79 РАСТЕНИЕВЪДНИ НАУКИ, ГОД. LI, No. 6 PLANT SCIENCE, VOL. LI, No. 6 София. 2014. Sofa Soil fumigation is a common and important phy- tosanitary practice in horticultural plant cultivation. However, soil disinfection is still not widely practiced in Poland. Several soil plant pathogens (Fusarium spp., Phytophthora cactorum, Phytophthora fragariae and species of the genera Pythium, Leptosphaeria, Cylin- dricarpon, Rhizoctonia, and Phoma) and nematodes (Pratylenchus spp., Ditylenchus dipsaci, Longidorus spp. and Xiphinema spp.) can cause signifcant losses in nurseries and other plantations. It can also restrict the export potential of plants in case of presence of regu- lated quarantine pathogen species (Mumford, 2002). The phase out of methyl bromide (MB) under the Montreal Protocol has stimulated research on chemi- cal fumigants as well as alternative methods for the control of soil-borne pathogens (Colla et al., 2012). Biofumigation with Brassica species and steaming can substitute chemical fumigation (Nederpel, 1979), but their practical application is still limited. We have thus evaluated the effect of both chemical fumigants and alternative methods on the fungal and bacterial populations in soils characterized by different chemi- cal-physical characteristics. MATERIAL AND METHODS Soil disinfection The disinfection of soil was performed in three loca- tions characterized by soils with very different chemi- cal and physical characteristics: Przytyk, having a CHANGES IN SOIL MICROBIAL POPULATIONS AFTER FUMIGATION AND ALTERNATIVE METHODS TO CONTROL SOIL-BORNE DISEASES PIOTR SOBICZEWSKI*, BEATA MESZKA, HANNA BRYK, ELIGIO MALUSÁ Research Institute of Horticulture, Konstytucji 3 Maja 1/3, 96-100 Skierniewice, Poland *E-mail: piotr.sobiczewski@inhort.pl Abstract The study was carried out in 2010 – 2012 on three farms. Soils were disinfested by chemical fumigation, bio- fumigation and active steam. Chemical fumigation was carried out in autumn of 2010 and 2011 with two different rates of either dazomet, metam sodium or chloropicrin + 1,3D. Steam disinfection with addition of CaO, maintaining soil temperature of about 70 ºC for 2 h, or biofumigation with Brassica carinata seeds meal were performed in spring of 2011 and 2012 at two or one locations, respectively. Soil bacteria and fungi populations were assessed 4 weeks after the treatments. All chemical treatments and steam disinfection caused a signifcant decrease of the total number of fungi in comparison to control, while biofumigation induced an increase of total soil fungi. The total number of bacteria generally increased by the chemical fumigation with all tested products in all soils. The bac- teria population was not changed or increased, depending on the season, by active steam treatment, whereas it was 3-fold decreased by biofumigation, in comparison to not disinfected soil. In conclusion, the applied disinfec- tion techniques modifed the populations of soil microorganisms irrespective of the characteristics of the soil. Key words: active steam, biofumigation, chloropicrin, dazomet, metam sodium, 1,3 dichloropropene light podsol, Lisowola, having a clay sandy soil, and Kozienice, having a heavy alluvial loamy clay soil. The soil fumigation was carried out in the months of Oc- tober 2010 and November 2011 using the following products and doses: a – Basamid 97 GR (97% dazomet) at a dose of 30 or 40 g/m 2 ; b – Nemasol 510 SL (510 g/l metam sodium) at a dose of 60 or 90 ml/m 2 ; c – Chloropicrin (99%) at the dose of 30 ml/m 2 ; d – Telopic C-35 (a mixture of 35% chloropicrin and 65% 1,3 Dichloropropene) at the dose of 35 or 50 ml/m 2 . The disinfection with active steam or biofumigation was applied in April 2011 and 2012 only in Przytyk. Basamid 97 GR was applied to the soil with a machine formed by a dosing system mounted over a rotating mechanical hoe which was ploughing the soil and mixing the product up to 35 cm of depth. The liquid products (Nemasol 510 SL, Chloropicrin and Telopic C-35) were applied to 30 – 35 cm depth by means of injection. In both cases, the soil was then compacted with a roller and covered with virtually impermeable polyethylene flm (VIF) that was removed 10 days after the application of the fumigants. The treatment with active steam was performed with the self-propelled tractor Eco Star SC 600 (Biofash System™; Tesi et al., 2007). The machine distributed CaO on the soil (400 g/m 2 ) and mixed it while injecting water steam