Pick your state and enter your soil values. Zone Forge resolves your state's calibrated land-grant source — every rate auditable, every citation linked, no hidden weights, no black-box ML. The same engine behind Zone Forge's variable-rate prescriptions, calibrated across all 50 states.
Pick your state and enter your crop, yield target, and soil values on the left. We'll resolve your state's calibrated land-grant source and show the rate it recommends — with reference sources alongside where the methods line up.
Most platforms either pick one recommendation engine and call it a day, or run an opaque ML model that won't tell you why. We do neither.
Pick your state and Zone Forge resolves the calibrated land-grant recommendation agronomists rely on there — and names it right on the result. Iowa State PM 1688 anchors the western and central Corn Belt (Bray-P1); the Tri-State 2020 recommendations cover Ohio, Indiana, and Michigan (Mehlich-3 or Bray-P1); the Penn State Agronomy Guide covers the Mid-Atlantic. Those three just cover the most acres — they're examples, not the whole list. The same holds the rest of the way around the map: Cornell in New York, K-State in Kansas, LSU in Louisiana, WSU in Washington, and on through all 50 states, each on its own state university's extension source. Lime is the same story — your state's own buffer method (Mehlich Buffer, Sikora, Adams-Evans, Woodruff, and more), calibrated for all 50 states. Every one is a published, citable document — not a proprietary calibration we made up.
Upload your soil test in the app and Zone Forge turns it into a worst-first report card — each nutrient color- and word-coded so the thing that needs attention is at the top. In 26 of 50 states we grade nutrients in your state university's own published rating words — Arkansas Very Low to Above Optimum, Delaware its Fertility Index Value, Oklahoma Low / Sufficient. In the other 24 states we show the measured value with a note on why we don't grade that lab's format yet — we'd rather say measured than grade it wrong. pH and lime are calibrated for all 50 states.
This page calls Zone Forge's production recommendation engine via a public, rate-limited HTTP endpoint. Inside the app the same engine generates per-zone variable-rate prescriptions from your soil sample grid. Outside the app — here — it answers the same question for a single point so you can see the math and the citation before you sign up.
If your soil report uses Mehlich-3 and you apply an Iowa PM 1688 table calibrated for Bray-P1, your P recommendation can be off by 20-40 lb P₂O₅/ac. Our engine refuses to apply a table whose extractant doesn't match your soil sample — this page surfaces that as a warning rather than silently giving you the wrong number.
Variable-rate prescriptions in Zone Forge take your full soil sample grid and generate a zoned shapefile that pushes straight to John Deere Operations Center. Both visible as a Map Layer and selectable from the in-cab Files tab. The same engine, the same state source and citations, but per zone instead of per point.
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