Soil Test Methods: Principles and Practices - PowerPoint PPT Presentation

1 / 45
About This Presentation
Title:

Soil Test Methods: Principles and Practices

Description:

Soil Test Methods: Principles and Practices – PowerPoint PPT presentation

Number of Views:4232
Avg rating:3.0/5.0
Slides: 46
Provided by: ValuedGate2059
Category:

less

Transcript and Presenter's Notes

Title: Soil Test Methods: Principles and Practices


1
Soil Test MethodsPrinciples and Practices
Ann Wolf Ag Analytical Services Lab Penn State
University
2
Todays talk
  • Soil testing-basic principles
  • Commonly used soil tests and how they differ
  • Why do test results among labs differ?
  • Quality control and quality services
  • Selecting a lab to meet your testing needs

3
Basics of a good soil test
  • Rapid, cost-effective and relatively easy to
    perform
  • Reproducible results
  • Correlated to crop response
  • Environmentally friendly

4
Soil Tests
  • pH and acidity
  • Phosphorus
  • Potassium, calcium, magnesium
  • CEC
  • Trace elements
  • Nitrogen

5
pH and Lime Requirement
pH and acidity (lime requirement)
6
Soil pH and Soil Acidity
Soil solution pH
Reserve Acidity
7
Soil pH Measurement
  • Soil pH is measure of H activity in the soil
    solution.
  • Determined by mixing soil with water and
    measuring with pH electrode
  • Results should not vary significantly among labs

8
Soils with same pH can have different levels of
reserve acidity and different lime requirements
9
Soil Acidity Measurement
  • A buffer solution is added to the soil to react
    with the soil acidity. The drop in pH of the
    buffer is directly proportional to soil acidity
    present.
  • The test must be calibrated on soils from region
    to be meaningful.

10
Soil Acidity/Lime requirement
  • Common buffers
  • SMP Buffer
  • Most common buffer in Mid-Atlantic/North Central
    US
  • Contains chromium Hazard to lab technicians
    all waste collected for hazardous landfill
  • Mehlich Buffer
  • Only buffer that contains no hazardous components
  • Adams-Evans Buffer (Primarily for Southeast
    Soils)
  • Recommended for Pennsylvania soils

11
Calibration of Buffer Tests PASoils
SMP Buffer
Mehlich Buffer
  • Mehlich Buffer
  • better predictor of LR than SMP
  • Safer in the Lab
  • No hazardous waste
  • PSU switched from SMP to Mehlich Buffer, July 2004

12
Soil Acidity/Lime requirement
  • Other methods used
  • Estimate from pH/base saturation
  • Hand Texture (estimate of clay)

13
PHOSPHORUS
PHOSPHORUS SOIL TESTS
14
Phosphorus Soil Tests
15
Soil Test P Response Curve
Mehlich 3. Bray P (PA)
50
30
Mehlich 1 P (Md)
50
25
Morgan P (NY)
20
5
Above Optimum
Optimum
Low
Yield
Soil Test Level (ppm)
16
Effect of instrumentation on P measurement
ICP vs Color for Mehlich 3 P
ICP
P
P
P
P
Color
P
Soil Extract
17
Instrumentation effecton Mehlich 3 P measurement
18
Cations and Cation Exchange Capacity
19
Cations K, Ca, Mg
K
-
Ca
-
-
Mg
Mg
-
-
-
-
-
K
Cations are held on negatively charged sites on
soil particles
-
-
Ca
Soil Colloid
-
-
Mg
-
K
-
-
-
-
Mg
-
-
-
K
Ca
Ca
20
Soil Tests for Cations
Replace cations from exchange sites with counter
ion
Extracting solution
K
Ca
-
-
Mg
-
Mg
-
-
-
-
-
K
NH4
H
-
H
-
Ca
Soil Colloid
NH4
-
-
NH4
Mg
-
K
NH4
NH4
-
-
-
-
Mg
H
-
-
-
H
K
Ca
Ca
21
Soil Tests for Cations
Measure cations in soil extract ICP, AA, Color
NH4
Soil Extract
H
-
-
NH4
-
NH4
-
-
-
-
Mg
K
Ca
-
NH4
-
K
K
-
H
Soil Colloid
-
Ca
Mg
-
Ca
NH4
-
H
NH4
Mg
-
-
NH4
-
-
-
H
-
-
K
NH4
H
Ca
Mg
H
NH4
H
22
Soil Tests for K, Ca, Mg
  • Mehlich 3 (H, NH4)
  • Current PA test
  • Ammonium Acetate pH 7 (NH4)
  • PA test before 1991
  • Mehlich 1 (H)
  • Morgan/Mod Morgan (Na or NH4 )

