Spectrophotometric determination of calcium in soilsA study is presented on the determination of calcium in soil extracts by flame photometry, using a Beckman Model DU spectrophotometer. Flame composition, gas pressure, interferences and their elimination were studied. Results showed it to be necessary to eliminate interferences due to aluminum, iron and phosphate ions in amounts normally present in soils. Enough EDTA solution at pH 9.0 was added to the soil extract until a concentration of 0.01 M in EDTA was reached.