7 Soil Sampling

Sampling for Nematodes

Taking soil samples for nematodes is an important part of scouting soybeans. The only reliable way to determine the kinds and number of plant-parasitic nematodes present is through a carefully and properly taken soil assay. An effective control program can be developed on the basis of the information gained. The control tactics will be effective only if directed at the nematode species present in the field.
    Nematode samples should be taken in late August or early September while populations are at their peak and the crop is still in the field. After harvest, nematode populations decrease greatly, reducing the possibility of discovering damaging levels.
    Proper sampling consists of collecting a composite of 1-inch-diameter soil cores taken in a systematic, zig-zag pattern. Take 20 cores (which will constitute one sample) per 5 acres. For larger fields with a similar soil type and cropping history throughout, select two to five random representative 4- to 5-acre sections per field for similar sampling. Try to allocate samples evenly throughout each block.
    Insert the sampling tube at a slight angle under the plant and deep enough (8 to 10 inches) so that it cuts through the root zone, thus ensuring that soil and roots are included. After all samples have been taken, thoroughly mix the soil before removing enough to fill the shipping box.
    To be properly identified, nematodes must arrive at the nematode laboratory alive. Thus nematode samples must be protected from temperature extremes and should not be stored for longer than two days. Keep the samples in a cool storage room or in a refrigerator until they are prepared for shipment. The samples should be transported soon after collection to the Nematode Advisory Service, North Carolina Department of Agriculture, Raleigh, N.C. If prolonged storage is necessary, the sample should be kept at 50^o to 60^oF.
 

Fertility Sampling

Samples taken to determine soil fertility are usually collected in the fall after crops have been harvested. However, they can be taken at any time during the year if the soil is dry enough to obtain a representative sample. The key to successful sampling is to obtain a sample that adequately and fairly represents the soil throughout the field. A separate sample should be taken for each 5 acres, for each different soil type, and for each area that has been or will be managed differently from the rest of the field. Take a minimum of 20 cores per sample (one core in each of 20 or more different locations) to a constant depth, typically 8 inches. Thoroughly mix all the cores in a plastic pail, then fill the soil sample box with the mixed cores from the pail.
    It is generally better to take separate samples and customize lime or fertilizer applications to suit each area than to mix samples and obtain only a single result. Be sure to write down what portion of which field each sample came from. For additional information see North Carolina Agricultural Extension Service publication AG-372, Careful Soil Sampling.