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Soil tests provide a chemical estimate of nutrient availability and a sound basis to predict crop response to fertilizer. Soil tests are valuable fertility management aids to increase on-farm or gardening productivity. Soils testing low in fertility require fertilizer materials and/or crop rotations to supply plant nutrient requirements. Soils testing high in certain nutrients can supply 100 percent of the crop requirement and no fertilizer is needed. Amounts of essential elements required for optimum growth vary with the crop, yield, soil and environment. Improper use of soil test results may lead to increased production costs with yield and quality losses or related problems.
Soil test results and other information will help answer the question, “Should I fertilize? And, if so, how much fertilizer should I apply?”
A soil test will only be as accurate as the sample submitted. Proper soil sampling technique is discussed in the MSU MontGuide MT8602AG “Soil Sampling.” Samples are routinely evaluated for pH (acidity or alkalinity), organic matter, electrical conductivity, nitrate-nitrogen, phosphorus and potassium. Calcium, magnesium, sulfate-sulfur, zinc, manganese, boron and sodium can be analyzed when a specific problem is suspected.
Time of sampling is best at any time after harvest and before planting. To obtain an accurate estimate of nitrogen availability, take samples as close to planting time as possible. Adequate lead time should be allowed for sample analysis, data interpretation, fertilizer recommendation and actual application.
To account for seasonal variations, soil samples should be collected at approximately the same time each year. Soils should be re-tested as often as necessary to determine the influence of cultural practices and crop production on soil chemical properties. Nitrate-nitrogen concentrations should be determined on an annual basis. Phosphorus and potassium determinations should be made every three to four years.
To get complete information on nutrients, testing for nutrients and soil test interpretation, contact the MSU Lake County Extension Office in Ronan at 406-676-4271 or lake1@montana.edu.
