Extension and Ag Research News


Producers Face Many Fertilizer Considerations This Spring

There are many considerations for growers following field flooding or at least delayed field conditions due to wetness. These include logistics, delayed or shallow applications, nutrient transformations and nutrient leaching.

“Logistically, this spring was shaping up to be challenging even before the current inundation,” says Dave Franzen, North Dakota State University Extension Service soil science specialist. “The planting season calendar is now even more compressed. On the good side, fields will not all dry at once, so that will help with the distribution of fertilizer on a regional and local scale. On the not-so-good side, road conditions are terrible. It certainly will slow the transport of nutrients to retail locations and the farm.”

At the warehouses, the supply of fertilizer appears to be good. Fertilizer costs are lower compared with last spring, except for potash.

Little fertilizer was applied in the Red River Valley region last fall. In most years, more than half is applied during the fall. More than half of the fertilizer nitrogen in the state is normally anhydrous ammonia. However, with wet soils, it will be impractical to apply ammonia due to the mucky conditions in medium and heavier soils.

“I expect that many growers will choose to broadcast or band urea and, in some cases, even broadcast or band liquid 28-0-0,” Franzen says. “In many years, the cost of 28-0-0 (UAN) is substantially higher than urea, but this year costs often are very similar. UAN might be used because of the small difference in costs, particularly if custom-applied by the retailer who is set up with a sprayer and nurse equipment.”

An option for row crops is to delay the ammonia application until side-dress season when corn and rowed sunflowers are at four to six leaves. If the weather continues wet through this period and anhydrous is still impractical to use, rigging an applicator with coulters and dribbling UAN into the shallow slit made by the coulter or even dribbling UAN between the rows on the soil surface often is an acceptable method of application.

An application of urea for sugar beets at preplant should be no more than 75 pounds of nitrogen (N) per acre. Last year, under dry conditions, a reduced stand was seen in a Crookston, Minn., study, even at levels this low. Because of the restriction on preplant N for sugar beets, a split application may be needed. Applying half of the N on preplant and then side-dressing or dribbling between rows later will provide the N required.

Small grains need N at seeding or before. Small grains grow so quickly that the logistics and weather cooperation required to make a delayed N application work often is thwarted. Dry weather following a top-dress application can result in N not getting to the plants early enough for full benefit. A series of studies across the state several years ago showed that using a top-dress N application was not as consistently efficient as preplant N applications.

Canola would not require the N as soon as small grains, but the weather still is against the growers. It is wet now, but it could be dry during a critical stage of growth and the top-dressed N would be rendered inefficient as a result.

Growers probably will be able to seed small grains faster than fertilizer can be supplied logistically.

“If this happens to a grower, it is more important to seed than to wait for fertilizer,” Franzen says. “The grower definitely should apply a small amount of starter phosphorus (P) with the crop. Beyond that, avoiding planting delays is critical. If a grower is forced to seed and fertilize later, urea or UAN can be used.”

If urea is used and the forecast for at least one-half inch of rain is less than 90 percent in the next couple of days, have the urea impregnated with Agrotain to have about 10 days of assurance that the urea will not be lost. Another option is to stream-bar UAN as soon as possible after seeding. Half of the UAN is ammonium nitrate that cannot be lost by the volatilization of the urea. The urea half is aided by the concentrated effect of surface banding, which reduces the rate of urease enzyme activity and subsequent urea loss.

If fall anhydrous was applied last year after the soils cooled (after Oct. 15 in the southeastern part of the state), then any flooding to date has had little if any effect on residual N. Also, soils in the southeastern part of the state did not lose surface frost until about April 10. A grower can access local information by going to the North Dakota Agricultural Weather Network Web site (http://ndawn.ndsu.nodak.edu/) and clicking on bare soil temperature for the nearest NDAWN station.

Any residual N that was present from before freeze-up (Thanksgiving week) to April 10 was frozen in place. If flooding was present after that date, then that N will start to change into nitrous oxide gas through the activity of denitrifying microorganisms and may be lost. Also, even if water does not cover the soil, but the soil remains saturated, denitrification losses could occur.

“Because of the wetness last fall, lighter soils, including sandy loams and loamy sand textures, were subject to nitrate and sulfate leaching,” Franzen says. “Any continued wetness from about April 10 on in the southeastern part of the state to whenever the frost leaves the rest of the state will result in substantial nitrate and sulfate leaching. Growers may benefit from the application of sulfate forms of sulfur on sandier soils with less than 3 percent organic matter, especially on hilltops and slopes this spring. Heavier soils in depressions and footslopes and soils higher than 3 percent in organic matter are far less likely to need sulfur this spring.”

Any crop grown in the region will respond to sulfur if it is short. Growers with sandy soils also should consider that any residual N tested for in early fall 2008 probably will not be as high when planting finally takes place, so application rates may need to be higher than originally planned. Loam or heavier soils probably will not require enhancement.

“I would expect our spring organic matter/residue N mineralization rates to be much higher this spring than last year,” Franzen says. “This should fill in any gaps in leaching from early fall through this preplant spring period.”

NDSU Agriculture Communication

Source:Dave Franzen, (701) 231-8884, david.franzen@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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