A diffuser assembly (1) for diffusing a liquid in irrigation plants (2) having a supply conduit (3), which comprises a diffuser (10) with a nozzle (12) adapted to direct a jet of liquid along a longitudinal axis (L), at least one deflector (13) facing the nozzle (12) for radially spraying the jet outwards, and a connection device (18) for ensuring fluid connection of the diffuser (10) to a supply conduit (3) of the plant (2). The diffuser (3) is mounted to the irrigation plant (2) with the axis (L) extending in a substantially vertical direction and with the nozzle (12) facing up, and the deflector (13) is susceptible of rotating about the longitudinal axis (L) thereby causing oscillations in the assembly (1). The connection device (18) comprises a tubular body (27) with end joints (28, 29) for connection to the diffuser (10) and the supply conduit (3) and the body (27) is monolithic with the joints (28, 29) and is made of a thermoplastic elastomeric base material. Furthermore, the body (27) comprises an outer surface (38) with annular folds (39), which impart elasticity and damp the oscillations induced by the deflector (13). A pivot or linear irrigation plant (2) comprising a plurality of said diffuser assemblies (1).