Many strip-tillers incorporate application of various fertilizers — nitrogen, phosphate and potash — when strips are being made.
Anhydrous ammonia, a common source of nitrogen, can be toxic to germinating seeds and root systems when applied too close to the seed. Anhydrous must have sufficient time and moisture to convert the ammonia form (NH3) to usable nutrients (ammonium and nitrate) that plants can utilize.
The most important factor of determining ideal time for applying nitrogen is adequate soil moisture, says Brian Arnall, an Oklahoma State University precision nutrient management specialist.
Bob Olsen, retired owner of Olsen’s Laboratories in McCook, Neb., agrees with Arnall.
“The two key factors that will determine ideal application timing are soil moisture and soil texture,” Olsen says.
When making strips and/or applying anhydrous, the soil needs adequate moisture without being too moist or too dry.
And soil texture will dictate the rate of application. Sandier soils may require a reduced rate of anhydrous. Farmers should not have to exceed 200 pounds of anhydrous, even on heavier soils. Yield goals, and whether or not the field is irrigated, will also be determining factors on the rate of application.
Olsen says that the most common questions strip-tillers have about nitrogen application are how muchanhydrous they can apply and when they should apply it.
His recommendation is simple: Apply anhydrous prior to planting, at a rate based on yield goals and a nitrate soil test.
Olsen also recommends anhydrous in strip-till fields be placed 6 to 7 inches below the seed. In areas with cold winter temperatures and drier weather conditions, farmers can apply anhydrous in the fall.
"Higher anhydrous rates should be placed farther from the seed, but lower rates can be applied closer to the seed."
- Brian Arnall,
Oklahoma State University precision nutrient management professor
Applying anhydrous when soil temperatures are less than 60 F will prevent it from converting to nitrate. When it converts to nitrate, there is a risk of leaching. For those who apply anhydrous in the spring, the fertilizer should be applied at least 2 to 4 weeks before planting to prevent it from burning the roots of the seed.
Olsen recommends leaving at least 5 inches between the anhydrous point of injection and where the seed will be planted. Strip-tillers need to be aware of the ramifications of placing anhydrous too close to the seed. High concentrations of salts, such as ammonium hydroxide and nitrates, will injure the germinating crop.
Salt injury can occur if too much fertilizer — nitrogen, phosphorus, potassium or sulfur — is applied as a starter fertilizer.
“Higher anhydrous rates should be placed farther from the seed, but lower rates can be applied closer to the seed,” Arnall says.
The higher the rate of nitrogen applied, the higher the rate of burn. Mother Nature can also cause root burn. Anhydrous applied in sufficient moisture only to be followed by very warm and very dry conditions may not allow enough time for anhydrous ammonia to convert to nitrates, thus causing damage to the germinating seed.
Proper timing, location and rate of anhydrous are the best management tools for preventing root burn.
Another option is split application of nitrogen. Producers don’t have to do everything with pre-planting, Arnall says. They can split applications if irrigating (fertigation) increases utilization and efficiency.
As an example, Arnall points to a Maryland farmer who used a total of nine split applications on deep, sandy soils, averaging a total of 0.6 pounds of nitrogen per bushel of corn. The average Oklahoma farmer, for example, applies an average of 0.9 pounds of nitrogen per bushel. So the efficiency gained outweighs the cost difference.
Olsen also recommends the use of fertigation on irrigated fields. He says approximately 33% of the nitrogen can be applied via fertigation after about 66% of the nitrogen is applied before planting.
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