About this calculator

How-to: enter expected baseline yield (with zero added N), maximum attainable yield, current crop price and fertilizer cost per kg N. We fit a quadratic-plateau response Y(N) = Y0 + (Ymax − Y0)·(1 − e^(−k·N)) and find where dY/dN × crop price = cost per kg N. Above the EONR, you are burning cash and leaching nitrate.

Frequently asked questions

Does this replace a soil / N-min test?

No. Baseline yield y0 should be adjusted downwards if soil mineral N is low or upwards after a good legume break crop. Use N-min sampling in February for cereals.

What about the EU Nitrates Directive?

In Nitrate Vulnerable Zones, closed periods and 170 kg N/ha organic-manure limits apply regardless of EONR. Check your regional NAP before applying.

Why is my EONR sometimes zero?

When crop price × yield response is less than fertilizer cost per kg N, the first kg of N loses money. Common in low-price years for high-N crops like feed wheat.

What does the Crop Yield vs. Fertilizer ROI Calculator do?

Economic optimum nitrogen rate (EONR) and marginal ROI for cereal, oilseed and root crops — models the yield-response curve and stops at the point where the last kg of N no longer pays for itself. How-to: enter expected baseline yield (with zero added N), maximum attainable yield, current crop price and fertilizer cost per kg N. We fit a quadratic-plateau response Y(N) = Y0 + (Ymax − Y0)·(1 − e^(−k·N)) and find where dY/dN × crop price = cost per kg N. Above the EONR, you are burning cash and leaching nitrate.

Is the Crop Yield vs. Fertilizer ROI Calculator free to use?

Yes. Every calculator on Calcurly.com is free, works in your browser without sign-up, and can be embedded on your own website.

How accurate is the Crop Yield vs. Fertilizer ROI Calculator?

Results are calculated in real time using industry-standard formulas. Treat the output as a well-informed estimate — always cross-check with local regulations, product datasheets, or a qualified agriculture & farming professional before committing to a purchase or a job.

What inputs does the Crop Yield vs. Fertilizer ROI Calculator need?

Enter values for: Zero-N baseline yield (t/ha), Attainable maximum yield (t/ha), Crop price (€/tonne), Fertilizer cost (€/kg N), Response steepness k, Field area (ha). Sensible defaults are pre-filled where possible so you can start with a single change.

Can I embed the Crop Yield vs. Fertilizer ROI Calculator on my own website?

Yes — copy the iframe snippet at the bottom of this page, or use the Embed Generator to customise the size. The embedded version stays in sync with the live calculator on Calcurly.com.