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. Nutrient recommendations follow each state's published method; lime is a separate rail — live for six states today, advisory for six alkaline regions, and coming soon elsewhere. Status is always labeled before you rely on a number.
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 for nutrients. Lime is mapped the same way, but only six methods compute live rates today (CA, GA, MT, PA, TX, VT); six alkaline states stay advisory-only; the rest are labeled coming soon and never borrow another state's lime formula.
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. Lime calculation availability is labeled state by state.
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 formulas 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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