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Determining Nutrient Supplying Ability of Soils

Posted Jul. 1, 1997

Determining the nutrient supplying ability of soils can guide decisions that may make the difference between profit and loss. Technology offers sophisticated electronic tools to manage farming in a site specific manner. Large data files contain soil test results and production records providing information for making accurate electronic decisions.

Variable Rate Technology (VRT) is actually making rate decisions on the go. Until this futuristic technology is available in our area, composite soil sampling is the best way to predict fertilizer and lime response.

The results from composite soil samples are adequate to make fertilizer and liming decisions. To refine those recommendations, a map would help identify areas of production differences. The map could be a simple color photograph taken from above to show differences.

Scout those areas, taking samples for comparison. If some treatment is practical and the limitation can be efficiently corrected, apply that specific corrective measure. It could be accumulation of acidity, a nutrient deficiency, a hard pan, or maybe a problem soil. If it is a problem soil, it may be best to ignore the problem area and properly manage the most productive areas.

For fields to be planted to small grain this fall, soil sampling must be completed by the first of August. Submit the samples to a reputable laboratory in time for analysis, recommendations, and reports to be mailed. The process has to be completed in time for preplant treatments if necessary.

A soil sample should consist of 15 or more cores taken randomly across a field or pasture no more than 40 acres in size. Avoid atypical areas that would alter the results. For most soil management decisions, a sampling depth of six inches is adequate. Sampling the subsoil from 6 to 12 inches, or below the plow layer, can provide additional information, especially for crops grown in tilled fields.

A soil sample should be taken every two to three years except when intensively managed, then annual sampling is necessary. Test results should become part of a trend for acidity, phosphorus, potassium, or other test values. Making management decisions from trends is advantageous over one test value.

Continue to observe visual symptoms as indicated by vigor, color, or production differences. When differences appear, examine the soil profile, look for insect infestations, disease infections, and take plenty samples. Please feel free to contact one of our consultants when questions arise.

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