Effect of humic substances on phosphorus absorption in italian Ray-Grass

Numerous authors have investigated the effect of humic compounds on plant production. Certain, using field trials or growth vessels (SCHNITZER and POAPST, 1967; TAN et al., 1979 a; MULLER-WEGENER, 1988), attributed the favourable effect of such compounds to their action on various soil properties i.e. cation exchange capacity, water retention, structural stability, etc. Other authors observed positive effects on mycorrhizal formation (TAN et al., 1979 b; SCHISLER and LINDERMAN, 1989), rhizogenesis (FORTIN and LOPEZ-FANDO, 1982) yield (LEMAIRE, 1972) and mineral supply, especially phosphate: already in 1880, DEHERAIN and KAYSER verified that humic substances improve phosphorus plant nutrition. CHAMINADE (1944) confirmed that fact like a lot authors an LOBARTINI et al. (1994) and BIDEGAIN (1995) for the last. In this latter case, the effects of humic substances on phosphorus availability were attributed to the ability of such to produce complexes with cations which, in their absence, would otherwise form insoluble compounds with posphates (KUTE, 1967; GARAPIN, 1989; HAFIDI, 1990; BRUN, 1993). The aim of this work was to investigate this hypothesis more thoroughly by examining the effect of the addition of humic substances on phosphate nutrition and growth in rye-grass depending on whether the phosphates were likely to be retrograted or not.