Soil Testing and Soil Fertility Update

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Soil Testing and Soil Fertility Update

• Jim Gerwing
• Howard Woodard
• Anthony Bly
• Ron Gelderman

SOUTH DAKOTA STATE UNIVERSITY
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What we hope to do

• Present whats new in soil fertility and soil
  testing
• Give factual information
• - Answer questions
• Learn what your needs are
• Soil Testing
• Soil Fertility

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2004 SDSU Soil Fertility Updates
Presentations can be found online at
http//plantsci.sdstate.edu/soiltest/
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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• Based on tri-state recommendations (MN, ND,SD)
• Based on some new data
• Reworking of some old data
• Recommendations are only as good as the research
  data behind them

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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• 1. Nitrogen Rate adjustment for Date of
  sampling.
• Now N rec. minus (days before Sept. 15 x 0.5
  lb/a) up to maximum of 23 lbs/a.
• In theory, nitrate forms in soil if warm and
  moist.
• In practice, because sometimes was not moist, and
  limited tillage, was very difficult to show a
  consistent increase in nitrate over time
• Proposed No N rec. adjustment for date of
  sampling

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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• Nitrogen credit for soybean as previous crop
• Now 1.0 lb per bu of soybeans grown.
• Proposed 40 lb/a across all yields for soybeans
  as previous crop.
• - N rate studies on corn after soybeans shows an
  average of a 40 lb/a credit.

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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• Legume credit after short-season crops
• Now ½ credit for legume credit followed by a
  short-season crop.
• Proposed Full credit
• Why? Not so much a residue breakdown process as a
  tie-up process of N. Therefore N credit based on
  length of time of breakdown is not a factor.
• Tillage of a high residue legume such as alfalfa
  will release N by residue breakdown but is
  relatively quick ( Wisc. research). Exception
  would be no-till into alfalfa .

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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• Phosphorus recommendations for flax
• Now Recommend relatively low rates of P
• Proposed Recommend no P
• Why? Data shows little response to P from flax.
• Flax has a high infection of mycorrhizae fungi
  which act as root extenders and uptake soil P.
• Perhaps respond after fallow
• Will keep the same P recs but footnote to
  document probably wont increase yield but just
  maintain soil test P

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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• 5. A Minimum potassium recommendation for corn
  when we would rec K.
• Now We have a minimum of 10 lb/a K2O, i.e. if
  the calculated rec is 1-10 we report 10 lb/a.
• Proposed We would rec a minimum of 60 lb K20/a
  (100 lbs of potash) i.e., if the calculated rec
  is 1-60 60 lb/a
• Why? Some data and many observations show that
  lower levels still leave many K deficient areas
  in field.
• Perhaps a composite soil sample has lower and
  higher testing areas in the field.

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SDSU K recommendations for Corn
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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• Sulfur Recommendation changes
• Now S recs vary by S soil test and texture
• Proposed Vary by soil test, texture and
  tillage.
• Why? Below 40 lb/a soil test (all textures)
  there is still only a 30 chance to get a yield
  response. Try to improve the odds.

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SDSU Sulfur Recommendations
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Proposed SDSU Sulfur Recommendations
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SDSU Soil Test Nutrient Recommendation Changes
for 2005

• 7. Other changes
• Tillage classifications
• 1 Conventional primary(chisel, disk)
  secondary.
• 2 Very reduced strip-till, zone-till,
  ridge-till
• 3 No-till
• Some smaller changes, statements, Test series
  added, etc.
• All these changes programmed by end of Jan 2005.
• Fertilizer Guide (EC 750) done by March 1 2005.

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Nutrient recommendations not carved in
stone. Even Mt. Rushmore needs a patch now and
then.
Questions ?