A baler comprises a pick-up assembly configured to pick-up crop material; a compression assembly comprising at least one pair of opposing compression rollers configured to generate a pressure on the crop material as it passes between the compression rollers; and a bale chamber, wherein the pre-compressed crop forms a bale. The compression rollers define an adjustable gap therebetween. By adjusting the gap, pressure exerted on the crop material as it passes between the compression rollers may be controlled, resulting in bales of varying density.