Regular nutrient testing helps develop and maintain productive soil. Soil tests indicate potential plant nutrients deficiencies and, if so, what amounts are needed for optimum growth. Soil testing is also a useful diagnostic tool to identify problems related to excessive levels of nutrients and salts, high pH, low organic matter, and poor drainage.
Soil sampling should occur in late fall after harvest or in early spring prior to seeding to allow samples to be collected and analyzed in time for fall or spring fertilization. Fall testing has the advantage of allowing the application and incorporation of fertilizers with fall tillage or winter precipitation. Spring testing, however, often provides a better indication of nutrient (especially nitrogen) availability immediately prior to plant growth.
Allow a minimum of two to three weeks for analyses, fertilizer purchase and application, and any other corrective measures to be taken before planting. Soil sampling can also be done during the growing season to aid in diagnosing plant growth problems. Landowners who observe a problem may want to sample the soil while symptoms are present to diagnose the problem and take corrective action during the current growing season
Soil should be tested once every two years. Generally, as the intensity of management increases so should the frequency of soil testing. Highly productive growers should test more frequently to monitor changing soil conditions and prevent the build-up of excess levels of nutrients or salts.
Divide the area to be sampled into different units depending on variations in soil conditions, historic fertilizer applications, or other management differences. Problem areas within a field should be sampled separately from the rest of the field to help diagnose issues related to soil nutrients. A minimum of five to ten samples should be collected from throughout each area sampled and then combined together into one composite sample to submit for analysis. This ensures that the sample submitted is representative of the area. Samples should be collected to a depth of 6 to 12 inches. The most efficient way to collect samples is with a hollow tube soil probe. A shovel can also be used to collect soil samples although this is more time consuming and care must be taken to ensure that the sample is collected to the desired depth. If you are sampling for available (nitrate) nitrogen, a second sample representing the 12 to 24 inch depth is also necessary.
Three different soil nutrient tests are available through the Discovery Nutrient Analysis lab. A BASIC test package for general sampling situations is available that measures Nitrate-N, P, K, Sulphate-S, pH, and EC. An ADVANCED soil test package is also available which includes all of the BASIC test measurements as well as OM, Ca, Mg, Na, BS, and CEC. A PREMIUM soil test package is also available that provides all of the BASIC and ADVANCED test measurements as well as Cl, Fe, Cu, Zn, B, and Mn.
Nutrient recommendations are provided on soil test reports. Additional publications are also available to help refine nutrient recommendations for specific crops and to aid in correcting other problems diagnosed with a soil test. Contact your local agronomist or retail to discuss potential recommendations based on your soil testing results and specific crop yield targets.