Terry Wyciskalla, with Wyciskalla Consulting, LLC, describes how to collect a soil sample, identify spatial patterns to follow, the range of tests to consider, and interpret soil testing results.

Key Takeaways:

  1. Objectives of soil testing
    1. Estimate the nutrient status of the soil
    2. Make appropriate recommendations for fertilizer and lime applications by identifying variability in nutrient status of the sampled area
    3. Predict the likelihood of crop response to applying additional nutrients
  2. Soil sampling
    1. A good soil sample is the first step in a successful nutrient management program
    2. Base sampling intensity on expected field variability
    3. The greatest potential for error in soil testing is in taking the sample
      • Soil test results are only as good as the sample collected
    4. Soil sampling procedures
      1. Be prepared—have required equipment and supplies
      2. Divide field into uniform areas—group by crop history, soil type, topography, soil color, degree of erosion, or other obvious categories
    5. Follow lab instructions
      1. Suggested sampling depth
      2. Results interpretation
      3. Place cores in a clean plastic pack or soil sample bag and mix thoroughly
    6. Why acidic soils should be limed
      1. The performance of soil-applied herbicides can be adversely affected
      2. Reduced activity of symbiotic N-fixing bacteria
      3. Clay soils high in acidity are less highly aggregated
      4. Availability of nutrients such as P, K and Mo is reduced
      5. Tendency for K to leach is increased
    7. Function of P in Plants
      1. Energy transfer in the plant (ADP/ATP)
      2. Essential part of phytin, nucleic acids and phospholipids
    8. P availability is affected by:
      1. Amount and type of clay
      2. Application time and method
      3. Aeration and compaction of the soil
      4. Level of soil P and other nutrient interactions
      5. Soil moisture and temperature
      6. Soil pH (6.8 – 7.1)
    9. Function of K in Plants
      1. Enzyme activation
      2. Stomal activity (water use)
      3. Photosynthesis
      4. Transport of sugars
      5. Water and nutrient transport
      6. Protein and starch synthesis
      7. Crop quality, lodging and disease resistance
    10. What happens when fertilizer K is applied to the soil?
      1. It can be held in the exchangeable form (CEC)
      2. Some will remain in soil solution
      3. Some will be taken up by the crop
      4. Part will be “fixed” by the clays
      5. Some may leach in very sandy or acidic soils
    11. Annual fertilization options
      1. Soil tests not increasing with build-up rates
      2. Sandy soils (very low CEC)
      3. Unknown or short tenure arrangement
      4. Financial situation
      5. 1.25 times maintenance for P
      6. 1.50 times maintenance for K
    12. P and K help by contributing to:
      1. A larger root system
      2. More above-ground residue
      3. Quicker ground cover/row closure
      4. Improved water use efficiency
      5. Crop resistance to stresses/diseases
    13. Cutting back on fertilizer will not:
      1. Cut land taxes
      2. Cut interest rates
      3. Cut seed and pesticide costs
      4. Cut machinery costs
      5. Cut fuel costs
    14. Cutting back on fertilizer will:
      1. Reduce yields per unit area
      2. Mine soil nutrients
      3. Reduce crop resistance to drought, disease, insect and other stresses
      4. Reduce crop cover and residue resulting in greater risk of erosion
      5. Reduce profits

Header Image Credit: United Soybean Board

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