Department of Plant Sciences

Soil samples (from Czech and German long term field experiments) were used for estimating soil phosphorus (P) fractions. More then 100 topsoil (0-30 cm) samples from different fertilizing treatments were taken. These were analysed for P in soil solution (PCaCl2), exchangeable sorbed P (Pex) and bioavailable P. The methods used were 0,01M CaCl2 extracts, anion exchange (AE) membranes, Doppel-Lactat (PDL) and Mehlich 3 (PM3). Other fractions analysed were total inorganic (Pin), total (PM-tot) and organic (Porg) P estimated with Marks (1977) fractionation, P sorbed on Fe and Al (PFeAl) and residual P (Par). Comparison of medians appeared to be better for evaluating extraction abilities. Phosphorus fractions increased in the following order: [Par =100%]; PCaCl2 (0.1%) < Pex (10%) < PDL (12%) < PM3 (17%) < Pin (25%) < Porg (38%) < PM-tot (60%) < PFeAl (62%). Low amounts of Pin, Porg and PM-tot did not verified the applicability of Marks fractionation for the set of studied soils. Close correlations at α<0.001 were found for all methods for estimating the fractions of bioavailable phosphates (PCaCl2, Pex, PDL a PM3). Statistically significant relations were observed between Pin with Par, PM-tot and PFeAl.