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Potassium and Phosphorus as Plant Nutrients

Secondary Nutrients and Micronutrients

Potassium is required in large amounts by many crops

Yield K2O taken up

Crop level/ac in total crop, lb

Alfalfa 8 tons 480Lettuce 830 boxes 207Oranges 540 cwt 330Almonds 3,000 lbs 270Corn 160 bu 213Tomato 35 tons 200Wheat 60bu 122Cotton (lint) 1,000 lb 85

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Potassium in Soils

• Soils may contain as much as 20,000 lb/A total K, or more.

• Most of this K is held in undissolved minerals (1o)

• Only a small amount of K is plant available during the growing season.

Singer and Munns, Soils: An Introduction. 2002, page 229

Potassium Cycle

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K deficiency in almond

K deficiency in cotton

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K deficiency in pears

Roots contact onlya small percentage

of available nutrients

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Fate of Fertilizer K in the Soil

• Held in exchangeable form• Remains in soil solution• Move to roots largely by

diffusion.• Taken up by growing crop• Leached in sandy or organic

soils• Fixed (unavailable or slowly

available) by clays or silts of certain mineralogy.

Factors Reducing Rate of Diffusion and Root Growth Impact K Uptake

• Soil aeration

• K fixation

• Cation Exchange Capacity (CEC)

• Compaction

• Soil test K

• Soil temperature

• Soil moisture

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Method of fertilizer applicationdepends on crop, soil and

other management practices

Row application of K

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Broadcast application of K

Banding Potassium sulfate in Almonds

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Fertigation

Certain Soil Stresses WarrantPlacement of K in Root Zone to improve

plant K availability

•Cold soils•Compacted soils•Dry soils•High CEC soils•Weathered igneous

parent material

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Phosphorus

Singer and Munns, Soils: An Introduction. 2002, page 229

Phosphorus Cycle

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Phosphorus Is Taken Upby Plants as:

• primary orthophosphate ion: H2PO4

- (pH < 7.0)

• secondary orthophosphate ion: HPO4

= (pH > 7.0)

• The form most common is a function of soil pH – both equally present at neutral

Solution P

Seeds Contain More Phosphorusthan Other Plant Parts

Plant Yield P content, P removal,

Crop part level % lb/A

Corn Grain 150 bu 0.22 18Stover 7,500 lb 0.17 13

Cotton Seed 2,000 lb 0.66 13Stalks 2,500 lb 0.24 6

Soybeans Grain 50 bu 0.42 13Straw 7,000 lb 0.18 13

Wheat Grain 60 bu 0.42 15Straw 5,400 lb 0.12 6

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Some Roles PhosphorusPlays in Plant Growth

• Photosynthesis and respiration

• Energy storage and transfer

• Cell division and enlargement

• Early root formation and growth

• Improves quality

• Vital to seed formation

• Transfer of hereditary traits

Relative Movement of N, P, K in the Soil

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Factors Influencing Amount of P RecoveredDuring First Year After Fertilization

Amount of clayType of clayTime of applicationTemperatureSoil pHCrop grown

AerationMoistureCompactionOther nutrientsSoil P status

Several Factors InfluencePhosphorus Placement

• Soil fertility levels

–Olsen test (bicarbonate extraction) alkaline soils

–Bray-1 test (mild acid extraction) (acid soils)

• Crop(s) to be grown

• Tillage methods, equipment and timing

• P fixing capacity of the soil

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N Improves P Uptake• When applied with N, P is

more available to plants

• Ammonium (NH4+) N has

significant effects on P availability and absorption.

• In high concentrations, NH4+-

N slows P fixation reactions

• Ammonium absorption helps maintain an acidic condition at the root surface, improving P absorption

Western Lake Erie, summer, 2011

Cleveland

Detroit

Toledo

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http://nutrients.utah.gov/

Micronutrients

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Element SymbolTypical leaf concentration

(dry weight basis)Form(s) taken up from

soil

Nitrogen N 2-5% NO3-, NH4

+

Phosphorus P 0.2-0.6% HPO42-, H2PO4

-

Potassium K 2-5% K+

Calcium Ca 0.5-4.0% Ca2+

Magnesium Mg 0.4-1.0% Mg2+

Sulfur S 0.25-1.0% SO42-

Chlorine Cl 0.3-1.5% Cl-

Iron Fe 50-250 PPM Fe2+, Fe3+

Manganese Mn 30-250 PPM Mn2+

Boron B 20-80 PPM H3BO30

Zinc Zn 20-70 PPM Zn2+

Copper Co 5-20 PPM Cu2+

Molybdenum Mo < 1 PPM MoO42-

Cobalt Co < 1 PPM Co2+

Nickel Ni < 5 PPM Ni2+

Essential elements for plant growth and development.

