This is covered in Chapter 25 in the iAVs Handbook.
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It saves energy and provides a protracted opportunity for the biofilters to drain while still retaining sufficient moisture to sustain the plants. This also allows for microbes to proliferate in the presence of abundant oxygen.
Pumping water at night does not provide any benefit to fish, microbes, or plants, and it can potentially harm plant rhizosphere and metabolism. Plants have different metabolic processes at night and do not transpire or uptake water. Allowing time between irrigation for aerobic microbes to proliferate without interruption is also mentioned. Additional reasons given include the potential for fungal and bacterial disease development from excess moisture at night.
The key reasons given for no irrigation at night in iAVs are:
- No photosynthesis occurs to benefit plants
- Potential harm to plant rhizosphere and metabolism
- Plants do not transpire or uptake water at night
- Allow aerobic microbes time to proliferate
- Avoid excess moisture that can lead to plant diseases