A support layer for supporting an artificial turf assembly. The support layer being formed of a polymeric foam, preferably having a density of between 20 and 70 grams per liter, such as a polyolefin foam; and having an upper side and a lower side, wherein in use the support layer has been placed with the lower side thereof on a base surface and supports, on the upper side thereof, the artificial turf assembly, the support layer including a plurality of through drainage holes extending from the upper side to the lower side for allowing liquid such as rain water to flow via the plurality of drainage holes from the upper side to the lower side, and also including a plurality of channels at the lower side for allowing liquid such as rain water to flow through the channels along the lower side, wherein each of said plurality of drainage holes debouches into one of the plurality of channels. The support layer is further included in an artificial turf system, that includes an artificial turf assembly with the support layer supported on a base surface such as a layer of sand, wherein the support layer forms, at the upper sides thereof, a closed support surface supporting the artificial turf assembly.