Soil Fertility and Plant Nutrition 2, Course Module - University of Idaho

Soil FertilityandPlant Nutrition 2Soils 446-02Course ModuleLecture Note Packet

Purpose of CourseSoil Fertility and Plant Nutrition 2 is a short course consisting of 15lectures. This short course covers the elements phosphorus, potassium,sulfur, calcium, magnesium, boron, chlorine, copper, iron, manganese,molybdenum, nickel, and zinc. This course emphasizes principles of soilfertility management and the availability of plant nutrients and theirrelationship to plant growth and fertilization practices.This short course is the second in a series of six modules in soil fertilityand plant nutrition offered by the University of Idaho. Your comments on thiscourse will be appreciated.

Outline of CourseSoils 446Module 2: Soil Fertility and Plant Nutrition 2Lesson 1: Introduction; Fertilizer PlacementLesson 2: PhosphorusLesson 3: PhosphorusLesson 4: PhosphorusLesson 5: PotassiumLesson 6: SulfurLesson 7: Potassium FertilizersNote: there are no Lessons 8 and 9Lesson 10: Calcium; MagnesiumLesson 11: BoronLesson 12: ZincLesson 13: Molybdenum; ChlorineLesson 14: Copper, IronLesson 15: Iron; Manganese

Table of ContentsPage #Lesson 1: Introduction; Fertilizer Placement .......................................................... 7A. Nutrient Coverage ........................................................................................ 7B. Basic Methods of Solid Fertilizer Application .............................................. 8Lesson 2: Phosphorus ........................................................................................... 13A. General Information about Phosphorus .................................................... 13B. The P Cycle in Soils ................................................................................... 14C. P Reactions in Soils ................................................................................... 15D. Is P an Environmental Problem? ............................................................... 19E. Organic P .................................................................................................... 19Lesson 3: Phosphorus ........................................................................................... 21F. Historical and Current Phosphorus Use .................................................... 21G. Fertilizer Calculations and Terminilogy...................................................... 23H. Phosphate Fertilizers .................................................................................. 25Lesson 4: Phosphorus ........................................................................................... 32I. Phosphorus Uptake by Plants.................................................................... 32J. Using P Fertilizers ...................................................................................... 34K. Soil Testing ................................................................................................. 38Lesson 5: Potassium.............................................................................................. 41A. General Information about Potassium ....................................................... 41B. Potassium in Soils ...................................................................................... 42C. Plant and Soil Potassium Relationships.................................................... 46D. Potassium in the Pacific Northwest ........................................................... 48Lesson 6: Sulfur ..................................................................................................... 50A. General Information about Sulfur ............................................................... 50B. The Sulfur Cycle .......................................................................................... 52C. Sulfur Retention and Transformations in Soils.......................................... 54D. Deficiencies of Sulfur ................................................................................. 56E. Fertilizer Recommendations for S in the PNW ......................................... 57Lesson 7: Potassium and Sulfur Fertilizers .......................................................... 59A. Historical and Current K Use ..................................................................... 59B. K Fertilizer Calculations ............................................................................. 60C. Potassium Fertilizers .................................................................................. 61D. Sulfur Fertilizers ......................................................................................... 62E. Fertilizer Calculations................................................................................. 66

Page #Note: There are no Lessons 8 and 9Lesson 10: Calcium; Magnesium .......................................................................... 71A. Calcium and Magnesium ............................................................................ 71B. General Comments .................................................................................... 73C. Soil and Plant Ca and Mg .......................................................................... 73D. Specifics — Calcium and Magnesium ....................................................... 74E. Calcium and Magnesium Fertilizers .......................................................... 76F. Calcium and Magnesium as Lime Materials ............................................. 77Lesson 11: Boron ................................................................................................... 80A. Boron Introduction ...................................................................................... 80B. Factors Affecting Crop Response to Boron............................................... 81C. Corrections of Boron Deficiencies in Field Situations .............................. 82D. Boron Fertilizer Sources ............................................................................ 83E. Boron Fertilizer Applications ...................................................................... 84F. Idaho Recommendations for Boron ........................................................... 85Lesson 12: Zinc ...................................................................................................... 86A. Zinc Introduction ......................................................................................... 86B. Factors Affecting Crop Response to Zinc.................................................. 87C. Corrections of Zinc Deficiencies in Field Situations ................................. 88D. Zinc Fertilizer Sources ............................................................................... 88E. Zinc Fertilizer Applications ......................................................................... 89F. Idaho Recommendations for Zinc .............................................................. 91Lesson 13: Molybdenum; Chlorine........................................................................ 92A. Molybdenum Introduction........................................................................... 92B. Factor Affecting Crop Response to Molybdenum ..................................... 93C. Correction of Molybdenum Deficiencies in Field Situations ..................... 93D. Molybdenum Fertilizer Sources ................................................................. 94E. Molybdenum Fertilizer Applications ........................................................... 95F. Idaho Recommendations for Molybdenum................................................ 97A. Forms and Function of Chlorine ................................................................. 97B. Factors Affecting Crop Response to Chlorine ........................................... 98C. Correction of Chlorine Deficiencies in Field Situations ............................ 98Lesson 14: Copper; Iron ........................................................................................ 99A. Copper Introduction..................................................................................... 99B. Factors Affecting Crop Response to Copper .......................................... 100C. Correction of Copper Deficiencies in Field Situations ............................ 101D. Copper Fertilizer Sources ........................................................................ 101E. Copper Fertilizer Applications .................................................................. 102F. Idaho Recommendations for Copper....................................................... 104

Page #Lesson 14: Copper; Iron (cont.)A. Iron Introduction ........................................................................................ 105B. Factors Affecting Crop Response to Iron ................................................ 105Lesson 15: Iron; Manganese ............................................................................... 107C. Correction of Iron Deficiencies in Field Situations .................................. 107D. Iron Fertilizer Sources .............................................................................. 107E. Iron Fertilizers Applications ...................................................................... 108F. Idaho Recommendations for Iron ............................................................ 109A. Manganese Introduction........................................................................... 110B. Factors Affecting Crop Response to Manganese ................................... 110C. Correction of Manganese Deficiencies in Field Situations ..................... 112D. Manganese Fertilizer Sources ................................................................. 113E. Manganese Fertilizer Applications........................................................... 114F. Idaho Recommendations for Manganese ............................................... 115Appendix MaterialsCIS 757 Fertilizer PlacementPNW 276 Current Nutrient Status of Soils in Idaho, Oregon, and WashingtonCIS 165 Sulfur Fertilizer Improves Yield and Quality of Soft White WinterWheatCIS 1085 Boron in IdahoCIS 1088 Zinc in IdahoCIS 1087 Molybdenum in IdahoCIS 682 Copper in Idaho

LESSON 1IntroductionFertilizer PlacementA. Nutrient Coverageu14 soil derived essential nutrientsu N covered in 446-01uThe other 13 covered in this classMACROSP —K —S —Ca —Mg —MICROSB —Cl —Cu —Fe —Mn —Mo —

Zn —Ni —B. Basic Methods of Solid Fertilizer Application1. Broadcast Method2. Pup-Up3. Banding1. Broadcast Methodsa. Broadcast topdressb. Broadcast incorporate(moldboard plow)c. Broadcast incorporate(chisel plow)d. Broadcast incorporate(disk)

uuuEach method of broadcast is an adequate one for theapplication of some nutrientsEach method is poor for some of the plant nutrients appliesA majority of fertilizer applied in the U.S. is put on as broadcastapplicationsBroadcast, preplant (PP) applications of solid fertilizers hasbecome very popular in recent years due to:1. The desire to lessen the time involved in handling fertilizers2.3. To reduce fertilizer injury to seedlings4. Development of bulk blends to put a lot of material on at onetimeBiggest problems with broadcast applications are:1.2.The following plant nutrients are generally broadcast:1.2.3.4.

5.6.7.8.Separate Cases:9. Potassium — generally applied either way (broadcast or band)broadcast —banding — preferred in soils contianing a lot of vermiculiteand/or illite — where K fixation occursFor K — in most soils it does not make any difference!!10.Phosphorus — broadcast only when you have moderate to highP levels already in the soil — at soil pHs 5.5 to 6.5Generally not boradcast:11.12.13.14.2. Pop-upuurefers to the placement of small amounts of nutrients in directseed contactusually for row crops

Pop-upuumore common in colder climatesP gives plant vigor in cold soils3. Band FertilizersuBand placement of nutrients here is intended to mean:uthe placement of the fertilizer in bands on one or both sidesof the seeds or seedlingsa. Band — Single Sideb. Band — Double Sidec. Band — Below Seedd. Band — Split Boot

uuFertilizer is place away from the seed to prevent salt damageFertilizer is commonly placed at a depth greater than the seedbecause:1. Prevents salt damage2. Avoids weed germinationuBand placement of nutrients is popular forP, K, Some MicrosTOPDRESS — Imply post-emergence applicationsSIDEDRESS — Post-emergence usually surface band

LESSON 2PHOSPHORUSA. General Information about PhosphorusuuMacronutrientPlant Available Forms:–––uFunction in the PlantPPuMobility in Plant–uConcentration in Plants:––

uDeficiency SymptomsPPB. The Phosphorus Cycle in SoilsuuuSee diagram of P cycle in your text for more details (Havlinet al.)

