For a soil to be productive, it must first be fertile. Therefore, proper management and the utilization of soil resources are crucial to support and sustain the agricultural resources of Missouri. To manage nutrient and soil amendment inputs, producers have heavily relied on soil testing to provide updated information on the status of their soil.

Each year, hundreds of soil samples are analyzed by the MU Soil and Plant Testing Laboratory to provide members of the agricultural community with quality information about soils located throughout the state of Missouri. The lab continuously monitors research conducted by university faculty to provide the most accurate and up-to-date information and fertilizer recommendations. Once a sample is submitted, the lab can provide information about soil pH, organic matter, neutralizable acidity, ammonium acetate, extractable potassium (K), calcium, and magnesium, Bray 1-Phosphorus (P), extractable sulfate, micro-nutrients, nitrate, ammonium, boron, electrical conductivity, and textural analysis. This information, however, is specific to the site from which the sample was collected and does not reference typical trends of surrounding areas or regions.

To offer general geographic information, 10 years of soil data (2007-2017) generated by the MU lab was compiled and reported by county in this summary. In total, 315,504 samples were utilized. The dominant response of pH, Bray 1-Phosphorus (P), and extractable potassium (K) for the 10-year period are reported. Soil pH is classified as low, medium, and high (Figure 1), while phosphorus and potassium are categorized as low, medium, high, and very high (Figures 2 and 3).

Figure 1 Dominant Soil pH Levels in Missouri by County (2007-2017).

Figure 2 Dominant Soil Phosphorus Levels in Missouri by County (2007-2017).

Figure 3 Dominant Soil Potassium Levels in Missouri by County (2007-2017).

Soil pH levels throughout the state are typically classified as medium (5.4-6.0) or high (≥ 6.1) with exception to south-central counties that contain the Ozark Mountain range (Figure 1). Phosphorus levels are generally low (≤ 22 lb/ac) (Figure 2). However, some counties in the Missouri River valley in west-central Missouri, counties in the southwest prairie region, and counties in the extensively cropped southeast delta region average medium (23-45 lb/ac) or very high (≥ 70 lb/ac) soil P levels (Figure 2). Potassium levels are classified as medium (111-220 lb/ac) for most of the state (Figure 3). However, the highly field cropped northwest and southeast corners of the state exhibited high (221-330 lb/ac) and very high (≥ 331 lb/ac) levels of residual soil K (Figure 3).

Given our state summary results, three fertility management strategies should be strongly considered for the 2022 season:

1. Soil Testing Is Necessary - Soil testing provides location specific and accurate information for determining soil characteristics. Our summary data indicates that soil pH and nutrient distribution are variable depending on geographical environment. Because Missouri contains an extremely diverse range of soil environments, fertility management strategies must account for variability within those environments and are not universal on a state-wide level.
2. Reactionary May Be Better Than Precautionary - Unfortunately, fertility management often consists of applying a fertilizers or amendments to large areas as a precautionary measure without consideration of what residual characteristics already exist within the soil. During seasons of high fertilizer cost, this strategy tends to be rather ineffective economically. Therefore, utilizing soil testing and basing fertility management on those results are extremely important. As an example, consider K values in Figure 3. Precautionary K applications to soils in counties in the northeast and southeast regions where high or very high residual levels already exist may not be economically beneficial.
3. Consider Realistic Yield Goals to Determine Fertilizer Rate - Producers often assume perfect conditions and highest yield potential when seeking fertilizer rate recommendations. Unfortunately, conditions are rarely perfect for crops to reach their complete yield potential. As a result, fertilizers are often over applied and not efficiently utilized. Our statewide summary of soil fertility in combination with regional yield results may be effective at refining realistic yield goals and soil fertility rates and recommendations.

For more information about having your soil tested, please visit https://extension.missouri.edu/programs/soil-and-plant-testing-laboratory.