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Potassium management for Vegetable Production

Dr. Ajay Nair

Department of Horticulture

Iowa State University

Essential Plant Nutrients

Macronutrients

Nitrogen

Phosphorus

Potassium

Calcium

Magnesium

Sulfur

Micronutrients

Manganese

Zinc

Boron

Copper

Iron

Molybdenum

Sodium, Chloride, Nickel, Cobalt, Silica

Carbon, Hydrogen, Oxygen

Soil management

• Regular soil

sampling

• Nutrient

management

• Soil pH and EC

• Soil organic matter

When to Take Soil Samples?

• For fall planting, sample should be taken in

the spring.

• For spring planting, sample should be taken

in the fall.

SpringFall

pH and lime recommendations

Organic matter

Cation Exchange Capacity

Phosphorus and Potassium

– Nutrient recommendations based on crop

Mg and Ca

Micro nutrients upon request

Nitrogen

– Recommendation, but not generally based on tests

What does a soil test indicate?

• Iowa State University Soil Testing LaboratoryG501 Agronomy Hall, Iowa State University, Ames, Iowa 50011-1010

• A&L Heartland Laboratories, Inc.111 Linn Street, PO Box 455Atlantic, IA 50022800-434-0109 712-243-6933

Where to send samples?

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High tunnel challenge: nutrient

supply

o Crops under high tunnels

often outperform field

grown plants

o Nutrient management is

critical

o Nutrient imbalance can

cause deficiency or toxicity

o Potassium is used in carbohydrate

metabolism and increases water-use

efficiency

o It promotes flower and fruit production and

is vital for maintaining growth and helping

plants resist diseases

Importance of potassium

o Regulates transpiration by stomata and

transport of assimilates

o Increases leaf area and chlorophyll

content

o Delays leaf senescence and thus

contributes to greater canopy

photosynthesis and crop growth

o Chemical fertilizers

o Potassium chloride (Muriate of potash)

(50% K)

o

o Potassium nitrate (37% K, 13% N )

o Potassium sulfate (40–43% K, 18% S)

Sources of potassium

Commercial Forms of potassium

o Potassium chloride (0-0-60)

o Potassium sulfate (0-0-50)

Apply 1/2 - 1/3 of the total potassium before planting

o Potassium Sulfate (0-0-50, 18S)

o K-Mag (0-0-22, 22S, 11Mg)

o Langbeinite

o Muriate of potash (0-0-60) KCl, only if

mined, chloride buildup

o Kelp (0-0-2)

Potassium Sources

OMRI approved

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Compost

o Excellent organic amendmento Incorporate 4-6 incheso Be careful about the qualityo Key issues

Needed in large quantityhigh salt contentherbicide residue

Manure type Nitrogen P K

% dry weight basis

Dairy manure 1-2 0.5-1.5 1-2

Feedlot manure 2-3 1-1.5 1-2

Poultry manure 2-4 1-3 1-3

Crop residue 1.5-2.5 0.2-0.5 1-2

Compost nutrient levels

Calculation of N credit from

compost

Tomato crop requires around 120-150 lbs/A nitrogen

Say you apply 10 t/A

50% is moisture so technically you applied 5

t/A (10,000 lbs)

N present = 1.5% of 10,000 = 150lbs

Only 20% is available in the first growing

season

Crop availability = 30lbs

Compost applied 5t/A (dry weight

basis)

1.5% P = 150 lbs/A P2O5 equivalent

1.5% K = 150 lbs/A K2O equivalent

Compost application can result in

excessive P and K

Calculation of K credit from

compost

P rapidly accumulates

Material % P content in

Organic form Inorganic form

Dairy manure 25 75

Poultry manure 10 96

Composted manure

16 84

Swine manure 9 91

Earlier example of P

75% available = 112 lbs

Optimum nutrient management

o Preplant

o Phosphorus is usually

completely applied pre-

plant

o Fertigation:

Mostly used to apply

nitrogen and potassium

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Ranges

SOIL ORGANIC MATTER

Low Medium High

Soil organic matter

Less than 3% 3.1 – 10.0 More than 10.1

Relative soil test levels for Phosphorus and Potassium (ppm)

Low Medium Med.-High High V. High

P 0-10 11-20 21-30 31-40 41+

K 0-80 81-120 121-160 161-220 220+

Potassium from soil test(ppm)

Apply (lb/A)

0-80 200

81-120 150

121-160 100

161-220 50

220 + 0

Potassium management for tomato

production

Days after planting

Weekly Nlb/A

Weekly K20lb/A

Pre-plant - -

Up to 3 weeks 3.5 7

3 – 7 weeks 5.0 10

7 – 10 weeks 7.0 15

10 – 13 weeks 7.5 15

13 – 16 weeks 7.0 15

At pre-plant apply 50 and 100 lb/A of N and K2O respectively

Fertigation schedule

pH is a measure of the soil’s level of

acidity and is the single most important

factor to know about your soil!

Availability of soil nutrients depends

upon soil pH

pH

If pH >7, less available

•Phosphorus

•Boron

•Copper

•Iron

•Manganese

•Zinc

pH <5.5, less available

•Calcium

•Magnesium

•MolybdenumBest range for most veggies

on mineral soils Source: Swiader and Ware

Beets

Cabbage

Muskmelon

Peas

Spinach

Celery

Chives

Lettuce

Onion

Radishes

Cauliflower

Sweet corn

Pumpkins

Tomatoes

Snap beans

Carrots

Cucumbers

Parsnips

Peppers

Hubbard squash

Eggplant

Watermelon

Potatoes

Asparagus

Tolerance of vegetables to pH

Most sensitive

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Check your soil EC

• Based on saturated paste extract method

< 2 mmhos/cm = optimum3-4 = plants show initial symptoms5-7 = growth affected> 8 = detrimental; plant death

Deficiency Symptoms of Potassium in Tomato

o Woody stems and slow growth. Stems

become weak and fall down

o Leaves may also have a bronzed

appearance and yellow and orange

patches may develop on some of the

leaflets

o Older leaves may look scorched around

the edges and/or wilted. Symptoms first

appear on older leaves

Deficiency symptoms of K in leaves

Source: http://5e.plantphys.net/article.php?ch=t&id=289

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Tomato water needs

Lewis Jett, WVU

Cover crop for high tunnels

o An excellent opportunity to

build organic matter

o Improve soil physical,

chemical, and biological

properties

o Nutrient management

o Crop rotation

Yellow mustard

1/30/2016

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Brandon Carpenter

Dana Jokela

Jennifer Tillman

Ray Kruse

Kyle Tester

Bernie Havlovic

Nick Howell

Vince Lawson

Many Thanks

Blossom end rot

in pepper

Its gonna come !

Contact

Dr. Ajay NairEmail: nairajay@iastate.eduPhone: 515-294-7080

iowavegetables.blogspot.comextension.iastate.edu/vegetablelab