Soil, follow soil science glossary is: The un- consolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. As soil fertility depends on physical, chemical and biological characteristics, the macromineral composition of soils is an important subject in agricultural studies (Tiessen 1994, Mäder 2002). All plants are characterized by certain nutrient requirements. Therefore, to maintain soil fertility, the used nutrients must be replaced by fertilizers. Macrominerals consist of elements, which can exist in soil in diferent chemical forms: cations (Na, K, Ca, Mg), anions (e.g. P, C, Cl, N, S), or be built into organic molecules. Determination of four alkali and alkaline earth elements has been of vast importance to soil studies for over 50 years (David 1960). Although in the past there have been many approaches to colorimetric determination of Na (Arnold 1943), K (Takagi 1977), Mg (Pieters et al. 1948), and Ca (Peaslee 1964), the fame photometry used to be a leading method of determination of these elements in agrolaboratories, nowadays these techniques seem outdated. Te rapid growth of spectrometric techniques, like atomic absorption spectrometry (AAS), microwave induced plasma optical emission spectrometry (MIP-OES), induc- tively coupled plasma optical emission spectrometry (ICP-OES) have caused these older techniques to lose their primal signifcance in analytical chemistry. MIP-OES, with its first analytical application in 1960s (Mavrodineanu 1964) and later commerciali- zation of instruments (Jankowski 2001a) comes to increase significance in modern determination of elements. The application of the method for de- termination of: Na (Jankowski 2001b), K, Ca, Mg (Matusiewicz 2010), is based on laboratory-made analytical instruments. MIP-OES can easily com- pete with technique based on inductively coupled plasma source (ICP-OES), due to the possibility of using nitrogen (in opposition to more expensive Ar) as a plasma gas (Arai 2013) and may offer lower detection limits for Na and K (Jankowski 2001), which is especially important in this study. The low cost of instrumentation and low run- ning cost (nitrogen can be produced from air by nitrogen generator) are very attractive for routine use of MIP-OES instruments. Microwave induced plasma optical emission spectrometry in agricultural analysis P. Niedzielski, L. Kozak, K. Jakubowski, W. Wachowiak, J. Wybieralska Adam Mickiewicz University, Poznan, Poland ABSTRACT Te article describes the use of the recently commercially available technique of microwave induced plasma optical emission spectrometry with plasma gas (nitrogen) generation for the determination of calcium, magnesium, phos- phorus and potassium in Mehlich 3 extracts. Te specifcs of the analysis of the agricultural samples for soil fertility assessment mean there are often a great number of samples to analyse in laboratory (the daily throughput of 500 or more samples). Te analytical procedures were adapted to special requirements by the use of the new multielemen- tal instrumental techniques. Te detection limits were 0.43; 0.86; 0.20 and 0.06 mg/L; the precision for real sample analysis: 4.6; 1.0; 1.8 and 1.0%; the mean accuracy 97; 92; 107 and 100% for P, Ca, Mg and K, respectively, the real throughput reached 100 samples per hour. Keywords: spectrometric techniques; nutrients extraction; fertilization; macromineral composition Supported by the National Science Centre Poland, Project No. DEC-2013/09/B/ST10/00610 215 Plant Soil Environ. Vol. 62, 2016, No. 5: 215–221 doi: 10.17221/781/2015-PSE