C.Phosphorus Reactions in Soils1. Basic ConceptsIn the soil:Plant Available PNon-Available PSoil Solution P Labile P Non-labile PNot Plant Available2. Basic Terms and DefinitionsSOIL SOLUTION P — includes H 2PO 4-, HPO 42-, PO 43-; consideredplant available P; approximately 1% of the P in the soilLABILE P — not plant available; consists of the more soluble Al-Pand Ca-P compounds in the soil; replaces soil solution P asplant uptake occursNON-LABILE P — not plant available; consists of very insolubleCa-P, Al-P, and Fe-P compounds; can replace labile P as it istransformed to soil solution P

P Fixation — any change that fertilizer P undergoes that lessensits availability to plantsP Adsorption — retention of P at the surface of somethingP Absorption — retention within a solid phase (plants absorb P)Sorption — P solubility has been reduced (no mechanism implied)3. How is P Retained in Soils?uclays; the higher the percentage clay in the soil the greater theP retention–– the more clay you haveP ACID SOILS — have Al and FeAdd Al +++Add FeP ALKALINE SOILS —Add Ca ++P NEUTRAL TO SLIGHTLY ACID SOILS (pH 6.0-7.2)––

Relation of soil pH to labile and non-labile P compounds in thesoil:Where is max P availability?– where most of the P is in the labile form — pH 5.5–6.5–

Relationship of soil pH to labile and non-labile P in soils:Soil pH Labile P Non-labile P-----------------------%-----------------------4 < 20 > 8056789 < 10 > 90Initial P in soils:---------------------------------- P form ----------------------------------Soil pH Fe-P Al-P(N) Al-P(L) Ca-P(L) Ca-P(N) Apatite---------------------------------- ppm P -----------------------------------Mollisol 6.2 – 4 12 118 170 16Aridisol 8.1 – – – 80 370 180Ultisol 5.6 20 85 102 30 26 –Ultisol 4.8 80 71 15 1 – –Now add 300 lbs PMollisol 6.2 –Aridisol 8.1 – – –Ultisol 5.6 –Ultisol 4.8 – –What does the table say?– When you add fertilizer P —– Where pH values are favorable —

D.Is P an Environmental Problem?a. Human Health–b. Groundwater––c. Surface waters– major problem —– erosion of soils puts P into surface water bodies–––E. Organic PhosphorusuuOrganic P is a major source of P in many soils; may constituteup to 50% of P in many USA soilsOrganic P is mineralized by microbes into the plant availableform; once made available is subject to fixation processesin the soil

u––

LESSON 3PHOSPHORUSF. Historical and Current Phosphorus UseuMost of the P produced in the world is used in agricultureu Worldwide P fertilizer use has grown dramatically since 1960------P fertilizer use (tons)------Year USA World total1960 2,572,000 9,970,0001980 5,431,000 31,700,0001999 4,345,000 31,018,000–

–– Major users are: China (8.8 m tons), USA (4.3 m tons), India(2.9 m tons), Brazil (1.5 m tons), France (1.0 m tons)uP fertilizer production is concentrated in four regions of theworld:–– most P in the USA is produced in 5 states

uFuture Phosphorus MaterialsCountry*** Reserves* Resources**-------------------- tons --------------------Morocco 5,900,000,000 21,000,000,000USAOtherWorld total 11,000,000,000 33,000,000,000* Reserves are based on a production cost of $36.00 per ton** Resources are based on a production cost of $90.00 per ton*** World has reserves for 80 years, resources for 240 yearsG. Fertilizer Calculations and Terminology1. Calculation of P Content in Fertilizersa. N - P - KuHistorically, the P content of fertilizers has been expressedin terms of its P 2O 5equivalentuub. Conversion FactorsuTo convert %P to %P 2O 5and %P 2O 5to %P:

uFor instance, if we wanted to know the %P 2O 5in dicalciumphosphate (CaHPO 4) we would first calculate the %P:Ca = 40; H = 1; 0 = 16; P = 31

2. Phosphate Fertilizer TechnologyuThe solubility of P in different carriers (fertilizers) is variable.Therefore certain terms should be understood:Water Soluble Phosphorus — fertilizer extracted with water;expressed as a percentage by weight of sampleCitrate Soluble Phosphorus — residue from water soluble PCitrate Insoluble Phosphorus — the residue remaining fromthe water and citrate extraction is analyzed. Theamount of P remaining is termed citrate-insolubleAvailable Phosphorus —Example: 0 – 18 – 0 — Rock phosphateTotal Phosphorus —H.Phosphate FertilizersuThe original sources of P fertilizers were bones and sewagewastes from ancient cities

u––1. Organic P Fertilizer MaterialsuThe organic P fertilizer materials used in the USA consist of:–––uManures are becoming a more important source of PDairy cattleSwinePoultryHorsesSludge (municipal)% P (average)2. Inorganic P FertilizersuAlmost all commercial P fertilizers are made from rockphosphate

Phosphorus Fertilizer Manufacture:a. Rock phosphateuuRock phosphate by itself is not a good fertilizer. It must betreated with chemicals to break Ca-P bonds and render thecontained P more plant available

. Acid Treated PhosphatesuSulfuric AciduPhosphoric Acid - manufactured by treating rockphosphate with sulfuric acid (high concentration)P Rock phosphate + sulfuric acid (high concentration)P White or Furnace Acid––––Phosphoric acid contains:17 – 24% PP H 3PO 4can be used directly in calcareous soils byinjection or added to irrigation water

c. Calcium Orthophosphates — traditional P fertilizersuOrdinary Superphosphate (OSP)– made by reacting– known as OSP (ordinary superphosphate) or NSP (normalsuperphosphate) or SSP (single superphosphate)–uTriple Superphosphate (TSP)– made by reacting––d. Ammonium Phosphatesuu Are completely water soluble (100% available P)

uMonoammonium phosphate (MAP)–––uDiammonium phosphate (DAP)–––––e. Ammonium Polyphosphates (APP)–– 100% available P––

–f. Acidity– Liquid APP can be reacted with urea to produce ureaammoniumphosphate (UAP)– UAP is a solid and has a common grade of 28 – 12 – 0–––

LESSON 4PHOSPHORUSI. Phosphorus Uptake by Plants1. Yield ResponseOne can expect a yield response to P when:uu2. Crop QualityuuThere is frequently a quality effect in addition to the yieldincrease which has an influence on the dollar return for thecropCorn data from Illinois: There was a definite improvement inquality following P application in Illinois. This improvementcame about as a result of earlier crop maturityP 2O 5Rate Moisture in Grain Dockageat Harvestlb/acre % $/bu080Cost of P per acre = $14.40Quality of grain per acre = $33.00

3. Moisturea. General AspectsuAdequate fertility including P helps crops use moistureefficiently. The following aspects are affected by P:––––b. Soil Moisture and AlfalfauComments:– Alfalfa is more efficient at using water when adequate Pis applied–

J. Using Phosphorus Fertilizersu When P fertilizers are added to soils fixation takes place in a 2stage process:Phase A —Phase B —uWant to reduce the speed of fixationOptions:PP

1. Availability of P Fertilizersa. Water Solubility and Granule SizeBAND APPLICATIONSWater Sol P (%)----------Fertilizer Material----------OSP (-6 +14)* OSP (-35)**Wheat dry weight (grams)70 7.34 7.4057 7.19 7.0653 7.00 6.5132 5.72 4.9814 4.49 4.51No P 2.93 2.93* -6 +14 means the fertilizer material passes through a 6 mesh sieve butis held by a 14 mesh sieve** -35 means the fertilizer material passes through a 35 mesh sieveLSD = 0.51 for yield differenceTable meaning:uu

BROADCAST INCORPORATED APPLICATIONSWater Sol P (%)----------Fertilizer Material----------OSP (-6 +14)* OSP (-35)**Wheat dry weight (grams)70 4.77 2.9657 4.37 2.4753 3.00 2.2032 2.87 1.6714 2.40 1.70No P 1.30 1.30LSD = 1.40Table meaning:uuu2. Temperature and PlacementPlacement Regimes–––

Wheat yields as a function of P placement:---------------Placement---------------Banded BandedLocation Broadcast below seed with seed LSD---------------yield bu/ac---------------MoscowSandpoint (colder)Table comments:PPP

K. Soil Testing — PhosphorusA lot of soil test correlation research has been done with PSOIL pH FePO 4AlPO 4CaPO 4Apatite34567891011uuSoil test extractants for P differ because of the form of P held insoilsIn alkaline soils most P is held as Ca-P so you want:uIn acid soils most P is held as Al-P so you want:

uIn neutral pH soils P is held as both Al-P and Ca-P so you want:Common phosphorus soil tests:Soil testBray IBray IIExtractants0.025N HCl + 0.03N NH 4F0.1N HCl + 0.03N NH 4FNorth Carolina 0.05N HCl + 0.025N H 2SO 4(double acid)Troug 0.002N H 2SO 4Citric AcidEngerMorgan1% citric acid0.02N Ca-lactate + 0.02N HCl0.54N HOAc + 0.7N NaOAcOlsen 0.5M NaHCO 3Phosphorus tests in the Pacific Northwest:Acid soils:PPNuetral/alkaline soils:P

P research needs:1. Standardization in region for wheat:Soil testNaOAcNaHCO 3Critical P level4 ppm10 ppm2. Correlation between P values for different soil tests3. Development of a better (universal) soil test4. More international standardizaitonThe Idaho Situation:

