Soil air pressure under successive border irrigations and simulated rain1

LINDEN, D. R.; DIXON, R. M.; Guitjens, J. C.

Soil air pressure under successive border irrigations and simulated rain1

1977

LINDEN, D. R. | DIXON, R. M. | Guitjens, J. C.

Soil air pressure and surface water head were measured at a single field site during eight irrigations of alfalfa during the 1972 growing season. Soil air pressure hs and surface water head hw are presented as functions of elapsed irrigation time to illustrate the short-term and seasonal variation of these parameters. It is shown that ha varies directly with hw, and that the head imbalance ha - hw increased at a decreasing rate during each irrigation, until it reached a plateau ranging between 4 and 7 cm, and therefore, it remained nearly constant until headgate closure. Small differences in ha – hw between irrigations may have had a significant effect on infiltration because total field application decreased as ha – hw increased. Soil air pressure increased under simulated rain when ponding began where airflow was restricted by an impermeable barrier at a 20-cm depth. This air pressure increase had little apparent effect on infiltration. Soil air pressure created and maintained from the onset of infiltration reduced infiltration by about 20 percent.

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