The effect of medium disinfestation on cut rose productivity and on some chemical properties of tuff 1 M. Raviv * , A. Silber 2 , Sh. Medina Department of Ornamental Horticulture, Agricultural Research Organization, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel Accepted 20 January 1998 Abstract Rose plants grown in untreated used tuff are less productive than those grown in new, unused tuff. The objectives of the present work were to evaluate the effect of disinfestation of used tuff on the productivity of roses and to determine the effects of disinfestation treatments on the chemical properties of tuff. Rose (Rosahybrida cv. `Mercedes') plants were grown in tuff media: unused; used, in which roses had been grown for 8 years, without disinfestation; or used, following one of three disinfestation methods: fumigation with 0.5% metham-sodium, solarization; or solariza- tionfumigation with 0.3% metham-sodium. Rose plants grown in untreated used tuff had lower yield than those grown in unused tuff. Solarized or fumigated tuff produced yields which were similar to those of unused tuff, while the combination of the two treatments resulted in yields which were superior to those of either unused or single disinfested used tuff. Flower quality was not affected by any of the treatments. Soluble organic matter (SOM) and N±NO 3 ions do not exist in unused tuff and gradually accumulate in used tuff. SOM affects nutrients availability, specially phosphorus through their effect on surface charge density and by preventing the precipitation of insoluble of Ca±P and Al±P compounds. This positive effect can be translated to higher yield only after used tuff is disinfested. Disinfestation further increased the content of SOM and of N±NO 3 thus additionally increasing nutrient availability. # 1998 Elsevier Science B.V. Keywords: Nutrients availability; Replant disease; Root exudates; Rosahybrida; Tuff Scientia Horticulturae 74 (1998) 285±293 * Corresponding author. Fax: +972 4 9836936; e-mail: vfnraviv@volcani.agri.gov.il Abbreviation: EC, electrical conductivity; SOM, soluble organic matter 1 Contribution from the Agricultural Research Orgaization, The Volcani Center, Bet Dagan, Israel. No. 2057 E, 1997 series. 2 Present address: A.R.O., Institute of Soil and Water, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel. 0304-4238/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved PII S0304-4238(98)00093-4