Now’s the time to plan in-season fertilizer programs to take full advantage of strong corn prices, says Jason Mefford, an AgriGold agronomist based in Missouri.
“Although the cost of nitrogen is high, the cost of missing out on bushels per acre is even higher,” Mefford says. In-season applications have the advantage of providing N at the time plants need it, while potentially stretching fertilizer dollars.
“Although time and weather limitations may require anhydrous ammonia applications before the season, up to 20% of the usable N may be lost before the V9 to V10 stage,” Mefford says. “At $1,400 per ton or more for anhydrous, those losses add up.”
The amount of N needed in-season depends on several factors, including how much was applied in the fall or early spring.
“Farmers who front-loaded with 220 pounds of N upfront may not see much difference from adding another 40 to 60 pounds in-season,” Mefford says. “That front-loading may be sufficient to meet crop needs depending on yield goals and soil type.”
For farmers choosing in-season applications to bolster N availability, Mefford advises a planned approach based on soil nitrate testing, tissue sampling or nitrogen availability modeling through crop monitoring software.
Soil and plant tissue tests provide snapshots in time. Modeling systems consider factors such as soil type, pH, organic matter, planting date, rainfall and cation exchange capacity to predict the level of nutrients available in the soil and help determine how much N to supplement.
Consider in-season application options
Corn growers have multiple options for in-season N applications. Depending on their situations, growers can apply in-season fertilizer through sidedressing, topdressing or Y-drop applications to meet crop needs, Mefford says. Consider timing, as well as fuel and application costs, when determining the best approach. For best results, make in-season applications before corn tassels.
One option for sidedressing N is UAN — a solution combining urea and ammonium nitrate. It has the advantage of being immediately available to the plant and can be applied using several methods. However, farmers should be aware of applying UAN on wet fields, Mefford says.
“What can get you into trouble in-season is soil moisture,” he says. “Knifing or injecting N into the ground results in less nutrient loss. But if the soil is too wet, these incorporation methods can create sidewalls that dry into compacted barriers that make it difficult for roots to reach the N in the rows.”
Topdressing a granular, urea-based product across the field eliminates that concern because the product is broadcast across the field rather than being applied in a single band. This option allows for even application, and N reaches the plant more quickly.
Spreaders with 60-foot swaths can cover a wide area in a short period of time. However, the application window is short because the spreader needs to get into the field before corn reaches the V8 to V10 stage because of clearance concerns.
Be aware of N losses
“When topdressing urea, farmers do need to be aware that urea volatizes easily, converting to ammonia gas that is easily lost to the atmosphere,” Mefford says. “Urea applied on the soil surface may be more susceptible to N losses.”
Incorporating urea into the soil can help minimize volatilization. Another option is using a nitrogen stabilizer or urease inhibitor containing the active ingredient N-butyl-thiophosphoric triamide to prevent urea or UAN losses.
Y-drop systems are growing in popularity for in-season UAN applications using high-clearance sprayers. These systems reach below the canopy to apply UAN closer to the ground. With up to 120-foot booms, sprayers can cover large areas very quickly and apply when corn is taller.
Although most farmers make just one fertilizer application in-season, the Y-drop system allows for one application at the V6 to V8 stage, and another at pre-tassel if needed.
Don’t forget sulfur
If applying liquid N forms in-season, Mefford advises adding a source of sulfur — preferably ammonium thiosulfate. The nutrient needs to be in the sulfate form to be taken up by plants. Elemental sulfur applied in-season takes too long to convert to sulfate. Ammonium sulfate is also a very good dry source of sulfate sulfur that can be blended with urea in topdress situations.
“After N, phosphorus and potassium, sulfur is the next most important nutrient for corn. Sulfur and N go hand-in-hand. If soils lack sulfur, it can affect N efficiency,” Mefford says. “When testing soil nitrate, include sulfur tests, too. However, if you did soil testing in the fall, keep in mind that nutrient dynamics may change by the time the season starts.”
Monitor droughty soils
In areas of the Corn Belt that remain under drought conditions, fields may have little N loss and therefore less need for in-season fertilization.
“If dry trends continue, test for soil nitrates,” Mefford says. “You might have more N left than you would have with normal rainfall.”
The agronomist’s bottom line: “Ensure you have adequate N available at critical times throughout the season, such as grain fill. There are many ways to accomplish in-season applications. Consult with your crop adviser to select the option that fits your farm and management,” Mefford says.