Hyperlink 11. Testing for Nutrient Status in Your Yard

Suppose a homeowner wanted to know whether to apply lawn fertilizer. One approach would be to collect a small sample of soil from the center of the front yard and then put about a thimble-full into a nutrient test kit. A result of low nitrogen might then lead to the decision to apply fertilizer. But should it be applied to the entire front and back yards? How big an area did that one sample represent? A better approach would be to take samples from all over the front and back yard and mix them together before taking the thimble-full for the analysis step. In fact, that is the procedure recommended by the directions that come with soil test kits. A composite sample is preferable because (a) there may be different types of soil over the lawn area; (b) previous fertilizer applications were not distributed evenly, resulting in different nutrient levels in different parts of the yard; and (c) different plants and trees use nitrogen at different rates. A single sample provides information about only that location. It does not necessarily represent conditions in the rest of the yard. Chances are the yard is heterogeneous; one part is different from another part. Heterogeneity occurs at many different spatial scales, from microscopic, to the size of a yard, to thousands of times the size of a yard. Heterogeneity is the reason it is unwise to take just one or two soil samples and trust that the results apply to all the soil in an entire yard.