Nitrogen management needs to be tailored to your specific crop rotation, types of tillage, or lack of tillage, and the needs of your crop.
Stabilizers and controlled-release products help keep the Houdini of nutrients where your crop needs it
Applying nitrogen—corn’s most important and trickiest nutrient—doesn’t do a lick of good if it escapes into the air or, even worse, into water sources before plants can use it.
Products that slow the loss of nitrogen can help you hold it in place, to feed hungry corn and boost yield—but only if you understand them well enough to choose the right one, says Farm Journal Field Agronomist Ken Ferrie.
To select the right product, consult the table on page 32. But first, decide what type of nitrogen loss—denitrification, leaching or volatilization—you need to prevent.
Denitrification and leaching occur only with the portion of your soil nitrogen that is in the nitrate form. Denitrification occurs when soil is saturated with water, especially when standing water is combined with warm temperatures and a carbon source. In those con- ditions, denitrifying bacteria increase. They strip oxygen away from nitrate-nitrogen (NO3-N) molecules, releasing nitrogen as a gas.
Sandy and well drained soils, where water percolates through, can leach NO3-N. "Stabilizers that reduce denitrification and leaching do it by slowing the nitrification process, in which ammonium is converted to nitrate," Ferrie says. "They either kill some of the nitrifying bacteria or slow down their activity."
Since you can’t protect nitrate, you have to keep it in the stable ammonium form, by preventing nitrification, until the crop is ready to use it, Ferrie summarizes. Soils that stay wet and sandy soils that are subject to leaching are situations where nitrification inhi-bitors can help.
Volatilization affects surface-applied urea, which must break down, or hydrolyze, into ammonium. The ammonium then goes through the nitrification process to produce nitrate. Both forms can be used by corn plants, but until it is either tilled into the soil or washed in by rainfall or irrigation,
ammonia can be created during the hydrolysis process and be lost as a gas.
The urease enzyme. Bio-inhibitor products reduce the risk of volatilization of urea prior to tillage or rainfall by blocking the urease enzyme. That enzyme, found in crop residue and in the upper few inches of soil, triggers the breakdown process that creates the risk of volatilization.
Managing urease enzymes is very important if urea is applied on the surface and not incorporated—which is becoming more common as farmers adopt no-till, strip-till and pre-emergence weed and feed programs. That’s because urea hydrolysis causes soil pH to go up around the nitrogen molecule; high pH speeds the conversion of stable ammonium molecules to ammonia gas, which can be lost by volatilization.
The same concern arises in soils with a naturally high pH and where lime is applied without incorporation, also a no-till/strip-till situation.
Another approach to nitrogen stabilization involves controlled-release products, which slow the breakdown of urea by encapsulating the particles. They can reduce both volatilization and denitrification.
So far, so good, but it gets more complicated in the field because you have to understand your nitrogen source. "For example, 28% and 32% UAN [urea-ammonium nitrate] solutions contain 50% urea, 25% ammonium and 25% nitrate," Ferrie says. "So you may need two products: one to help prevent the urea from volatilizing—unless you incorporate immediately after application—and one to slow the conversion of stable ammonium into nitrate, which is easily lost."
Picking the correct stabilizer depends on various factors, including your nitrogen product and whether you plan to incorporate. "Say you’re in no-till or strip-till and you apply 28% UAN solution on the soil surface and you added a stabilizer that protects only against denitrification and leaching," Ferrie says. "Late in the growing season, you’ll be wondering why your crop ran out of nitrogen.
- February 2013
, Farm Business
, Nutrient Navigator
, Soil Health
, Spring Planting 2013