Optimizing Nitrogen Fertilizer Applications
Corn crop prices are low and fertilizer prices are high. Farmers are looking for ways to lower their nitrogen (N) fertilizer bill. University N recommendations have changed over the years. University N research in the 1950’s advocated heavy N fertilizer because yield increased as N application increased?? Extra N fertilizer was a cheap fertilizer insurance policy.
About 10–15 years ago, universities re-examined that original data and found little direct relationship between higher corn yields and higher N rates. The relationship was quite variable! Five major factors like temperature, moisture (weather), soil pH, soil oxygen levels, and soil organic matter (SOM) affects plant N uptake. The N relationship to yield is so variable that universities went to a N application rate based on the price of N relative to crop prices. As N prices increase and crop prices decrease, economically it’s better to cut back while if N is cheap and corn prices high, the N rate is increased to increased. How can a farmer optimize crop yield based on N while still making a profit?
Corn uses large quantities of N to grow and produce a corn yield. About 1 pound (#) of N is removed for each bushel of corn produced. A 250-bushel corn crop requires about 250# actual N. When N was cheap, farmers applied 1.2# N per bushel grown. A more reasonable goal is 1# N per bushel but some farmers with good soil health are now applying .5 to .7# N per corn bushel produced and still getting good yields. Some of the extra N comes from cover crops, manure, compost, or higher microbial activity. Here are ways to reduce your N fertilizer bill but still remain profitable.
SOM is a big factor. Every 1% SOM holds roughly 1000# N with about 1–3% of that N mineralizing or coming microbially available each year. A typical tilled soil with 2% SOM and 1% mineralization releases 20# N per year. Healthy soils with higher SOM and higher microbial activity release more N. Compare a 4% SOM, 2% mineralization rate, and 80# N released compared to a 6% SOM, 2.5% rate and 150# N released. Keeping soils healthy pays dividends when fertilizer prices soar. Virgin soils that have not been disturbed produce high yields with little or no fertilizer needed until SOM and soil structure are destroyed, or N is lost to denitrification (saturated soils), or leached away. Free living bacteria in healthy soils may produce 20–100# of free N, but these microbes are highly sensitive to soil disturbance and the five factors mentioned above.
One way to increase your N use efficiency is to apply N as close to when the plant needs it as possible. Even with N inhibitors, putting N on in the fall or early spring should be avoided. From the seedling stage to V5 (five leaf stage), corn uses about 10% of its total N requirement. The corn plant determines ear size, number of corn rows, and row length at this stage, so adequate N is critical. From V6–V18 (6–18 leaf stage), corn can take up 8# N and grow 4 inches per day. About 65% of a corn plant’s N needs occurs by V18. From silking to maturity, a corn plant needs about 35% of its total N needs. Farmers get their biggest corn yield increases from the first 75–100# N fertilizer applied. Extra N applied after that might pay off if crop growing conditions are optimal.
Due to time constraints, many farmers side dress N immediately after planting. To get the best N efficiency, apply N when the corn is taller but before it gets knocked down by the drawbar. With Y drops and highboy applicators, farmers now may apply N much later and closer to the corn plant stalk and roots. In no-till situations, avoid applying N to the surface residue to avoid N tie up. Farmers can use the pre-side dress nitrogen (PSNT) test when N is applied to adjust N rates. If soil conditions are cold and excessively wet, avoid taking this test. The best and most accurate time to test is right before N is being applied.
Producing corn at a profit due to high N fertilizer prices and low crop prices will be a challenge this year. Actual 2025 farm example when money is tight. Farmer getting 200-bushel corn was applying 200# total N. He cut his N rate to 140# N (60# reduction * $.70/N#), eliminated a fungicide application ($35), and used a cheaper corn hybrid ($80) totaling $157 in savings. He got 165-bushel corn or 35 bushel less worth $140 in lost income. He had less bushels to haul but made about the same profit.
