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Soil Sampling Behind the Combine (08/17/17)

Early crops are starting to be harvested and soil sampling may begin at any time. Years ago, NDSU published a ‘sampling date adjustment’, meant to allow for additional nitrate to develop later in the fall should a sampler decide to collect soil before mid-September.

Soil Sampling Behind the Combine

Early crops are starting to be harvested and soil sampling may begin at any time. Years ago, NDSU published a ‘sampling date adjustment’, meant to allow for additional nitrate to develop later in the fall should a sampler decide to collect soil before mid-September. However, on review of the original data on sampling date within North Dakota from August through the following spring, I did not see a trend in nitrate level changes from early dates through spring. Sometimes nitrate levels increased, sometimes they decreased and sometimes they stayed the same. The sampling date adjustment has not been included in any of our fertilizer recommendations for at least ten years.

What is clear, however, is that N recommendations have to be based on soil test nitrate for N responses in our trials in spring wheat, barley, canola, corn, corn, sugar beets and all other N-requiring crops to make any sense.

I would encourage sampling behind the combine first to make sure the job gets done, secondly for the sampler to obtain a more consistent 0-6 inch core for use in determining P, K, pH, organic matter and Zn. Obtaining a consistent 0-6 inch core in worked ground is difficult and usually is done by taking the core over a wheel track, or getting out the pickup and stepping on the intended area to take the core, to make sure the soil just doesn’t flow away from the soil probe when it contacts the surface.

Dave Franzen

NDSU Extension Soil Specialist

701-799-2565

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