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Principles of Soil and Plant Testing December 2009

Principles of Soil and Plant Testing December 2009

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Principles of Soil and Plant Testing December 2009

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  1. Principles of Soil and Plant Testing December 2009 Eugenia Pena-Yewtukhiw and Jeff Skousen West Virginia University

  2. Techniques to Assess Field Nutrient Status • Deficiency Symptoms of Plants • Plant Analysis • Soil Testing


  4. Visual Deficiency Symptoms • Use only as supplement; to monitor the crop • Deficiency = nutrient stress has affected yield • Visual symptoms may be caused by more than one nutrient (or ..) • Deficiency of one nutrient may be related to excess of another • Difficult (sometimes) to distinguish among deficiency symptoms in the field

  5. Objectives of Plant Tissue Analysis • To help identify/confirm deficiency symptoms and to determine nutrient shortages before they appear in the plant • To identify potential problems in fields with inadequate nutrient management history • To aid in determining the effect of fertility management on nutrient acquired by crop • To study the relationship between nutrient status of the plant and crop performance

  6. Plant Tissue Analysis • Nutrient status at the time of sampling • Easy to perform • Deficiency may have already caused yield loss – TOO LATE! • The crop may not respond to added nutrient • The crop may be too large for nutrient application • Climate conditions may be unfavorable for nutrient application

  7. Plant Tissue Analysis • Sample at peak periods of nutrient demand • Compare plants from deficient areas and normal areas • Genetic variability among plants, so composite samples taken from 10 to 15 plants to give a single sample

  8. New Developments In Plant Analysis • Corn Stalk Nitrate Test • An end-of-season test that can be used at the end of the season to verify whether the N management program supplied sufficient N for optimum yields, or it can be used to compare alternative N management practices. • The test cannot be used to fine-tune the N management program during the season of growth.

  9. New Developments In Plant Analysis • Sampling For The Corn Stalk Nitrate Test: • Samples taken within 3-week period beginning at grain ‘black layer’ formation. Typically, this is about 2 weeks after silage harvest, but about 2 weeks before grain harvest • Take 15 stalks per field/area being monitored. • Take stalks undamaged by insects, etc. • Cut 8-inch portion of stalk, starting 6 inches above ground – remove outer stalk sheath.

  10. Handout:Corn Stalk Nitrate Testby Lloyd Murdock and Greg Schwab.University of Kentucky

  11. Techniques to AssessField Nutrient Status • Deficiency Symptoms of Plants • Plant Analysis • Soil Testing

  12. SOIL Testing

  13. Objectives of soil testing a) To give an index of nutrient availability b) To predict the probability of obtaining a profitable response to lime and fertilizers c) To provide a basis for recommendations regarding the amount of lime and fertilizers to apply d) To evaluate the fertility status of soils on a geographic area basis

  14. Components of Soil Testing • Sampling • Analyze the quantity of plant available nutrients in the soil (based on extraction) • Interpret soil test results • Estimate the additional nutrients required by the crop

  15. Soil Sampling • Critical aspect of soil testing • The weakest link in the soil testing process • Less than 10 g of soil are used in the laboratory to ‘represent’ a field that may weigh more than 2 million lbs per acre-furrow-slice • Use soil testing guidelines for collecting ‘representative’ soil samples

  16. Where to Sample?

  17. Capability Classes USDA NRCS

  18. Soil Sampling • Define “field”, by size or other management unit • Collect separate samples from areas that are to be managed separately • Collect separate samples from areas with different: • soil types? • past cropping/management histories • production potential

  19. Soil Sampling Techniques • Field average sampling • Grid sampling • point sampling

  20. Soil Variability

  21. Other Soil Sampling Considerations • Depth of sampling • tillage depth • 0-2 and 2-8 inch for no-tillage • 0-2 for pastures

  22. Influence of Tillage on Stratification of Soil Test P

  23. Chemical Analysis • Simple, rapid, accurate ‘index’ of soil nutrient availability – inversely related to plant response to additional nutrient(s) applied as fertilizer(s) • Laboratory test procedures vary among states • Analytical results generated by different procedures are not interchangeable (Mehlich I  Mehlich III) • Amounts extracted depend upon extracting solution chemistry, extracting solution strength, soil to extracting solution ratio, shaking time, and filtering procedures

  24. Common Extracting Solutions • Mehlich-I (double acid) • Mehlich-III (ammonium fluoride & acetic acid) • Olson’s extractant • Morgan’s extractant • Bray’s extractants (Bray I and Bray II)

  25. Approaches to Soil Test Interpretation • Maintenance approach • Cation saturation ratio approach • Sufficiency level approach

  26. Maintenance Approach • Rapid build up of the soil test to high soil test levels • Annual application of amounts removed by a crop • Some fertilizer applied, regardless of soil test • If a soil’s delivery capacity for a given nutrient is adequate for optimum yields, then this approach causes over-fertilization

  27. Cation Saturation Ratio • Approach attempts to create an “ideal” ratio, balance, among nutrients, especially K, Ca and Mg • Base saturation 80% • Cation ratio: 65% Ca, 10% Mg, 5% K, 20% (H + Al) • Ca/Mg = 6.5 • Ca/K = 13 • Mg/K = 2

  28. Problems With The Cation Ratio Saturation Approach • No consistent relationship between crop response and cation ratio • Ideal ratios likely vary among soils

  29. Sufficiency Level Approach • Based on a soil test taken every two or three years, add nutrients according to the results of those regular soil tests. • If soil test indicates available nutrient(s) levels are ‘sufficient’, no lime or fertilizer(s) recommended

  30. New Developments In Soil Testing • A new soil test for nitrogen: • Pre-Sidedress Nitrate Test • (PSNT) for Corn • (and only for corn)

  31. New Developments In Soil Testing • The basis for this new soil test for N is to take soil samples just before side-dressing --- after the early spring wet period but before the period of corn’s major N demand --- and determine the nitrate-N already in the soil at that time. The results are used to make side-dress N rate recommendations. • Works best on soils with prior manure or killed legume history. • Samples taken between rows, after crop emergence, to a depth of 12 inches (see handout).

  32. Handout:Pre-Sidedress Soil Nitrate Test for CornbyDouglas Beegle, Richard Fox, Gregory Roth, and William Piekielek. Penn State University

  33. EXAMPLESSoil Testing LaboratoryAnalysis Results

  34. Conclusions • Time of sampling is vital for plant tissue analysis. • Soil testing is the easiest approach to maintaining soil fertility

  35. Conclusions • Soil test values depend upon soil test methods • Recommended nutrient application rates vary with soil test results and the interpretation of those results