Due to the dramatic rise in nitrogen prices over the past several years, producers are wondering how they can get the most bang for their buck.

Crop budgets from Virginia Tech show that nitrogen accounts for nearly 57 percent ($102) of total fertilizer input costs ($177) to produce 150 bushels of corn per acre.

Virginia Tech agronomists have stated that 146 pounds of nitrogen are needed to grow 150 bushels of corn per acre.

The nitrogen requirement for corn can be met in several ways:

• The decay of organic matter by soil organisms provides available nitrogen.

• Legumes (e.g. alfalfa, clover, soybeans) fix nitrogen from the air that can be used to meet the nitrogen requirements.

• Many Virginia producers apply cow and swine manure, poultry litter and biosolids (municipal wastewater treatment sewage sludge) and grow cover crops to help meet the corn’s nitrogen requirements.

The nitrogen in organic form becomes available to help meet the nitrogen requirement for the crop. When there is little available nitrogen from legumes, manure and biosolids, the requirements for the crop can be supplied with commercial fertilizer (e.g. urea, ammonium sulfate, liquid N).

Many producers split-apply fertilizer at planting and later in the growing season when nitrogen requirements are the greatest and yields estimates are more certain.

Corn requires only small amounts of nitrogen during the first month of growth because the plants are small and the root systems are not well developed.

Leaching losses

Nitrogen applied pre-plant or released from organic matter (crop residues), manure and biosolids can be lost by leaching during the time when nitrogen requirements are low and soil moisture is high.

Therefore, only small amounts of starter nitrogen (25-30 pounds per acre) should be applied prior to or at corn planting to meet the crop needs during the first 30-45 days after emergence”

Additional nitrogen can be side-dressed before the crop begins its most rapid growth rate when the corn is 12 -24 inches tall. A Pre-sidedress Soil Nitrate Test (PSNT) can be conducted at this time to reflect the actual availability of soil nitrogen to meet the crop’s requirements.

The PSNT measures the plant-available nitrogen from the soil sample by taking cores across the field to a depth of 12 inches. The sampling should be done after the spring wet season and when the corn is 12 -24 inches tall.

It is recommended that multiple samples be taken in a field to reflect differences in soil types, drainage and fertility levels. Combine, mix, crumble and dry the samples to create a composite sample for a field.

The samples may be dried by spreading the soil in a thin layer over newspaper in a warm place or in the sun.

In order to speed up the drying process, the sample can be dried in convection and microwave ovens. Since this is a relatively simple test, turnaround time is usually 24–48 hours.

Virginia Tech agronomists recommend that producers conduct PSNTs on fields that have had dairy and swine manure, poultry litter and biosolids.

Extension agents, crop consultants and industry sales consultants perform PSNTs for farmers in Virginia. These professionals can take the PSNT results and make recommendations for side-dressing the corn crop.

Growing seasons vary from year to year. PSNTs provide producers the opportunity to measure the levels of nitrogen available in the soil that can be used to meet the nitrogen requirements for a corn crop.

Under- or over-fertilizing the crop can cost producers money in the form of not providing sufficient nutrients to meet the field’s yield potential or applying nitrogen that is in excess of the field’s yield potential.

PSNTs are a win-win proposition for the producers’ pocketbooks because producers can apply the optimal pounds of nitrogen needed to achieve the field’s yield potential.

(This is one step in getting more yield from a corn crop. For other practices that can take corn production to the next level, click here).