LESSON 5POTASSIUMA.General Information about PotassiumuuMacronutrientPlant Available Form–uMobility in Plant–uFunction in the Plant––– energy relations–uPlant Content– average:– range:

uDeficiency SymptomsP spots, yellowish-brownish color along margins of olderleavesPPotassium uptake by plants:Crop Yield K (lbs/acre)Corn120 bu200 buWheat100 buPotatoes600 cwtAlfalfa6 tonsB. Potassium in Soils1. Content in SoilsuOn an elemental basis, many soils contain large amounts ofpotassiumuuIn the USA: 0.2 – 1.8% K– Western USA– Southcentral States– Southeast States– Northeast States

2. Chemical Forms of Potassium in SoilsMineral K non-exchangeable K exchangeable K soil soln. K–P consists of 90 to 98% of the K in the soil– exchangeable K and soil solution K are plant available formsof KP consists of 2 to 10% of the K in the soil3. Losses of Potassium from Soilsa. Crop Removalub. Leaching LossesuThe annual loss of N, P, and K in drainage water from columnsof fertilized and unfertilized sandy soils in South Carolina:--------------------Annual Loss--------------------Treatment Nitrogen Phosphorus Potassium--------------------------kg/ha-------------------------FertilizedUnfertilizedProportion ofadded nutrientlost 56% 1% 44%

c. ErosionuuPotassium losses are seldom taken as seriously as N lossesbecause of the differences within the soil profileSoil profile distribution of N, P and K:

4. Weathering of Unavailable Potassium in Soilsa. Mineralogical Formsi. Feldsparsii. MicaMuscovite–Biotite–iii. Clay mica (illite)5. Potassium FixationuuSame as ammonium fixationPhysical process­­u

Ca ++ Mg ++ K + Al +++ 2:1 clayC. Plant and Soil Potassium Relationships1. Potassium Status Defined in Plant Availabilitya. Immediately Available–b. Moderately Available––c. Very Slowly Available–2. Management Practices to Reduce Leaching Lossesa. Amount and Nature of CECEase of Cation Release:1:1 clay

. Broadcasting vs Banding:Rules of thumb:––– Band in potential for K fixation–Keys:3 meq / 100g

D.Potassium in the Pacific Northwest1. Soil KuuuSee Map2. Soil Test ValuesExtractant:NaOAc ––NaHCO 3––Potassium fertilizer rates for winter wheat based on soil tests forboth sodium bicarbonate and sodium acetate.----------Soil Test K ----------Apply (lbs/acre)Sodium acetate Sodium bicarbonate K 2O K------------ppm K ------------0 to 35 0 to 4035 to 75 40 to 70over 75 over 70

LESSON 6SULFURA.General Information about Sulfur1. Forms and Function of Sulfura. Function of Sulfur in Plantsu–––uub. Plant Available Forms of Sulfuruuc. Sulfur Mobility in Plantsuu

ud. Sulfur Content in Plantsuue. Sulfur Deficiency Symptoms in Plants:uPlants turn yellow-greenuuf. Sulfur Levels in PNW SoilsuWidely deficient in soils of the Pacific Northwestg. Soil Testing for SuPoor soil test; must use in combination with other methods ofdiagnosisSulfur uptake by common crops:Crop Yield S (lbs/acre)Corn120 bu200 bu

WheatPotatoesAlfalfa100 bu600 cwt6 tonsB.The Sulfur CycleuuChemical phaseMicrobiological phase(from Soil Fertility and Fertilizers by Havlin, Beaton, Tisdale, andNelson)uu1. Sources of Sulfur in Soilsa. Igneous Rocksu

ub. AtmosphereuuSO 2can be directly absorbed by plant leavesuc. Organic MatteruOrganic matter is generally the largest source of soils intemperate regionsud. Secondary MineralsuuuuC.Sulfur Retention and Transformations in Soils1. Organic SulfurMineralization — conversion of unavailable S (organic S) to SO 42-

uImmobilization — conversion of plant available S to organic SuuuuSulfur oxidation and mineralization processes are carriedout by microbes2. S Transformationsa. Sulfur MineralizationuuDRY — Microbes die and add bodies to OMWET — DEAD bodies mineralized

. SO 42-udominant form of plant available S in soilsu SO 42-u SO 42-c. Sulfate Retention in SoilsAcid soils:uPuif no AECAlkaline soils:

uD.Deficiencies of Sulfur1. SoilsThe following conditions create a tendency for deficiencies ofsulfur:uucoarse textured soilsuuulow concentration of industry (lack of air pollution)uP The more of the above tendencies — the greater the chance ofsulfur deficienciesuThe Idaho situation:llllLow organic matter in southern IdahoulDeficiencies found throughout the state — except in areas ofthe south where irrigation water contains plenty of sulfur

and in forests which are not fertilized with nitrogen2. PlantsSoil N:S =Plant N:S =Amino acids —uuIf S is limiting in the soil, plants can not use high rates of NE. Fertilizer Recommendations for Sulfur in the PNW1. Soil Test Correlation DatauYield response data (correlation) in the PNW is pooru2. Will Sulfur Additions Improve Yields?u Yes —uS additions may improve crop quality (see wheat qualityhandout)3. Sulfur Rates to Apply:

uSoil test values below 10 ppm:PuMaximum rates of S to apply:P4. Frequency of S Soil TestinguuTake soil samples to the effective rooting depth of cropuLESSON 7

POTASSIUM AND SULFUR FERTILIZERSA.Historical and Current K UseuOver 98% of the K produced in the world is used in agricultureu------K fertilizer use (tons)------Year USA World total1960 2,153,300 8,710,0001980 6,245,100 24,054,0001999 5,015,800 21,110,000– K use peaked in the USA in 1981 (6,319,500 tons)–– Major users are: USA (4.9 m tons), China (3.1 m tons), Brazil(1.7 m tons), France (1.5 m tons), India (1.2 m tons)uPotassium fertilizer production is concentrated in 55 mines in

just a few countries:–– in North America most K is produced in SaskatoonuFuture Potassium Materials:Country Reserves Resources---------------------- tons ------------------------Canada 4,500,000,000 10,500,000,000Russia/Belarus 2,600,000,000 3,400,000,000World total 8,000,000,000 17,000,000,000B. Potassium Fertilizer Calculations1. N - P - Kuu% K ¹ % K 2O2. Conversion Factors

u To convert % K to % K 2O and % K 2O to % K:% K% K 2OC.Potassium Fertilizers1. Potassium Chloride (KCl)––– also known as muriate of potash– > 85% of K sold in the USA is KCl––– comes primarily from Canada2. Potassium Sulfate (K 2SO 4)–––– also known as sulfate of potash–

–– more expensive than KCl3. Organic K Sources– Animal wastes (0.2 – 2% K)––4. Other Inorganic K Sources– Potassium nitrate (KNO 3)P– Potassium magnesium sulfate (K 2SO 4l MgSO 4)PD.Sulfur Fertilizers1. The PastuuTraditionally:

OSPAmmonium SPuNewer High Analysis Materials:MAPTSP2. Modern Sources:uSupply sulfur because of need; nutrient is not a give-awayanymorea. Ammonium Sulfate (NH 4) 2SO 4––– major S source–b. Ammonium phosphate — ammonium sulfate

––– common source–c. Gypsum CaSO 4l XH 2O––– S. Idaho– N. Idahod. Elemental sulfur– an unavailable form of S––e. Sulfur coated urea (SCU)

––– S is elemental Sf. Urea-ammonium sulfate––g. Ammonium nitrate-sulfate–– two forms of N (NH 4, NO 3)E. Fertilizer Calculations

Sample Problems:1. Formulate 3 tons (6,000 lbs) of a 0-0-25 fertilizer using thefollowing sources:a. Potassium source: KClb. Potassium source: K 2SO 42. Formulate 2 tons of a 10-0-10 fertilizer. Your fertilizer sources

are KCl and urea:3. Formulate 5 tons of a 12-6-8 fertilizer using urea, triplesuperphosphate, and potassium sulfate:4. Formulate 4 tons of a 20-0-0-8 fertilizer using ammonium sulfate

and urea:5. Formulate 5 tons of a 6-3-10-2 fertilizer using 16-20-0-15,0-44-0, 34-0-0, and 0-0-60:6. Formulate 3 tons of a 10-10-10-5 fertilizer using urea,

ammonium sulfate, potassium chloride, and triplesuperphosphate:7. Formulate 6 tons of a 10-0-25-4 fertilizer using ammoniumnitrate, potassium chloride, and potassium sulfate:8. Formulate 5 tons of a 10-10-0-4 fertilizer using monoammonium

phosphate, ammonium sulfate, and urea:

LESSON 10CalciumMagnesiumA. Calcium and Magnesium1. Forms and Functions of Ca and Mga. FunctionCALCIUM:uuuMAGNESIUM:ub. Plant Available FormsCALCIUM:uMAGNESIUM:uc. Mobility in PlantsCa –Mg –

d. Content in PlantsCa ––Mg––e. Deficiency Symptoms in PlantsCALCIUM:uuMAGNESIUM:uuf. Ca and Mg Levels in PNW SoilsCALCIUM:uNot a problemMAGNESIUM:uProblems are limited to low Mg levels in grass pasturesGRASS TETANY

