Comparison of Mehlich II and Mehlich III extraction for determination of available phosphorus, potassium, magnesium and calcium in soils of the CzechRepublic

Mehlich II (MII) extractant was introduced in 1978 and ii has been used for soil testing in the Czech Republic for more than ten years. Mehlich III (M III) extractant as a modification of MII extractant was introduced in 1981. The modification enabled determination of copper and minimized corrosive p roperties of the former MII extractant. MIII became very popular and widely used and replaced MII very quickly. The objective of this study was to com pare MII and MIII extractants to determine available Phosphorus, potassium, magnesium and calcium in Czech agricultural soils, 2799 agricultural soils were collected for the study (311 light soils, 1889 medium soils, 599 heav y soils, 369 soils with carbonate content higher than 5%). The soil samples represented all major soil types, climatic regions and proportion of agron omic cultures in the Czech Republic. Samples were air dried and a fraction under 2 mm in diameter was used for analysis. The quantity of phosphorus ex tracted by MIII exceeded that extracted by MII 20 to 25%. Extractions of bo th magnesium anti calcium by MIII were 7 to 9% higher than those by MII and extractions of potassium were 10% higher. Regression analysis was performe d after rejection of outliers. Highly significant correlations were found b etween the methods for all the elements and soil types. Regression coeffici ents ranged between 0.97 and 0.99. The values measured by MIII were compare d by pair-test to the values calculated from the values measured by MII usi ng the conversion equations. For ail the elements and soil types the pail t est showed that the measured and the calculated values were highly signific antly equal and that the conversion equations ard reliable and suitable For recalculating of the values of nutrient contents categories. Conversion eq uations can be used instead of a new expensive and time-consuming field cal ibrating study.