Soil Sampling and Nutrient Additions for Crop Production Edwin Ritchey Extension Soil Specialist UK-REC.

Soil Sampling and Nutrient Additions for Crop Production

Edwin RitcheyExtension Soil Specialist

UK-REC

2

Soil Sampling

• Indicates the current nutrient status of soil

• A guide for nutrient additions

• Diagnose nutrient deficiencies or toxicities

• Saves money• Cost is small compared

to over/under fertilization

Photo, Josh McGrath

Random Soil Sampling

• Want a representative sample (AFS=2,000,000 lb)• Uniform areas - based on drainage, cropping history,

erosion, past management • e.g. feeding areas (manure), fencerows, etc.

• Collect at least 10 cores, more for larger areas• The more samples (cores) collected, the closer to the

true field value obtained• Every two years, or so…• Fall or Spring?• Depth?

4

MANURE SAMPLING & TESTING

Recommendations are only as good as the sample they are based on

Determining Nutrients Present

H

H

H

H

_ _ _

Na+

Al3+

Mg2+

K+

Ca2+

_ _

_ _

_ _

soil pH 5 Mehlich 3

NH4+

NH4+NH4

+

NH4+

NH4+NH4

+

NH4+

NH4+NH4

+

NH4+

NH4+NH4

+

NH4+

Base cations analyzed in leachate

How much fertilizer do I add?

• Soil Test (UK, Waters, A&L)• Considerations for soil lab

– Must be easily repeatable– Relatively quick– Must be “equivalent” to what is available to plant

• Correlation• Calibration

Nutrient availability to plants

Readily available

Slowly available

Soil solution

Image: Raising-chicken.org

0 1Soil Test P (lbs/acre)

40

50

60

70

80

90

100

110

Y ie l

d (%

of m

axim

um)

60305

Soil Test P (lbs/acre)

Correlation: Is a soil test a good predictor of nutrient ……………………..availability?

0 1Soil Test P (lbs/acre)

40

50

60

70

80

90

100

110

Y ie l

d (%

of m

axim

um)

60305

Soil Test P (lbs/acre)

Low

Med

High

V.low

Calibration: How much fertilizer is needed below threshold?

Arrows represent the amount of fertilizer needed to achieve maximum yield

Response Curve

0 25 50 75 100 125 150 175 2000

20

40

60

80

100

120

f(x) = − 0.00384761904761905 x² + 0.974285714285715 x + 39.4761904761905R² = 0.998301113063855

Fertilizer Applied

Whe

at Y

ield

(Bu/

A)

0 20 40 60 80 100 120 140 16040

50

60

70

80

90

100

f(x) = − 0.00285714285714286 x + 85.2142857142857R² = 0.0357142857142827

Fertilizer Rate

Whe

at y

ield

(bu/

A)

No Response to Fertilizer

UK Soil Test Levels

• Low testing soils, expect a yield response to added fertilizers and large amounts are added

• Medium testing soils, yield response is small to none, add fertilizer to maintenance levels

• High testing soils, no yield response expected, no fertilizer recommended

Time (years)

Soil

test

P o

r K

9 lb/ac P2O5 remaining in soil increases soil test 1 lb/ac

4 lb/ac K2O remaining in soil increases soil test 1 lb/ac

Agronomic Threshold

Sufficiency

2 Philosophies with a Low Soil Test

2 Philosophies with a Low Soil Test

Time (years)

Soil

test

P o

r K

Agronomic Threshold

Rapid Build-up

Time (years)

Soil

test

P o

r K

Agronomic Threshold

maintenance

sufficiency

buildup

3 Philosophies with a High Soil Test

Differences in Soil Labs

• Many labs use Mehlich III extractions– UK, Waters, A&L, etc– Test for pH, Bu pH, K, P, Ca, Mg, Zn

• “Similar” nutrient results from all labs • Differ some in philosophy (so do people)• Sufficiency, Maintenance, Build-Up

– Micronutrients, Soil Cation Balance

Soil Test Labs

• One soil sample mixed and submitted to– UK: P = 84 lbs/A, K = 234 lbs/A– Waters: P = 79 lbs lbs/A; K = 243 lbs/A– A&L: P = 47 ppm (94 lbs/A); K = 135 ppm (270 lbs/A)

• Recommendations for corn– UK: P2O5 = 0 lbs/A; K2O = 40 lbs/A

– Waters: P2O5 = 85 lbs/A; K2O = 125 lbs/A

– A&L: P2O5 = 60 lbs/A; K2O = 80 lbs/A

• Differ some, more philosophy than test

High

Med

Low

V.Low

Soil Test Level

100%

70-100%

50-70%

<50%

Sufficiency Level

Nutrients available from soil

External nutrients required

soil

soil

soil

soil

fertilizer

fertilizer

fert.

Relative Sources of Nutrients

Profit Probability

100%

90%

60%

15%

V.low Low Medium High

Levels of Soil Fertility

Pro

bab

ility

of

Pro

fita

ble

Cro

p R

esp

on

se t

o F

erti

lizer

University of Kentucky AGR-1

K deficiency - yellowing of leaf margins of older soybean leaves. WHY???K deficiency - yellowing of leaf margins of older soybean leaves. WHY???

Photo: Greg Schwab

What is CEC and How Does CEC Influence Fertilizer Rates in KY?

