Farmers understand the importance of routine soil sampling and receiving quality soil fertility recommendations from their trusted advisors. Many farmers rely heavily on their agronomist to interpret a soil test and create fertilizer recommendations due to the complexity of the analysis report.
The basic purpose of a soil test is to provide an estimate of plant available nutrients, and from this information a fertilizer or soil amendment recommendation can be made. A soil test also provides a lot of insight about the composition of the field and an experienced agronomist will use this information to adjust recommendations to fit a field’s specific fertilizer needs. Measurements for Soil pH, Buffer pH, Organic Matter, and Cation Exchange Capacity (CEC) provides data about the soils ability to supply plant nutrients during the growing season, along with insight on the water holding capacity and maybe awareness toward developing problems. Organic matter changes very slowly over time and CEC is directly related to the soil’s physical makeup, meaning there are no quick fixes. Sandy soils have lower CEC values, and sometimes fertilizer needs require adjustments to avoid over fertilization that exceed the soils ability to hold the nutrients and lead to leaching. These types of adjustments should only be recommended by an experienced agronomist. Sodic soils can be identified by high exchageable sodium (Na+) on the CEC and may require a Gypsum application to alleviate problems. Acidic soils, below 7 pH, have a higher concentration of H+ ions in the soil, which will displace other nutrients on the CEC. A low soil pH can be corrected with Limestone applications.
The individual nutrient results on the report are not actual calculations of the nutrients contained in the soil. The soil test lab uses extractants to remove nutrients from the soil solution for measurement, and the result is a calculation/estimate of the potential nutrient availability from the soil to the crop. From this information, crop specific nutrient recommendations are developed. Crop recommendations were developed to meet crop specific nutrient requirements based upon field research, plus additional fertilizer to build soil test levels over time or maintain soil test levels. Recommendations from a soil test lab are a good place to start to determine you fertilizer needs, but lab recommendations can be a bit broad to fit a variety of soils across a large area.Working with your agronomist provides the best opportunity to dial in your fertilizer requirements based upon your individual needs.
Also understand that in some rare situations, high pH and excess lime may skew results. You may need to do some research after you receive soil test results and review potential situations that could have caused false results. Any information you can provide an agronomist or the soil test lab about your soils can be helpful in limiting incorrect results. Often an adjustment in testing methods and/or extractants used will correct the results.
Norder Supply agronomists are available to assist in collecting soil samples and providing fertilizer recommendations. Norder Supply works with the most reputable soil test labs in the state of Nebraska.