Results are only as good as sample

Jr. Stevens, Koske, Thomas J., Fontenot, Kathryn  |  2/17/2009 11:42:43 PM

Dig out a profile slab cut for sampling.

Professional soil sampling tools. Pull samples for lawn about 4-5 inches deep. Go 5-6 inches deep in gardens and beds.

Cut a strip from center of soil slab to represent a soil core of 3 to 6 inches deep.

The chemical analysis of a soil sample has been worked out and calibrated so the numbers reported mean something useful to the client. However, the results are only as good as the sample is representative of the area and crop’s root zone. In general, soils that differ in appearance, crop growth or past treatment should be sampled separately, provided the area or zone is large enough to be fertilized separately. For instance, most homeowners have distinguished gardening zones in their yards: lawn area, vegetable garden, ornamental flower/ shrub beds. A soil sample should be collected from each of these areas as they are all treated differently. Lawns are rarely tilled or soil worked , mowed often and the roots growth closer to the soils surface. Vegetable garden soil is worked seasonally, types of vegetables are also planted seasonally, soil is amended regularly and the roots penetrate much deeper than turfgrass. Ornamental beds may comprise of trees shrubs and annual flowers. The roots of these crops extend deep within the soil, and depending on type of plant you may or may not work the soil often.

For each sample, collect soil plugs from about 10 or more places in each sampling area. Use a zigzag fashion to obtain a good, representative sample across the block. Mix plugs or shovels of soil thoroughly in a bucket, large pot or other container that is large enough to hold the 10 sub samples you've collected. Select a sample (roughly about the size of a pint or a small sandwich plastic bag)  and place it in a sample carton or container that is mailed to the soil test lab. Many garden nurseries, hardware stores and local county agents offices now have soil boxes that are pre-addressed and include both sample bags and the necessary paperwork to send your soil sample to LSU AgCenter's facilities. One soil sample should represent 10 acres or less.

Avoid sampling directly in unusual spots unless you specifically want to examine those spots. The results you get will reflect only the sampled area. A bad spot is not representative of the larger, normal area. Those recommendations will apply just to that bad spot. Proper sampling depth depends on the kind of crop you plan to grow. We recommend that for pasture and turf you sample from the top 3 inches of soil, and for shrubs, vegetables and cultivated crops, you collect samples from the upper 5-6 inches of soil.

It is not necessary to chill or prevent sample desiccation that would be required for a nematode sample because  soil samples will be dried before analysis.

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