Understanding Soil Sampling and Interpreting Recommendations

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Understanding Soil Sampling and Interpreting
Recommendations

• Harold Watters CPAg - CCA
• OSU Extension Champaign County

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Soil Testing

• Soil testing provides information about the
• nutrient level of the soil and the
• amounts of lime and
• fertilizer necessary to
• economically maximize crop production.

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Typical soil analysis

• ?Soil pH and buffer pH
• ?Available phosphorus
• ?Exchangeable potassium
• ?Cation Exchange Capacity (CEC)
• ?Exchangeable calcium
• ?Exchangeable magnesium
• Additional soil analysis can includeOrganic
  matter, others
• Most soil testing labs report soil nutrient
  levels in parts per million (ppm). To convert
  from ppm to lb per acre, simply multiply ppm by 2.

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Soil Sampling

• Randomly collect 20 to 25 representative soil
  cores to a depth of eight inches.
• Four inches for no till for lime.
• Soil samples can be collected either in the fall
  after harvest or in the spring.
• Soil samples should be collected about the same
  time each year to avoid extreme changes in
  soil-test information.
• Soil samples should be collected every three to
  five years depending upon soil conditions.

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Comparison of sampling Methods - Iowa
4 acre point 4 acre cell by soil type
0.5 acre point
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Comparison of sampling methods - Iowa

• Variability
• Due to application equipment - pH, P K
• OM differences due to soil type
• A high level of variability can occur in very
  small areas
• Economics
• 2.5 A grid every four years
• Target known low areas - develop history
• Assume some type of variable rate application

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Soil recommendations by sampling method?

• Goal?
• Equipment capability
• History of field/ farm
• Soil variability
• Management unit
• Economics

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Very low level
High levels
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Optimum Soil Test Values for Most Crops in Ohio.

• Soil pH Lime Test Index
• 6.3 to 7.0 and/or 68-70 for mineral soils
• 5.3 to 5.8 and/or 68-70 for organic soils
• Soil Nutrients Soil Test Value
• Available P 15-40 ppm (30-80 lb per acre)
• Exchangeable K 100-200 ppm (200-400 lb per acre)
• Exchangeable Ca 200-8,000 ppm
• (400-16,000 lb per acre)
• Exchangeable Mg 50-1,000 ppm
• (100-2,000 lb per acre)
• These limits vary widely depending upon Cation
  Exchange Capacity, calcium to magnesium ratio,
  and percent base saturation.

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Nutrient availability by pH in mineral soils
http//www.avocadosource.com/tools/FertCalc_files/
pH.htm
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Long term impact of fertilizer applications on
yield (bu/A) Iowa
Trial began in 1979.
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Long term effect of annual P K applications on
soil-test values Iowa
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Economic returns to P K fertilization for corn
(/A/yr) Iowa
Average prices used - 2.25 corn, 6 soybeans,
0.24/lb P2O5, 0.12/lb K2O
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Economic returns to P K fertilization for
soybeans (/A/yr) Iowa
Average prices used - 2.25 corn, 6 soybeans,
0.24/lb P2O5, 0.12/lb K2O.
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Crop Nutrient Use
From the Ohio Agronomy Guide
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Tons of Aglime Needed to Raise the Soil pH
(Mineral soils) to the Desired Level
LTI 64
Based on the Shoemaker-McLean-Pratt (SMP) Buffer
pH and an Incorporation Depth of 8 (Effective
Neutralizing Power of 2,000 Lbs/Ton)
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Tri-State Recommendations for Phosphate (P2O5)
for Corn
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Tri-State Recommendations for Phosphate (P2O5)
for Wheat
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Tri-State Recommendations for Potash (K2O) for
Soybeans
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Potash (K2O) Recommendations for Soybeans -
Varies by CEC
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GuidelinesSampling to Recommendations

• Quality and representative sample
• Approved/ accepted lab
• Understand recommendations
• Sometimes varies by lab
• Ask if follow Tri-State Guidelines
• Discuss with applicator
• Consider the fertilizer application
• Field size, load, availability - economics
• Planter or field applied
• Timing

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Resources

• Ohio Agronomy Guide
• Tri-State Fertility Recommendations for Corn,
  Soybeans, Wheat and Alfalfa
• C.O.R.N. newsletter
• Maurice Watson, Robert Mullen Ed Lentz
• http//corn.osu.edu
• Agronomic Crops Team website
• http//agcrops.osu.edu
• Iowa State University
• Antonio Mallarino, John Sawyer
• http//www.ipm.iastate.edu/ipm/icm/indices/soilfer
  tility.html