A single draught horse can normally pull a single-furrow plough in clean light soil, but in heavier soils two horses are needed, one walking on the land and one in the furrow. Ploughs with two or more furrows call for more than two horses, and usually one or more have to walk on the ploughed sod, which is hard going for them and means they tread newly ploughed land down. It is usual to rest such horses every half-hour for about ten minutes.