Unsaturated Flow of Water in Field Soils and Its Effect on Soil Moisture Investigations

Measureable drainage of water within the soil profile in field plots was observed for periods of up to 8 days following irrigation under an actively transpiring alfalfa crop. Rates of movement from the 0 to 3 foot zone were of the order of 0.20 inch per day 2 days after irrigation and 0.11 inch per day 4 days after irrigation. Total drainage from the 0 to 3 foot zone for the period 2 to 8 days was 0.58 inch. This downward movement of water is shown to have material effects upon consumptive use measurements and the soil moisture extraction pattern. A computed error of 23 per cent in consumptive use for the first 8 days following irrigation is shown to have occurred in the present experiment as a result of drainage from the 0 to 3 foot zone.