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Do Plants Need Water at Night?
The question whether plants need water at night is a common one, and it is particularly relevant to the Integrated Aqua-Vegetable System (iAVs), which uses a timed irrigation system.
Night Time Irrigation
In iAVs, the pump is controlled by a timer, and irrigation events occur for 15 minutes every 2 hours, starting just before dawn. There are no irrigation schedules at night, which raises the question of whether plants need water at night.
Plant Needs and Transpiration
Plants do not transpire at night, which means that they are not “taking up” water at night. This is because plants have entirely different metabolic processes occurring in the dark. The roots and rhizosphere processes benefit from abundant oxygen, and all the aerobic soil organisms do also.
The “idea” around not flooding at night is to allow time for microbes to proliferate (multiply) and actively metabolize substrate without interruption. This helps plant dark-respiration/metabolism and conserves energy required for lifting water.
Energy Savings
Not pumping water at night saves energy and reduces the workload on the system. This is particularly important in areas where energy is scarce or expensive.
Microbes
Microbes in the Integrated Aqua-Vegetable System (iAVs) do not require water at night. In fact, the drainage time between irrigation cycles is important to provide excess oxygen to the plants and microbes. This drainage time allows the substrate to dry out slightly, which promotes healthy root growth and prevents waterlogging.
During the drainage time, excess water is removed from the substrate, which allows air to enter the system. This air provides oxygen to the plants and microbes, which is essential for their growth and survival. Microbes use oxygen in a process called respiration, which is the breakdown of organic matter into energy. Without a sufficient supply of oxygen, microbial life will suffer from stunted growth or even death.
While microbes do require moisture to survive, they do not require water at night. The moisture in the substrate is sufficient to support microbial growth and activity during the drainage time between irrigation cycles. In fact, allowing the substrate to dry out slightly during this time can promote healthy microbial growth and prevent the development of anaerobic conditions, which can be detrimental to both plants and microbes.