Growth and Water Use of Petunia as Affected by Substrate Water Content and Daily Light Integral

Abstract

More efficient irrigation practices are needed in ornamental plant production to reduce the amount of water used for production as well as runoff of fertilizers and pesticides. The objective of this study was to determine how different substrate volumetric water contents (θ) affected petunia (Petunia ×hybrida) growth and to quantify the daily water use of the plants. A soil moisture sensor-controlled irrigation system was used to maintain θ within ≈0.02 m3·m−3 of the θ threshold values for irrigation, which ranged from 0.05 to 0.40 m3·m−3. Shoot dry weight increased as the θ threshold increased from 0.05 to 0.25 m3·m−3 and was correlated with the total amount of irrigation water applied over the 3-week course of the experiment. The daily water use of the petunias grown with a θ threshold of 0.40 m3·m−3 was 12 to 44 mL/plant and was positively correlated with both plant age and daily light integral. Lower θ thresholds resulted in a decrease in both leaf water (ψ) and osmotic potential (ψS). A decrease in turgor pressure (P) at lower θ was seen at 11, but not 20 days after the start of the treatments. There were no significant effects of θ on ψ, ψS, or P on fully rehydrated plants at the end of the study. Plants were able to survive and grow at all θs, although water at a θ less than 0.20 m3·m−3 is generally considered to be unavailable to the plants. Results show that it is possible to automatically irrigate plants with the use of soil moisture sensors, and this approach to irrigation may have applications in controlling the growth of ornamental plants.