Colorimetric test methods are used for most test factors. Tests for calcium, sulfate and chlorides are based on turbidity measurements. Potassium analysis also employs a turbidity measurement, using a unique reading device designed in LaMotte laboratories to read directly in pounds per acre. A single extraction procedure, using Morgan Universal Extraction Solution, provides the liquid soil extract for all the nutrient tests with the exception of chloride, which is extracted with demineralized water. The Humus Screening Test, performed on a soil sample-demineralized water suspension, employs five color standards for rapid measurement of humus content of the soil.
Soil pH is determined colorimetrically, using a series of pH indicators and color charts covering the range of pH 3.8 to 9.6. The STH outfits also include simplified procedures for screening nitrates, phosphorus, and potassium in plant tissues. Complete reagent refill packages are available for each STH outfit.
Each kit includes complete instructions, a soil management handbook and a pad of soil analysis report forms. The LaMotte Soil Handbook contains general information on interpretation of test results for determination of lime and fertilizer requirements.