COMPARISON OF SOME METHODS FOR DETERMINATION OF COPPER, ZINC, MANGANESE AND IRON IN SOILS

The soil extraction procedure using DTPA extracting solution for the d etermination of copper, zinc, manganese and iron was introduced by Lin dsay, Norvell (1978). The method proved to be relatively sensitive to experimental conditions especially to the temperature during extractio n, extraction time and extraction intensity (Soltanpour et al., 1976; Lindsay, Norvell, 1978). Since 1978 the extraction procedure according to Lindsay, Norvell (1978) has become very popular and widely used in many countries of the world and international standardization of the procedure is now in the final stage. The internationally adopted proce dure (DTPA-ISO) uses lower extraction temperature and higher extractio n intensity than our national procedure (DTPA-CZ). The criteria for ev aluation of the results for DTPA-CZ method were based on the field and pot experiments. The main reason for this study was to find whether r ecalculation of these criteria defined for DTPA-CZ method was possible for DTPA-ISO method and to avoid expensive field and pot experiments. The second goal of this study was to find a relationship between the DTPA-ISO (resp. DTPA-CZ) method and the Mehlich III method (Mehlich, 1 984). The Mehlich III method (M III) is very suitable for simultaneous determination of macronutrients (K, P, Mg, Ca) and micronutrients and the method is very popular in many countries of the world. The M III method is very similar to the Mehlich II method, extensively used in t he Czech Republic for nutrient determination and fertilizer recommenda tion. 95 soil samples from soil monitoring plots were collected for th e study. The samples represented all major soil types, climatic region s and proportion of agronomic cultures in the Czech Republic (arable s oil 79, grassland 9, orchards 4, hopgardens 1, vineyards 2). Samples w ere air-dried and a fraction under 2 mm in diameter was used for analy sis. Samples were extracted and analyzed by all three methods (DTPA-IS O, DTPA-CZ, M III) in triplicates. Regression analysis clearly showed for DTPA-ISO and DTPA-CZ that the results achieved by both methods for all four elements are very near, and no recalculation of the criteria is needed. That means the expected increase in the results for the DT PA-ISO method by higher extraction intensity was compensated by the de crease due to the lower extraction temperature. It means from a practi cal point of view that laboratories in the Czech Republic can adopt th e international standard procedure without changing the criteria for t he evaluation of the results. We can conclude from regression analysis of the results for the DTPA-ISO and M III methods that the correlatio n for copper and zinc is very good and the recalculation of the criter ia is possible according to the equations: Cu_M III = 0.426 + 1.514 Cu _DTPA-ISO; Zn_M III = 0.408 + 1.802 Zn_DTPA-ISO. For iron and manganes e the correlation is not suitable for the recalculation of the criteri a. The determination of iron and manganese by the M III extracting sol ution would require more precise calibration of the method based on fi eld and pot experiments. The M III method is very suitable for simulta neous determination of nutrients, copper and zinc, where the criteria for evaluation can be recalculated. When only micronutrients are to be determined, or iron and/or manganese are required, the DTPA-ISO metho d should be used for the determination.