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Tri-state fertilizer recommendations changing

By Harold Watters, Ohio State University Extension agronomist

Things are changing for the Tri-State Fertilizer Recommendations for agronomic crops. We are giving these updates this winter in advance of the publication update likely to come at the end of winter, and maybe too late to put in your plans for 2019. First the work. Steve Culman our OSU soil fertility specialist coordinated much of it:

  • From 2014 to 2017, over 300 on-farm strip trials were conducted across Ohio.
  • Yield responses to P and K fertilizer in soils at or above the current maintenance range were very rare.
  • Long-term data shows that when Ohio soils are in the current maintenance range, they supply sufficient P and K to meet corn and soybean demand for many growing seasons without yearly fertilization.
  • Recommended corn N rates were updated and are based on maximizing farmer profitability, not maximizing yields (http://go.osu.edu/corn-n-rate).
  • Corn, soybean and wheat today yield more grain with less nutrients.

We also learned from the trial participants that most fields are in the maintenance range, unless it is rented. So we will provide recommendations for fields in the maintenance range for the most part. We learned that crop nutrient removal was less that it was in the past.

 

Ohio grain nutrient removal (lb/bu) for corn, soybean and wheat. As expected to be in the forth-coming Tri-State Fertilizer Recommendations.

NutrientCurrent Data1995 Tri-State% decrease
Corn
P2O50.340.375%
K2O0.190.2726%
Soybean
P2O50.800.80
K2O1.081.419%
Wheat
P2O50.490.6322%
K2O0.240.3735%

 

The other big news is that we will be making recommendations based on a Mehlich III soil test for both phosphorus and potassium. The previous Tri-State made recommendations based on Bray P1 for phosphorus and Ammonium acetate test for potassium. What Steve did was calibrate for the new recommendations based on the newer Mehlich III test, because that is what all the labs in Ohio are using. It’s quicker and should be cheaper to run. And if we stay in the agronomic ranges for P & K, then the tests are not that different.

So what are the new maintenance ranges?

Based on Mehlich III test, and our work here in Ohio the maintenance range:

  • for P is 20 to 40 ppm
  • for K is 100 to 150 ppm.

If soil test levels are above maintenance range, then no nutrient application (P and K) is needed. So that things do not get too out of whack, sample and retest every three to four years. Generally, we believe the research supports these remarks as well:

  • If P level is below the critical level, then make an annual application. A band application of P2O5 can be beneficial when P test is below maintenance range.
  • If the CEC is very low or very high an annual K2O application may be warranted. Low is below 6 meq/100g and high is above 25 meq/100g.

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