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Sample Handling and Soil Test Potassium

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Dry conditions affect soil tests for K. Decrease if soil test values are high ... Place sample in paper bags or cardboard box. Dry in cabinet equipped with exhaust fan ... – PowerPoint PPT presentation

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Title: Sample Handling and Soil Test Potassium


1
Sample Handling and Soil Test Potassium
  • George Rehm
  • Dept. of Soil, Water, and Climate

2
Major Points
  • Consultant observations
  • Basics of potassium in soils
  • Drying time and temperature

3
Past Research
  • Dry conditions affect soil tests for K
  • Decrease if soil test values are high
  • Increase if soil test values are low

4
Consultant ObservationsK Soil Tests
5
Consultant ObservationsK Soil Tests
6
Change in Soil Test KResearch Sites
0-0-60 applied between Spring (yr1) and Fall
(yr1) at a rate of 200 lb./acre
7
Potassium in Soils
Unavailable K 90-98 of Total
weathering
Slowly Available K 1-10 of Total
Readily Available K 1-2 of Total
Non Exchangeable K
Exchangeable K
Solution K
10
90
8
Soil Test K
  • Currently used ammonium acetate procedure
    measures total of exchangeable and solution K

9
Clay Minerals Play a Role
  • Kaolonite (not a factor)
  • Illite (fixing, slow release)
  • Montmorillonite
  • Expand and contract with drying
  • Dominate in Minnesota (cracks)
  • Trap K when dry

10
Illite
Non Exchangeable K
11
K
Montmorillonite
K
K
K
Exchangeable and fixed in dry soils
K
K
K
K
K
K
K
K
K
K
K
12
(No Transcript)
13
There is Reported Variability in Results of Split
Samples Sent to More Than One Laboratory
14
Possible Explanations
  • Variability in sample collection
  • Drying temperature and time
  • Extraction procedure

15
Temperature and Drying Time Affect Soil Test K
Source Gelderman, South Dakota
16
Standard Analytical Procedures
  • Sieve soil through 2 mm screen
  • Scoop with standard 1.7 cc scoop
  • Place soil in 50-ml flask
  • Add 1 N ammonium acetate
  • Shake for 5 minutes
  • Filter and measure K

17
Drying Procedure (NCR-13)
  • Place sample in paper bags or cardboard box
  • Dry in cabinet equipped with exhaust fan
  • If heat is necessary, temperature inside cabinet
    should not be high than 104ºF

18
Standard Handling Procedure is Necessary
  • Fertilizer recommendations from Land Grant
    Universities based on results of analysis using
    the standard procedures.
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