NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

October 8, 1998

NDSU Soil Scientist Says Soil Testing Essential

A good guess is that almost all fields in North Dakota now average between 10 and 150 pounds of nitrogen (N) per acre. But guessing on the low side of that range could waste $10 to $30 per acre in N fertilizer—fertilizer that was applied but not needed. Or, by guessing on the high side, a grower could forfeit $30 to $120 per acre in income (lost yield potential).

Knowing how much N is in the soil before fertilizer applications occur is always essential for efficient crop production in North Dakota—year in and year out, says a soil scientist at North Dakota State University. But current economic conditions demand that producers know, and not guess, about soil N levels.

"I have spent 25 years working with soil testing and fertilizers, and I cannot walk into a field and estimate soil N levels except in a few specific situations, so it is unlikely that most other people can predict the levels in a field without soil testing," says David Franzen, extension soil science specialist at NDSU.

There is only a narrow window of opportunity left to soil sample this fall so growers need to put their sampling plans into action soon to be ready for fall- or spring-applied N, Franzen says. Usually, turnaround of samples takes only a few days and so provides producers or crop consultants with time to receive the results prior to application.

Soil sampling for N is especially useful following small grains and grassy crops, Franzen says. Soil N sampling is also useful following annual legumes, such as soybeans, dry beans and field peas.

"Remember to subtract a previous crop credit from the N recommendation before application," Franzen cautions.

Soil testing is also important following potatoes, canola, sunflowers and other broadleaf crops. But soil sampling may not provide a good indication of N contribution following sugar beets since much of the N in the soil is tied up in the plant tops until they rot the next spring.

"Yellow beet tops are indicators that soil N levels may test out at about only 10 pounds per acre," Franzen continues. "Green beet tops indicate that there may or may not be significantly larger amounts of soil N."

Soil sampling is time-consuming when done correctly, and it requires some basic skills, as well as agronomic knowledge, to pick out the right areas to sample, Franzen says. A field-composite sample should consist of 20 to 30 selective random samples—selective because these samples should not come from unusual areas such as saline spots, eroded areas, or areas containing unusual soil textures or organic matter levels.

Franzen says most growers hire their soil sampling done by a professional. However, with the right tools and the time, growers can sample their own fields. A new extension publication on soil sampling, titled "Soil Sampling as a Basis for Fertilizer Application" (SF-990), is available through county offices of the NDSU Extension Service.

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Source: Dave Franzen (701) 231-8884

Editor: Dean Hulse (701) 231-6136