Soil Matters--Soil Testing and Soil Health Advancements
We all know that crops are grown on sites that have varying soil types with varying soil properties, but the different soil types are not equally productive based on fertility and non-fertility soil properties. However, soils at most sites can be productive if 1) properly tested and fertilized according to test results and the crop being grown on the site, and 2) their texture and organic matter content are known. Two items related to these facts are highlighted below.
Dr. Nathan Slaton at the Univ. of Arkansas was one of the leaders on a project that developed the Fertilizer Recommendation Support Tool [FRST], a tool that uses science-based interpretation of soil-test phosphorus [P] and potassium [K] values for crop fertilization decisions. Click here for the tool and here for a user manual that explains how the tool works and how to use it for a production site. FRST was developed from data collected across the country, and is designed to enhance P and K management to subsequently save farmers money and to reduce excess fertilization that leads to nutrient losses to the environment.
The tool is designed to provide critical P and K soil-test values to indicate where there is no expected yield increase from P and K fertilizer applications. The current version includes data from about 2,500 P and K trials that were conducted with mostly corn and soybeans in 40 states and Puerto Rico. Plans are to expand the tool to include other nutrients such as Sulfur. The database used for the tool is based on soil-test correlation data that will be constantly updated as more data become available.
According to Dr. Slaton, the FRST project has accomplished the following two objectives in advancing P and K management for crop production: 1) ensured that a national database was established to archive soil-test correlation and calibration research so that those data are not lost, and 2) provides a tool that anyone can use regardless of the crop they are growing or where/what site they are growing it on.
In an article by Univ. of Arkansas scientists Gerson L. Drescher et al. titled “Soil texture and organic matter prediction using Mehlich-3 extractable nutrients”, the authors present results from their evaluation of the determination of soil organic matter [SOM] content and soil texture predictions using Mehlich-3 extractable nutrients and pH in Arkansas soils. The objectives of and results from the research are summarized below.
• Soil Organic Matter [SOM] and soil texture are properties that influence the content and availability of both soil nutrients and soil water. However, both of these soil properties require complex analytical procedures to measure.
• The objective of the research was to evaluate SOM and soil texture predictions based on Mehlich-3-determined nutrients and soil pH in Arkansas soils. The authors hypothesized that 1) soil properties with a strong affinity to the soil mineral phase, such as Mehlich-3 magnesium [Mg] and estimated cation exchange capacity [CEC], are good predictors of a soil’s clay content and texture, 2) predicting sand content using routine soil-test results has a lower accuracy than predicting clay content, and 3) SOM prediction will be possible only when using multi-factor models that include several key nutrients because of the complex nature of the soil organic phase.
• Estimated CEC and Mehlich-3 nutrients were highly correlated with clay content of soil, and thus are good predictors of a soil’s clay content.
• Mehlich-3 extractable soil nutrients were only weakly correlated with sand content and SOM.
• Information from Mg and estimated CEC, or Mehlich-3 extractable P, can be used to estimate the clay content of Arkansas soils, which are similar to soils throughout the Midsouth that are used for soybean production.
• Using predicted sand and clay contents to separate soils into textural groups showed good accuracy in classifying soils into medium and fine categories, but not a coarse-textured category.
• SOM prediction based on soil pH and Mehlich-3 extractable P, calcium, manganese, and zinc was only moderately accurate.
• The authors concluded that 1) additional research is needed to investigate the potential use of clay and sand prediction models on diverse soils for calibration purposes and to determine the geographic extent of model application, and 2) additional information will be necessary for improving SOM prediction from soil test data.
Since the majority of Midsouth soybeans are grown on clayey soils, the above information can be used by a majority of the region’s soybean producers to estimate a soil’s native fertility and make fertilizer and herbicide application decisions based on its CEC and SOM properties that are estimated from soil test data when the Mehlich-3 extraction process is used. Also, the development of models to predict or estimate soil properties other than a soil’s nutrient status gleaned from routine soil testing should save the producer time and money.
Composed by Larry G. Heatherly, July 2024, larryh91746@gmail.com