FERTILIZERS FROM COMPOSTING OF OLIVE-MILL WASTEWATERS

The aerobic bioremediation of olive-mill wastewaters produces a high q uality compost, characterized by a considerable presence of nutrients, mainly organically-bound nitrogen (1.5-3%), a good level of humificat ion (degree of humification=78%; humification index=0.28), and by the absence of phytotoxicity. The agronomic value of a compost thus obtain ed was assayed both by the 'crop test' and following the plant-soil sy stem as influenced by compost supply. Field experiments performed on m aize showed that compost, when supplied before sowing in amounts of 60 -90 Mg ha(-1) (equivalent to a manuring on the basis of organic matter ) is able to reduce the need for chemical fertilization. The same quan tity supported the nutritional need of rye grass and horticultural pla nts. A good rest-effect was also recorded. Compost supply enhanced bot h soil oxygen consumption and nitrogen fixation in the open field. An improvement of activities in the plant-soil system was made evident by pot trials. (C) 1997 Elsevier Science Limitedd.