Integrating of Mehlich 3 extractant into the Czech soil testing scheme

Mehlich 2 (M2) and DTPA extractants have been used for soil testing in the Czech Republic for more than ten years. The objective of this study was to compare M2, DTPA and Mehlich 3 (M3) extractants for the determination of available nutrients (phosphorus, potassium, magnesium, calcium) and micronutrients (copper, zinc, iron, manganese) in Czech agricultural soils. For comparison of M2 and M3 extractants for nutrients 2799 agriculture soils were collected (311 light soils, 1889 medium soils, 599 heavy soils, 369 soils with carbonate content higher than 5%). For comparison of DTPA and M3 extractants for micronutrients 95 soils were collected. The soil samples represented all major soil types, climatic regions and proportion of agronomic cultures in the Czech Republic. Highly significant correlations were found between M2 and M3 for all nutrients (correlation coefficients in the range 0.97 - 0.99) and between DTPA and M3 for copper and zinc. (correlations coefficients in the range 0.86 - 0.88). For iron and manganese the correlation was also highly significant but not suitable for recalculation of the criteria. The determination of iron and manganese by M3 extracting solution would need more precise calibration of the method based on field and pot experiments. For all other elements conversion equations can be used instead of a new expensive and time-consuming field calibrating study.