Nitrogen Fertilizer Rate Calculator — N Balance Method for Maize, Wheat & Other Grains
Calculate how much nitrogen to apply per hectare with the N balance method — crop demand from target yield minus soil nitrate and mineralisation, divided by fertilizer efficiency — and the kg of urea or other product.
How it works
Crop N demand = target yield (t/ha) × N uptake (kg N/t) · N rate = (demand − soil nitrate-N − mineralised N) ÷ efficiency · Product (kg/ha) = N rate ÷ N content of the product
The N balance (mass-balance or Stanford) method, used by INTA, IPNI and many extension services, matches nitrogen supply to what the crop will take up. The crop’s demand is its target yield times the N it absorbs per tonne of grain (about 22 kg for maize and 30 kg for wheat in IPNI tables). Nitrate already in the root zone and N released from organic matter are subtracted, and the remainder is divided by fertilizer efficiency because the crop never recovers all the N applied. In the US Corn Belt the economic MRTN approach is often used instead; this method suits the soil-test-based systems common in Latin America.
Worked example
For a 10 t/ha maize crop at 22 kg N/t, demand is 220 kg N/ha. The soil supplies 60 + 40 = 100 kg N/ha, leaving 120 kg N/ha. At 70% efficiency you must apply 120 ÷ 0.70 = 171 kg N/ha — 373 kg/ha of urea (46% N), about 7.5 bags of 50 kg per hectare, or 153 lb N/acre.
Sources: IPNI / Profertil — Requerimientos nutricionales de los cultivos (N uptake per tonne of grain) · IPNI Cono Sur (García) — Criterios para el manejo de la fertilización del cultivo de maíz
Frequently asked questions
How much nitrogen does maize need per tonne of grain?
IPNI tables give about 20–22 kg of N absorbed per tonne of grain for maize (total plant uptake), around 30 kg for wheat and grain sorghum and about 40 kg for sunflower. Soybean needs much more N but fixes most of it biologically, so it is not normally fertilized with N.
How do I convert kg of N into kg of urea?
Divide by the N content: urea is 46% N, so 100 kg N ÷ 0.46 = 217 kg of urea. Ammonium sulfate (21% N) needs 476 kg for the same 100 kg of N.
What efficiency should I use?
With split applications or incorporated urea, 60–70% is realistic. Surface-broadcast urea in hot, dry conditions or on wet soils that lose nitrate can fall to 40–50%, so the required rate rises.
Should I apply all the nitrogen at planting?
Usually not. Splitting the dose — part at planting and the rest at V6 in maize or tillering in wheat — reduces losses and raises efficiency, especially on sandy soils or in high-rainfall areas.
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This calculator is for educational purposes. Double-check important results before acting on them.