The Convenience of Hydroponic Nutrient Application Systems
The application of a balanced nutrient solution to plant roots is a basic principle of hydroponic growing. Making this irrigation as efficient and effective as possible, however, is a little more complex.
Irrigation is a key component of hydroponic gardening and a common cause of concern for many indoor gardeners. Fortunately, the technology has come a long way since the early days of manual watering and gravity-fed systems.
Today, there is a wide range of highly efficient and advanced nutrient delivery equipment available for even the smallest grower. Of course, ensuring nutrients flow at the optimal rate, frequency, and concentration are all dependent on using the correct delivery system.
So, before you begin planting, give a little consideration to choosing suitable pumps, drippers, or emitters; match up the correct irrigation method and ensure even pressure within hydroponic system.
Application Methods for Hydroponic Nutrients
Different hydroponic systems employ a diverse range of nutrient delivery methods. Solution culture systems such as nutrient film technique (NFT) and deep flow technique (DFT) may appear to feature the simplest and straightforward methods of hydroponic nutrient application.
Nutrient solution is continuously pumped to the top of each growing channel or trough, through which it flows past the roots and back to a central reservoir. However, factors such as nutrient flow rate, equalized delivery volumes to each growing channel, and control over EC and pH back at the reservoir all become part of the nutrient management system. Similar considerations—nutrient application frequency and volume—are required with ebb and flow systems.
Drip irrigation, which is currently the most commonly used hydroponic nutrient delivery system, relies on even distribution of solution to each plant at the correct frequency; factors that are largely based on variables such as plant size, growing substrate properties, container volume and dimensions, and environmental conditions.
Aeroponics requires nutrient to be delivered directly to the root system via the use of high-pressure misters or foggers, which may be intermittent or continuous. Overhead sprinklers are also still used in some greenhouse and outdoor systems, though they are not popular in indoor gardens due to the leaf wetness and inefficiency of nutrient distribution. The exception to this may be in propagation areas where high humidity is beneficial to prevent desiccation of clones while they form new roots.
All these delivery systems need to be paired with a method of dosing or controlling the nutrient solution composition before it is applied to plants. Many indoor gardens are reliant on manual dosing to reach the correct EC and pH; however, automation of even small hydroponic systems is becoming increasingly popular.
Hydroponic System Pumps
Most NFT hydroponic systems utilize centrifugal pumps, which can produce a constant flow of nutrient solution rather than the pulsating flow associated with piston or diaphragm pumps. Centrifugal pumps will either pump a small volume of water to a high delivery head or a large volume of water to a low head.
A delivery head is the highest point that the pump must push water to in a system. With NFT systems, the delivery head is the height measured from the surface of the nutrient solution in the reservoir to the top of the growing channels.
To select the correct size of pump that will deliver the correct volume of nutrient solution, you need to determine the system’s delivery head height, flow rate in liters or gallons per minute, and—for basic NFT systems—the number of channels. (The standard rate of a basic NFT system is one liter per minute per channel.)
These specifications can be listed on pump packaging either as a pump performance curve showing head capacity at different flow rates, or simply as flow rate at a set head height. Also, growers should be aware that pump capacity and flow rates tend to fall over time, and with increasing nutrient temperature, and allowing for future system expansion is always a good idea.
Drip Irrigation Hydroponic Systems
As mentioned above, drip irrigated hydroponics is the most commonly used method of nutrient application. These may be set up and run as either a batch feed or inline dosing system.
Smaller indoor gardens often utilize batch feeding, in which a central tank containing several days’ worth of working-strength nutrient solution is made up and manually adjusted for EC and pH. This solution is irrigated onto the plants using a pump and timer or manually controlled by the grower as required. Batch feeding is easy to set up and run; however, time is required to mix up the working-strength solution every few days.
Inline dosing is a more automated system widely used in commercial hydroponic operations. Also known as ‘fertigation’ or ‘direct dilutor/injector systems’, inline dosing systems are installed on the main water supply. As water flows through, nutrient concentrates and pH control chemicals are directly dosed into the flow at the correct rate to obtain the EC and pH required for a crop. Inline injector systems may use several different designs for drawing up and blending concentrated stock solutions and other additives to create this balanced nutrient solution.
