Abstract: A vehicle having a boom assembly for applying herbicides, pesticides, or fertilizers in fluid form, i.e. as liquid, powders or granules, over tracts of land, has opposite end-portions of the boom projecting away from respective opposite sides of the vehicle. Each end-portion is connected by a universal joint to a central frame which is fixed to the vehicle, and its weight is supported by guys which are tensioned by a spring and interconnect the two boom end-portions. A spring leaf skid is provided under each boom end-portion and bears on the ground only if the vehicle rocks. The guying is so arranged that rocking of the vehicle in one direction causes the slack from the boom end-portion whose skid bears on the ground to be fed to the other boom end-portion so that the spacing from the ground of the two boom end-portions remains acceptably constant despite rocking of the vehicle.