MOBILITY AND AVAILABILITY OF PHOSPHORUS F ROM ORGANIC AND INORGANIC FORMS IN THE RHIZOSPHERE OF LOLIUM-PERENNE

1.) In Pots (sandwich-technique according to Helal and Sauerbeck), whe re the soil (A(p)-horizon of an Alfisol-Udalf from loess) was separate d into a root chamber and an outer chamber (up to 10 mm away from the root chamber), the phosphorus (P) availability of super-P, rock-P (Hyp er-P) and organic P [myo-inositol-2-mono-P di(cyclohexylammonium) salt ] was studied. P was applied at a rate of 50 mg P kg-1 soil only in th e outer chamber. This P fertilization resulted in significant increase of CAL- and water-extractable P in the treatment with organic P and s uper-P compared to the P0 treatment. During 6 cuts of Lolium perenne o rganic P showed the same effect on the P-uptake of plants as super-P. Compared to the treatment without P, rock-P had no effect on the P-upt ake. The higher P-uptake of Lolium perenne both in the super-P- and or ganic P-treatment was reflected at the end of the experiment only by t he CAL-P content differences between root chamber and outer chamber. T he highest activity of acid phosphatase, measured in air dried soil wa s found in the root chamber of the organic P treatment. The content of EUF extractable organic P was significantly higher in the root chambe r of the treatments with super-P and organic P than in the P0- and roc k-P-treatment. 2.) The P elution was studied with 2 soils (A(p)-horizo n of an Alfisol-Udalf from loess pH: 6.4; A(h)-horizon of a basaltic b rown soil pH: 5.4) under lab conditions in columns. In the super-P- an d organic P-treatment leached P was mainly inorganic. In the soil with low pH value (5.4), P was leached in the treatment with super-P or or ganic P in a higher amount of organic P than in the soil with pH 6.4. The results of this experiment do not show in which form the applied o rganic P was moved to the roots or displaced in the soil.