Accounting for slow drainage and hysteresis in irrigation scheduling

Summary

Soils continue to drain for several days following irrigation. Water budgeting predictions can be improved by accounting for this, provided hysteresis is recognized in the “field capacity” condition. Uncertainty in this condition was evident in experiments comparing predicted soil water depletions with neutron probe measurements. Comparisons were made for potato, lettuce and calabrese crops, irrigated by hose-reel machine. Best agreement between measurements and predictions was obtained when excess water storage above a lower field capacity condition was allowed for; corresponding to minimum root mean square errors of 3.2 mm–6.2 mm. These were comparable to the practical limits of uncertainty associated with field depletion measurements.