Before large-scale hydroponics adopted peristaltic pumping from the medical industry, growers of all sizes mixed solutions themselves or bought them pre-mixed. This method is still widely practiced by hobbyists, and usually involves dumping the nutrient reservoir every week or so and refilling it with a fresh batch of solution. Dumping nutrients is neither economically nor environmentally sustainable. But without a way to keep levels to their liking, growers have continued to use this method. It's more hands on, but the only cost is buying and monitoring nutrients.
A deficiency mystery
Measuring the initial and recirculated concentrations of nutrient solutions allows growers to monitor how much their plants are absorbing. Plants quickly remove their daily ration of some nutrients and store them in the plant tissue, while other less utilized nutrients accumulate in the reservoir (Bugbee). If your plants absorb all of the Phosphorous, does that mean they need more?
Adding more nutrient mixture in lieu of dumping and refilling with a fresh batch seems like… the solution to the problem. However, if the same Phosphorous level is maintained by adding more solution to the reservoir, the concentration in the plant tissue could spike far above the optimum level, causing iron and zinc deficiencies (Bugbee).
In short, a low level of a single nutrient should not warrant adding more to the reservoir. What seems like a deficiency may just be the fact that nutrients have been taken up and are being stored in plant tissue. This is part of the reason commercial farms conduct tissue analysis of leaves and stems. With an investment in water monitoring, peristaltic or vacuum pumps, and some software, you will no longer need to guess concentrations or dump your reservoir(s).
Fertigation is the solution
Fertigation provides direct injection of nutrient solutions (or pH buffer) into the system's water. In our case, we want to administer nutrient/chemical solutions, remeasure the concentrations after cycling through the root zone, and dose again depending on the concentration of nutrients desired. There are two types of fertigation systems used in soilless agriculture: peristaltic and vacuum.
Peristaltic pumps use positive displacement to transport liquids. A rotor spins inside the circular enclosure, pinching the vinyl tubing against the wall of its housing and creating a sealed occlusion of fluid.
Because fluids are isolated from the pump mechanicals and outside environment, peristaltic pumps are sanitary, easy to clean, and capable of transporting fluids with high viscosity and suspended solids.
Monitoring the nutrients
Precise nutrient delivery is easy when you’re able to monitor how much is being injected into the water and then taken up by plants. Peristaltic technology has reached the consumer market in the last year or so, and units are becoming cheaper. Connected with a multiparameter monitor and preset thresholds for each mixture or pH buffer, your system’s nutrient dosing can become nearly autonomous. With our "control strip" of relays to turn on/off pumps, we are building OsmoBots to allow for easy integration with peristaltic pumps.