In general, tests extract similar quantities of
Ca and Mg , but extracts that contain NH4
will extract more K
23
Cation exchange capacity (CEC)
  • Measure of negatively charged exchange sites for
    cations on soils (meq/100 g)
  • Determined by summation

24
CEC by Summation
K
H
-
-
Ca
Mg
Mg
-
Ca
-
-
-
-
-
-
-
H
-
-
K
Basic Soil
Acidic Soil
-
-
-
-
Ca
Ca
-
H
-
-
-
-
-
-
-
-
-
Mg
H
-
-
-
-
Ca
H
H
Ca
K
K
Ca
CEC KCaMg
CEC Acidity KCaMg
25
Potential errors with CEC by summation
K
Mg
Ca
-
Soil Extract
-
Mg
-
-
-
K
-
-
-
Mg
K
-
CaCO3
Ca
-
Ca
Ca
Soil with Free CaCO3
-
Ca
-
Ca
Mg
Ca
Ca
-
K
CaCO3
CaCO3
Ca
-
Mg
-
-
-
Ca
Mg
-
-
-
Ca
K
Ca
K
Ca
Ca non-exchangeable Ca dissolved directly
from calcium carbonate minerals
26
Errors in CEC measurements by summation
27
Trace Elements
28
Trace Elements
  • Trace element deficiencies are uncommon in PA
    soils making reliable interpretation and
    recommendations on basis of soil tests difficult.
  • Plant Analysis should be used in conjunction with
    soil testing to evaluate deficiencies and help
    guide fertilizer applications.

29
Mehlich 3 Cu distribution in PA soils
Concern with high levels from
dairy foot baths
0.5 Normal Range 15.0

30
Mehlich 3 Zn distribution in PA soils
Occasionally deficient in soils with high pH and
high P from fertilizer (not manure) additions
1.0 Normal Range 80.0

31
Mehlich 3 S distribution in PA soils
Not currently a common deficiency but could be in
the future if acid rain is reduced
10 Normal Range 75

32
NITROGEN
OSU Extension fact sheet
33
Nitrogen
  • Nitogen (N) is one of the most important
    nutrients required for optimum plant growth BUT
  • Given the complexity of the nitrogen soil cycle,
    no soil test can accurately predict nitrogen
    availability in soils over the growing season.

34
Tests for improving N management for corn
35
Reporting Units and element forms
P
P2O5
ppm
K2O
Mg/kg
Meq/100 g
K
sat
Lb/A
36
Units ppm vs mg/kg vs lb/A
1 ppm part per million 1 part/1 million 1
mg/kg
lb/A 1 lb/2 million lbs of soil part/2
million
37
Elemental vs Oxide forms
38
Quality Control
  • A good laboratory quality control program is
    essential for producing results that are accurate
    and reproducible.

39
Quality Control PSU example
  • 1 QC soil sample at start of day
  • 1 QC soil sample every 30 unknowns

40
Quality Control PSU example
Instrument calibration checks every 10-15 samples
41
Quality Control PSU example
Instrument calibration checks every 10-15 samples
Participation in North American Proficiency
Testing Program for soils
42
Quality Services
  • Rapid turn-around time
  • Results available electronically
  • Re-runs on questionable results
  • Prompt and accurate response to questions and
    problems
  • Supplemental materials to help use the results
    paper and web
  • Complete information on methods
  • All recommendation tables readily available
  • Confidentiality of results

43
Are you using the right lab?
  • Is it performing tests appropriate for PA soils?
  • SMP/Mehlich Buffer for acidity
  • Mehlich 3 for phosphorus and cations
  • Summation of cations and acidity for CEC
  • Have the tests it uses been calibrated for PA
    soils and growing conditions?

44
Are you using the right lab?
  • Are units and test methods clearly specified on
    reports?
  • Is it following appropriate quality control
    procedures and does laboratory staff have
    adequate background in soils/soil testing.
  • Does it provide the quality services you need?

45
The End
Write a Comment
User Comments (0)
About PowerShow.com