By Steve Watson
A little fertilizer at or near planting time can help jumpstart wheat toward a successful crop, but producers have to be careful to apply it correctly, said Dorivar Ruiz Diaz, associate professor of agronomy at Kansas State University.
In general, wheat is considered a highly responsive crop to starter fertilizers, particularly phosphorus and nitrogen, he said. When applying a starter fertilizer for wheat, application methods and rates are much more flexible with phosphorus than nitrogen.
“An application of phosphorus as starter fertilizer can be an effective method for part or even all the phosphorus needs of wheat. Wheat plants typically show a significant increase in fall tillers and better root development with the use of starter fertilizer – both phosphorus and nitrogen. Winterkill can also be reduced with the use of starter fertilizers, particularly in low phosphorus testing soils,” said Ruiz Diaz, who is a nutrient management specialist with K-State Research and Extension.
Most sources of phosphorus, except thiosulfate, can be safely applied at recommended rates and with any application method, including in the seed row.
“Phosphorus fertilizer application for wheat can be done through the drill with the seed,” Ruiz Diaz said. “This would either be in addition to, or instead of, any pre-plant phosphorus applications depending on soil test and recommended application rate.”
The use of dry fertilizer sources with air seeders can be a popular and practical option; however, other phosphorus sources, including liquid, are agronomically equivalent and decisions should be based on cost and adaptability for each operation, he added.
A little nitrogen in a starter fertilizer can also benefit wheat, but growers should be careful about how fertilizers containing nitrogen and potassium are applied as starters for wheat, he said.
When applying fertilizer with the seed, nitrogen and potassium rates should be limited to avoid potential toxicity to the seedling. When placing starter fertilizer in direct contact with wheat seed, Ruiz Diaz said producers should use the following guidelines:
* In 15-inch spaced rows, apply no more than 16 pounds of nitrogen-plus-potash for medium to fine textured soils, or 11 pounds for sandy or dry soils.
* In 10-inch rows, use a maximum of 24 pounds of nitrogen-plus-potash for medium to fine soils and 17 pounds for sandy or dry soils.
* For 6- to 8-inch rows, no more than 30 pounds of nitrogen-plus-potash should be applied to medium to fine soils and 21 pounds for sandy or dry soils.
* In general, no urea-based nitrogen should be applied with the seed in any row spacing or soil type.
Planting equipment can make a bit of difference in these guidelines, he added.
“Air seeders that place the starter fertilizer and seed in a band an inch or two wide, rather than a narrow seed slot, provide some margin of safety because the concentration of the fertilizer and seed is lower in these diffuse bands,” Ruiz Diaz said. “In this scenario, adding a little extra nitrogen fertilizer to the starter is less likely to injure the seed - but it is still a risk.”
What about blending dry 18-46-0 (DAP or Diammonium phosphate) or 11-52-0 (MAP or Monoammonium phosphate) directly with the seed in the hopper? Will the nitrogen in these products hurt the seed? The nitrogen in these fertilizer products is in the ammonium-nitrogen form, not the urea-nitrogen form, and is much less likely to injure the wheat seed, even though it is in direct seed contact, Ruiz Diaz said. As for rates, the guidelines mentioned previously should be used. If DAP or MAP is mixed with the seed, the mixture can safely be left in the seed hopper overnight without injuring the seed or gumming up the works.
Although the response of wheat to DAP and MAP dry or 10-34-0 liquid starter fertilizer products is primarily from the P, the small amount of N that is present in these products may also be important in some cases, he said.
“If no preplant nitrogen was applied, and the soil has little or no carryover nitrogen from the previous crop, then the nitrogen from these fertilizer products could benefit the wheat, in addition to the phosphorus,” the K-State nutrient management specialist said.