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How can the variability in my soil sample results be explained?

(from Dr. Terry Niblack , University of Illinois at Urbana-Champaign & Dr. Pat Donald, University of Missouri)

Soybean cyst nematodes (SCN) are not evenly distributed in a field. For example, in a single field with an average number of eggs of 50,000, the actual number of eggs in any one section of that field might be anywhere from 0 to 100,000. Due to this natural variability in the distribution of SCN, it is very important to take a sample. Some of the questions we've received about this variability in SCN egg counts are given below, along with the answers.

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Extraction of SCN eggs from cysts

Wash the cyst/sediment suspension (from the cyst extraction method) from the 100 ml beakers into the small PVC #60 sieve (250 micron diameter pores). Eggs of SCN average 47 microns by 100 microns in size.

Place a #200 sieve (75 micron diameter pores) over a #500 sieve (25 micron diameter pores) into the funnel below the rubber stopper, and start the drill press using the foot pedal. Bring the spinning rubber stopper into contact with the sieve surface.