Fertilizing Crops with Nitrogen

June is a busy month as farmers finish up planting, fertilizing, and spraying crops. For corn nitrogen (N), farmers have several options. Many farmers side-dress anhydrous nitrogen to corn. Anhydrous is a concentrated source of nitrogen, 82% by weight while liquid forms of N can be 28-32% or as high as 46%. Ammonia is usually the most economical, however, since it is stored at low temperatures (-28OF) with internal pressures of 250 psi , its more dangerous to apply.

Anhydrous is often applied in the fall or early spring with a N stabilizer, getting at least a portion of their N applied, before spring or early summer rains prevent timely fertilizer application. Advantages include applying N fertilizer during a slack time period and it is generally cheaper and the most economical. Soil bacteria can easily convert ammonia into nitrate. Generally, corn like to take up N as both ammonia and nitrate. Nitrate forms of N promote growth while ammonia forms promote yield. As the season progress, corn growers should be applying more ammonia forms to stimulate yield.

UAN 32% solutions are liquid nitrogen fertilizer solution made from 50% urea and 50% ammonium nitrate. One-fourth of the nitrogen is ammonic, one-fourth is nitrate and one-half is urea and weighs about 11.08 lbs. Although more expensive, some farmers like to apply ammonium sulfate (21% N and 24% Sulphur). Ammonium sulfate is a water loving nitrogen form that also supplies plant available sulfur to aid in plant growth. However, it is also highly acid (5.5 pH), so it should not be applied to acid soils with a low pH. Soil health farmers tend to use either liquid UAN or solid N sources because anhydrous is so cold, it freezes the soil and temporarily hurts soil microbes and other soil organisms in the vicinity. Generally, soils can recover fairly quickly.

Nitrogen can also be applied with Y drops at the base of the corn stalk. Ohio State University research shows that this can be an effective form of N application, applying N right when the crop needs it. Corn uptake of N is the highest after pollination. Most farmers are applying .7 to 1 pound of total N fertilizer for every bushel of corn they produce. For example, for 200-bushel corn, a typical application would be 140-200# of total N (including starter fertilizer).

Some soil health farmers are only applying .5 pounds N per bushel. How is that possible? For many years, it was thought that corn only took up two types of N fertilizer, ammonia and nitrate. Recent research discoveries show that crops can also take up ammino acids and even whole proteins. Corn needs 25% more energy to convert nitrate into an ammonium forms to make amino acids and proteins. Imagine the energy savings if the corn can take up already formed amino acids and proteins. Healthy soils are teaming with microbes. Their can be 1000-2000X more soil microbes associated with live roots, especially where cover crops are grown, and these microbes are just soluble bags of fertilizer. Microbes supply plant with many forms and types of essential fertilizer nutrients as metabolites from the microbial cells.

Crops can absorb soil nitrogen several ways. Legume crops (soybeans, alfalfa, and clovers) have rhizobia bacteria that can take atmospheric nitrogen and convert it to plant nitrogen. Arbuscular Mycorrhizae Fungus (AMF) are like root extenders, scavenging for soil N and transporting it back to the plant. A corn plant root can explore 1% of the soil volume but AMF are like a spider webs and only 1/10 the size of a human hair, exploring 20% of the soil volume. Metarhizium fungus (MET) also supply N to plants. MET fungi infect crop roots and are like Venus fly traps, sucking N as proteins from soil insect eggs, larvae, grubs, and even adult insects. MET are known to infect and ingest almost 200 different insect species, protecting crops from insect feeding while supplying crops with extra N in the form of amino acids and proteins.

Dr. James White, Rutgers University just recently discover a new process called rhizophagy. In rhizophagy, soil microbes are absorbed at the root tips, losing their cells walls. Once inside the roots, about 80-90% of microbes exchange nutrients for sugars. They then are expelled back into the soil and reform their cell walls. The other 10-20% of the microbes are consumed, giving the plant whole amino acids and proteins, vitamins, and enzymes. These are important forms of N and other essential nutrients which will be studied in the future.