That wise saying about computers, "garbage in, garbage out," applies equally to soil sampling for soybean cyst nematodes (SCN).
If you don't do it properly, you still may end up getting blindsided - even though you have taken the first big step toward controlling SCN.
For example, if you just take a few samples where it's handy in a sizable field and don't sample high-risk areas, you may get bogus information that will cost you where it hurts later - in yield.
"The high-risk areas include field entries, low spots, the area along a fenceline where wind- blown soil may accumulate or any part of a field that may have been flooded in the past," says Greg Tylka, Iowa State University nematologist.
Ideally, Tim Maloney of Agri-Tech Consulting, Janesville, WI, recommends that growers get out and scout fields in July and August to, among other things, look for areas where the beans may look fine but are shorter. If you dig up several plants in those areas and look closely, you may well find small female cyst nematodes on the roots.
"If you do, those are areas among others where you want to collect soil samples at harvesttime to determine the population density level you have," Maloney advises. "It's an excellent way to catch the problem at the same time you're looking for other potential problems."
State recommendations vary slightly. But here are general guidelines from SCN Coalition nematologists that will serve you well wherever you farm:
1) Limit the number of acres represented in a single sample. As a rule of thumb, a sample from every 10-20 acres is ideal. If a field is larger, break it into 10- to 20-acre units.
2) Collect 10-20 soil cores or samples from each field or unit using a soil probe, hand trowel or shovel. Intensity of sampling depends on the information at hand. If there are problem spots that show up year after year, sampling can be limited to those areas. When there aren't obvious problem spots, use the 10-20 cores or samples approach.
Regardless of the situation, it's never a good idea to take fewer than five soil cores or samples, nematologists say, because the sample will not be representative of the field. As with soil fertility testing, the more spots you sample, the better.
Collect each sample from a depth of 6-8" in the plant root zone. Then Tylka says to combine the soil from individual samples in a bucket and mix well. Place 1 pint of the mixed soil sample in a plastic bag or paper soil-test bag.
Keep samples out of the sun and ship them pronto to a university or private lab. Cost ranges from $5 to about $25, but some state soybean checkoff boards cover processing costs.
3) Include the following information when submitting samples:
* Name, address and telephone number of farmer or sample collector.
* County and nearest town where samples were collected.
* Estimated acreage of areas sampled.
* Cropping history of areas sampled.
* Current crops of areas sampled.
Each test will give an estimate of SCN population density based on the volume of soil. The standard volume used is 100 cubic centimeters (cc).
The story below gives more detail on the interpretation of SCN soil tests