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Current Status of Soil Test Calibration in Mississippi
Bobby R. GoldenDelta Research and Extension Center
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Lancaster unpublished data (19?)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Golden unpublished data (2012)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Golden unpublished data (2012)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Golden unpublished data (2012)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
