Differences between plant performances due to treatments were consistent but of different magnitude among sites. The FR location generally amplified the treatment effects because of a more imprecise management of the water schedule over the season, possibly explaining the appearance of the first symptoms in a location originally considered as symptoms-free (FR). Stresses on the silt loam soil were due to some water excess in the early season coupled with an oxia and early root damage determining poor root biomass and scarce development of fibrous portion.