CALCIUM AND MAGNESIUMPlant uptakeCorn Yield Ca Mglbs/acreCornWheatPotatoesAlfalfa120 bu200 bu100 bu600 cwt6 tonsB.General CommentsCa ++ and Mg ++ in the soil solution can be:1. lost in drainage water2. absorbed by microbes3. absorbed by plants4. adsorbed onto surrounding clay particles5. repreceipitated as a secondary Ca ++ and/or Mg ++ compoundC.Soil and Plant Ca and Mg1. Origin and forms of Calciuma. Origin in Rocks and Mineralsuuuuu

. Availabilityu Soil solution Ca ++u Exchangeable Ca ++2. Origin and Forms of Magnesiuma. Origin in Rocks and Mineralsuuuuub. Availabilityu Soil solution Mg ++u Exchangeable Mg ++D.Specifics — Calcium and Magnesium1. CALCIUMuuCalcium is rarely limiting crop growth in the Western USACalcium content of arid aoils is high — high levels of:u CaCO 3u CaSO 4uThe only place we have Ca problems is where the soils are veryacid (Al +++ crowds out Ca ++ on CEC)

uCalcium should occupy at least 15% of the CEC sites on clays(In Idaho, Ca generally occupies at least 85% of the sites)2. MAGNESIUMuuMagnesium is generally not limiting crop production in thePacific NorthwestPROBLEMS:GRASS TETANY –Forage Protein Content –Legumes –

E. Calcium and Magnesium Fertilizers1. CALCIUMuCalcium nitrateuCalcium cyanimideuPhosphate rockuGypsumuLime2. MAGNESIUMuMagnesium sulfateuMagnesium-Ammonium phosphate

uPotassium-Magnesium sulfateuMagnesium oxideuDolomiteF. Calcium and Magnesium as Lime MaterialsuuCa and Mg are most often applied as lime materials to raise soilpH valuesCommon lime materials include:Lime Material Quality(1) Chemical Composition(2) Particle Size

State REgulationsIdaho:Washington:Lime Requirement TestsIdaho Lime Requirement Test:

Washington:Oregon:When to request a lime requirement test:uuu

LESSON 11BoronA.Boron Introduction(Reading Assignment: Current Information SeriesNo. 1085, Boron in Idaho)1. Forms and Function of Borona. Function of Boron in Plantsuuub. Plant Available Forms of Boronc. Boron Mobility in Plantsd. Boron Content in Plantse. Boron Deficiency Symptoms in Plants

f. Boron Levels in PNW SoilsB.Factors Affecting Crop Response to Boron1. Soil pHuu2. Soil Moistureu3. Soil Organic MatteruSoil OM weathers to release plant available boronu4. Soil TextureuCoarse textured soils tend to be deficient because of leachingprocesses5. Soil Reservesu

uuC.Correction of Boron Deficiencies in Field SituationsuuuB deficiencies most often occur on coarse textured soils (lowOM), and in humid areas where precipitation has leached Bout of the soil profilePlants that are members of the grass family have a lower Brequirement than other plant species; monocots need onlyabout 25% as much B as do dicotsBoron deficiencies are most common on alfalfa and on certainroot and cruciferous crops such as turnips, cabbage,cauliflower, and rutabagasuuuBoron deficiencies in Idaho are widespread

D.Boron Fertilizer SourcesuInorganic sources of BuBoron fertilizer sources include:u Borated gypsum —u Borax —u Boric acid —u Solubor —u Boron frits —u Fertilizer borate 46 or 65 —

E. Soil Applications of Boron1. Soil ApplicationsuuAn application rate of 1 to 3 lbs B/acre is needed for soiltreatments of legumes and certain root and cruciferous rootcrops, while lower rates of 0.5 to 1 lb B/acre are needed forother cropsPlacement:uCropsuu2. Foliar Boron ApplicationsuPopular on tree fruitsuuProblem with foliar applications on row crops is a lack of Bmobility in plants; requiring repeated applications duringthe growing season for satisfactory resultsu

uFor a B deficient crop the need is often 0.5 lb B/acre; the 0.5 lbshould be divided by the number of times it will be appliedover the season to get the correct rate for each application3. Boron Seed Treatmentsu NEVER ! ! !4. Residual Boron Fertilization EffectsuPersistence determined by soil type, form of B applied, andclimate; from 1 to 5 years5. Boron Toxicity ProblemsuuuResults when plants take up too much BNarrow range between deficiency and toxicityApply B at low rates — after needs established by soil testingF. Idaho Recommendations for Boron1. Critical Soil Test Level2. Soil Test Extractantsu3. RecommendationsuSoil test every 3 years when a B demanding crop is in therotationu

LESSON 12ZincA.Zinc Introduction(Reading Assignment: Current Information SeriesNo. 1088, Zinc in Idaho)1. Forms and Function of Zinca. Function of Zinc in Plantsuuub. Plant Available Forms of Zincc. Zinc Mobility in Plantsd. Zinc Content in Plantse. Zinc Deficiency Symptoms in Plantsf. Zinc Levels in PNW Soils

B.Factors Affecting Crop Response to Zinc1. Soil pHuMost Zn deficiencies occur in high pH soiluuLow pH soils usually contain adequate levels of Zn2. Soil Organic Matteruu3. Adsorption in Calcareous SoilsuAffected by level of:uuuMagnesiteDolomiteCalciteuZn can replace Mg in the lattice of magnesite and dolomite4. Climateu

uIncreased temperature and daylength will often cause Znsymptoms to disappear5. Soil Phosphorus LeveluuHigh levels of soil P tend to promote Zn deficienciesWhen P:Zn ratios in plants are wide, deficiency symptomssometimes develop6. Soil ReservesuuC.Correction of Zinc Deficiencies in Field SituationsuuZn deficiencies have been recognized for a long timeProblems: low OM soils, calcareous soils, soils leveled forirrigationD.Zinc Fertilizer SourcesuuuBoth organic and inorganic sources of Zn can be used tocorrect deficienciesINORGANICORGANIC

uZn sources include:u Zinc sulfate —u Zinc chelates —u Zinc frits —u Zinc oxide —u Other sources —E. Soil Applications of Zinc1. Soil Applications of ZincuSoil applications are by far the most common and successfulmethods of correcting deficiencies for most crops

uZinc placement:2. Foliar Zinc ApplicationsuTemporary — only use in emergenciesuu3. Zinc Seed TreatmentsuNo proven success; most work with beans4. Residual EffectsuSoil applications of 5 to 10 lbs/acre last at least 3 years;probably more than 5 years

5. Zinc Toxicity ProblemsuF. Idaho Recommendations for Zinc1. Critical Soil Test Level2. RecommendationsuuuApplication rates range from 2 to 25 lbs/acre depending on thesituation and the cropIn Idaho, recommendation rates typically range from 5 to 10 lbsZn/acre for high Zn demanding cropsMany Idaho crops are not responsive to Zn additionsu

LESSON 13MolybdenumChlorineA.Molybdenum Introduction(Reading Assignment: Current Information SeriesNo. 1087, Molybdenum in Idaho)1. Forms and Function of Molybdenuma. Function of Molybdenum in Plantsuuub. Plant Available Form of Moc. Molybdenum Mobility in Plantsd. Molybdenum Content in Plants

e. Molybdenum Deficiency Symptoms in Plantsf. Molybdenum Levels in PNW SoilsB.Factors Affecting Crop Response to Molybdenum1. Soil pHuuMo availability is pH dependant; greatest availability in high pHsoils2. Soil TextureuSince Mo is mobile in soils, sandy soils, or areas with highprecipitation may tend toward Mo deficiencies3. Soil ReservesuDeficiencies can exist on leached sands, acid Inceptisols,Spodosols, and HistosolsC.Correction of Molybdenum Deficiencies in FieldSituationsuMo deficiencies are found worldwide; especially in Australia,New Zealand, and the USA

uuMo deficiencies are most often observed on legumes since Mois required for nitrogen fixationCommonly deficient crops in Idaho include:uuuuMolybdenum deficient areas in Idaho include:D.Molybdenum Fertilizer MaterialsuuuInorganic sources can be used to correct Mo deficienciesOrganic sources are not usedInorganic Mo sources include:u Sodium molybdate —u Ammonium molybdate —

u Molybdenum trioxide —u Molybdenum frits —u Molybdenum sulfide —E. Soil Applications of Molybdenum1. Soil Applications of MolybdenumuuThe quantity of Mo needed to correct deficiencies is very small(maximum of 1 lb Mo/acre)Difficult to distribute such a small amount over an acre2. Foliar Applications of Molybdenumuuu

3. Molybdenum Seed TreatmentsuuMost common method of correcting Mo problems in soilsCan be applied with Rhizobium inoculumu4. Residual Fertilizer EffectsuuSoil/seed application may last several years (5 or more) inneutral to alkaline soilsAcid soils may require applications every 2 to 4 years5. Molybdenum Toxicity Problemsuuu Animals eating plants lack Mo tolerance MOLYBDENOSISCu deficiency

F. Idaho Recommendations for Molybdenum1. Critical Soil Test Level2. RecommendationuChlorineA.Forms and Function of Chlorine1. Function of Chlorine in Plants2.`Plant Available Forms of Chlorine

B.Factors Affecting Crop Response to ChlorineuC.Correction of Chlorine Deficiencies in Field Situationsu