The advantage of this system is that it eliminates the need for a large central nutrient reservoir filled with working-strength solution and dosage rates can be adjusted as required. It also reduces the amount of labor and time required to make up batch feeding tanks.
In recirculating systems such as NFT, DFT, and float or pond systems, automatic controllers are often used maintain the correct EC and pH levels. These units use EC and pH probes permanently installed in the flow of nutrient to measure these parameters at regular intervals.
When the controller senses a drop in EC, more stock solutions are automatically dosed into the nutrient flow until a feedback system determines the EC is at the correct level. Water top-ups are also automatically controlled to keep the tank volume consistent.
While automatic controllers may seem like the ideal way to reduce time and labor in monitoring a nutrient solution, they can’t fully replace manual EC and pH checks as failures are known to occur occasionally even in well-designed equipment.
EC and pH probes also require frequent calibration and checking to ensure reliable monitoring and adjustment of the nutrient solution. In particular, pH probes have a limited lifespan and inaccurate readings from these can lead to crop damage and loss. That’s why automated doser units are reliant on correct and regular maintenance.
Misters, Drippers, and Emitters
Selecting the correct equipment for your nutrient delivery system is essential. Drippers, misters, and emitters are available in a range of flow rates and working pressures, and they are usually matched to a specific growing substrate and/or crop. Those with lower flow rates are typically used with coarser, freer draining substrates to slow the downward flow of nutrient and help uniformly wet the root zone.
Pressure compensating emitters allow for an even flow of nutrient to each plant in the system. Some dippers are designed to prevent unwanted leakage and solution loss between irrigations. Finally, indoor gardens that have a diverse range of plant sizes, maturity levels, and species on the same irrigation system are good candidates for adjustable flow rate drippers. These allow larger plants to receive higher flow rates than smaller plants on the same nutrient distribution system, and flow rates can increase as plants grow.
Design and Layout
Layout also affects the distribution of nutrient solution to individual plants around a drip irrigation system. Drip systems may consist of either in-line or microtube systems. In-line systems are more suited to large media beds where the emitters are directly attached to or embedded in the irrigation supply pipe, which runs down the center of the bed. Microtube systems use tubing of a smaller diameter, which is installed into the lateral irrigation lines with emitters or drippers fixed on the end.
Each plant or growing container can have one or two microtubes with emitters pegged into the substrate near the base of plant. Using microtubes allows a more uniform pressure at the emitters, provided the irrigation is correctly designed and has a pump of sufficient capacity.
One of the main issues encountered by hydroponic growers is the differences in volume of nutrient solution received by plants in various parts of the drip system. Some plants may end up overwatered while others are constantly too dry, and these issues become difficult to remedy once the irrigation system is in place.
To achieve uniform and constant nutrient flow rates to all emitters in the system, a ring or loop layout can be installed. This consists of emitters placed into lateral irrigation pipes connected at both ends to a ring main system, evening out the flow and pressure round an irrigation system. Each ring main is supplied by a main irrigation pipe running directly from a pump or pressure water supply. This largely prevents the issue of plants furthest away from the pump receiving the lowest volume of nutrient solution at each irrigation.
Selecting the correct irrigation pipe diameter is an aspect of hydroponic system design that is often overlooked. The type, number, and flow rate of the irrigation emitters determine the size of irrigation lateral pipe needed in terms of flow rate and pressure required.
As such, if the flow of nutrient appears too low from some emitters, it is often more effective to increase the diameter of the delivery pipes rather than invest in a more powerful pump. A large capacity pump will not compensate for irrigation pipes that are too small to carry the nutrient solution flow rate required.
Growers setting up hydroponic systems for the first time or renovating an established indoor garden to improve nutrient management and delivery need to take solution flow and delivery into consideration.
Under- or overwatering of individual plants, slow or insufficient flow rates in NFT systems, and inaccurate dosing can all be prevented with the correctly designed irrigation system.
Written by Lynette Morgan | Author, Partner at SUNTEC International Hydroponic Consultants
Dr. Lynette Morgan holds a B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. A partner with SUNTEC International Hydroponic Consultants, Lynette is involved in remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette has authored five hydroponic technical books and is working on her sixth.