oxide into air
- Higher plant yields, greater demands on soils
Sources of S
- Availability of soil S hard to determine-major portions come from organic matter (depends on decomposition, climate, temperature, etc.)
- Rainfall (can be toxic to fish, if S is too high)
- S also supplied as part of other fertilizers (rarely need to supply S separately, but the need has been observed)
Characteristics of Soil S
- decomposition can release much S
- Exists in many chemical forms, depending on the soil
- Easily leached
- Waterlogged soils can cause soil S source to convert to sulfide-toxic gas to plants
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
- Gypsum
Soil B (Boron) is essential for
- cell wall formation
- sugar movement
- pollination
Symptoms of B deficiencies
- terminal bud death
- reduced flowering, retention of flowers
- reduced pollen germination
- less fruiting
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 and minerals
- combined in soil organic matter
- adsorbed in soil clays
- Boric acid
Boron Deficiency and Amendments
- deficiency in grapes greatly reduces yield
- cost to supplement relatively inexpensive (if over-supplemented can be toxic; fine line between adequate and 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
Cl role
osmotic role-maintains/equalizes cell charges
Unique Features of Cl
- cycles easily
- Supplied by manures, KCl, rainfall, etc.
Cl can….
accumulate to toxic amounts
-especially in soils high in soluble salts
Symptoms of Cl deficiencies
- 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 with other fertilizers
Soil Cu
- essential for many enzymes
- very low solubility (solubility related to soil pH)
- Strongly adsorbed to soil clays
Problem Soils and Susceptible plants: Deficiencies
- Common in organic soils (bonds strongly to organic substances and won’t become soluble)
- Sandy Soils
- Calcareous soil-pH8-8.4
- High competition w/ other metals
-less common than other micro deficiencies
Symptoms of Cu deficiency
- yellowing of younger leaves
- off-color (bluish/green)
- small dead spots
- leaf curling
Sensitive plants to Cu deficiency
- Alfalfa
- Rice
- Wheat
- Oats
Cu amendments and their use
- Successful, when applied
- often only needed 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
Fe in soil solution- Chelates and availability
- pH has dominant effect of iron solubility
- Fe needs mostly provided by soil organic matter, stays bonded to something else to keep it soluble
- some supplied in chelate form
Fe in soil solution- Chelates and availability: pH has dominant effect of iron solubility;
very soluble at pH 3, solubility decreases by factor of 1000pH unit rise , at normal pH, soluble iron very low
Fe in soil solution- Chelates and availability: 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
Symptoms of Fe deficiency
-interveninal chlorosis
Soluble _____ supplementation will often correct deficiencies
chelate
- 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 systems
- Solubility increases w/ pH increases
- Organic matter decomposition aids Mn solubility
Toxicity, Problem soils
- Toxic concentrations more common than any other micro nutrient (soils may naturally have high Mn, conditions can cause Mn toxicity easily)
- High Mn soils may show toxicities at pH just below 6, excessive water, or even at high pH’s
Toxicity, Problem soils of Mn somewhat common in
Hawaii
treatment w/ lime and gypsum
Symptoms of Mn deficiencies
chlorosis of younger leaves
Soil Mo
- exists and needed in minute amounts
- important for enzyme function and N fixation
- Strongly adsorbed, yet soluble
Mo: Problems soils and susceptible plants
-deficiencies common in acid/sandy soils
-susceptible crops:
soybeans, alfalfa, corn, tomatoes, etc.
Mo: Toxicities usually only show up in grazing animals
- Known to happen on soils w/ high organic matter and neutral/alkaline pH
- Problem related to imbalances of Cu and 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 and susceptible plants: Deficiencies:
- occur in basic soils, limed soils, cropping with high Zn demand crops (corn, fruits, etc.)
- most expected at high soil pH
cotton responds to Zn supplementation in SW US
Symptoms of Zn deficiencies
- interveinal chlorosis in young and old leaves
- reduced stem elongation
- bunched leaves
- small, thick leaves
- early defoliation
Zn amendments
- ZnSO4 most commonly used to cure deficiencies
- Foliar application for treatment
- Soil application if problem is anticipated
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
Na
- essential for desert species to maintain turgor
- growers usually reluctant to add
V (Vanadium)
- essential for algae, microbes
- may substitute for Mo en enzyme activation
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
