Improving greenhouse irrigation using a wireless soil moisture sensor-based automated irrigation system
The timing and quantity of irrigation are perennial horticultural management issues that are common to virtually every commodity in controlled environment production. Frequently, a lack of homogeneity of environmental variables, such as temperature, light and humidity result in heterogeneous water status of crops and growing substrates in the greenhouse. Similarly, varying environmental conditions preclude the effectiveness of simple timed cycles of irrigation management. A soil moisture sensor based system was developed and used to monitor and control the substrate volumetric water content ([theta]) while physiological responses of two species, miniature roses ('Rosa' * hybrida 'Alicante') and greenhouse tomatoes ('Lycopersicum esculentum' L. 'Matrix Fl Hybrid'), were measured. The crops were grown in the greenhouse using two irrigation strategies: sub-irrigation ([theta] = 25, 20, 17, 14.5 and 12.5%) for miniature roses and drip irrigation ([theta] = 30, 25, 20, 17 and 15%) for tomatoes. Complications and logistical issues with wired sensors stimulated the development and application of a wireless sensor interface for these experiments. Total accumulated above ground shoot dry weight for miniature rose plants where [theta] = 12.5% was lower compared to both [theta] = 17% and 25% throughout the study; however, results demonstrated that [theta] between 12.5% - 25% exhibited no significant differences in other plant growth parameters. Tomato plant water lise resulted in a net water savings of 46.8%, an increase in plant effective water use efficiency (WUE) by 79.6%, and an increase in fruit effective WUE by 118% if irrigation was triggered at [theta] = 15% compared to 30%. However, results showed that [theta] between 15% - 30% had no significant differences in day-to-flowering, gas exchange, daytime leaf accumulated net CO2 assimilation, leaf chlorophyll content, maximum quantum efficiency of PSII photochemistry (Fv/Fm), root zone oxygen, plant growth, and instantaneous WUE. Successful operation of the wireless technology and irrigation system was demonstrated.