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NorthStar News

Spring Fertilization for Soybeans and Corn

By Maria Brown

Did the weather or other factors prevent you from applying fertilizer to your fields this fall? Are you concerned that putting these important nutrients on the soil will result in an even bigger battle this spring? Dr. David Franzen, a soil scientist with North Dakota State University Extension, said this scenario shouldn’t be alarming.

“We sometimes get in that situation and many farmers have been down this road before,” Franzen says.

His advice to corn and soybean growers is to think in the short term and focus on those nutrients that are critical to getting certain crops off to a strong start.

“I like to see farmers put on enough fertilizer in the spring to keep the crop healthy for a while,” Franzen says.

Managing the application and timing of nitrogen in corn provides the biggest year-round challenge.

“We grow a fair amount of corn here in North Dakota, some 2-3 million acres, and we have some soils that are susceptible to nitrogen loss,” Franzen says.

Higher clay soils, those containing from 35-50 percent clay, are very susceptible to denitrification. It certainly doesn’t help that the region’s wettest months of the year—May and June—are realized in late spring.

“Growers are better about timing than they used to be. Back in the 80s and 90s, when we had a drier environment, people would push fall nitrogen applications into September. We still have a few of those types but most farmers pay attention to guidelines for not putting any nitrogen down too early in the fall,” Franzen says.

Those practices have also been influenced as fertilizer preferences have changed.

“We have a lot more urea than we used to. It recently surpassed anhydrous ammonia as the fertilizer of choice here. In addition, the wetter years have moved corn farmers in the region into more side-dressed N,” Franzen says.

He notes that soil scientists are moving away from “yield goal-based” nitrogen recommendations in corn, among other crops, in favor of a “return to N” model. Franzen says his research projects have found that nitrogen needs are constant across the board, regardless of the yielding environment. That’s because low-yielding sites realize poor mineralization rates and are inefficient in nitrogen uptake while N-use efficiency is greater in high-yielding environments. The end result is that the same rate of N required to achieve highest yield/profit in a low-yielding environment is the same rate of N required in a high-yielding environment.

When it comes to phosphorous levels, row-placed or near-row-placed phosphorus is important for corn, but not for soybeans. Phosphorus in this region is important for both crops, but the most efficient placement of fertilizer is different.

“Corn is a highly-concentrated phosphate band-responding crop. They just have an inherent need for it. The response to a starter phosphate application is really large,” Franzen says. “Soybean yields are generally higher with broadcast phosphate compared with banded phosphate.”

Applying potash to reach desirable levels of potassium can be done in either the fall or spring, he notes.

Franzen notes that sandier soils in North Dakota, especially those that are home to continuous soybean crops, have seen their potassium levels plummet when that bean-on-bean scenario has lasted close to two decades.

Lime is something more growers are considering when they think about fall soil amendments. Its use has been pretty common in eastern parts of the state where sugar beets are grown, Franzen notes. The waste lime generated from sugar production was spread on fields and has been credited with bringing Aphanomyces root rot under control.

As site specific soil sampling has become more common, farmers in the western part of the state are surprised to see significant pH variation across their fields.

“Growers with pH levels below 5 are asking ‘do I need to lime or not?’” Franzen says.

He advises they investigate the difference in pH levels between the top soil and subsoil because acidity at the surface level isn’t a cause for concern unless herbicide carryover problems are possible with pH-sensitive chemistry.

Producers should consider supplemental iron, particularly when growing soybeans in regions where iron deficiency chlorosis is a common problem. In portions of the Upper Midwest, iron deficiency chlorosis can result in poor nodulation in beans and greatly reduced yields.

“In the east where we have more free lime and more moisture in the soil, iron deficiencies are very common and cover a high percentage of some fields,” Franzen says.

“There’s a whole suite of things we recommend for iron nutrition.”

It starts with selecting the right seed. Franzen says producers have plenty of options for when it comes to iron deficiency chlorosis-tolerant cultivars.

Growers must recognize the challenges that arise from salt in the soil too.

“Ninety-nine percent of the soils in North Dakota have soluble salts. This serves as another stress to the plant which, in turn, increases the severity of iron chlorosis.”

When it comes time to planting, soybeans benefit from being planted in wider rows coupled with the use of a companion cover crop, like oats or barley, which  can utilize any excess nitrates lingering in the ground and help dry out the soil.

“We also recommend use of an iron fertilizer, but it has to be specific,” Franzen says, adding that the best option out there is ortho-ortho-EDDHA which is applied at planting time, in-furrow with water.

Supplemental sulfur is sometimes needed in soybeans, particularly those grown on sandy soil, but Franzen says the legumes aren’t as responsive to this nutrient as corn.

“Growers should concentrate on sulfur in corn, small grains and of course canola,” he says.

“Always put sulfur on in the spring, close to planting time, and always use sulfate or thiosulfate.”

Research has also shown that corn grown in North Dakota benefits from applications of zinc, too. Franzen says the micronutrient can be banded with a phosphate starter fertilizer in the spring.