Ask our agronomist: Nitrogen management

While nitrogen is usually supplied in ample amounts, many times much of it is lost to the environment instead of being used by the plant. Management practices like timing, fertilizer source and N stabilizers can be used to reduce the chances of environmental loss.

Loss Mechanisms

Nitrogen fertilizer is lost from corn fields by two primary means:

• Leached through the soil profile in the Nitrate form.
• Converted from nitrate to N2 gas through the process of denitrification and lost to the atmosphere.

In both cases, nitrogen must either have been supplied as nitrate or converted to nitrate before losses can occur.

Fertilizer Source

The fertilizer source is important to determine how quickly nitrates are available for loss.

Anhydrous Ammonia

Quickly converts to ammonium at application. Kills soil organisms in the anhydrous band. Must repopulate bacteria in the band (10-14 days) before nitrification can occur. Requires an additional 7–14 days to convert to nitrate. Total conversion time 2-4 weeks. Application timing prior to heavy rains will determine how much was in the nitrate form available to leach or denitrify.

UAN (28%)

Roughly one quarter of the product is in the nitrate form at application. The remainder requires 7 -14 days to convert to nitrate.

Urea

Can be leached while in the urea form (12-24 hours after application). Hydrolyzes to ammonia quickly as temperatures warm. Converts from ammonia to nitrate in 7-14 days.

Managing Nitrogen with Stabilizers

Nitrification Inhibitors

Suppresses population of Nitrosomonas and slows or stops conversion of ammonium to nitrate. Rule of thumb is that you get an extra two to three weeks of protection. Hopefully by that time, the crop is rapidly taking up nitrogen and saturated soils are less likely.

Urease Inhibitors

Blocks function of the urease enzyme which reduces the potential for ammonia volatilization from the soil surface and allows time for water to move urea into soil. Rule of thumb is that you get an extra one to two weeks of protection.

Coatings

A polymer coating applied to a soluble fertilizer. The fertilizer diffuses through the coating. Rate of release is determined by polymer chemistry, coating thickness, moisture and temperature. When applying, consider how long before the crop will need nitrogen. Generally only a very small amount is available immediately with most releasing over subsequent months.

Should I use a stabilizer?

There are several questions that should be asked when deciding whether or not to use a stabilizer:

• Am I putting on nitrogen during a time of risk? This is basically any time that there are not crop plants available for uptake.
• Are environmental conditions conducive to loss? This depends on the fertilizer form and environment. (e.g., you want a rain if you apply urea to the soil surface without incorporating it to reduce chances of volatilization.)
• What is the cost of the stabilizer compared to the cost of purchasing additional nitrogen? With today’s N prices, usually it makes more sense to invest in the stabilizer.

When should I apply Nitrogen?

Generally the closer nitrogen can be applied to crop need, the better chance the N will be used by the crop, not lost to the environment. There have been many studies over the last forty years that confirm a side-dress N application around V6 growth stage in corn is the most efficient use of nitrogen. Unfortunately, many growers have been concerned about timely application due to unforeseen weather events, heavy workload during that time of year and lack of adequate side-dress equipment.

Recently research has shown that corn continues to take up nitrogen even into later growth stages. In fact today’s high yielding corn hybrids continue take to up approximately 2/3 of required N during vegetative growth stages and 1/3 during reproductive growth stages. As a result, many growers are applying a portion of their N either in the fall or pre-planting and then taking a pretty relaxed approach to the balance with a late-season application. This is dangerous, however.

Nitrogen moves in the soil via mass flow (water required) or through root interception. For those that apply N very late in the growing season (late V stages to early R stages), there is agronomic evidence that suggests this nitrogen may not be used at all. Why? In many cases weather is hot and dry during late V and early R growth stages throughout the Corn Belt. If urea is broadcast, it is very likely adequate moisture may not be available to move it into the soil for plant uptake before it is lost through hydrolysis. Similarly UAN that is applied may not have an adequate opportunity to move into the soil solution. Research conducted in southern Indiana during three seasons from 2012 – 2014 proved that nitrogen applied very late in the growing season had no effect on yield.

For these reasons it is much better to apply a third to a half of required N immediately prior to planting followed by the remainder from V6 – V10. In most cases, this earlier in-season application will provide adequate nitrogen during a portion of the season when timely rains are more likely. This is the least risky, most environmentally friendly and highest efficiency application method available. It also is very conducive to standard clearance tractors and sprayers that you or your ag retailer already own. With tightening margins, it is more important than ever to squeeze every dollar possible out of equipment investment and inputs while maximizing yield.

Nitrogen is the key nutrient for plant growth and health but it cannot simply be applied and forgotten. Techniques that stabilize, contain and introduce nitrogen to the plant at the right time, right rate, right source and right place (4R) will result in stronger plants and yield.

Darren Goebel is an agronomist and the Director of Global Commercial Crop Care for AGCO. He has been a crop consultant and agronomist through his work spanning virtually all crops and geographies with time spent in SE Asia, China, India, Eastern Europe, Mexico, U.S., and Canada. Darren has spent extensive time consulting on precision agricultural and holds degrees in Agronomy, Agricultural Economics and Business. He grew up on a grain, livestock and specialty produce farm in southwest Indiana.