Nitrogen Calculator for Corn
Estimate nitrogen rate from yield goal, then subtract credits for manure, legumes, and soil nitrate. Get a fertilizer N recommendation you can actually apply.
Corn Nitrogen Rate Calculator
Yield-goal method: N need = yield goal × 1.2 lb N/bu, minus credits
Use a realistic 5-year average plus 5%
1.0-1.4 range; 1.2 is standard
From pre-sidedress nitrate test (PSNT)
Legume credits from previous crop
From manure application this year or last
How the Nitrogen Calculation Works
Corn takes up roughly 1.0 to 1.4 pounds of nitrogen per bushel of grain produced, with 1.2 being the long-standing university recommendation. Multiply your yield goal by that factor and you get the total N the crop needs from all sources — soil, mineralized organic matter, manure, legume credits, and fertilizer. Subtract the credits and what remains is the fertilizer N you need to apply. The math is simple; the art is in setting an honest yield goal and accurately counting credits.
The yield-goal method has been the standard recommendation framework for decades and remains the baseline in most state extension guides. An alternative — the Maximum Return to N (MRTN) approach developed by Iowa State and adopted across the Corn Belt — uses regional trial data to find the N rate that maximizes profit given corn and fertilizer prices. Both methods give similar answers in most years; the yield-goal method is easier to run with a calculator and is what this page uses.
Setting an Honest Yield Goal
The most common mistake in N planning is setting a yield goal that's too high. Using a 250 bu/ac goal on ground that consistently makes 180 leads to over-application of 80+ pounds of N per acre — wasted money, leached nitrate, and potential lodging. The standard recommendation is to use the average of your last five crops plus 5 percent. For a field that's averaged 180 bu/ac over five years, the yield goal is 189 bu/ac. Bump it up only if you've made a real management change (drainage, irrigation, new hybrid class) that you expect to lift yields.
Counting Nitrogen Credits
Soybean credit: Corn following soybeans needs about 1 pound less N per bushel — or roughly 50 lb/ac total credit. The credit comes from the nitrogen fixed by the soybean crop and released as the residue decomposes, plus the lower residue load of soybeans compared to corn. Alfalfa credit: A good stand of alfalfa can credit 75 to 150 lb N/ac to the following corn crop, depending on stand density and soil type. The credit persists for two years after termination, declining by about half in year two. Manure credit: Manure applications supply both organic and inorganic N. Use a manure analysis to estimate available N — typically 40-60 percent of total N is available in the first year.
Soil Nitrate Testing (PSNT)
The Pre-Sidedress Nitrate Test (PSNT), taken when corn is 6 to 12 inches tall, measures nitrate-N in the top foot of soil and tells you how much N has mineralized from organic matter and previous crop residue. A PSNT result above 25 ppm generally means no additional sidedress N is needed; below 21 ppm means apply the full recommended rate. The PSNT is most useful on manured ground or following alfalfa, where mineralization is hard to predict. Enter your PSNT credit in the calculator to fine-tune the recommendation.
Converting N Rate to Fertilizer Rate
The calculator returns pounds of actual N needed. To convert to a fertilizer product, divide by the product's N percentage. Urea (46-0-0) at 46 percent N: 150 lb N ÷ 0.46 = 326 lb urea per acre. UAN 28 percent (28-0-0) at 2.9 lb/gal: 150 lb N ÷ (0.28 × 2.9) = 185 gallons per acre. Anhydrous ammonia (82-0-0) at 82 percent N: 150 lb N ÷ 0.82 = 183 lb per acre. The calculator handles the urea and UAN conversions for you.
Frequently Asked Questions
Everything you need to know
Corn takes up roughly 1.0-1.4 pounds of nitrogen per bushel of grain produced. The standard university recommendation is 1.2 lb N per bushel. For a 200 bu/ac yield goal, total N needed is about 240 lb/ac, before subtracting credits from soil nitrate, previous legume crop, and manure.
Corn following soybeans typically receives a 40-50 lb N/ac credit, often expressed as using 1 lb less N per bushel of yield goal. The credit comes from nitrogen fixed by the soybean crop and released as residue decomposes, plus lower corn residue to decompose. This is the main reason corn-after-soybeans needs less fertilizer N than continuous corn.
Sidedress N is typically applied when corn is 6 to 12 inches tall (V4-V6), just before the rapid uptake phase begins. Corn takes up most of its N between V6 and tasseling. Sidedressing at this timing reduces the window for leaching and denitrification losses compared to all pre-plant N. Use a PSNT (pre-sidedress nitrate test) at this stage to fine-tune the rate.
Divide the pounds of actual N needed by the N percentage in the fertilizer product. For urea (46% N): 150 lb N / 0.46 = 326 lb urea per acre. For UAN 28% at 10.67 lb/gal: 150 lb N / (0.28 x 10.67) = 50 gallons per acre. For anhydrous ammonia (82% N): 150 lb N / 0.82 = 183 lb per acre. The calculator handles urea and UAN conversions automatically.
Editorial Standards & Sources
All formulas and benchmarks on this page are based on the USDA Yield Component Method (Nielsen, R.L., Purdue University Extension) and USDA NASS crop production data. Our calculators are reviewed annually against the latest extension publications from Iowa State, University of Illinois, University of Nebraska, and Ohio State.
Methodology: The default 90,000-kernels-per-bushel divisor and the 15.5% moisture standard used throughout this site come directly from published USDA and land-grant extension guidance rather than an internal estimate. Where a figure is our own approximation — such as the ±10% accuracy range for the ear count method — we say so explicitly rather than presenting it as an official statistic.
Known limitations: Pre-harvest estimates from any ear-count-based calculator are a planning tool, not a substitute for actual combine yield-monitor data or elevator scale tickets. Accuracy depends heavily on how representative the field samples are; we recommend a minimum of five sample locations per field, as outlined in the sampling guidance on this page.
Content last reviewed for accuracy in August 2025. Have a correction or suggestion? Contact our editorial team — we respond to all substantive feedback within 5 business days.