The aim of this study was to examine mycorrhizal spore abundance, its infection rate and biological activity of soil depending on different rootstock, Fe sources or Fe doses. A field experiment was carried out to determine the effects of rootstocks on mychorizal abundance and root infection as well as CO(2) production and dehydrogenase activity of soil. Doses of 25, 50 and 75g tree(-1) Fe-EDDHA or FeSO(4) were applied to apple trees (Red Chief cv.) grafted on dwarf (M9 and M26) and semi-dwarf (MM 106) rootstocks. At flowering stages soil and root samples were collected and analyzed for their dehidrogenase activity, CO(2) production, microbial biomass-C or mycorrhizal abundance and infection rate. Results revealed that neither rootstock nor Fe applications effect on mycorrhiza number in rhizosphere soil. The higher value was observed in the soil M26 planted and 75 g da(-1) Fe-EDDHA applied plot (15 spores per g of soil). Therefore, infection rate showed significant variations related to rootstocks and Fe applications. The most adapted rootstocks was MM 106 which 37.1 % of the roots infected by mycorrhiza. Fe-EDDHA was more effective than FeSO(4) whereas both of them increased infection rate compared to control. There was no statistical difference between rootstocks in CO(2) production; however, Fe-EDDHA is stimulated CO(2) formation. The highest CO(2) formation (11.55 mg CO(2) 100 g soil(-1)) observed in 50 g of Fe-EDDHA applied MM 106 plot whereas the lowest was in M26 plot where Fe application not realized. Dehydrogenase activity was not affected by Fe sources; however, increased Fe application increased dehydrogenase activity. Rootstock of MM 106 is statistically more effective on dehydrogenase and highest dehydrogenase value was observed in 50 g of Fe-EDDHA applied MM 106 plot as 328 mu g TPF 10 g soil(-1). The highest biomass-C value was observed in 50 g of Fe-EDDHA applied MM 106 plot, whereas the lowest was observed in 50 g of FeSO(4) applied M9 plot. In general, Fe-EDDHA application was promote biomass-C more than FeSO(4). Comparing to rootstocks, the highest effective rootstock was MM 106 and followed by M26 and M29, respectively.