Recently a farmer asked how to take a good soil sample for soybean cyst nematode (SCN). This is a question we're getting asked more often, especially at this time of year.

There is both a science and an art to collecting good soil samples.

The Science of Sampling

The science part is pretty easy:

  • Use a clean probe and bucket to avoid contaminating samples, which could lead to a false positives.
  • Sample an area no larger than 40 acres per sample (less is better).
  • Take a minimum of 20 to 25 soil cores from randomly selected areas.
  • If the field has standing soybean stubble, take your sample just a couple inches to the side of the old soybean row and go 6 to 8 inches deep. (This way you'll be probing through the old root system and are more likely to detect SCN if it is there.)
  • If you are sampling in a field that wasn't in soybeans this year but will be going to soybeans in 2015, randomly collect samples from across the area to be tested. (If you find SCN, this information will be important when you order seed. When selecting an SCN-resistant variety, remember to also evaluate other traits you want, including emergence, lodging or chlorosis ratings and resistance to other diseases, etc.)
  • Thoroughly mix the cores you collected and submit the soil sample in bags available at your local UNL Extension office for a free SCN analysis. The cost of the analysis (normally $25 per sample) is being covered by the Nebraska Soybean Board.
  • Submit your sample to the UNL Plant and Pest Diagnostic Clinic at the address listed on the bag. These samples do not require any special handling (such as being refrigerated, frozen, etc.) until they are delivered to the lab.

The Art of Sampling

When selecting which areas within a field to sample, remember: Anything that will move soil will also move SCN, including wind, water, wildlife, humans, and equipment.

Think about the areas in your field where soil may have been moved because these are areas where SCN is likely to have first become established. Take several cores in each of these areas. These areas include:

  • Along a stream that periodically floods. An upstream field may have had SCN that washed down to your field.
  • Low areas where water drains after a heavy rain. Light infestations throughout the field may be concentrated in these low areas where water stands.
  • Along fence lines. In the past when fall tillage was more common, fences would act like a trap for the blowing soil and SCN.
  • By field entryways or driveways. This is the most likely place for soil from another SCN-infested field to travel in on equipment and be brushed off.

There are two other major areas that I encourage farmers to sample:

  • Areas with a higher incidence of sudden death syndrome (SDS) or brown stem rot (BSR). You can have either SDS or BSR without having SCN or you can have SCN without having either of these diseases. However, if you have SCN in a field or even part of a field, you are more likely to have SDS or BSR in the affected area.
  • Areas where soybean yields are less than expected and there is no difference in soil type or incidence of soil compaction, herbicide injury, weed, insect or disease pressure, or other explanation for lower yields. This can be a whole field, but more commonly is an area in the field.

In either of these situations, take a sample where a problem is suspected and one close by but outside this area. This can help you confirm or eliminate SCN as the cause in the suspect area.

Resources

For more information on sampling for or managing SCN, see