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Why is Soil Sample Why is Soil Sample Depth ImportantDepth Important
Dick WolkowskiExtension Soil ScientistUW-Madison
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The Purpose of Soil Sampling
Determine the nutrient and lime need of fields to optimize profitability and preserve environmental qualityIdentify the “central tendency” of nutrient levels OR assess and manage spatial variability of soil test in fields Monitor effects of nutrient application over timeThe only preplant nutrient diagnostic toolIncreasingly becoming a regulatory index
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1999 SPAL Survey – 912 Reports (Kelling And Peters)
05
101520253035404550
1 2 1 2 3 4 1 2 3 4 5 6NUMBER OF SAMPLES
%
95%<10 a 10-20 a >20 a
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Describing Soil Test Variability
VARIABILITY CLASS
DISTANCE
MICRO < 2”
2” – 6 ‘
> 6 ‘
MESO
MACRO
SOURCE
PEDS vs. PORESMICRO MORPH.FERT. BANDING
CROP ROWSLANDSCAPE FIELD MGT.
JAMES AND WELLS, 1990
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Have We Paid Too Much Attention to X and Y, But Not Z
SOIL TEST PSoil test P Soil test P distribution indistribution ina Rock Co.a Rock Co.fieldfield
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Current Sample Depth Recommendations
Moldboard plowingDepth of tillage
Chisel plowing or offset disking ¾ depth of tillage
No-till 6-7 in.0-2 in. sample for pH in long-term no-till
Influence of soil moisture condition and consistency between samplers ??
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King Kong vs. MickeyKing Kong vs. Mickey
It wouldn’t be a fair fight,It wouldn’t be a fair fight,so could we expect them so could we expect them to take samples similarlyto take samples similarly
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Incremental Soil Sampling Comparisons
Arlington tillage x rotation x fertilizer placement study. Started in 1997.
Chisel, strip-till, no-tillContinuous corn, corn/soybeanw/ or w/o broadcast (200 lb 9-23-30)
9 cores to 8 inches in 2 inch increments over four replications in 2005Examine effects of 4, 6, 8 in. sample depthPlano silt loam (subsoil group B)
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Incremental Soil Sampling Comparisons
Lancaster tillage x fertilizer placement study. No-till for 10+ years, 2 chisel, 1 moldboard.
Corn/soybeanSampled the unfertilized plots
9 cores to 8 inches in 2 inch increments in single repRozetta silt loam (subsoil group A)
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Incremental Soil Sampling Comparisons
Arlington tillage x herbicide study. No-till, chisel, moldboard for 20+ years.
Continuous cornRecommended NPK fertilization, no lime
Arlington production alfalfa fieldNT Corn in 2003, seeded in 2004, two hay yearsLight manure applicationPrevious chisel tillage history
Both Plano silt loam (subsoil group B)
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Tillage and Soil Test Stratification
Acidification due to nitrification of surface-applied ammonium containing fertilizer; OM accumulation in no-till
Would lead to higher lime rec. in surfacePossible consequences on herbicide activity and nutrient availability
P and K stratificationSurface application with little or no incorporationLeaching from crop residueIncomplete mixing by conservation tillage
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Soil Test Stratification as Affected by Tillage Management, Arlington, Wis., 2005
2 2.5 3 3.5 4 4.5
CH
NT
SOIL ORGANIC MATTER (%)5 5.5 6 6.5 7 7.5
CH
NT
SOIL pH
CONTINUOUS CORNCONTINUOUS CORN
00--22 22--44 44--66 66--88
