INFLUENCE OF LEGUMES AND FERTILIZATION ON DEEP DISTRIBUTION OF AVAILABLE PHOSPHORUS (OLSEN-P) IN A THIN BLACK CHERNOZEMIC SOIL

Inorganic phosphorus (P) is generally believed to be relatively immobi le in Chernozemic soils. However, available P (e.g., Olsen-P) has been found at depth in some soils and this has been postulated to be eithe r the result of leaching or of transportation by plant roots. Lagumes, in particular, are believed to be involved in the latter mechanism. A long-term (34-yr) crop rotation study conducted on a heavy clay, thin Black Chernozemic soil at Indian Head, Saskatchewan, was sampled to a depth of 4.5 m in May and September 199 1, to determine the influence of fertilization, cropping frequency, legume green manure and legume- grass hay crops on Olsen-P distribution in the soil profile. The resul ts indicated that Olsen-P may indeed leach in Chernozemic soils, espec ially when fallow-containing cropping systems are fertilized. It also appeared that deep-rooted legumes, such as sweetclover Melilotus offic inalis L.) green manure and alfalfa-bromegrass (Medicago sativa L. - B romus intermis Leyss) hay crops do increase Olsen-P in the subsoil, po ssibly through root decomposition in situ.