LESSON 14CopperIronA. Copper Introduction(Reading Assignment: Current Information SeriesNo. 682, Copper in Idaho)1. Forms and Function of Coppera. Function of Cu in Plantsub. Plant Available Form of Copperuc. Copper Mobility in Plantsd. Copper Content in Plantse. Copper Deficiency Symptoms in PlantsuuIndistinctDeficiencies appear in younger leaves firstf. Copper Levels in PNW Soils

B.Factors Affecting Crop Response to Copper1. Soil pHuuCu is more available in acid soils; however, Cu deficiencies arerarely observed on alkaline soilsConsequently, most deficiencies occur in low pH soils2. Soil Organic MatteruCu forms complexes with organic matter; these complexesreduce Cu availabilityu3. Competition with other MicronutrientsuSoils high in Fe ++ are often Cu deficient; antagonism4. Aluminum in the Soil SolutionuAl is competitive and will inhibit Cu uptakeu5. Soil Reservesu

uC.Correction of Copper Deficiencies in Field SituationsuCopper deficiencies have been associated with:1. soils high in organic matter, or2. highly weathered sandy mineral soilsu Peat soils are usually low in Cu ++30% OMuDeficiencies in various crops produce abnormal coloring,abnormal development, reduced fruit and grain quality, andreduced grain yieldD.Copper Fertilizer MaterialsuuBoth inorganic and organic sources of Cu can be used tocorrect deficienciesCommon sources include:u Copper sulfate —u Copper chelates —

u Copper frits —E. Copper Fertilizer Applications1. Soil Applications of CopperuuCu is more frequently soil applied than used as a foliar sprayInorganic sources — copper sulfate is the most commonlyused Cu sourceuApplication recommendations:u Organic sources —uuu2. Foliar Copper ApplicationsuBordeaux mixtures — contain copper sulfate and wererecognized to stimulate growth and yields of plants thatwere not related to the control of fungal diseasesu Cu foliar sprays —

uu Cu spray materials —u3. Copper Seed TreatmentsuuOccasional responses to seed applications of Cu have beenobserved — but these responses are uncommon and notreliableAvoid this type of treatment4. Residual Copper Fertilization EffectsuuUsually long lasting — up to 8 yearsDepending on rate and type of soil application5. Copper Toxicity ProblemsuToo many applications of Cu may lead to toxicity problemsIn Florida —In Australia —

Remedy —F. Idaho Recommendations for Copper1. Critical Soil Test Levelu2. Soil Test Extractantsu3. Recommendationsu High Organic Matter Soils: >8%uApply 3 to 5 lbs Cu/acre as a soil application; if organicmatter >25% raise the application rate to 5 to 8 lbs Cu/acreWheat:Wheat + High organic matter:

A.Iron Introduction1. Forms and Function of Irona. Function of Iron in Plantsuuub. Plant Available Form of Ironuc. Iron Mobility in Plantsud. Fe Content in Plantsue. Fe Deficiency Symptons in PlantsuuAppears first in younger leavesInterveinal chlorosisf. Fe Levels in PNW SoilsuB.Factors Affecting Crop Response to Iron1. Soil pHuuFe deficiencies are common in high pH soilsFe deficiencies also occur in very acid soils, where Fe and Mnantagonisms exist

2. Soil MoistureuExcess irrigation of calcareous soils can cause iron chlorosis;it is estimated that 50% of the Fe problems observed in Utahsoils could be prevented with better water management3. Soil AerationuPoor drainage promotes Fe availabilityu Fe +++ Fe ++4. Presence of BicarbonateuHCO 3in irrigation water induces Fe chlorosis. Water qualitydependantu HCO3 induces P solubility which interferes with Fenutrition5. Soil ReservesuLow levels of Fe are often found under the followingconditions:uuuu

LESSON 15IronManganeseC.Correction of Iron Deficiencies in Field SituationsuuCalcareous soils are most likely to be Fe deficientThere are many Fe sensitive crops. These crops include:uBeans, corn, sorghum, fruit trees, grasses, legumes, rice,nut trees, tomatoes, and many vegetablesuuFe deficiencies can be observed in the irrigated arid regions ofthe PNWIdaho problems include:uuuuD.Iron Fertilizer SourcesuuBoth inorganic and organic Fe fertilizer sources have beenusedFe sources include:u Ferrous sulfate —

u Ferric sulfate —u Iron chelates —u Iron frits —E. Iron Fertilizer Applications1. Soil Applications of IronuuuGreat variation in successInorganic sources have many problemsOrganic sources are better but costly2. Foliar Iron ApplicationsuAdvantages:1. Elimination of complicated soil reactions2.3.4. More rapid response to applicationuDisadvantages:1. Greater chance of toxicity2. Don’t correct soil problem3. Repeated applications may be necessary

3. Applications in Irrigation WateruUse same iron sources used in foliar applications4. Residual EffectsuPoor responses to soil applied iron fertilizers has lead to a lackof data5. Iron Toxicity ProblemsuuuOnly toxicity potential is with foliar spray applicationsF. Idaho Recommendations for Iron1. Critical Soil Test Level2. Recommendations

A.Manganese Introduction1. Forms and Function of Manganesea. Function of Mn in Plantsuub. Plant Available Form of Mnuc. Mn Mobility in Plantsud. Mn Plant Contentue. Mn Levels in PNW SoilsuB.Factors Affecting Crop Response to Manganese1. Soil pHuIn acid soils the divalent form of Mn (Mn ++ ) is generally foundu At high soil pH values the tetravalent form (MnO 2)predominates

2. Soil Moistureu Poor drainage reducing conditions which favorincreased availabilityuFe and Mn precipitate and clog drainage tiles3. Soil AerationuLow aeration increases soil Mn ++ supply for plant roots(toxicity?)4. Soil MicroorganismsuBecause Mn exists in several oxidation states of dissimilaravailability to plants, the availability of microflora totransform Mn has considerable importanceuOXIDATIONuConversion from plant available to unavailable form;u Mn ++ MnO 2(Mn ++++ )uProcess is biological; occurs under high pH conditions(pH 5.5 - 8.9)Organisms responsible:uuMn oxidizers often comprise 5-15% of total living microflorapopulationuProblem when a soil over-limed

uREDUCTION:uConversion of plant unavailable to available form of Mn;u MnO 2Mn ++u MnO 2+ 4H + + 2e- Mn ++ + 2H 2OuuProcess is biological; occurs under acid conditions,waterlogged conditionsOrganisms responsible:uUnder very acid conditions or prolonged waterloggingtoo much Mntoxicityu Lateral flow H 2O off, get Mn deficienciesC.Correction of Manganese Deficiencies in FieldSituationsuuuuMn deficiencies most often occur on well-drained soils of highpHGrains and large seeded legumes are most often Mn deficientLime additions can induce a Mn deficiencyProblem areas in PNW:u

uuuD.Manganese SourcesuuBoth organic and inorganic sources of Mn can be used tocorrect deficienciesCommon Mn fertilizer sources include:u Manganese sulfate —u Manganese oxide —u Manganese-EDTA —u Manganese carbonate —

u Manganese chloride —u Manganese frits —E. Manganese Fertilizer Applications1. Soil ApplicationsuuMost common method to correct Mn deficiencySoluble Mn quickly reverts to unavailable forms — so theeffectiveness can be influenced by method of applicationuu2. Foliar Manganese ApplicationsuMn deficiencies of fruit trees are almost always corrected byfoliar spraysu

F. Idaho Recommendations for Manganese1. Critical Soil Test Levelu2. Recommendationu

Essential Plant MicronutrientsBoron in IdahoR. L. Mahler, Soil ScientistBoron (B)—like chlorine (Cl), copper (Cu), iron(Fe), manganese (Mn), molybdenum (Mo), nickel (Ni),and zinc (Zn)—is a micronutrient necessary for plantgrowth. Micronutrients are so named because plantsrequire them in lesser amounts than nitrogen (N), phosphorus(P), potassium (K), and sulfur (S). Nevertheless,too little or too much boron will reduce plant yield thesame as a lack of nitrogen.Boron regulates transport of sugars through membranes,cell division, cell development, and auxin metabolism.Without adequate levels of boron, plants maycontinue to grow and add new leaves but fail to producefruits or seeds. A continuous supply of boron is importantfor adequate plant growth and optimum yields.Low soil levels of boron have been found to limitplant growth in many parts of Idaho (Fig. 1). Cropsgrown on northern Idaho soils have been shown torespond to boron fertilizer applications since the 1950s.Recent research has indicated that lack of boron may bea limiting factor for tree growth in northern Idahoforests. In addition, several crops north of the SnakeRiver in southern Idaho also have been shown responsive.As land continues to be intensively cultivated inother areas of southern Idaho, responses to boron fertilizerare likely to increase.Factors Affecting Crop ResponseSoil texture, soil organic matter content, and soilmoisture (annual precipitation, irrigation) are the threemost important factors affecting boron availability insoils. Coarse textured soils (sands, loamy sands, sandyloams) that are low in organic matter are often low inplant-available boron. Boron deficiencies are especiallypronounced in high rainfall areas (greater than 25 inches)where boron may have been leached from the soilprofile. Over-irrigation may cause the same results.The availability of boron in the soil is also influencedby pH. Maximum boron availability occurs betweensoil pH 5 and 7. Most soils in northern Idaho fall into thisrange, however, many soils of southern Idaho have pHvalues above the optimum range for boron availability.Soils in northern Idaho with optimum pH values areoften low in available boron because of high crop usageof this element over the past several decades.Boron■ Often Deficient■ Occasionally Deficient■ Seldom DeficientFig. 1. Areas in Idaho with soils deficient in boron.Cooperative Extension System ❖ Agricultural Experiment Station CIS 1085

