How Much Nitrogen Per Acre Do You Need to Plant Corn?

Over the course of the 20th century, corn yields increased drastically. Because lack of nitrogen often limits corn growth, a major reason for such dramatic increases was the use of nitrogen fertilizers. Although one of the grower's largest expenses, nitrogen fertilizers, if used properly, pay for themselves with higher yields. However, concerns over the environmental safety of nitrogen fertilizers require careful and considerate use.

Corn plants require nitrogen across the entirety of their life cycle. Nitrogen promotes the growth of stems, foliage and the grain itself. Within a week after germination, corn exhausts the nutrient supply in its seed and begins extracting nitrogen from the soil. Corn requires the largest amount of nitrogen about a month before producing tassels, the period of most rapid growth.

Research conducted by the Virginia Cooperative Extension compared the yields obtained from nine cornfields over the course of two growing seasons to determine the most productive use of nitrogen fertilizer to start corn seed. Productivity not only takes into account the increases in yield but also the cost of the fertilizer and the potential risk of fertilizer salt damage to the seedlings. With all of these considerations in mind, the extension concluded that 50 lbs. of nitrogen fertilizer administered in starter bands produced the best yields. Although broadcasting fertilizer onto the soil surface is less effective, the extension recommends 60 lbs. per acre, if you choose to use this method.

Starter bands make fertilizer directly available to the roots of the young seedlings by concentrating the fertilizer in the place where the roots will grow. The Virginia Cooperative Extension recommends working nitrogen fertilizer 2 inches deep into the soil, 2 inches from each side of the seed. Placing the initial fertilizer application closer to the seed risks salt damage to the tender new roots.

Sidedressing refers to the application of nitrogen over the root systems of plants after growth has begun. According to George Rehm on the University of Minnesota's website, since corn plants use the most nitrogen prior to forming tassels, this is the most efficient time to apply nitrogen fertilizer. You can sidedress nitrogen in combination with a starter-band application. Sidedress rates can range as high as 125 lbs. per acre, depending on the needs of a particular soil.

Several factors influence the amount of nitrogen needed per acre of corn. The previous crop in the field affects the amount of nitrogen naturally available, and the tillage system used affects how quickly natural sources of nitrogen break down. Soil type also affects nitrogen availability. Before planning a nitrogen fertilization program, have a soil test done to determine the need for nitrogen in your soil and adjust recommended rates accordingly. The pre-sidedress soil nitrate test (PSNT), particularly, helps growers choose sidedress rates.