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Soil Test Stratification as Affected by Tillage Management, Arlington, Wis., 2005
10 20 30 40 50 60 70 80
CH
NT
SOIL TEST P (ppm)50 75 100 125 150 175
CH
NT
SOIL TEST K (ppm)
CONTINUOUS CORNCONTINUOUS CORN
00--22 22--44 44--66 66--88
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Effect of Sampling Depth on Soil pH and Organic Matter
SOIL TESTDepth pH OM (%)
in CH NT CH NT
0-4 5.9 6.1 3.7 3.7
0-6 6.2 6.4 3.6 3.5
0-8 6.4 6.5 3.5 3.3
CONTINUOUS CORNCONTINUOUS CORN
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Effect of Sampling Depth on the Estimated Lime Requirement
LIME REQUIREMENTt/a 60-69 ( target pH = 6.8)
Depth Chisel No-Till
0-4 5.3
3.4
2.2
4.1
0-6 2.3
0-8 1.7
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Effect of Sampling Depth on Soil Test P and K
Depth Soil Test P Soil Test K
--------------- ppm ----------------in CH NT CH NT
0-4 43 EH 61 EH 132 H 131 H
0-6 36 EH 53 EH 113 H 113 H
0-8 32 EH 47 EH 102 O 103 O
CONTINUOUS CORNCONTINUOUS CORN
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Effect of Sampling Depth on P and K Recommendations for Corn
Depth Soil Test P Soil Test K
--------------- ppm ----------------in CH NT CH NT
0-4 0 0 25 25
0-6 0 0 25 25
0-8 0 0 55 55
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Effect of Sampling Depth on P and K Recommendations for Alfalfa
Depth Soil Test P Soil Test K
--------------- ppm ----------------in CH NT CH NT
0-4 0 0 150 150
0-6 0 0 300 300
0-8 0 0 300 300
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Soil Test Stratification Following 20 Years Of Tillage Management, Arlington, Wis., 2006
50 70 90 110 130 150
NT
CH
MB
SOIL TEST K (ppm)
00--22 22--44 44--66 66--88
5.5 6 6.5 7
NT
CH
MB
SOIL pH
CONTINUOUS CORNCONTINUOUS CORN
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Effect of Sampling Depth Soil pH
Depth Soil pH
in MB CH NT
0-4 5.8 5.6 6.1
0-6 5.9 5.7 6.2
0-8 5.9 5.8 6.3
Tillage in place 20 yearsTillage in place 20 years
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Effect of Sampling Depth the Lime Recommendation for Corn and Alfalfa
Corn Alfalfa
--------------- ton 60-69/a ---------------
Tillage Sampling depth (in) Sampling depth (in)
0-6 0-4 0-6 0-8
5.9 5.37.23.7
8.15.56.2
4.7 3.0
0-4 0-8
MB 1.2 0.4 0.6CH 2.7 2.0 1.2NT 0 0 0
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Effect of Sampling Depth Soil Test K
Depth Soil Test K
in MB CH NT--------------- ppm ---------------
0-4 87 L 131 H 97 O
0-6 87 L 117 H 89 L
0-8 88 L 105 O 85 L
Tillage in place 20 yearsTillage in place 20 years
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Effect of Sampling Depth the Potash Recommendation for Corn and Alfalfa
Corn Alfalfa
----------------- lb K2O/a -----------------
Tillage Sampling depth (in) Sampling depth (in)
0-6 0-4 0-6 0-8
330 330150330
150330300
300 330
0-4 0-8
MB 80 80 80CH 20 20 20NT 50 80 80
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Effect of Sampling Depth Soil Test K in a Production Alfalfa Field
DepthIncrement
Soil Test (ppm)
Sample Depth
Soil Test (ppm)
K in P K
265 208
150 171
15199
906-8 11
in P
0-2 20 0-4 16
2-4 12 0-6 14
4-6 11 0-8 14
510 lb K510 lb K22O/a since 2004O/a since 2004
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SummaryFarmer profitability and regulatory compliance depends on proper soil sampling and testingMaintain management of surface variability, but attention must also be paid to depth variabilityStratification and how it effects fertilizer or lime recommendations emphasizes the need to sample to proper depth
Too shallow = excessive recommendationToo deep = inadequate recommendation
Chisel tillage does not remove stratificationBest advice is to sample to depth of the dominant tillage and maintain consistency