Cation Exchange Capacity

Ca++

Plant Root

H+

K+H+

K+

-----

- - --

-

-

-

- - --

H+NH4+Ca++

Ca++

H+

H+

K+

K+

Mg++

Mg++

Ca++

Ca++Ca++

Ca++

Mg++

Mg++

Mg++

H+H+ H+

K+

K+

H+

K+

Ca++

Ca++

NH4+

NH4+

NH4+

Clay

ClayClay

Clay

Soil Solution

Determining Nutrients Present

H

H

H

H

_ _ _

Na+

Al3+

Mg2+

K+

Ca2+

_ _

_ _

_ _

soil pH 5 Mehlich 3

NH4+

NH4+NH4

+

NH4+

NH4+NH4

+

NH4+

NH4+NH4

+

NH4+

NH4+NH4

+

NH4+

Base cations analyzed in leachate

Calculated CEC

Measured CEC

Number of marbles are estimated

Number of marbles are counted

0 5 10 15 20 25 300

5

10

15

20

25

30

Calculated CEC (meq / 100 g)

Mea

sure

d CE

C (m

eq /

100

g)

557 Kentucky soils

Uncertainty in Calculated CEC

For CEC less than 10 meq/100 g: ± 2 meq/100 g

For CEC between 10 and 20 meq/100 g: ± 3 meq/100 g

7 meq/100 g 5 to 9 meq/100 g

15 meq/100 g 12 to 18 meq/100 g

What does CEC and cation saturation tell you?

Soil texture (sandy vs clayey soil)

% base saturation as another indicator of soil acidity

Ability to Buffer Change

Indiana soils

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 270

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

CEC (meq/100 g)

Num

ber o

f sam

ples

Ag samples with soil pH <= 7 inAll counties

Year = 2011Total number = 28,658

14 % >181 % <10

Frank Sikora, 2012

8 9 10 11 12 13 14 15 16 17 18 19 20 21 220

50

100

150

200

250

300

350

400

450

CEC (meq/100 g)

Num

ber o

f sam

ples

Ag samples with soil pH <= 7 inBreckinridge, Daviess, Hancock, Henderson, McLean, Ohio, Webster

Year = 2011Total number = 1915

4 % >181 % <10

Why Do We Lime?

• Proper pH is the foundation of a good soil fertility program – BIG BANG FOR YOUR BUCK

• Adjust soil pH (neutralize acidity)• Soil pH influences:

– Nutrient Availability– Root Growth– Herbicide Activity

• Soil pH can limit crop yield w/out noticing

Corn Alfalfa THE MASTER

VARIABLE

The effect of soil pH on the activity of soil micro-organisms, availability of plant nutrients, and occurrence of toxic elements

Effect of pH on Root Growth

Soil pH6.6 6.2 4.7

Penn State

Effect of Soil pH on Soil Tests of Nutrients

1. Availability of many nutrients is changed by changing soil pH.

2. Maintaining proper pH will maximize nutrient availability and reduce fertilizer need.

3. Soil tests will rise faster and reduce slower if pH is properly maintained.

Sources of Soil Acidity

1. Kentucky soils have a naturally low pH due to high rainfall and the leaching of calcium from the soil.

2. Main source of acidity in modern farming is nitrogen

- Most common nitrogen sources lower pH Urea, Anhydrous Ammonia, liquid nitrogen, and ammonium nitrate.

NH4+ + O2- NO3

- + H2O + 2H+

3. In general, 3 lbs of ag lime are needed to neutralize acidity from one pound of nitrogen

Sources used to neutralize acidity

• Lime: Calcitic: CaCO3 or dolomitic: CaMg(CO3)2

– CaCO3 + 2H+ H2CO3 H2O + CO2

• Quick lime: CaO• Hydrated lime: Ca(OH)2

• Pelletize Lime: CaCO3

• Waste products: biosolids, paper waste, shells• Gypsum: CaSO4

– CaSO4 + 2H20 + 2H+ Ca2+ + SO42- + 2H2O + 2H+

Liming soil

H

H

H

H

_ _ _

Na+

Mg2+

K+

Ca2+

_ _

_ _

_ _

soil pH 5

CaCO3

Ca2+

CO32-

H2CO3

H2O and CO2

_

_

Liming soil

H

H

H

H

_ _ _

Na+

Mg2+

K+

Ca2+

_ _

_ _

_ _

soil pH 6

CaCO3

Ca2+ Ca2+

_

_

Summary

• Soil testing is the foundation – DON’T GUESS, SOIL TEST

• Labs differ little in results, more in recs• CEC is important, but don’t worry about it• Yield responses are typically not seen when

soil fertility is adequate• Mind the fundamentals • pH management – basis of good fertility

Questions or Comments

Manganese Deficiency Symptoms

Interveinal chlorosis

Photo Greg Schwab

Soil pH Affect on Herbicide Activity1. The effectiveness of several

herbicides is influenced by soil pH.

2. Herbicides in Triazine family (Atrazine and Princep) are widely used with corn.

3. The effectiveness of weed control of Triazines is reduced below a pH of 6.0 and greatly reduced at 5.5 pH.

4. Extends persistence of many Sulfonylurea herbicides above pH 7 and may cause carry over problems.