It is a kind of surface irrigation system. A ridge is the part of the layout of the field that is elevated at different angles based on the type of soil. This is actually where the plants are planted. The furrows are the troughs that let the water flow through it. The crop is usually grown on the ridges between the furrows or the crop is grown on the ridge whereas irrigation water is applied to the furrow.
Furrow ratios and supplemental irrigation on crop production in ridge and furrow rainfall harvesting system.
Ridge and furrow method of potato cultivation