Current Status of Soil Test Calibration in Mississippi

Bobby R. GoldenDelta Research and Extension Center

479-409-6191bgolden@drec.msstate.edu

Mississippi-crops.com

Updating Soil Test Correlations in MS

• Why are we interested in doing this ?

• Changing crop rotational mix

• Improved production practices since last major update

Lancaster unpublished data (19?)

Interpretation of Soil Test Results

• A soil-test value is an INDEX, is not “the” total amount available (snapshot in time)

• Field calibrations with crop response give a meaning to soil-test values by different testing methods.– critical/optimum value or range– interpretation classes– application rate for responsive ranges

How do we get there ?

• Program Development for Correlation/Calibration

• Currently working on Corn, Soybeans, and Cotton.

• P, K, Zn• Major Goal:

– Field correlate soil test index to yield response and tissue concentrations

Potassium and Corn

• Soil test K in the top 6” of soil is an indicator of corn yield responsiveness in the Midwest.

• Does this hold true for the Midsouth?

• However corn is new to the Midsouth and little research has been conducted to establish critical values

0 lb K2O/acre

160 lb K2O/acre

Corn Response to K Fertilization

Leflore Co

Potash rate (lb K2O/acre)

0 40 80 120 160 200

Me

an

co

rn g

rain

yie

ld (b

u/a

cre

)

100

150

200

250 Bolivar Co.

Potash rate (lb K2O/acre)

0 40 80 120 160 200

Me

an

co

rn g

rain

yie

ld (b

u/a

cre

)

100

150

200

250

Golden unpublished data (2012)

73 bu/ac yield response 27 bu/ac yield response

Corn Response to K Fertilization

Lancaster Soil Test K

Lancaster extractable K (ppm)

0 50 100 150 200 250 300 350

Rela

tive c

orn

yield (%

)

50

60

70

80

90

100

110

Non ResponsiveResponsive

Mehlich-3 Soil Test K

Mehlich-3 extractable K (ppm)

0 50 100 150 200 250 300 350

Rela

tive co

rn yield

(%)

50

60

70

80

90

100

110

Non ResponsiveResponsive

Golden unpublished data (2012)

Potassium and Soybean

• Soil-test K in the top 4 or 6 inches of soil is an excellent predictor of soybean responsiveness to K fertilization.• Slaton et al. 2010• Mallarino et al., 2005• Clover and Mallarino, 2009

Soybean Actual Yield at Responsive sites

Golden unpublished data (2012)

Responsive sites

K fertilizer rate (lbs K2O/acre)

0 40 80 120 160 200

So

yb

ea

n y

ield

(bu

/ac

re)

40

50

60

70

80

90

100Humpherys CoBolivar Co

10 bu/ac response8 bu/ac response

Soybean Yield Response to K Fertilization

Lancaster Soil Test K

Lancaster extractable K (ppm)

50 100 150 200 250 300 350

Rela

tive so

ybea

n yie

ld (%

)

0

20

40

60

80

100

120

Non Responsive SitesResponsive Sites

Mehlich-3 Soil Test K

Mehlich-3 extractable K (ppm)

50 100 150 200 250 300 350

Rela

tive s

oyb

ean

yield

(%)

0

20

40

60

80

100

120

Non ResponsiveResponsive

Golden unpublished data (2012)

Soybean Tissue Response to K Fertilization

Lancaster Extractable K (ppm)

50 100 150 200 250 300 350

So

yb

ea

n T

iss

ue

K @

R2

(%

)

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

Non Responsive SitesResponsive Sites

Mehlich-3 Extractable K (ppm)

50 100 150 200 250 300 350

So

yb

ea

n T

iss

ue

K @

R2

(%)

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3Non Resonsive SitesResponsive sites

Golden unpublished data (2012)

Mehlich 3 - Lancaster Correlation

Lancaster Extractable K (ppm)

0 100 200 300 400 500

Me

hlic

h-3

Ex

tra

cta

ble

K (

pp

m)

0

100

200

300

400

500

600M3K = 4.102 + 0.9547(lancaster K)

Golden unpublished data (2012)

Mehlich 3 – Lancaster Correlation

M3P = -10.149+0.8140(lancaster)

Lancaster Extractable P (ppm)

0 20 40 60 80 100 120 140 160

Me

hlic

h 3

Ex

tra

cta

ble

P (

pp

m)

-20

0

20

40

60

80

100

120

140

Golden unpublished data (2012)

Zinc Deficiency Symptomology

Methods of Zn Fertilization

• Soil Applied– 10 lb Zn/acre as a

granular fertilizer– Adjust rates based on

water solubility of Zn sources

• Foliar Applied– Apply 1-2 lb Zn/acre after

emergence– Chelated for soil

application (Little foliage for interception)

– Sulfate for foliar application (larger plants)

Zinc Rate Response Trials 2012

Zn application rate (lb Zn/acre)

0 2.5 5 7.5 10

Mean

corn

grain

yield (b

u/acre)

0

50

100

150

200

250

300Bolivar Co (29 bu increase) DREC7 (16 bu increase)

Corn Response to Zn Rate

Lancaster Extractable Zn (ppm)

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Re

lati

ve

Co

rn G

rain

Yie

ld (

%)

86

88

90

92

94

96

98

100Responsive SitesNon Responsive Sites

Mehlich-3 Extractable Zn (ppm)

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Re

lati

ve

Co

rn G

rain

Yie

ld (

%)

86

88

90

92

94

96

98

100Responsive SitesNon Responsive Sites

Corn Yield Response to Zn Fertilization

M3Zn=0.4914 +1.44(lancaster)

Lancaster Extractable Zn (ppm)

0 2 4 6

Me

hlic

h 3

Ex

tra

cta

ble

Zn

(p

pm

)

0

2

4

6

8

10

Mehlich 3 - Lancaster Correlation

Zn Product Foliar Burn

EDTA Chelate @ 2lb ZnCitric Acid Chelate @ 2lb Zn

Zinc Product Foliar Burn @ 6d after application

Zn application rate (lb Zn ac-1)

0.5 1 2

Vis

ua

l Inju

ry Ra

ting

(%)

0

10

20

30

40

50

60

70EDTA ChelatedCitrate Chelated

Zinc Foliar Burn - Tissue Concentration @ 2 WAA

Zn application rate (lbs Zn acre-1)

0.5 1 2Co

rn leaf tiss

ue Z

n c

on

cen

tration

(pp

m)

0

20

40

60

80

100

120

140Main effect of Zn rate (p =<0.0001)

Golden unpublished data (2012)

Zinc Foliar Burn Tissue Concentration @ 2 WAA

Zn Product

Citrate EDTA

Co

rn L

ea

f T

iss

ue

Zn

Co

nce

ntr

ati

on

(p

pm

)

0

20

40

60

80

100

120Main effect of Zn product (p=0.0091)

Golden unpublished data (2012)

Zn Foliar Burn Grain Yield

Zn Rate (lb Zn/acre)

0.5 1 2

Me

an

co

rn g

rain

yie

ld (b

u/a

cre

)

0

50

100

150

200

250

300EDTA ChelateCitric Acid Chelate

Golden unpublished data (2012)

Zinc Basics

• Soil test Zn coupled with pH is a good indicator of need

• Use the Right rate for the Zn source and soil

• Remember not all Zn fertilizers are created equal– Must take into account water solubility– Supply Zn early

At the End of the Day

• Fertilizer costs money, but yield pays the bills: High fixed production costs for land, good seed, equipment

– relative costs, and business management approach