Irrigation water quality is crucial at the start of cultivation. The young crop is vulnerable and can suffer considerable damage if the water quality is not good. At the start of a new crop on substrate, a lot of fertilized water is used before the plants arrive. In this process, careless operations can lead to losses of large amounts of water and fertilizer, especially at four places in the system: 1) cultivation gutter, 2) collection at the end of cultivation gutter, 3) drain pit, and 4) drain tanks. Proper planning of filling and draining the mats can ensure that discharges from overflowing gutters and tanks are avoided. Arthur van den Berg of Glastuinbouw Nederland explains more at Glastuinbouw Waterproof.
1) Prevent overflow of the drain channel when draining the substrate slab. When making the full drain cut out directly, the slab drains completely in a very short time, creating a wave of water that spills over the edge of the drain channel onto the ground. By first pricking a drain hole with a dripper, for example, the mat can drain slowly. Then, after draining, the drain cut-out can be made.
2) Avoid overflow of the drain from the drain channel to the drain pit. If too many mats are drained out at the same time, a wave may form in the drain trough, causing overflow from the catch basin. By starting at the catch basin and moving further and further away from it, overflow can be prevented.
3) Prevent overflow of the drain pit. The drain pit has a pump that pumps the water to the holding tanks. If more water enters the drain pit at the same time than the pump can handle, the drain pit will overflow. Therefore, do not allow more mats to drain at the same time on the same drain pit than the discharge capacity of the pump in the drain pit. A properly functioning float is also crucial at this stage. Therefore, check the float for operation and remove any blockages.
4) Avoid overflow of the drain tanks (dirty and clean). The drain tanks have a limited volume for drain water storage. All the water released when crossing the substrate mats should be able to be collected in these tanks. If the storage capacity is limited, it can be chosen to fill and drain the slabs in phases, e.g., per tap section or group of tap sections. The water released during drainage of the first section can then be reused (possibly after disinfection) to fill the next section.
A point of attention is the capacity of the water treatment unit (e.g., disinfector): this can also be limiting in getting the water from the dirty to the clean drain tank fast enough to allow reuse.
Analyse drain water more frequently
During the start-up phase, you can analyze the pouring water more frequently for cleaning and plant protection product residues to assess whether you can reuse the drain water. Checking for hydrogen peroxide (H2O2) for reuse of the cleaning water in cultivation is easy to do with test strips. Other substances require analysis in a laboratory. One has the result after a few days.
More information on water quality during crop rotation can be found here.
Source: Glastuinbouw Waterproof