Analysis of Mehlich III soil extracts by ICP-AES

Inductively coupled plasma atomic emission spectroscopy (ICP-AES) has prove d to be a time and cost effective analytical technique for simultaneous det ermination of many elements. Universal soil extractants are well suited for adoption of ICP-AES. The object of this study was to optimize ICP-AES dete rmination of phosphorus, potassium, magnesium, calcium, sulphur, iron, alum inium, manganese, copper, zinc and boron in Mehlich III soil extracts. The most suitable wavelengths and background corrections were chosen, the conce ntration ranges for calibration were Found and matrix effects of Mehlich II I extractant were studied. The results fur phosphorus, potassium, magnesium , calcium and sulphur determined by ICP-AES were compared to the results ac hieved by commonly used methods (FAAS - flame atomic absorption spectrophot ometry, flame photometry, spectrophotometry). 147 topsoil and 29 subsoil sa mples collected from the soil monitoring plots were used for evaluation of the relationships between the analytical techniques. The results for potass ium and magnesium were statistically significantly different but the differ ence was small (2 to 8%) and it did not influence the classification of ava ilable 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 F AAS could not completely reduce the chemical interferences even in the pres ence of lanthanum. The results for phosphorus determined by ICP-AES in tops oils were 8 to 14% higher than the results of spectrophotometric determinat ion. In subsoil samples the results of both analytical techniques were stat istically equal. The reason is that spectrophotometry (molybdate blue metho d) can determine only the ortho-phosphate form of phosphorus. ICP-AES deter mines the total content of phosphorus present in a soil extract.