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How does the Tri-State (Indiana, Ohio, Michigan) calculator determine my phosphorus needs?

The Tri-State calculator can be used to help create phosphorus recommendations for your fertility strategies.

The Tri-State calculator utilizes the following equations:

Nutrient

Crop

Build/Maintenance

Phosphorus

Corn

Bray P1 or Mehlich 3-COL:

If STP < = 15 then P Rec = (15 - STP) * 5 + (Yield * 0.37)

If STP > 15 and STP < 30 then P Rec = (Yield * 0.37)

If STP >= 30 then P Rec = (Yield * 0.37) - ((Yield * 0.37) * (STP - 30)) / 10

Mehlich 3-COL: STP = (0.84 * STP as M3-COL) + 1.21

Olsen Bicarbonate: STP = (2.27 * STP as Olsen) - 7.045

Mehlich 3-ICP: STP = (0.778 * STP as M3-ICP) - 6.4667

Phosphorus

Soybeans

Bray P1 or Mehlich 3-COL:

If STP < = 15 then P Rec = (15 - STP) * 5 + (Yield * 0.80)

If STP > 15 and STP < 30 then P Rec = (Yield * 0.80)

If STP >= 30 then P Rec = (Yield * 0.80) - ((Yield * 0.80) * (STP - 30)) / 10

Mehlich 3-COL: STP = (0.84 * STP as M3-COL) + 1.21

Olsen Bicarbonate: STP = (2.27 * STP as Olsen) - 7.045

Mehlich 3-ICP: STP = (0.778 * STP as M3-ICP) - 6.4667

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