Soil moisture and organic matter contentare also factors that affect crop response toavailable soil boron. Organic matter is themajor source of boron in most soils. Consequently,soils that are highly eroded ornaturally low in organic matter tend to below in boron. Boron deficiencies are alsomore prevalent in dry conditions (causedby lack of organic matter decomposition)and in soils with less than 2 percent organicmatter.Boron Deficiency SymptomsBoron deficiencies first appear at thegrowing point of plants. Growing tips maydie, and plant growth fails when no boron ispresent. When fruits on trees or vegetablesare growing rapidly or when tuberous rootsof fleshy plants are expanding rapidly, theplants develop a larger amount of meristemtissue to provide for this growth. A lack ofadequate boron to the meristem at this timemay result in soft or necrotic (dead) spots inthe fruit or tuber. In addition to a reductionof top growth, a boron deficiency also retardsroot growth (Fig. 2).• Alfalfa—Boron deficiency in alfalfain its mildest form goes unrecognized becauseit occurs as a reduction in floweringand seed set. Such mild deficiency reflectsa decrease in seed yield but is seldom detectablein hay yields from any single cutting.Reduced flowering may delay cuttingand could result in poorer quality hay.Boron deficiencies in alfalfa are commonlymistaken for drought damage. Withoutsufficient boron, the youngest leaves ofthe plant become chlorotic. The upper portionof the plant becomes yellow or red incolor (often called “alfalfa yellows” whichshould not be mistaken with the alfalfavirus disease) while the lower, older leavesremain green and healthy. As the deficiencyprogresses, the internodes of theyoung top growth become increasinglyshorter until the plant assumes a rosetteappearance (circular cluster of leaves andother plant parts, see Figs. 3 and 4). At thisstage, the growing tip may become dormantor die.• Sugarbeets—The first symptoms occurin the crown’s young, center leaves.The young leaves will appear smaller andchlorotic, and the petioles tend to be brittle.Eventually, the petioles will become se-Fig. 2. Lack of boron stunts plant vegetative growth and greatly reducesroot growth (right). Decreased root growth reduces the plants’ability to obtain water and nutrients from the soil.Fig. 3. Boron deficiency in alfalfa evidenced by yellowed and stuntedleaves on plants at right.Fig. 4. Differing degrees of boron deficiency in alfalfa plants.

Fig. 5. Severe boron deficiency in young sugarbeet plants. Note thatthe deficiency is so severe that the leaves are difficult to identify.Fig. 6. Boron deficiency in young clover leaves. The leaves on the rightexhibit typical boron deficiency symptoms. The leaves are smaller,slightly deformed, and exhibit a bronzing on the leaf margins.Fig. 7. Boron deficiency results in smaller, deformed, and darker potatotubers (left). During vegetative growth boron-deficient plantsproduced 20 percent less biomass—but the real difference becomesapparent at harvest.Fig. 8. Boron deficiencyin grapes (right) isknown as “hen andchick” symptom.verely cracked, and the young leaves willdie. The growing point of the crown may dieand rot. Under a severe boron deficiencyplant leaves become severely deformed(Fig. 5).• Tree Fruits—Variable boron deficiencysymptoms occur on tree fruits. Inapples, the fruit becomes corky, and the skinmay die; wounds or greenish round spotsoccur on the fruit. Other types of fruit treesmay show symptoms such as cracked fruit,blossom blast (failure of flowers to open, orfailure of fruit or seeds to mature), chloroticfruit skins, and surface pitting of the fruit.• Peas, Lentils, and Chickpeas—A minorboron deficiency is usually visually unrecognizable;however, seed set will often bereduced by up to 25 percent. As the deficiencybecomes more severe, deformationwill occur at the growing tip of the plant.• Clovers—Boron deficiency in cloveroften results in poor stands, reduced growth,and poor seed set. The upper leaves arefrequently smaller in size and may exhibitbronzing around the margins (Fig. 6).• Rapeseed and Canola—Reduced seedset is a characteristic boron deficiency inboth rapeseed and canola. Plants appearstunted at the growing tip, and the new leavesare often deformed and brittle.• Potatoes—Potato plants deficient inboron usually have reduced biomass. Withsevere deficiencies the leaves near the growingtip appear stunted. Lack of boron reducesboth tuber quality and quantity (Fig. 7).• Grapes—Characteristic boron deficiencysymptoms in grapes include chlorosisof the terminal leaves, dieback of the shoottips, and poor fruit set. Under severe deficiencysymptoms, clusters of fruit often dryup or burn off, leaving only cluster stemswith occasional berries. This condition isknown as the “hen and chick” symptom(Fig. 8).Soil Analysis and Plant TissueSamplingSoils should be tested for available boronthree years after a soil application of boronwas made and when the fourth year crop willbe alfalfa, peas, lentils, chickpeas, canola,rapeseed, or a root crop. If an annual rowcrop was sprayed with boron (foliar application)the previous year, a boron soil test is

needed for the next crop because foliar applications areintercepted by the plant canopy and boron does notreach the soil.Deficiencies can be most easily avoided by frequently(every third year) having a soil analyzed foravailable boron. For testing, a soil sample should becollected from the surface 12 inches of a soil profile. Asoil test level of 0.5 ppm boron is sufficient for highboron demanding crops (alfalfa, grain legumes, canola,rapeseed, root crops) while a soil test level of 0.3 ppmboron is sufficient for low boron requiring crops.The boron status of plants can be monitored throughoutthe growing season through the use of plant tissuetesting. Monitoring boron levels in high-value cashcrops can help to prevent severe boron nutrient deficiencysymptoms from developing. Table 1 lists theplant parts and stages of plant growth to sample forboron tissue analysis for major Idaho crops. Take careto sample the correct plant part at the correct stage ofplant growth and to sample in a manner that is representativeof the field.Detection of Boron ProblemsIf you suspect a possible boron deficiency, have thesoil tested for available boron. When soils test less than0.5 ppm boron, addition of a fertilizer containing boronis recommended. Plants belonging to the grass (cereals,corn) family generally require only about 25 percent asmuch boron for normal growth as do dicotyledons(beans, potatoes, tomatoes, sugarbeets, etc.). Borondeficiencies are usually most pronounced on alfalfa andon certain root and cruciferous crops (sugarbeets, cabbage,cauliflower, rutabagas, and turnips). More boronfertilizer is used on alfalfa than any other crop in Idaho.Crop Response to BoronApplications in IdahoField trials conducted on peas, lentils, chickpeas,alfalfa, clover, birdsfoot trefoil, rapeseed, and canola innorthern Idaho between 1970 and 1995 showed thesecrops respond to applications of boron fertilizers whensoils were initially boron deficient. Average yield increasesattributable to fertilizer boron applications ofone pound per acre (soils initially contained less than0.5 ppm B) are shown in Table 2. Cereal crops have notbeen responsive to boron applications.Boron FertilizerSeveral fertilizer sources of boron are available foruse in Idaho (Table 3). Borax, borated gypsum, Solubor,and boric acid are the most commonly used boronfertilizers in Idaho. All four sources of boron are gener-Table 1. Procedures for sampling Idaho crops for boron tissue levels.No. of plantsCrop Stage of growth Plant part to sample to sample CNR*Field cropsAlfalfa Before or at 1/10 bloom stage Upper 3 to 4 inches 40 to 50 20 to 30 ppmClovers Before bloom Mature leaf blades taken about 40 to 50 20 to 30 ppm1/3 of the way down from topof the plantPeas, lentils, Early to mid-season Mature leaf blades taken about 30 to 40 20 to 30 ppmchickpeas1/3 of the way down from topof the plantSugarbeets Early to mid-season 4 th petiole 30 to 40 20 to 40 ppmPotatoes Early to mid-season 4 th petiole 30 to 40 20 to 30 ppmFruit cropsApples, apricots Mid-season Leaves near base of current 50 to 100 20 to 25 ppmpeaches, pears,year’s growth or from spurscherriesStrawberries Mid-season Youngest fully expanded mature 50 to 75 20 to 30 ppmleavesVegetable cropsRoot crops Before root or bulb Center mature leaves 20 to 30 30 to 60 ppm(carrots, onions, enlargementbeets, etc.)Sweet corn 1. Before tasseling The entire fully mature leaf below 20 to 30the whorl2. At tasseling The entire leaf at the ear node 20 to 30*CNR—Critical Nutrient Ranges for boron in plant tissue.

