6 Soil Sampling 

Sampling for Nematodes

Taking soil samples for nematodes is an important part of scouting corn. 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 from the assay. 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, when nematode 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 involves the collection of composite samples, each of which is made up of 20 1-inch-diameter soil cores. The cores should be collected in a systematic, zig-zag pattern. Take one sample per 5 acres. For larger fields with a similar soil type and cropping history throughout, collect samples from two to five randomly selected 4- to 5-acre sections that are representative of the field.
    When collecting soil cores, insert a sampling tube at a slight angle under the plant. Insert the tube deep enough (8 to 10 inches) that it cuts through the root zone, thus ensuring that soil and roots are included in the core. After all cores 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 ready for shipment. The samples should be transported soon after collection to: The Nematode Advisory Service, Agronomic Division, North Carolina Department of Agriculture, 4300 Reedy Creek Road, Raleigh, NC 27607-6465 . If prolonged storage is necessary, samples should be stored at 50 OF to 60 OF.
 

Fertility Sampling

Samples taken to determine soil fertility are usually collected in the fall after crops have been harvested. They can, however, 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. Separate samples 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. Collect a minimum of 20 cores per 5 acres (one core from 20 different locations within the 5-acre area). The cores should be collected at a constant depth, typically 8 inches. Thoroughly mix the cores that make up a single sample in a plastic pail, then fill a soil sample box with the mixed cores. Deliver the boxed sample to: Soil Testing, Agronomic Division, North Carolina Department of Agriculture, Blue Ridge Road Center, Raleigh, NC 27611. (Be sure to write down the area of the field from which each sample came.)
    Lime or fertilizer applications may be customized to suit the specific area from which the samples were taken. It is generally better not to mix samples. For additional information see North Carolina Agricultural Extension Service publication AG-372, Careful Soil Sampling.