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Collecting Representative Soil Samples

Conventional whole field sampling: Research has shown that 15-20 soil cores are required to provide a representative soil sample for conventional whole field sampling (see example).

In the example a saline area and a sand ridge in the field are avoided. By avoiding those areas, the sample best represents the whole field. For additional information it may be desirable to collect separate samples from the sand ridge and the saline area. Once sampling is completed, the soil cores from each depth must be thoroughly blended, placed in separate soil sample bags and sent to the laboratory.

Soil sampling by Topography, Soil Type, Vegetative index etc. All of these types of soil sampling involve dividing fields into several areas for sampling (see example).

In this topography example, the field is split into three landscape positions for sampling by topography (high sand ridge, sloping area and low saline area). Notice how the sloping area sample is actually made up of two areas, one on each side of the sand ridge. When a field is represented by two or more soil samples, by any of these methods, each sample should contain a minimum of 15-20 cores.

Grid Soil Sampling: Grid soil sampling involves dividing whole fields into small equal sized areas or grids (1-5 acres) (see example). The soil cores from each grid are collected either from the center point of the grid or from random cores within the grid. A minimum of 8-10 cores from each grid is required to provide enough soil for all laboratory analysis to be completed.

Sample Handling - Soil Fertility Analysis

Proper soil sample handling procedures depend on which nutrient analysis is requested. Soil samples that will be analyzed for nitrate-N should be kept cool or shipped to the laboratory immediately. If samples are stored in a warm area for extended periods of time, the nitrate level in the sample will increase. Warm temperatures during shipping or storage increase the activity of microbes in the soil sample. This microbial activity causes the release of additional nitrate-N in the soil sample bag. If this happens, the laboratory analysis for nitrogen will be incorrectly high, due to improper sample handling.

Soil samples that will be analyzed for all other nutrients are not affected by temperature and do not need special handling.

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