Aspergillus niger was successfully cultivated on sugar-beet-waste material (SE) supplemented with 3.0 g/l rock phosphate (RP) acidifying the medium and thus decreasing the pH to 3.0-3.5. The fermented mixture finally contained mineralized organic matter rock phosphate solubilized to 224 mu g P per mililiter and fungal mycelium. Various combinations of SB and RP, previously treated or untreated by the fungus, were introduced into soil to improve the growth of Trifolium repens Compared to other treatments, the results showed a higher growth rate and shoot phosphorus concentration when microbially treated SE and RP were applied to both mycorrhizal and non-mycorrhizal plants. However combined introduction of both the filamentous and arbuscular fungi led to improved plant growth when degraded organic matter supplemented or unsupplemented with RP was used. (C) 1996 Elsevier Science Ltd.