The Nine Micronutrients

• Boron (B)• Chloride (Cl)• Copper (Cu)• Iron (Fe)

• Manganese (Mn)• Molybdenum (Mo)• Nickel (Ni)• Zinc (Zn)• Cobalt (Co)*

*Needed in legumes, only, for microorganisms fixing N2

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Use Diagnostic Tools to DetermineNeed for Micronutrient Fertilization

• Soil testing

• Plant analysis

• Field demonstrations

• Field observations

Micronutrient Contents in Soilsand Crop Removal

Range in soils, Corn Cotton

Nutrient total, lb/A 150 bu 1,000 lb lint

Boron 20-200 1 0.8

Copper 2-400 0.8 0.5

Iron 10,000-200,000

1.6 1.1

Manganese 100-10,000 1.3 4.8

Molybdenum 1-7 0.5 0.3

Zinc 20-600 2.4 1.0

Est. crop removal, oz/A

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Soil pH affects availability of certain nutrients.

Liming Influences the Availabilityof Micronutrients in Different Ways

• Reduces toxicity of Mn

• Increases availability of Mo

• Has no affect on Cl

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Boron deficienciesare widespread in many

parts of the world

Some Roles of Boron in Plants -Essential:

• In germination of pollen grains

• For growth of pollen tubes

• For seed and cell wall formation

• For protein formation

• For sugar translocation

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Boron Deficiency Symptomson Crops

Celery Crooked stem

Peanuts Hollow heart

Apples Corky core

Alfalfa Rosetting, yellow top, death of terminal bud

Beets Black heart

Cotton Ruptured squares, dieback of terminal bud, rosetting

Responsiveness of Crops to Boron

Alfalfa

Cauliflower

Celery

Sugarbeets

Table beets

Turnips

Peanuts

Cotton

Apples

Clover

Most response Medium response Least response

Broccoli

Cabbage

Carrots

Lettuce

Spinach

Sweet corn

Tomatoes

Asparagus

Canola

Radish

Beans

Blueberries

Cucumbers

Corn

Onions

Potatoes

Small grains

Sorghum

Sudan grass

Soybeans

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Factors Affecting Boron Availability

• Organic matter

• Weather conditions

• Soil pH

• Soil texture

• LeachingB

Boron deficiency symptoms

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Excess Boron Symptoms

Copper Deficiency Symptoms

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Organic soils are most

likely to be Cu deficient

Iron (Fe) deficiency in prune

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Functions of Manganesein the Plant

• Part of the plant enzyme system

• Activates several metabolic reactions

• Aids in chlorophyll synthesis

• Accelerates germination and crop maturity

• Increases plant availability of P and Ca

Some Causes ofManganese Deficiency

• High soil pH

• Imbalance with other nutrients such as Ca, Mg and Fe

• Soil moisture

• High organic matter soils during cool spring when soils are waterlogged

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Manganese (Mn) deficiency

Zinc (Zn) Deficiency

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Some Plant Functionsof Zinc

• Aids in the synthesis of enzyme systems

• Promotes certain metabolic functions

• Necessary for the production of chlorophyll and carbohydrates

• Key for growing points

Factors and ConditionsAffecting Zinc Availability

• Soil texture and pH• Soil phosphate

levels• Soil organic matter• Leveling for

irrigation

• Leaching

•Cold, wet soils

•Soil biological activity

Zn

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Some Functions of Chloride in Plants

• Involved in energy reactions, including the chemical breakdown of water

• Activates several enzyme systems

• Involved in the transport of cations

• Regulates stomatal guard cells, thus controlling water loss and maintaining turgor