Automated sensor-control strategies for drip irrigation of containerized chrysanthemum

Precision irrigation control of containerized plant material is essential to not only reduce the frequency of irrigation events of plants grown in porous soilless substrates, but also to reduce nutrient runoff to containment ponds and surface water bodies. Water source reduction strategies are being investigated as part of an integrated national project (i.e., to reduce, remediate and recycle irrigation water, SCRI-WateR3). From June through September 2015, two production blocks of chrysanthemum in a commercial operation were each monitored with a wireless sensor network using capacitance moisture sensors attached to monitoring and control nodes. The major objectives of this initial study were to (1) quantify drip irrigation system and substrate moisture variability within each block, (2) compare irrigation protocols, and (3) determine the specific placement of monitoring nodes and sensors, to minimise the number required for making good irrigation decisions, based upon a set-point substrate volumetric water content (VWC). Irrigation scheduling in the grower-controlled (GC) block used a timed irrigation protocol for chrysanthemum. Irrigation in the sensor-controlled (SC) block was managed using a VWC set-point just below the container capacity of 39%. The variability of daily substrate VWC in the GC block was significantly greater than in SC block. Sensor-controlled irrigation saved from 9-22% of total monthly water applications, compared to GC irrigation (total study savings of 13%) due to the relatively high set-point, but there were no significant differences between plant canopy dry mass (or canopy volume/number of flower buds) between treatments. It appears that chrysanthemum is tolerant of periodic low substrate VWC during the day, as long as those periods of temporary water deficit do not lead to visible signs of wilt. Lowering substrate set-points in continuing work should allow an increase in water savings, without any significant effect on production time, or crop quality.