Soil Testing Bray-1 Phosphorus with Non-Reagent Grade Hydrochloric and Sulfuric Acids

Abstract

ABSTRACTPortable instruments have reduced on-site testing costs for soil pH and potassium in isolated locations. Acids could not be shipped to a remote Africa field laboratory. Bray-1 phosphorus (P) testing is difficult because hydrochloric (HCl) is required in the extraction solution and sulfuric acid (H2SO4) is used in color development stock solutions. Muriatic HCl acid and battery H2SO4 were available in a local stores. The objectives of this study were to evaluate the accuracy of P soil testing using diluted, non-reagent HCl for making modified Bray1-P extractant and non-reagent H2SO4 for color development. Experiment 1 was conducted with soil samples from fields using Sunnyside™ and Klean Strip™ HCl muriatic acids. Soil samples extracted with diluted reagent HCl were closely related to P results using diluted Klean Strip (R2 = 0.96) and Sunnyside (R2 = 0.84) HCl. In Experiment 2, two commercial brands of H2SO4 acid used to refill car battery cells were evaluated. Test results suggested that the battery H2SO4 acids are not suitable for making color development solution. In Experiment 3, a small battery powered spectrometer for P testing aquarium water was calibrated for soils. Samples from the Soil Science Society of America –North American Proficiency Testing program (NAPT) were tested with the meter and non-reagent HCl. Fiske-Subbarrow reducing agent and HCl were used in a variation procedure which does not require H2SO4 for color development. Eight of 10 samples tested proficient based on NAPT limits (2.5 x Median Absolute Deviation).