soil fertility management by allah dad khan objectives understand objectives of soil fertility...

Soil Fertility Soil Fertility Management By Management By Allah dad Khan Allah dad Khan

ObjectivesObjectives

Understand objectives of soil fertility Understand objectives of soil fertility managementmanagement

Philosophies/techniques of precision farmingPhilosophies/techniques of precision farming Using & obtaining valid soil samplesUsing & obtaining valid soil samples Considerations in making/following fertilizer Considerations in making/following fertilizer

recommendationsrecommendations Knowledge of fertilizer qualityKnowledge of fertilizer quality How to calculate fertilizer blendsHow to calculate fertilizer blends Fertilizer application methodsFertilizer application methods Benefits/limitations of manure useBenefits/limitations of manure use

IntroductionIntroduction

Fertilizer is one management Fertilizer is one management option used almost universallyoption used almost universally

Must replace soil nutrients lost by Must replace soil nutrients lost by harvestharvest

Over-fertilization can result in Over-fertilization can result in dangerous pollutiondangerous pollution

Technology has increased Technology has increased fertilizer efficiencyfertilizer efficiency

Goals & Concerns in Goals & Concerns in Fertility ManagementFertility Management Goals regarding fertilityGoals regarding fertility

– Increase yieldIncrease yield– Reduce costs/unit productionReduce costs/unit production– Improve product qualityImprove product quality– Avoid environmental pollutionAvoid environmental pollution– Improve environmental health & Improve environmental health &

aestheticsaesthetics

Goals & Concerns in Goals & Concerns in Fertility ManagementFertility Management Efficient land managers: spend Efficient land managers: spend

<20% of production costs on <20% of production costs on fertilizers, expect >50% increase in fertilizers, expect >50% increase in yieldsyields

Fertilizers may not be profitable if:Fertilizers may not be profitable if:– Water is the most limiting factorWater is the most limiting factor– Other growth hindrances – insects, Other growth hindrances – insects,

diseases, acidity, extreme colddiseases, acidity, extreme cold– Increased yield has less market value Increased yield has less market value

than the cost of buying/app of fertilizerthan the cost of buying/app of fertilizer

Goals & Concerns in Goals & Concerns in Fertility ManagementFertility Management Fertilizers – generally most Fertilizers – generally most

profitable farm inputprofitable farm input Soil fertility problems usually the Soil fertility problems usually the

easiest to solveeasiest to solve Soil nutrients typically present in Soil nutrients typically present in

finite amounts, don’t replenish finite amounts, don’t replenish themselvesthemselves

Crops typically contain: (in rank of Crops typically contain: (in rank of amount found in the plant) N, K, Ca, amount found in the plant) N, K, Ca, P, Mg, SP, Mg, S

Goals & Concerns in Goals & Concerns in Fertility ManagementFertility Management Utilizing fertilizers may help cut unit Utilizing fertilizers may help cut unit

cost of production by maximizing cost of production by maximizing yieldyield– Improved fertility = improved yields, Improved fertility = improved yields,

improved aesthetic appealimproved aesthetic appeal Environmental concerns aboundEnvironmental concerns abound

– Fertilizer laws viewed as lax by someFertilizer laws viewed as lax by some– Farmers may be the primary cause of Farmers may be the primary cause of

non-point-source pollutionnon-point-source pollution

Goals & Concerns in Goals & Concerns in Fertility ManagementFertility Management

– Three common pollutants:Three common pollutants: NitratesNitrates

– Percolate through to groundwaterPercolate through to groundwater– Not safe to drinkNot safe to drink– Cause “Blue-baby” syndrome – inhibits Cause “Blue-baby” syndrome – inhibits

oxygenation of bloodoxygenation of blood– Becoming common near heavily fertilized Becoming common near heavily fertilized

