Nitrogen loss paths, management topics discussed

GENESEO, Ill. — Nitrogen is among the costliest and yield-limiting inputs in corn production, and there are three pathways that investment can be lost during the growing season.

Eric Wilson, Wyffels Hybrids agronomy manager, detailed the nitrogen loss scenarios of leaching, denitrification and volatilization, along with management tips.

Here is what he had to say about each topic:

On Leaching

Leaching is the loss of nitrate through the soil water profile and the primary nitrogen loss pathway often discussed.

Nitrate is the most abundant form of nitrogen because typically under warm spring conditions all forms of nitrogen convert to nitrate. It does have a negative charge, so it’s not held by the soil cation exchange and it readily moves with water.

Losses are directly dependent on rainfall and temperature. However, it’s not always associated with heavy rainfall events.

In fact, a lot of heavy rainfall events result in surface runoff that doesn’t move down through that soil profile.

Something to keep in mind, if you had early-season heavy rainfall events, some of that nitrogen that you applied in particular as anhydrous, is likely not converted to nitrate yet.

Temperature is the key. You have to have those warm temperatures for ammonia to convert to nitrate in order for it to be leached through the soil profile.

On Denitrification

This would be the primary loss pathway under flooded conditions. This is very dependent on temperature and losses per day can range from 2%, 50 to 60 degrees, to 5% or greater, 65 degrees-plus.

Significant loss does happen under saturated soil conditions, especially when we have warmer temperatures later in the spring.

On Volatilization

Volatilization is typically not a primary loss pathway for a lot of us, but it can happen. It’s directly associated with surface-applied fertilizers that are left unincorporated.

Keep in mind, we have to have a little bit of rainfall to get nitrogen to move down into the soil profile unless we’re doing some early spring tillage to incorporate that.

On Management

Know when to act if you suspect that you’ve had some nitrogen loss. Above-average spring rainfall, specifically between May and June, usually justifies additional nitrogen applications above what you’ve already done.

If ponding or saturated soils exist for extended periods, assume significant nitrogen loss to denitrification.

Keep in mind, these are all temperature-dependent. If it’s happening early season, and we don’t have the warm temperatures to get conversion to occur, it’s unlikely that we’ve lost a lot of nitrogen, especially if it’s still in the ammonium form.

Spring soil nitrate testing — if you’re using a spring soil nitrate test and it’s coming back low, that absolutely justifies doing an additional nitrogen application.