Analysis of Mehlich III soil extracts by ICP-AES

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) has proved to be a time and cost effective analytical technique for simultaneous determination of many elements. Universal soil extractants are well suited for adoption of ICP-AES. The object of this study was to optimize ICP-AES determination of phosphorus, potassium, magnesium, calcium, sulphur, iron, aluminium, manganese, copper, zinc and boron in Mehlich III soil extracts. The most suitable wavelengths and background corrections were chosen, the concentration ranges for calibration were Found and matrix effects of Mehlich III extractant were studied. The results fur phosphorus, potassium, magnesium, calcium and sulphur determined by ICP-AES were compared to the results achieved by commonly used methods (FAAS - flame atomic absorption spectrophotometry, flame photometry, spectrophotometry). 147 topsoil and 29 subsoil samples collected from the soil monitoring plots were used for evaluation of the relationships between the analytical techniques. The results for potassium and magnesium were statistically significantly different but the difference was small (2 to 8%) and it did not influence the classification of available nutrients. ICP-AES determination of calcium gave the results 7 to 12% higher than those obtained from flame atomic absorption spectrophotometry. The increase can be explained by reducing the interferences in plasma due to a higher temperature. The Lower temperature of air-acetylene flame in FAAS could not completely reduce the chemical interferences even in the presence of lanthanum. The results for phosphorus determined by ICP-AES in topsoils were 8 to 14% higher than the results of spectrophotometric determination. In subsoil samples the results of both analytical techniques were statistically equal. The reason is that spectrophotometry (molybdate blue method) can determine only the ortho-phosphate form of phosphorus. ICP-AES determines the total content of phosphorus present in a soil extract.