Phosphorus fractions of fertiliser-derived P in an allophanic soil under Pinus radiata seedlings grown with broom and ryegrass

摘要

Changes in phosphorus (P) fractions in a P deficient allophanic soil under P. radiata seedlings grown with broom (Cytisus scoparius L.) and ryegrass (Lolium multiflorum) in pots were studied 14 months after the application of triple superphosphate at the rates of 0, 50, and 100 mu g center dot g(-1), to determine the fate of fertiliser-derived P in the rhizosphere soils. Application of P fertiliser increased NaOH-P-i, NaOH-P-o, and H2SO4-P-i concentrations in the soil, but decreased the residual-P concentration. The resin-P-i concentration, which is extremely low in this soil (1 to 3 mu g center dot g(-1)), remained the same. The majority of the added fertiliser P was however recovered in the NaOH-P-i fraction (40%-49%). This is due to the high P fixation in this soil (92%). The second highest P recovery was in NaOH-P-o fraction (7%-19%). Under P deficient condition or addition at the rate of 0 mu g center dot g(-1), the NaOH-P-i concentration in the radiata rhizosphere soil was lower than that in the bulk soil and broom and grass rhizosphere soils. This may be due to higher oxalate production by the roots and mycorrhiza under P deficient conditions which released some of the P fixed to the soils in the rhizosphere, which needs to be tested in future studies.