Subirrigation System Control for Water use Efficiency

Abstract

ABSTRACT Afield experiment and a computer simulation analysis were conducted to evaluate the water requirements of subirrigation under three methods of system control. First year results from the field experiment indicate that irrigation water requirements can be reduced by controlling the system such that the midpoint water table depth is allowed to fluctuate within certain limits. A simulation model based on numerical solutions to the Boussinesq equation was developed to allow comparison between the control methods using historical weather records. Several simulations were conducted for each control method to optimize the set points for starting and stopping subirrigation for the given method. Using the optimum set points, the simulations predicted a decreased irrigation requirement when the midpoint water table depth was allowed to fluctuate. The irrigation requirement was decreased by an average of 6.7% over constant water level control for five years of simulations. Much larger differences could have occurred had the set points not been optimized. That is, there is potentially more difference in irrigation water requirements for different set points within a given control method than between two different control methods. The results indicate that there is a good potential for reducing irrigation requirements of subirrigation. A slight modification in the way in which subirrigation systems are currently controlled can result in decreased subirrigation water usage.