fields, feedlots, dairiesfields, feedlots, dairies PhosphatesPhosphates

– Pollute surface waters by runoffPollute surface waters by runoff– Promotes algae growth in rivers/pondsPromotes algae growth in rivers/ponds– Depletes available oxygen in the water for Depletes available oxygen in the water for

fishfish

Goals & Concerns in Goals & Concerns in Fertility ManagementFertility Management

– Wise use of fertilizers must be Wise use of fertilizers must be encouraged, actually improve the encouraged, actually improve the environmentenvironment Crops, trees, etc. - remove more CO2, Crops, trees, etc. - remove more CO2,

decrease sediment, dust, erosiondecrease sediment, dust, erosion Plays important role for future of the Plays important role for future of the

planetplanet

Scale of Land Scale of Land ManagementManagement Large- & Medium-Scale Large- & Medium-Scale

ManagementManagement– Large-ScaleLarge-Scale

Low levels of operational precision, little Low levels of operational precision, little reliance on sophisticated technologyreliance on sophisticated technology

May be most feasible/profitable for someMay be most feasible/profitable for some Simple & low-techSimple & low-tech Some shy away from high tech for other Some shy away from high tech for other

reasonsreasons

Scale of Land Scale of Land ManagementManagement

DisadvantagesDisadvantages– Some parts of field may receive too much/little Some parts of field may receive too much/little

fertilizer or pesticidefertilizer or pesticide– Less than optimal yieldsLess than optimal yields– Inefficient use of fertilizers & pesticidesInefficient use of fertilizers & pesticides– Higher cost of production/unitHigher cost of production/unit– Environmental pollution due to over applicationEnvironmental pollution due to over application

AdvantagesAdvantages– Minimal technological training & Minimal technological training &

instrumentation neededinstrumentation needed– Field operations can be performed w/ standard, Field operations can be performed w/ standard,

readily available, cheaper equipmentreadily available, cheaper equipment


– Medium-ScaleMedium-Scale Subdivide field into two+ management Subdivide field into two+ management

unitsunits– Delineation may be based on:Delineation may be based on:

Soil typesSoil types Past management differencesPast management differences Farmer’s observationsFarmer’s observations

Ex. High, medium, low N application areas Ex. High, medium, low N application areas in the fieldin the field

Same equipment/technology needs as for Same equipment/technology needs as for large-scale management farmerslarge-scale management farmers


Does improve efficiency of farm inputsDoes improve efficiency of farm inputs Can reduce excessive applications of Can reduce excessive applications of

chemicals/fertilizerschemicals/fertilizers– May do spot treatments/applications w/in a May do spot treatments/applications w/in a

field due to field observationsfield due to field observations

Small-Scale Management Small-Scale Management (Precision Farming)(Precision Farming)– Global Positioning System (GPS)Global Positioning System (GPS) – –

network of U.S. satellites w/ a signal network of U.S. satellites w/ a signal detection system used to locate detection system used to locate positions on the groundpositions on the ground


– Soil sample fields on a gridSoil sample fields on a grid– Data collection points no more than Data collection points no more than

a few feet aparta few feet apart– Each sample site mapped using GPSEach sample site mapped using GPS– Custom applicators can custom Custom applicators can custom

apply fertilizers at variable rates apply fertilizers at variable rates that change constantly as the that change constantly as the applicator travels the field – applicator travels the field – variable variable rate application, site-specific rate application, site-specific management, precision farmingmanagement, precision farming


– Potential to substantially decrease Potential to substantially decrease fertilizer/chemical application ratesfertilizer/chemical application rates

– Potential to substantially decrease Potential to substantially decrease input costsinput costs

– Does require expensive technology, Does require expensive technology, equipment & extensive technical equipment & extensive technical knowledgeknowledge

Soil TestsSoil Tests

Law of the Minimum:Law of the Minimum: growth of the growth of the plant is limited most by the essential plant is limited most by the essential plant nutrient present in the least plant nutrient present in the least relative amount (first-limiting)relative amount (first-limiting)

