Furrow Irrigation.—By this method it is intended to soak the land uniformly by allowing the water to flow through furrows drawn 3 to 8 feet apart, with a gentle slope from the supply or head ditch; the flow being continued until the water has reached the far end of the furrows, or longer according to the nature of the soil, especially if another ditch to receive the surplus flow lies below. The furrows should subsequently be closed by means of the plow or cultivator; but even if left open they are much less a source of waste by evaporation than would be a flooded surface. The water thus, in the main, soaks downward and only reaches the surface by capillary rise, so that the land between the furrows is not sensibly compacted when the furrows have been made deep enough. Evidently this is a much more rational procedure than surface flooding, as it tends to leave most of the surface in loose tilth, while penetrating to much greater advantage, because of the ready escape of the air from the soil. It is the system naturally and almost exclusively used in truck gardens and orchards, and generally where crops are grown in drills or rows sufficiently far apart to permit of cultivation.
Furrows 6 inches deep in Heavy Loam Soil
Narrow and Wide Furrows in Sandy Loam Soil
Furrows 5 and 10 inches deep in Sandy Loam Soil
Water running, in each, seven hours
Fig. 43.—Profiles of Water penetration in Furrow Irrigation.
The figure annexed[90] shows the manner in which water sinks and spreads from furrows of various depths and widths, as actually observed in the work of the Irrigation Division of the U. S. Dep’t of Agriculture, under the direct supervision of Prof. R. H. Loughridge of the California Station. The mode of percolation is shown for two soils, a heavy loam and a sandy one, both in the vicinity of Riverside, Cal.
The upper section shows the variation in penetration in one and the same soil with the same kind of furrow, the broken line indicating the cessation of the flow in the furrows; after which there was a still farther penetration of the water to from 6 to 9 inches deeper.