Étude comparative de méthodes pour la détermination du phosphore total dans différents types d'andosols

The total phosphorus in eight different andosoil profiles of Canary Islands, was determined using seven methods. SDome are specific such as; the attack by a mixture HF/HNO2 (Ximenez Herrais, 1975) in a pressure reactor, and digestion with HCIO4 (Jackson, 1964); and others non specific for total phosphorus, but nevertheless used for the study of phosphorus in soils; such as, the methods of Mehta (1954), Harrap (1963), Steward-Oades (1972), Saunders-Williams (1955) and Krivonosova (1972). The results obtained by the attack HF/HNO2 give the highest values of all the methods used, white the HCIO4 digestion largely used to determine total P in soils, gives even lower values than those obtained by the methods of Mehta and Krivonosova, used respectively for organic phosphorus and organic phosphate fractions. The procedures of Mehta and Krivonosova give acceptable values in the determination of total phosphorus in Canary Andosoils, white the other methods give values which are too low. Study of the regression lines of the total phosphorus values obtained by the various methods as against the attack by HF/HNO3 shown in Graph nº 1, give us an overall idea of the effectiveness, trends, similarities and differences between all methods. It can also be that all methods should be good if the soils contain up to 1.000 ppm of total phosphorus, white for higher values great differences are shown by the various methods. The content of phosphorus decreases according to the sequence : Vitrandepts, Evolved Vitrandepts, Dystrandepts and Integrades Andosoils-Brown Earths oligotrophic.