Soil Acidity EvaluationSoil Acidity Evaluation– pH measured w/ electrode & solutionpH measured w/ electrode & solution– Lime requirementLime requirement – amount of lime – amount of lime

required to achieve desired pHrequired to achieve desired pH Reported as Reported as buffer pHbuffer pH


Soil Test for NSoil Test for N– No good tests for soil available NNo good tests for soil available N– Most states provide N recommendations Most states provide N recommendations

based on yrs of field plots trials on various based on yrs of field plots trials on various crops, soils, management, fertilizerscrops, soils, management, fertilizers

– N recommendations consider:N recommendations consider: Previous cropsPrevious crops Estimates N carryoverEstimates N carryover N needed to decompose residuesN needed to decompose residues Projected yieldsProjected yields ClimateClimate


– Lab N tests accurate, but nearly Lab N tests accurate, but nearly impossible to interpretimpossible to interpret Some will discourage N testingSome will discourage N testing

– Behavior of carryover N unpredictable Behavior of carryover N unpredictable – can make analyses invalid– can make analyses invalid LeachingLeaching DenitrificationDenitrification MineralizationMineralization ClimateClimate


– N recommendations based on yield N recommendations based on yield goals rather than soil reservesgoals rather than soil reserves

– Corn RuleCorn Rule – 1.2-1.4#N/bu of yield – 1.2-1.4#N/bu of yield goalgoal How much N should be recommended How much N should be recommended

for corn following corn, expected yield for corn following corn, expected yield 120 bu/ac?120 bu/ac?

How much N should be recommended How much N should be recommended for corn following soybeans, expected for corn following soybeans, expected yield 195 bu/ac?yield 195 bu/ac?


Soil Tests for P & KSoil Tests for P & K– Widely used to predict probability of Widely used to predict probability of

crop response to fertilizationcrop response to fertilization– Survey:Survey:

47% soil tested medium to low for P47% soil tested medium to low for P 43% soil tested medium to low for K43% soil tested medium to low for K P & K soil levels declining in many P & K soil levels declining in many

statesstates

– P testingP testing Quite reliable – soil P is very stable from Quite reliable – soil P is very stable from

yr to yryr to yr


Most soil P unavailable to cropsMost soil P unavailable to crops Soil test extracts & measures what may Soil test extracts & measures what may

actually be availableactually be available

– K testingK testing Tests both exchangeable & soluble reservesTests both exchangeable & soluble reserves Conflicting testing procedures over which is Conflicting testing procedures over which is

most accuratemost accurate– Some estimate upper threshold needs ~159-Some estimate upper threshold needs ~159-

246#/ac (above which no response to K fertilizer)246#/ac (above which no response to K fertilizer)– Others - 335#/ac on clay soils (calculated based Others - 335#/ac on clay soils (calculated based

on soil CEC – higher CEC = decreased available K)on soil CEC – higher CEC = decreased available K)

– Some experimentation w/ soil probes Some experimentation w/ soil probes checking K, NOchecking K, NO33, PO, PO44, SO, SO44


Soil Test for Ca & MgSoil Test for Ca & Mg– Related to need for limeRelated to need for lime– Well-limed soils rarely Ca & Mg Well-limed soils rarely Ca & Mg

deficientdeficient– Mg deficiency more common than CaMg deficiency more common than Ca

Coarse-textured or acidic soilsCoarse-textured or acidic soils Many yrs using non-Mg containing limeMany yrs using non-Mg containing lime

– Mg testing for:Mg testing for: Exchangeable soil MgExchangeable soil Mg % Mg saturation of soil colloids% Mg saturation of soil colloids Ratio of K:MgRatio of K:Mg


Soil Test for S & BSoil Test for S & B– S testing inaccurate – acts much like S testing inaccurate – acts much like

NN Can test – but must take variability into Can test – but must take variability into

accountaccount

– Boron level recommendationsBoron level recommendations <1.0 ppm – deficient for plant growth<1.0 ppm – deficient for plant growth 1-5.0 ppm – adequate1-5.0 ppm – adequate >5.0 ppm – excess/toxicity risks>5.0 ppm – excess/toxicity risks


