Examining Solvita Soil Tests in Soils of the Southeast United States

Abstract

Nitrogen (N) an essential nutrient for healthy crop growth. Nitrogen fertilizer may be over applied because standard soil tests do not account for nitrogen mineralized by soil microorganisms throughout the growing season. Quantification of potentially mineralizable soil N by multiweek incubations is time-consuming, and highly variable with soil-type and other soil conditions. Other methods for measuring N mineralization such as CO2 base trap titrations, or analysis via gas chromatography are also not fit for high volume use. The Solvita soil tests are a commercially available alternative that require only a 24-hour incubation period and minimal soil, where evolved CO2 or labile amino soil nitrogen is directly correlated to the quantity of N mineralized. However, the Solvita tests have not been widely examined in some soils and cropping systems, especially in the southern United States. The objective of this project was to conduct incubations, titrations, and gas analysis on sets of soils from: 1) fields throughout the state of Alabama managed under a variety of cropping systems, and 2) the Cullars Rotation at Auburn University, and to compare N mineralization results from those measures to that predicted via Solvita testing. In two separate studies initial Solvita data was collected, and subsequent titration or gas chromatograph data was collected to assay the utility of the Solvita method to predict inorganic N release from mineralization. Correlation between gas chromatography, base trap titration, Solvita methods, and inorganic nitrogen varied from study to study. However, the Solvita methods were consistently well-correlated to inorganic nitrogen content at the end of the incubation period.