ally applied to the soil. Borax and borated gypsum areused as solid forms of boron fertilizers, while boric acidand Solubor are versatile boron sources that can be usedeither for soil or foliar application.Methods and Application RatesThe two principal methods of correcting boron deficienciesin the field are by (1) soil application and (2)foliar application to the plant. Boron deficiencies aremost commonly corrected by applying boron fertilizerto the soil. While foliar sprays of boron compounds areoften beneficial, soil applications remain effective muchlonger. Most boron compounds used in foliar sprays canbe mixed with other liquid fertilizers for applications tothe soil. Seed applications of boron should not be usedas they can be toxic.• Soil Treatments—A fertilizer application rate of1 to 2 pounds of boron per acre is needed for soiltreatments on certain legumes and root crops. Lowerrates (0 to 1 lb per acre) are needed for other crops.Applying boron to the soil is the most efficient way ofmeeting the nutritional needs of most Idaho crops.Significant responses to soil-applied boron are oftenreported for alfalfa, peas, lentils, chickpeas, rapeseed,and canola in northern Idaho.Table 2. Average yield increases of crops grown in northernIdaho when fertilized with 1 pound of boronper acre. (Note: Soils were initially boron deficientbefore fertilizer applications.)Crop Average yield increase, %LegumesAlfalfa 13Birdsfoot trefoil 9Chickpeas 15Clovers 9Lentils 23Peas 17Non-legumesCanola 15Rapeseed 12If using a solid fertilizer material such as boratedgypsum, borate 48, or borate 68, boron can be surfacebroadcast on the soil and plowed or disked in beforeseedbed preparation. Often boron materials such asboric acid or Solubor are first liquified then sprayed onthe soil surface. Fertilizer boron should never be bandedbecause at high concentrations it can be toxic to seeds,seedlings, and plant roots.• Foliar Treatments—Foliar boron applicationsare commonly used on perennial tree fruits. Foliar boronis compatible and can be mixed with many pesticidesprays. Foliar boron application rates of 0.1 to 0.4 poundper acre are sufficient for most tree fruits. Foliar boroncan also be used to prevent boron deficiencies in rapidlygrowing annual crops.Foliar applications must be made several times duringthe growing season because boron is not mobile inthe plant. As new growth appears, repeated spraying arerequired to get boron into the new growth. Five to sevenfoliar applications of boron over the growing seasonmay be needed to get the same plant yield effects as 1pound of boron broadcast and incorporated into the soilbefore planting.Because of the high cost of repeated applications,foliar spraying of row crops should be used only whenboron is needed to prevent yield reductions. Annual rowcrops generally require about one pound of boron peracre. The one pound can be divided by the number oftimes boron will be sprayed over the season to give thecorrect rate for each application.• Reduced Tillage Situations—In reduced tillagesituations most fertilizers are often banded. Boron cannotbe banded! Potential B application strategies in suchsituations include: (1) apply B fertilizer as a surfacebroadcast in the solid or liquid forms, or (2) apply Bfertilizer as a tank-mix application together with apesticide.• Residual Effects—Boron persistence in soils islargely determined by the soil type and the form ofboron applied to the soil. Boron will rapidly leach fromTable 3. Boron fertilizer materials available for use on Idaho crops.Rates per acreBoron material Chemical formula % boron 0.5 lb B 1 lb B 2 lb B(B)(application of material, lb)Borated gypsum CaSO 4, 2H 2O + Na 2B 4O 71 50 100 200Borax Na 2B 4O 710H 2O 11.4 4.4 8.8 17.6Boric acid H 3BO 317 2.9 5.8 11.8Boron frits variable 10 to 17 ----------------------- depends on % B -----------------------Fertilizer Borate 48 Na 2B 4O 75H 2O 14.3 3.5 7 14Fertilizer Borate 68 Na 2B 4O 720.2 2.5 5 9.9Solubor Na 2B 4O 75H 2O + 20.5 2.4 4.8 9.8Na 2B 10O 1610H 2O

sandy soils that are overirrigated or that have highrainfall but will persist for several years in soils high insilt and clay. Soil-applied boron rates of 1 to 2 poundsper acre will generally result in sufficient soil levels ofboron for at least three years for all but very sandy soils.Foliar applications leave little soil residual boron sincemost of the applied boron is taken up by the plant and notthe soil.Boron ToxicityBoron toxicity can result when plants have taken uptoo much boron; excessive levels of boron are toxic toplant growth. The best way to avoid boron toxicityproblems is through proper management of fertilizerand a crop rotation program. Boron should be applied tothe soil at low rates only after a demonstrated need hasbeen established through plant tissue and/or soil testing.A very narrow range exists between toxicity anddeficiency. Plants differ in their sensitivity to excessboron. Beans and peas are extremely sensitive, whilealfalfa is relatively tolerant to high boron levels. Amountsof boron commonly applied to alfalfa are toxic to beans.When required, boron should be applied uniformly to afield (broadcast, not banded) at rates not to exceed 4pounds of boron per acre.Issued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914,in cooperation with the U.S. Department of Agriculture, LeRoy D. Luft, Director of Cooperative Extension System,University of Idaho, Moscow, Idaho 83844. The University of Idaho provides equal opportunity in education and employment on the basisof race, color, religion, national origin, gender, age, disability, or status as a Vietnam-era veteran, as required by state and federal laws.5,000 12-81; 2,000 3-00 (formerly CIS 608) $3.00

Essential Plant and Animal MicronutrientsMolybdenum in IdahoR. L. Mahler, Soil ScientistPlants require trace amounts of molybdenum (Mo)for normal growth. While animals also require traceamounts, they are more likely than plants to be adverselyaffected by excessive Mo. Management of Moin crop rotations should take into account both animaland plant needs.Molybdenum and PlantsMo—like boron (B), chlorine (Cl), copper (Cu), iron(Fe), manganese (Mn), nickel (Ni), and zinc (Zn)—is anecessary micronutrient for plant growth. Molybdenumis called a micronutrient because plants require it insmaller amounts than the macronutrients—nitrogen (N),phosphorus (P), potassium (K), sulfur (S), calcium (Ca),and magnesium (Mg). Plants take up Mo in the MoO 42-ionic form.Mo has several functions in plant growth. Plantsrequire a constant and continuous supply of Mo fornormal assimilation of N. Mo is also a component of theenzyme nitrogenase, which is required in N fixation andplays a role in P utilization. Because of Mo’s role in Nfixation, legumes require more of it than cereals and arethus more sensitive to low Mo levels in soil (Table 1).Molybdenum Availability in SoilLow soil Mo levels in some parts of northern Idahohave been found to limit plant growth in alfalfa, clover,birdsfoot trefoil, peas, and lentils (Fig. 1). In contrast,Mo deficiencies are rare in crops growing on the SnakeRiver Plain in southern Idaho.Some plants growing in mountain valleys of northcentralIdaho have abnormally high Mo levels. Mofertilizers should not be applied to soils in these mountainvalleys unless a need has been demonstrated.Table 1. The relative Mo requirements of Idaho crops.LowHighBarley Onions Alfalfa LentilsBluegrass Potatoes Beans PeasCorn Rapeseed Birdsfoot trefoil Red cloversFruit trees Sugarbeets Chickpeas WhiteHops Vegetable cloversMint seed cropsOats WheatFig. 1. Idaho soils that may be deficient or extremelyhigh in plant-available molybdenum.Cooperative Extension System ❖ Agricultural Experiment Station CIS 1087

Fig. 2. Molybdenum deficiency in a crop, such as thissoybean field, turns healthy, dark green leavesyellowish-green. This symptom is often misdiagnosedas a nitrogen or sulfur nutritional problem.Mo availability in the soil increases with pH. Modeficiencies are uncommon in high pH soils (pH 7 orabove). That is why Mo deficiencies are rare in southernIdaho. Most Mo deficiencies occur in acidic northernIdaho soils with pH values less than 6.0. In addition,acid, sandy, leached soils or soils high in organic matter(greater than 25 percent organic matter) may be deficientin plant-available Mo.Most Mo deficiencies in Idaho occur in fields withlow pH values and a long-term history of legume production.Soils high in iron may have plants that exhibitMo deficiencies.Crop ResponseSoils normally contain 0.5 ppm of Mo. However,plants usually require only 0.2 to 5 ppm of Mo in theirtissue.Mo may be harmful when its available form, MoO 42,is in the soil in excessive quantities. For example,although Mo may be beneficial to plant growth whenadded to the soil as a seed treatment at rates as low as0.03 pound per acre, an application of 3 to 4 pounds peracre would be toxic to many plants or to the animals thatconsume them.Molybdenum Deficiency SymptomsWhen Idaho crops show Mo-deficiency symptoms,economic loss probably has already occurred. In thefield, Mo-deficiency symptoms are difficult to distinguishfrom N and S nutritional problems and often aremisdiagnosed. Mildly Mo-deficient plant leaves appearyellow, similar to their appearance when they are deficientin N or S (Fig. 2). Most growers assume yellowpeas, lentils, clover, and alfalfa have N or S problems,however, the problem may be Mo deficiency. Mo deficiencysymptoms are similar to N symptoms in legumesbecause Mo is required in the N 2fixation process—thuswhen Mo is deficient plants cannot get the N needed forgrowth. In non-legumes, without Mo plants cannotFig. 3. Molybdenum deficiency in white clover. Note thehealthy, green leaves on the left, compared to theyellowish-green Mo deficient plants on the right.Fig. 4. Molybdenum deficiency in beets. Note the stunted,yellowish-green leaves in the Mo deficient pot.utilize the N taken up by roots—thus resulting in Ndeficiency symptoms.Initially Mo deficiency is characterized by a lightgreen or yellow-green color (Figs. 3 and 4). Underconditions of severe Mo deficiency young leaves wiltand necrotic (dead) tissue appears along their margins(Fig. 5). When a Mo deficiency is suspected, the planttissue should be sampled and evaluated.Molybdenum FertilizerSeveral Mo fertilizer materials are commerciallyavailable (Table 2). Sodium molybdate (Na 2MoO 4•2H 2O) and ammonium molybdate [(NH 4) 6Mo 7O 24•4H 2O] are the Mo fertilizer materials most commonlyused in Idaho. Molybdenum trioxide (MoO 3) is muchless soluble (which often means less available to theplant) than sodium molybdate or ammonium molybdate.The molybdenum trioxide form is not widely usedin Idaho. Molybdenum sulfide (MoS 2) is a poor sourceof plant-available Mo and should be avoided in Idaho.In the frits form, Mo is fused with glass. The glass isthen shattered and applied to soils. As the glass slowlydissolves in the soil, Mo becomes available. Molybdenumfrits are actually slow-release fertilizers. The amountof Mo can be varied by controlling the amount of Mofused with glass. Molybdenum frits is an uncommonfertilizer in the Pacific Northwest and should only beapplied to acid soils (pH values less than 6.5).