Soil Test for Micronutrient NeedsSoil Test for Micronutrient Needs– Difficult to develop accurate tests Difficult to develop accurate tests

due to relatively infrequent need for due to relatively infrequent need for field supplementationfield supplementation

– Can be done, if requested for a Can be done, if requested for a specific needspecific need

– Adds expense to soil analysisAdds expense to soil analysis


How Good Is Soil Testing?How Good Is Soil Testing?– Analyses recalibrated regularly Analyses recalibrated regularly

based on field trial studiesbased on field trial studies– Validity of analysis related directly Validity of analysis related directly

to accuracy of sample, information to accuracy of sample, information provided to the labprovided to the lab

– Soil analyses generally very valid Soil analyses generally very valid for: P, K, soluble salts, pH, limefor: P, K, soluble salts, pH, lime Other tests should only be used on as-Other tests should only be used on as-

needed basisneeded basis– Extra costExtra cost– Less accurateLess accurate

Analysis of PlantsAnalysis of Plants

Only way to be sure of soil nutrient Only way to be sure of soil nutrient availabilityavailability

Plant Analysis vs. Soil TestingPlant Analysis vs. Soil Testing– Plant most accurate report on what Plant most accurate report on what

nutrients are nutrients are actuallyactually available available– Plant analysis leaves little to no room Plant analysis leaves little to no room

for amendments to the soilfor amendments to the soil– When deficiencies are acknowledged, When deficiencies are acknowledged,

yield usually already affectedyield usually already affected


– When is plant analysis most helpful?When is plant analysis most helpful? Treatment of an easily-corrected Treatment of an easily-corrected

deficiencydeficiency Long-growing crops: turf, tree fruits, Long-growing crops: turf, tree fruits,

forests, sugar caneforests, sugar cane

Quick Tests in the FieldQuick Tests in the Field– Can test for N, K status in plants Can test for N, K status in plants

Collect ~20 leaves for sampleCollect ~20 leaves for sample– Must be random from different locationsMust be random from different locations– Don’t select only affected-looking leavesDon’t select only affected-looking leaves


Chop/mix, squeeze sap & testChop/mix, squeeze sap & test Most effective for greenhouse/nursery growersMost effective for greenhouse/nursery growers

– Amendments can easily be madeAmendments can easily be made– High possible economic lossesHigh possible economic losses

Total Plant AnalysisTotal Plant Analysis– Done in a labDone in a lab– Should be tested by stage of developmentShould be tested by stage of development– Random sampling keyRandom sampling key


– Indicate part of plant sampled & be Indicate part of plant sampled & be consistent consistent

– Dry to prevent spoilage (confounds Dry to prevent spoilage (confounds results)results)

– Wrap in paper and mail w/ complete Wrap in paper and mail w/ complete report – complete history, report – complete history, information criticalinformation critical


Interpreting Plant AnalysesInterpreting Plant Analyses– Accurate interpretation difficult if not Accurate interpretation difficult if not

all critical information providedall critical information provided– Element classified as deficient if Element classified as deficient if

below threshold nutrient levelsbelow threshold nutrient levels Levels change through season, stage of Levels change through season, stage of

development, etc.development, etc.

