Ontario crop nutrient planner · OMAFRA Pub. 811
CropGPT turns your soil test into a fertilizer plan. Enter your crop, a realistic yield goal and your Olsen phosphorus and potassium values, and it returns nitrogen, phosphate and potash rates drawn from the OMAFRA Agronomy Guide for Field Crops (Publication 811) sufficiency tables — the same tables Ontario agronomists work from. It covers grain corn, soybeans, winter wheat, spring wheat, barley, oats and canola.
Every rate shows its own arithmetic. You can see the base nitrogen for your soil texture, the yield component, the credit deducted for last year's crop, and the soil-test band each phosphate and potash rate came from. Nothing is hidden behind a black box, which matters whether you are checking your own numbers or defending a recommendation to a client.
Manure, compost and biological inputs are treated as real fertilizer, not an afterthought. Choose the organic pathway and the tool sizes the tonnage needed and shows delivered versus required for every nutrient. Choose the synthetic pathway and it solves phosphate first, credits the nitrogen carried in MAP or DAP, then sizes the remaining nitrogen and potash so you do not pay twice for the same nutrient.
It is a single page with no sign-up, no account and no tracking of your field data — everything is calculated in your browser. Once loaded it keeps working without a signal, so it is usable in a cab or at a field edge. Farmer mode asks plain questions with picture guides; agrologist mode exposes soil-test categories, response ratings and editable rates for Certified Crop Advisers.
No. Soybeans fix their own nitrogen through Bradyrhizobium nodulation, and OMAFRA does not recommend fertilizer nitrogen for soybeans in Ontario. Applied nitrogen suppresses nodulation and rarely pays. Spend the money on inoculant for fields new to soybeans, and on potash where the soil test calls for it.
Ontario research found the most economic starter response when Olsen phosphorus sat between 12 and 18 ppm. Above roughly 30 ppm a phosphate response is rare, and above 60 ppm none is expected. Potassium behaves similarly, with the economic range around 100 to 130 ppm.
OMAFRA guidelines are calibrated to the Olsen (sodium bicarbonate) phosphorus extraction. Mehlich-3 and Bray-P1, standard across much of the United States, return different numbers that do not map onto Ontario recommendation tables. Use an OMAFRA-accredited laboratory.
It depends on three things, not one: the base requirement for your soil texture, your yield goal, and the credit for last year's crop. Corn following ploughed-down alfalfa can carry a credit of 110 kg N/ha — about 98 lb/ac. Ignoring that credit is the most common way Ontario growers over-apply nitrogen. The corn fertilizer guide sets out the full calculation.
Yes — completely free, with no account and no paywall.
Built for Canadian farming & sustainability
CropGPT is a free, practical tool that puts trustworthy agronomy in every grower's pocket. My ambition is to help Ontario and Canadian farmers cut input waste, protect soil and water, and make confident nutrient decisions — whether you read a soil report for a living or have never filled one out.
Every recommendation here is grounded in the OMAFRA Agronomy Guide for Field Crops (Publication 811) sufficiency guidelines, with transparent math you can check. It pairs an organic pathway (compost, manure, biologicals) with a synthetic pathway so you can compare both honestly — because sustainable farming is about choice, not dogma.
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Authentic Ontario sources — regulations, soil labs, weather & advisors. Every link goes to a government or association site.