Unit 8: Plant Nutrients Chapter 9

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 Secondary Nutrients Micronutrients 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 solubility P 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 Phosphates in Anaerobic Soils 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 Organic Soil P Works out good for rice growers 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

The P Problem The more favorable conditions are for microbe decomposition, > available 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 Phosphate fertilizer effectiveness ~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 Maximizing P efficiency 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 N-P Fertilizers 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 K Losses & Gains 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 Soluble K losses 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 Managing 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 Plant Need for 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 Ca Fertilizers 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 Plant Need for 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 Mg Mg Fertilizers Dolomitic limestone Can also use Mg salts 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 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 Sulfur Fertilizers or Amendments 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: Deficiencies: 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 Cl Amendments 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 enzymes Very 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 Less common than other micro deficiencies 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 Cu Amendments & Their Use 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 Problem Soils, Susceptible Plants, & Fe Amendments 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 systems Solubility increases w/ pH increases Organic 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 amounts Important for enzyme function & N fixation Strongly 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 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

Assignment