– Some general disagreement from Some general disagreement from scientists on what threshold levels scientists on what threshold levels areare


Critical Nutrient RangeCritical Nutrient Range– CNR – ranges at which nutrients are:CNR – ranges at which nutrients are:

Visually deficientVisually deficient Hidden deficientHidden deficient Slightly deficientSlightly deficient Sufficient supplySufficient supply ToxicToxic


Visual Nutrient Deficiency SymptomsVisual Nutrient Deficiency Symptoms– ChlorosisChlorosis – yellowish to whitish – yellowish to whitish

appearance to foliage, stemappearance to foliage, stem– NecrosisNecrosis – dead tissue – dead tissue– Causes: disease, insect damage, salt Causes: disease, insect damage, salt

accumulation, stress, nutrient accumulation, stress, nutrient deficienciesdeficiencies

– Some visual symptoms same for many Some visual symptoms same for many diseases/deficienciesdiseases/deficiencies


– Nutrients are relocated in the plant Nutrients are relocated in the plant by two pathwaysby two pathways XylemXylem – water-carrying vessels – water-carrying vessels

– All nutrients can pass throughAll nutrients can pass through PhloemPhloem – sugar-carrying vessels – sugar-carrying vessels

– Not all nutrients can relocateNot all nutrients can relocate– Mobile nutrientsMobile nutrients – travel freely – travel freely– Immobile nutrientsImmobile nutrients – can’t be moved from – can’t be moved from

their location in the planttheir location in the plant

– Mobile nutrient deficiencies tend to Mobile nutrient deficiencies tend to occur on older leaves – plant occur on older leaves – plant sacrifices old for new tissuesacrifices old for new tissue


– Immobile nutrient deficiencies – Immobile nutrient deficiencies – symptoms on shoot/root tips, fruitssymptoms on shoot/root tips, fruits Can’t be treated from the soil w/ Can’t be treated from the soil w/

fertilizer – plant can’t send Ca (ex) to fertilizer – plant can’t send Ca (ex) to the ripening fruitthe ripening fruit

– Mobile nutrients:Mobile nutrients: N, P, K, Cl, Mg, SN, P, K, Cl, Mg, S

– Immobile nutrients:Immobile nutrients: Cu, Mn, Zn, Fe, Mo, SCu, Mn, Zn, Fe, Mo, S

– Very immobile nutrients:Very immobile nutrients: B, CaB, Ca

Fertilizer Fertilizer RecommendationsRecommendations

Different labs make different Different labs make different recommendationsrecommendations

Traditional philosophies being Traditional philosophies being challengedchallenged

P application ratesP application rates Yield-based N recommendationsYield-based N recommendations

Fertilizer Fertilizer RecommendationsRecommendations Developing a Fertilizer Developing a Fertilizer

RecommendationRecommendation– Must have sufficient plot data to Must have sufficient plot data to

correlate yields & nutrient needscorrelate yields & nutrient needs– Once a general amount of fertilizer Once a general amount of fertilizer

is known:is known: Subtract for manure applicationSubtract for manure application Subtract for residual P or NSubtract for residual P or N Add/subtract for N, P, S because of soil Add/subtract for N, P, S because of soil

organic matter levels – can count on organic matter levels – can count on them supplying somethem supplying some

Fertilizer EfficiencyFertilizer Efficiency

Typical fertilizer efficiencies:Typical fertilizer efficiencies:– 30-70% for N30-70% for N– 5-30% for P5-30% for P– 50-80% for K50-80% for K

Maximum profits rarely at maximum yieldsMaximum profits rarely at maximum yields– Last amounts of fertilizer to produce more yield Last amounts of fertilizer to produce more yield

cost more than yield increasecost more than yield increase– Management also keyManagement also key

Use of Use of BMP’sBMP’s increasing increasing– Encourage environmental protectionEncourage environmental protection– Couple w/ agronomic successCouple w/ agronomic success– Increase economic yields, leading to Increase economic yields, leading to

sustainable agsustainable ag


Plant Root SystemsPlant Root Systems– Some plants better scavengers than Some plants better scavengers than

othersothers– Absorption greatly affected by Absorption greatly affected by

fertilizer distributionfertilizer distribution– Smaller root system = shorter Smaller root system = shorter

growing season = >dependence on growing season = >dependence on fertilizerfertilizer

– Growth rates & size also effect Growth rates & size also effect amount of nutrients demandedamount of nutrients demanded


