Rhuanito Soranz Ferrarezi

Subirrigation automated by capacitance sensors for salvia production

Subirrigation is typically controlled using timers to periodically irrigate plants based on a pre-determined schedule. The objective of this study was to evaluate the usefulness of capacitance-type sensors to monitor substrate water content and to control subirrigation automatically for salvia production in greenhouse. Additionally, we quantified the effect of different substrate volumetric water content (VWC) on growth of plants cultivated in 15-cm diameter × 13.75-cm height pots. Automation was performed using three EC-5 capacitance soil moisture sensors per experimental unit, connected to a system with a CR10X data logger, AM16/32 multiplexer, SDM-CD16AC relay driver and NK-2 submersible pumps. Substrate moisture readings were taken every 15 minutes, and plants were irrigated only if the readings dropped below pre-set VWC thresholds. We evaluated five levels of substrate VWC (0.1, 0.2, 0.3, 0.4 and 0.5 m3 m-3), with two replications, in a completely randomized design. The system effectively monitored and recorded VWC, and controlled irrigation accordingly. Substrate VWC ranged from 0.1 to 0.41, 0.2 to 0.39, 0.3 to 0.41, 0.4 to 0.43 and 0.5 to 0.53 m3 m-3, in ascending order of the treatments, with the highest values recorded after irrigation events. The number of irrigation events, total volume of nutrient solution applied, net photosynthesis, dry weight, number of branches and leaves, shoot height, leaf area, canopy light interception, and leaf chlorophyll content all increased significantly with the increase in VWC (p<0.0001). The VWC of 0.5 m3m-3 provided the highest plant growth (p<0.0001). Capacitance sensors can be used to both monitor soil moisture and control subirrigation for salvia production in soilless substrate, reducing the possibility of water stress caused by daily irrigation schedule using timers.

Use of subirrigation for water stress imposition in a semi-continuous CO2-exchange system

The objectives of this work were to evaluate the effects of distinct moisture contents to trigger subirrigation on salvia photosynthesis and plant growth, and to verify the feasibility of subirrigation use in water stress imposition research in this crop. We evaluated two substrate volumetric water contents (VWC) as treatments (0.2 and 0.4 m3 m-3) to trigger subirrigation, with 4 replications. Each replication was composed of 10 plants. An automated semi-continuous multi-chamber crop CO2 - exchange system was used, with capacitance soil moisture sensors for continuous moisture monitoring. Manual subirrigation with nutrient solution was performed when VWC dropped below the thresholds. In both treatments, the values of net photosynthesis, daily carbon gain and carbon use efficiency reduced over time, from 2 to 1.1 µmol s-1 from 2.2 to 1 µmol d-1 from 0.7 to 0.45 mol mol-1, respectively, in both soil moisture treatments. Total shoot dry mass (p=0.0129), shoot height in the tip of the highest flower (p<0.0001) and total leaf area (p=0.0007) were statistically higher at 0.4 m3 m-3 treatment. The subirrigation system was not efficient to impose water stress, due to excessive variation on VWC values after each irrigation event in both treatments. Higher soil moisture promoted positive plant growth responses in salvia cultivated by subirrigation