A Method for Precision Closed-Loop Irrigation Control.

The control of water supply in growth experiments is an area where experimental difficulties persist (Whalley et al. 2000). This study evaluates a precision soil moisture sensor controlled irrigation system that maintains the plant water status so that either: a) plant water status is consistent throughout the experiment or b) the system can be used to investigate the effects of varying soil water deficit irrigation on plant growth. The instrumentation described enables precision closed-loop irrigation control and consists of soil moisture sensors and irrigation control equipment with data logging capability. PC based software enables easy adjustment of irrigation parameters based on soil conditions and sensor responses to irrigation events. The data presented is from a tomato crop grown in a poly-tunnel and shows a method that can provide a stable soil matric potential environment using irrigation-frequency-modulation techniques. The irrigation protocol takes into account the soil moisture sensor response to irrigation events where the aim has been to deliver a known quantity of water that avoids significant soil moisture overshoot from the desired soil moisture set-point without significantly stressing the crop. Using this plant water availability control/logging system, the plant water availability status can be maintained at pre-set values with minimal deviation so that the plant is subjected to the same conditions throughout the experiment. The plant water availability can be adjusted simply and easily at any time without the need to stop data logging. In this poster we demonstrate an approach that is much simpler than the use of weighing lysimeters or the use of tension tables.  We present diagrams of our new approach as wells as some example data sets.

Whalley, W.R.,  Lipiec, J., Stepniewski, W. and Tardieu, F. (2000) Control and measurement of the physical environment in root growth experiments. In: Root Methods – A Handbook (eds. Smit et al.)  Springer-Verlag, Hiedelberg. 75- 112.