Fig. 5. Molybdenum deficiency in peas grown in northernIdaho. The Mo deficient pea plants on the leftare stunted and exhibit severe yellowing of theplant tissue when compared to healthy plants onthe right.Application Methods and RatesThree principal methods of applying Mo fertilizersare (1) soil application, (2) foliar application, and (3)application directly to the seed at planting time. Mo isapplied most commonly as a seed treatment. Whilefoliar applications of Mo are often beneficial, seed andsoil applications remain effective much longer. Seedapplication is the most effective Mo application methodfollowed, in order, by soil application and foliar application.Optimum application rates of Mo vary. Actual applicationrates depend on the pH of the soil, the crop to begrown, and the application method. Typical applicationrates range from 0.03 pound (seed and foliar applications)to 1.0 pound (soil applications) of Mo per acre.Soil Applications—Differences in soils, the crop tobe grown, Mo fertilizer sources, and incorporation techniqueslead to differing recommended rates of applica-tion. Recommended rates in Idaho range from 0.5 to 1.0pound of actual Mo per acre. The major problem withapplying Mo directly to the soil is that it is difficult toevenly distribute such small amounts. Because of this,soil application of Mo is not recommended in Idaho. Ifa soil application is desired, the fertilizer Mo should besolubized in water and sprayed directly on the soil. Thiswill allow for a uniform Mo application.Foliar Applications—Although correcting Mo deficienciesin growing plants with foliar sprays is possible,this method is rarely used. Common foliar sprayrates range from 0.03 to 0.14 pound of Mo per acre.Spraying such a small amount of material is expensiveand difficult. Also, foliar Mo applications correct onlythe existing plant deficiency, may not last throughmaturity, and do not add Mo to the soil for use bysubsequent crops because the fertilizer material is interceptedby the plant tissues and not the soil.Seed Treatments—Most of the time the best way toapply Mo is as a seed treatment. Seed application hasdistinct advantages over both soil and foliar treatments.Seed treatment results in an even Mo application. Seedtreatment also requires lower Mo rates than are used forsoil application—0.03 to 0.06 pound per acre. Researchindicates that 1/8 ounce per acre of Mo applied as a seedtreatment will increase pea yields the same amount as 1pound per acre of Mo applied directly to the soil.Avoid treating seeds with more than 1 ounce of Moper acre. Higher Mo rates can lower seed germinationand inhibit the growth of the N-fixing bacteria neededfor nodulation on legumes. Rhizobium inocula containingMo is commercially available. Excessive rates alsoallow plants to take up excessive amounts of Mo. Molevels are rarely toxic to plants, however, they can betoxic to animals that consume them.Residual EffectsIn neutral to alkaline soils (pH 7 and above), Mo soilapplications at rates of 0.5 to 1 pound per acre shouldremain effective for several crop years. Seed treatmentsof Mo should supply Mo to plants for 3 or 4 years. Soilsthat are slightly acid (pH 5.7 to 7.0) may require Moapplications every 4 or 5 years. Soils that are regularlyTable 2. Application rates of common Mo fertilizer materials available for use on Idaho crops.Mo rate (lb/acre)Fertilizer material Chemical formula % Mo 1/8 1/4 1/2 1------------- Amount of material to apply (lb/acre) -----------Ammonium molybdate (NH 4) 6Mo 7O 24 • 4H 2O 54 0.23 0.45 0.93 1.85Molybdenum frits 1 silicates 2 to 3Molybdenum sulfide MoS 260 0.21 0.42 0.83 1.67Molybdenum trioxide MoO 366 0.19 0.38 0.76 1.52Sodium molybdate Na 2MoO 4 • 2H 2O 39 0.32 0.64 1.28 2.561Application amounts of Mo frits depend on the percentage of Mo.

cropped with a legume (peas, lentils, alfalfa, clover, andbirdsfoot trefoil) and have pH values less than 5.6 mayrequire Mo applications every 2 or 3 years.Soil analysis and Plant Tissue TestingBecause plant-available Mo is present in soil in verysmall amounts, soil Mo analysis is technically impreciseand, therefore, not commercially available. Consequently,a soil test cannot be used to assess the need forMo. Instead, use plant tissue analysis to determine Molevels. The need for Mo analysis in plant tissue ariseswhen either (1) you suspect toxic Mo levels in plantmaterial that animals will consume or (2) you observe asuspected Mo deficiency symptom. Little work hasbeen done to establish optimum Mo concentration valuesin plant tissue, however, plant Mo concentrationsbetween 0.1 and 1.2 ppm are known to be adequate forplant nutrition and safe for animal consumption.When Should I Apply Mo?Southern Idaho—Due to high soil pH values (pH 7or above), Mo levels should be adequate throughoutsouthern Idaho. If a Mo deficiency is suspected (basedon visual symptoms), have a plant tissue sample fromthe field tested for Mo. If the plant tissue contains lessthan 0.1 ppm consider a foliar application of Mo duringthe present cropping year, or a soil or seed Mo applicationto next year’s crop.Northern Idaho—Because a reliable soil test for Mois not available, Mo should be managed on the basis ofcrop rotation history and soil pH. Molybdenum is morelikely to be deficient if a legume (peas, lentils, chickpeas,alfalfa, clovers, birdsfoot trefoil), canola, or rapeseed isin the crop rotation. Soils with pH values of 5.6 or lessare also more likely to be Mo deficient. Based on thesefacts Mo fertilization recommendations are as follows:• If soil pH is less than 5.6 and legume or oilseed inrotation:✓ seed treat legume/oilseed once every 8 years• If soil pH is greater than or equal to 5.6 and legume/oilseed in rotation less than 50 percent of the time:✓ seed treat legume/oilseed once every 6 years• If soil pH is greater than or equal to 5.6 and legume/oilseed in rotation is less than or equal to 50 percentof time:✓ seed treat legume/oilseed once every 4 years.Molybdenum and AnimalsMo is an essential trace mineral for animals. Mo levelin most forages ranges from 0.1 to 3 ppm on a dry matterbasis. Beef cattle only require 0.01 ppm Mo in their diet,so a Mo deficiency is usually not of concern. The commonsymptom of animal Mo deficiency is a blockedurinary tract.Molybdenum Toxicity in AnimalsMany animals cannot tolerate high Mo levels in theirdiets. Mo can impair utilization of copper (Cu), anotheressential micronutrient, especially if the diet is alsorelatively high in suflur (S). A Cu-S antagonism lowersthe biological availability of Cu by forming a Cu-Mo orCu-Mo-S complex in the digestive tract. Forage Molevels of 3 ppm and above will significantly reduce Cuavailability from the diet.Cu is often deficient in animal diets, and the deficiencygenerally occurs where plant-available Cu islow, often in high organic matter and poorly drainedsoils (muck soils). If a muck soil has an abundant supplyof Mo, plant Mo uptake increases while Cu uptake isreduced.Severe Mo toxicity (molybdenosis) occurs in cattlewhere natural forages contain 20 to 100 ppm Mo. Thistoxicity causes a condition called “teart” in which cattledevelop scours. Scours can be mild to debilitating,resulting in permanent injury to the digestive tract andsometimes death. This condition can be corrected byadding a copper-sulfate supplement to the cattle diet.For Further ReadingYou may order other publications about micronutrientsin soils from the University of Idaho CooperativeExtension System office in your county or Ag Publications,P.O. Box 442240, University of Idaho, Moscow,Idaho 83844-2240, or phone 208/885-7982 or email:cking@uidaho.eduBUL 704, Soil Sampling, $2.00CIS 617, Essential Plant and Animal Micronutrients:Copper in Idaho, 50¢CIS 757, Nitrogen and Phosphorus BMP: FertilizerPlacement, 50¢CIS 882, Long-Term Effects of Lime on Soil pH inSome Acidic Soils in Northern Idaho, 35¢CIS 1085, Essential Plant Micronutrients: Boron inIdaho, $3.00CIS 1088 (formerly CIS 617), Essential PlantMicronutrients: Zinc in IdahoIssued in furtherance of cooperative extension work in agriculture and home economics, Acts of May 8 and June 30, 1914,in cooperation with the U.S. Department of Agriculture, LeRoy D. Luft, Director of Cooperative Extension System,University of Idaho, Moscow, Idaho 83844. The University of Idaho provides equal opportunity in education and employment on the basisof race, color, religion, national origin, gender, age, disability, or status as a Vietnam-era veteran, as required by state and federal laws.1,000 1-93; 2,000 5-00 (formerly CIS 589) $1.00