WeedsWeeds– Response to fertilizer much like Response to fertilizer much like

cropscrops– N fertilization may increase weed N fertilization may increase weed

growth > crop growthgrowth > crop growth– Application method can also affect Application method can also affect

weed growthweed growth Ex – broadcast fertilizer can tend to help Ex – broadcast fertilizer can tend to help

weeds get good startweeds get good start


Fertilizer-Water InteractionsFertilizer-Water Interactions– Availability of nutrients directed Availability of nutrients directed

impacted by soil water contentimpacted by soil water content– Drip fertigation may be most Drip fertigation may be most

efficient use of water & fertilizerefficient use of water & fertilizer Common in greenhousesCommon in greenhouses Can be effective in field useCan be effective in field use

– Israeli farming uses drip irrigationIsraeli farming uses drip irrigation


Fertilizing for High EfficiencyFertilizing for High Efficiency– Guides to optimal fertilization:Guides to optimal fertilization:

Avoid large additions of N or K (50#/ac Avoid large additions of N or K (50#/ac +) on sandy soils – use split application+) on sandy soils – use split application

Avoid broadcast applications of urea & Avoid broadcast applications of urea & ammonia on warm/moist soils – ammonia on warm/moist soils – volatilizes easily – incorporatevolatilizes easily – incorporate

Avoid N losses on poorly drained soils Avoid N losses on poorly drained soils by using ammoniumby using ammonium

Band PBand P Use starter fertilizerUse starter fertilizer


Keep N & K fertilizers out of seedling Keep N & K fertilizers out of seedling zone to avoid burnzone to avoid burn

Reduce leaching by avoiding application Reduce leaching by avoiding application before rain or irrigationbefore rain or irrigation

Foliar apply, if feasible/appropriateFoliar apply, if feasible/appropriate Know nutrient demands of cropKnow nutrient demands of crop Improve managementImprove management Remember law of minimumRemember law of minimum Soil testSoil test

Livestock Manure as Livestock Manure as FertilizerFertilizer

Many benefits of using manure:Many benefits of using manure: Recycles nutrientsRecycles nutrients Potential to reduce pollutionPotential to reduce pollution Adds C to soilAdds C to soil Improve aggregation, infiltration, Improve aggregation, infiltration,

microbial vigormicrobial vigor

Risks:Risks: Increased weed pressureIncreased weed pressure High cost of obtaining/applying if you High cost of obtaining/applying if you

don’t own itdon’t own it


Not as convenient as commercial Not as convenient as commercial fertilizerfertilizer

Pollution anxietyPollution anxiety

Nutrient Production & RecoveryNutrient Production & Recovery– Production rates predictable & Production rates predictable &

measurablemeasurable– Ration has heavy influence on Ration has heavy influence on

nutrients in manurenutrients in manure

Livestock Manure as Livestock Manure as FertilizerFertilizer Manure & Nutrient BudgetsManure & Nutrient Budgets

– Generous applications of manure no Generous applications of manure no longer normlonger norm Some states require & enforce strict Some states require & enforce strict

manure management guidelinesmanure management guidelines

– Restricted application due to soil P Restricted application due to soil P levels instead of Nlevels instead of N

– Manure still can’t meet plant needs Manure still can’t meet plant needs alonealone Crops remove much higher levels of Crops remove much higher levels of

nutrients/acnutrients/ac

Livestock Manure as Livestock Manure as FertilizerFertilizer Using ManureUsing Manure

– Most recognize advantages of using Most recognize advantages of using manuremanure

– Manure production unevenly Manure production unevenly distributed in farmlanddistributed in farmland

– Expensive to transport very farExpensive to transport very far– Too abundant in areas, not enough Too abundant in areas, not enough

land for applicationland for application


– Must balance three factorsMust balance three factors Supply crop nutrientsSupply crop nutrients Dispose of wasteDispose of waste Protect environmentProtect environment

– More focus on manure laterMore focus on manure later

soil fertility management by allah dad khan objectives understand objectives of soil fertility...

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