river.io/maizerunner
Coming to the App Store · iPhone · iOS 17

MaizeRunner.
Know your soil. Grow better.

A real-world, soil-first companion for corn farmers — the practical sibling of the Corn 3000 game. Map your fields, learn what your ground is actually made of, and watch it get better year after year. Everything runs on your phone: no account, no login, no analytics. Your farm data never leaves the device.

MaizeRunner app icon
01 · The season, end to end

From an unmapped field to ground that improves every year.

MaizeRunner walks a brand-new user through the whole arc — mapping, sampling, the growing season, and the long game of building fertility — in the order the work actually happens. Nothing here needs a signal in the field.

01

Map

Draw or walk field boundaries on satellite imagery.

02

Detect

Soil type auto-read from USDA and ISRIC data by location.

03

Sample

A step-by-step guide to taking a proper soil sample.

04

Record

Enter lab results; a measurement always beats an estimate.

05

Track

Log planting; follow growing-degree days to the current stage.

06

Outlook

A caveated yield range — never a single false promise.

07

Project

Ten years of organic matter, pH and soil life, modeled.

08

Log

Every operation recorded, so the trend line is real.

Grounded in USDA, NRCS and land-grant university research · honest numbers, plainly explained

02 · Capabilities

Soil and the growing season, made legible.

Soil is the spine. Every feature exists to help a working farmer understand their ground, track a real season against it, and make it better over time.

Field mapping

Your fields, on the map

Draw a boundary by hand or walk it with the phone in your pocket. Split a field into management zones and track each part of it on its own.

Soil detection

What your ground is made of

Auto-detect soil type by location — USDA SSURGO in the US, ISRIC SoilGrids worldwide. Every survey value carries an estimated badge; it is never dressed up as a lab result.

Sampling

A real test, made easy

A plain, step-by-step guide to pulling a proper soil sample, and a place to record the lab results when they come back. The app's job is to make a real test legible, not replace it.

Season tracking

Growing-degree days, live

Log planting and follow the real season — weather to growing-degree days to the current corn growth stage — so you always know where the crop stands.

Yield outlook

A range, with its reasons

A caveated low–high band with the factors helping and hurting, and its state-level caveat in plain sight. Withheld mid-season when the weather-to-date would only mislead.

Soil projection

Ten years, restored

Project organic matter, pH and soil life a decade out under cover crops, reduced tillage, manure and rotation. Record every operation and watch the trend the numbers actually make.

03 · Sacred invariants

Five things MaizeRunner is not allowed to do.

These are architectural, not preferences. They are what keep the numbers honest and the farm data yours.

Farm data stays on the device
No backend, no account, no login, no analytics, no outbound telemetry. Fields, soil tests, seasons, photos and notes live only in on-device SQLite and the local filesystem.
A measurement beats an estimate
A lab result always overrides a survey or model value, and estimates are never dressed as measurements — every survey-derived number carries an "estimated" provenance badge.
The yield outlook is a range
Always a caveated low–high band with its factor breakdown and state-level caveat — never a single-number "prediction," and withheld when the season-to-date would mislead.
Agronomy stays cited and honest
Model coefficients carry provenance and citations to USDA, NRCS and land-grant research; the trajectory math is locked by golden tests. A change is a conscious, cited decision.
Free is three fields; Pro is a hundred
Every other feature works identically in the free tier. The paywall appears only when you add a fourth field — nothing else is gated.
04 · The particulars

Native, offline, and honest about what it is.

A greenfield SwiftUI app for iOS 17, on-device from the ground up. GRDB/SQLite for storage; public soil and weather sources sit behind protocols so a new backend slots in without touching the app.

Platform
iPhone · iOS 17 and later
Price
Free for 3 fields · MaizeRunner Pro (in-app) for up to 100
Data
On device. No account, no network beyond public soil and weather sources you look up.
Languages
Localized into 33 languages
Sources
USDA SSURGO · ISRIC SoilGrids · Open-Meteo · NRCS and land-grant research
Sibling
Corn 3000, the historical farming game it grew out of
Availability
Coming to the App Store — link pending
05 · Support

A person answers this mail.

Questions, trouble, a soil number that looks wrong, or a purchase that did not land: write to us and you will get a reply from a human, usually within two business days. MaizeRunner has no account system, so there is nothing to verify and nothing to reset: just describe what you saw.

When something is broken, the fastest fix comes from telling us your iOS version, your iPhone model, and what you tapped just before it went wrong. Screenshots help. No farm data is ever attached to a support mail unless you choose to send it.

No soil data for my field
Automatic soil detection needs a network connection the first time you draw a field. USDA SSURGO covers the United States in high detail; everywhere else falls back to ISRIC SoilGrids, which is coarser. If a field sits on water, pavement, or a surveyed gap, neither source will return a profile. Enter your lab results by hand instead.
I bought Pro and it is not showing
Open Settings inside the app and tap Restore Purchase. Purchases are tied to the Apple Account that bought them, so make sure you are signed in with the same one. MaizeRunner Pro is a one-time purchase, not a subscription, and it restores on every device on that Apple Account.
Where is my data, and is it backed up?
Everything lives in a database on your iPhone, and we hold no copy of it. That is the whole point of the app. It is included in your encrypted iPhone or iCloud device backup. Deleting the app deletes your fields, so take a backup before you do.
How many fields can I map?
Three on the free tier, and up to one hundred with MaizeRunner Pro. Every other feature works identically whether or not you buy Pro: soil reports, the sampling walkthrough, season tracking, and the ten-year planner.
The app is not in my language
MaizeRunner follows your iPhone's language setting across 33 languages. If yours reads badly, tell us which language and which screen. The agronomy terms were translated by hand, so corrections from a grower who works in that language are genuinely useful.
A yield or soil projection looks wrong
Send us the field's soil figures and what you expected. The projections come from USDA, NRCS, and land-grant research, and the app is built never to show a single confident number where the honest answer is a range. If it is doing that, it is a bug we want.