Abstract
With water resources constantly becoming scarcer, and 70% of freshwater used for the agriculture sector, there is a growing need for innovative methods to increase water use efficiency (WUE) of food production systems and provide nutrient-dense food to an increasing population. Sensor technology has recently been introduced to the horticulture industry to increase resource use efficiency and minimize the environmental impacts of excessive water use. Identifying the effects of irrigation levels on crop performance is crucial for the success of sensor-based water management. This research aimed to optimize WUE in a soilless microgreen production system through identification of an optimal irrigation level using a sensor that could facilitate the development of a more efficient, low-cost automated irrigation system. A dielectric moisture sensor was implemented to monitor water levels at five irrigation setpoints: 7.5, 17.5, 25, 30, and 35 percent of the effective volume of the container (EVC) during a 14-day growth cycle. To validate the sensor performance, the same irrigation levels were applied to a parallel trial, without sensor, and water levels were monitored gravimetrically. Plant water status and stress reaction were evaluated using infrared thermal imaging, and the accumulation of osmolytes (proline) was determined. Results showed that, proline concentration, canopy temperature (Tc), canopy temperature depression (CTD), and crop water stress index (CWSI) increased at 7.5% EVC in both sensor-based and gravimetric treatments, and infrared index (Ig) and fresh yield decreased. The dielectric moisture sensor was effective in increasing WUE. The irrigation level of 17.5% EVC was found to be optimal. It resulted in a WUE of 88 g/L, an improvement of 30% over the gravimetric method at the same irrigation level. Furthermore, fresh yield increased by 11.5%. The outcome of this study could contribute to the automation of precision irrigation in hydroponically grown microgreens.
Highlights
Irrigated agriculture is the greatest water user in many countries
At the lowest irrigation setpoint, in both irrigation methods (7.5% effective volume of the container (EVC)), dry matter (DM) significantly increased to 7 g. 100 g−1 FW (Table 3)
Statistical differences were not detected at every irrigation level, water use efficiency (WUE) was significantly improved at 17.5% EVC where the sensor-based irrigation increased this parameter by 30% in comparison with the gravimetric method (p = 0.001)
Summary
Irrigated agriculture is the greatest water user in many countries. Due to the increasing threat of water scarcity caused by climate change, efficient irrigation management is of critical importance for sustainable food production. It is essential to implement research-driven sustainable agricultural practices such as optimized irrigation management to minimize water waste and promote water use efficiency. The adoption of modern high-tech growing strategies such as indoor soilless cultivation has contributed to improving water use efficiency (WUE) (Pignata et al, 2017). There is little established literature regarding optimisation of growing practices and water management in soilless cultivation systems for growing some herbs and specialty crops including the emerging class of herbs known as microgreens. The minimal space requirement and compatibility with indoor farms make microgreens a perfect crop of choice to be grown in indoor soilless systems such as vertical farms and plant factories (Kyriacou et al, 2016). Kale is rich in minerals at all growth stages, including as a microgreen, baby green, or fully grown vegetable (Waterland et al, 2017)
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