Crop prices are high, but fertilizer prices are rising even higher. Farmers are looking for ways to reduce their fertilizer bill, especially on nitrogen (N). Almost all nitrogen is processed by soil microbes before it is taken up by plants. About 85% of N is used to form about 20 amino acids which are converted into proteins and enzymes with about 10% of N used in plant genetics (DNA, RNA). Optimization of the N fertilizer is essential.
Academic recommendations for N have changed over the years. University nitrogen research in the 1950s advocated heavy nitrogen fertilizer because yield increased as nitrogen application increased? Nitrogen was relatively cheap, and no researcher wanted farmers to lose yield, as the extra nitrogen was an insurance policy for cheap fertilizers. This has caused some water quality issues, so universities have adjusted their nitrogen levels over the years.
About 10 years ago, universities re-examined this original data and found little direct relationship between higher corn yields and higher nitrogen levels. The relationship between nitrogen fertilizers and corn yields was quite variable. Factors like temperature, humidity (weather), soil pH, soil oxygen levels, and soil organic matter (SOM) have affected nitrogen uptake by plants. The relationship N with return is so variable that universities have opted for an application rate N based on the price of N. As the prices of N increase, it is economically better to reduce while N is cheap – the N rate is increased to increase net profit. The real question is, how can a farmer optimize the yield of his crops on the basis of N while making a profit?
Maize uses large amounts of nitrogen to grow and produce a maize yield. Approximately 1 pound (#) of nitrogen is taken for each bushel of corn produced. A 250 bushel corn crop requires about 250 actual # N. When N was cheap, farmers applied N 1.2 # per bushel grown. A more reasonable target is 1 # N per bushel, but some farmers with good soil health now apply 0.5-0.7 # N per bushel of corn produced and still have good yields. Some of the extra nitrogen comes from cover crops, manure, compost, or higher microbial activity. Here are some ways to lower your N fertilizer bill without sacrificing yield.
SOM is an important factor. Each 1% SOM contains about 1000 # N with about 1 to 3% of this N mineralizing or available in microbial form each year. A typical plowed soil with 2% MOS and 1% mineralization releases 20 # N per year. Healthy soils with a higher SOM and higher microbial activity release more N. Compare a SOM of 4%, a mineralization rate of 2% and 80 # N released versus a SOM of 6%, a rate of 2.5% and 150 # N. Keeping soils healthy pays dividends when fertilizer prices soar. Virgin soils that have not been disturbed produce high yields with little or no fertilizer required until SOM and soil structure are destroyed, or N is lost through denitrification (saturated soils) or leached out. . Free bacteria in healthy soils can produce 20 to 100 # of free N, but these microbes are very sensitive to soil disturbances and to the five factors mentioned above.
One way to increase your nitrogen use efficiency is to apply nitrogen as close as possible to when the plant needs it. Even with N inhibitors, avoid putting N in the fall. From seedling stage to V5 (five leaf stage), corn uses about 10% of its total N requirement. The corn plant determines the ear size, number of corn rows and row length at this stage , therefore an adequate N is essential. From V6 to V18 (6-18 leaf stage), corn can occupy 8 # N and grow 4 inches per day. About 65% of a maize plant’s N requirement occurs through V18. From the onset of silks to maturity, a corn plant needs about 35% of its total N requirement. Farmers get their greatest increases in corn yield with the first 75-100 # N fertilizer applied.
Due to time constraints, many farmers dress on the N side immediately after planting. For best N efficiency, apply N when corn is higher but before it is knocked over by the tongue. With Y drops and highboy applicators, farmers can apply N much later and closer to the stalk and roots of the corn plant. In no-till situations, avoid applying N to surface residue to avoid N binding. Farmers can use the pre-treatment nitrogen test (PSNT) when N is applied to adjust rates of N. nitrogen. If the soil conditions are cold and excessively wet, avoid doing this test. The best and most accurate time to test is when N is applied. Producing corn profitably due to high nitrogen fertilizer prices will be a challenge this year.