Nitrogen is a key nutrient required by corn and one of the greatest input expenses on a per-acre basis.
It can be purchased in multiple forms including dry granular, liquid, and as a liquid kept under constant pressure which vaporizes upon release.
The latter is the product we know to be anhydrous ammonia — the nitrogen source from which all other purchased nitrogen sources are derived. Most of the nitrogen applied before planting corn is in the form of anhydrous ammonia, and the application window is now open.
Always a concern with applying nitrogen pre-plant is the risk of loss if soil conditions are wet for long periods between application and when corn can take it up.
Anhydrous Ammonia enters the soil as ammonia (NH3). It immediately interacts with soil water (H2O) to become ammonium (NH4). Ammonium cannot be lost from the soil in any way other than plant uptake. After having hydrogen stripped, water in and near the application zone becomes hydroxide (OH), which has a very high pH.
In the days soon after ammonia application soil pH can increase to as high as 11 and time is required for water to move into the application zone to normalize the soil pH. This is the reason we strongly encourage waiting no less than two weeks after ammonia application before planting.
Bacteria in the soil convert into ammonium nitrate (NO3) in a process called nitrification. Loss due to excessive water can occur when it is in the nitrate form by leaching or by denitrification.
Leaching is loss of nitrate through gravitational soil drainage. In-season loss to leaching is not common in our area. It is a greater risk in sandy well-drained soils which are limited here.
Denitrification is different.
It is caused by bacteria in the soil which after three days of saturated conditions have depleted oxygen in the soil which they need to live.
Their answer is to consume oxygen from the nitrate (NO3) turning it into nitrogen dioxide (NO2), a gas that rises out of the soil returning to the atmosphere.
Fortunately, upland soils wet from constant rain will probably not lose much nitrogen because soils have to be constantly saturated for two-three days to begin the denitrification process.
When soils drain out and oxygen returns, the process resets. There are exceptions, but most well-drained soils do not remain saturated very long after rain.
Even low land fields subject to periods of flooding and prolonged saturation may not lose as much nitrogen as one would assume.
Three weeks after application, only 20% of anhydrous ammonia is in the nitrate form and just 10% if N-Serve nitrification inhibitor was used. At six weeks, 65% will be in the nitrate form and 50% if N-Serve was used. Nitrification inhibitors work by killing off bacteria in the soil.
So if nitrogen during the summer growing season is relatively stable in the soil, why are applications after planting becoming more popular?
There is a long list of answers. First, and most important in my opinion, if you can not wait two weeks to plant following an ammonia application, you need to plan to apply nitrogen after planting.
An exception to this can be justified if autosteer technology on the application and planter tractor provides the ability to plant in between the ammonia application zones.
Early planted soybeans are becoming more popular. In the past, many farms ran ammonia, started planting corn two weeks later, and then planted soybeans when the corn was finished.
Several farms have made a goal of planting soybeans early, during the window when nitrogen would have historically been applied with plans to now apply nitrogen when they would have been planting soybeans.
This plan is working. The past few years have proven that soybeans planted between late March and early April can produce excellent yields.
Timing nitrogen application closer to when it will be used by the corn plant has been gaining traction. Corn uses very little applied nitrogen in the first weeks after planting.
As much as half of its nitrogen requirement is not taken up until after tasseling. There is interest in timing nitrogen application later in the growing season, closer to when corn will actually use it.
Upcoming WebinarThis Thursday, March 18, at 6:30 p.m., Dr. David Kohl will present a webinar titled, “Agriculture Today: New Era of Prosperity or Temporary Opportunity.” Preregistration is required at http://bit.ly/3pMFGly.
Clint Hardy is the agricultural extension agent for the Daviess County Extension Office. He can be reached at 270-685-8480.
March 14, 2021 at 01:00PM
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