Sustaining Cannabis Production with Fertigation
Written By: Argus Control Systems and Conviron, Edited By: Alex Fermon
“Sustainable irrigation is the rational practice of all activities related with the irrigation of plants, whether in the areas of horticulture, landscape, and ornamentals, so that it helps satisfying the respective survival and welfare needs of the present without compromising those of future generations”. It considers the impacts of manufacturing and transportation of required equipment and materials, as well as incurred discharges and waste impacts. (1) For traditional horticulture and commercial agriculture, irrigation is a necessary process for plant growth and, although it can be done manually, automating this process could bring several benefits to growers. In addition, improving irrigation efficiency can contribute greatly to reducing production costs, making the industry more competitive and sustainable. Through proper irrigation, average yields can be maintained (or increased) while minimizing environmental impacts caused by excess applied water and subsequent agrichemical leaching. (2)
Fertigation, the process of delivering plants nutrients and water to produce a quality crop with higher yields through automated irrigation, could be a path towards achieving sustainability. One of the benefits of using an automated system is that it saves on labor costs by eliminating the need for employees to constantly monitor and water plants which provides producers with alternatives to a more sustainable use of their resources. In addition to labor costs, hand watering could also affect the quality of the product. Using an automated system improves how production is controlled.
Fertigation is a key concept in cannabis cultivation and there are two common ways to supply fertilizers through an irrigation system for sustainable cannabis production: dilute tank control and in-line injection.
DILUTE TANK CONTROL - Batch Method
Using the dilute tank control method, fertilizers are premixed at the final feed strength concentration for the crop and stored in a tank or reservoir until used. This method is the simplest, safest and potentially most accurate way to achieve the final dilution strength. Dilute tank batches can be prepared by hand or the process can be fully automated. Since the mixing process is separate from distribution, the dilute solution can be removed from the tank at practically any flow rate without ever affecting the concentration accuracy.
Additionally, the volume of ready-made feed solution acts as a safety reserve in case of problems with chemical or water supply.
Despite these positive features, dilute tanks are not as popular as in-line injection systems, particularly for larger operations. Large, costly storage tanks are required and each combination of fertilizer formulation and concentration requires its own tank. It is generally only practical to adjust the fertilizer strength and formulation when refilling a tank from empty. A re-pressurizing irrigation pump is also required to deliver the dilute solution to the irrigation system.
Dilute Tank Control dosing system
IN-LINE INJECTION - Continuous Methods
In-line injection equipment can range from simple mechanical injectors driven by water flow to fully automated nutrient control systems. Pressurized in-line systems preserve the pressure and flow characteristics of the water supply system, eliminating the need for a re-pressurizing pump. In contrast, atmospheric injection systems blend the fertilizer and water in a non-pressurized tank and require a re- pressurizing pump.
In-line injection is generally more popular than dilute tank systems since it does not require large holding tanks and they offer more flexibility. With in-line systems, concentrated stock solutions are continuously injected into the water stream as irrigation events are underway. Mixing usually occurs in the downstream section of the irrigation pipe or in a small mixing section of the injector. Injection volumes are based on system flow rates, electrical conductivity (EC) sensor feedback or a combination of the two.
When automated injection controls are used, it is possible to rapidly change the dilute solution concentration by adding more or less stock materials relative to the water flow. This is useful if the feed strength needs to be adjusted throughout the day to match growing conditions or if the feed recipes or nutrient concentration need to be changed for various crops. In some instances, the actual fertilizer formulation can be changed by either switching to different sets of stock tanks or employing a ‘single-element’ dosing design where the individual fertilizer constituents are separated into several stock tanks. This enables an in-line injection system to operate in a multiplexing capacity, where the operator can simply ‘dial-in’ different feed recipes on the same irrigation system (although only one at a time).
In-line injection systems do have some weaknesses compared to dilute tank systems. Low buffer volumes and poor blending may result in dosing accuracy errors and poor final product uniformity. These problems can become more pronounced at low flow rates relative to the design flow rate. If, however, the system is well-designed, tuned, and managed, prevention strategies within the software can counteract these issues. For example, the multi-feed injection system from Argus tracks EC and pH targets for each recipe to ensure accuracy and as a basis for automatic feed strength correction, alarm monitoring, and quality assurance. Rather than rely exclusively on typical deviation based closed loop control, Argus ‘Feed Forward’ software intelligence on this nutrient system can achieve precision dosing at all design flow rates without any striping inaccuracies, settling times or feedback loop oscillations.
Single-element nutrient dosing system
CONSIDERING AUTOMATED SYSTEMS FOR A MORE EFFICIENT AND SUSTAINABLE PROCESS
Whether you select dilute tank feeding or an in-line injection system there are a range of options for automating the nutrient dosing process. While automated dosing systems offer many management and productivity and sustainability features, including reduced fertilizer and water runoff, and better crop quality, they do so at a higher cost and complexity.
Consider a Dilute Tank Control system when:
The whole crop can be administered with a single feed solution.
The dilute feed composition and strength (EC) does not change often.
The pH of water does not need frequent adjustment.
Consider an In-Line Injection system when:
Irrigation scheduling and nutrient dosing are integrated.
Supplying more than one nutrient formulation on the same irrigation system (different crop requirements).
The ability is needed to vary the feeding strength (EC) without having to prepare new stock solutions.
Some automated environmental control systems only manage the nutrient dosing equipment while other horticulture nutrient systems can integrate irrigation scheduling with nutrient dosing activities. An automated fertigation system can be integrated with the facility’s environmental control system where it can be monitored and managed from a centralized user interface along with all the other controlled processes within the grow operation.
Fertigation equipment and systems vary with each application and should be capable of adapting to the design and operation of the overall facility. This may include controls and monitoring for:
Tank levels
EC
pH
Acid/base dosing equipment
Water temperature
Soil moisture levels
Leaching rates (over drain)
Nutrient dosing equipment
Pump controls
Irrigation zone valves
Line purging
Recirculation management
Water treatment equipment (filters, pasteurizers, ozone, UV, etc.)
Argus Controls Multi-Feed Injector Panel and Flow Schematic
There are a number of factors to consider when planning, designing and automating an irrigation or fertigation solution in a horticultural facility; however, planning for sustainability will result in a more efficient use of available resources and longer-term viability and success. Continuous improvement and development of solutions for the horticultural industry, including greenhouse automation systes, are a key and the future of irrigation controls promises more intricate, smarter systems with more sensitive sensors which will help improve and create more sustainable practices.
REFERENCES:
(1) What we understand for sustainable irrigation. “Asociacion del Riego Sostenible”. Available at: http://www.riego.org/asociacion-riego-sostenible/la-asociacion/sustainable-irrigation-definition/ (Accessed: 29 January 2021).
(2) Munoz-Carpena, Dukes (2018) Automatic Irrigation Based on Soil Moisture for Vegetable Crops. University of Florida. Available at: https://edis.ifas.ufl.edu/ae354 (Accessed: 21 January 2021).
(3) Neff, Jeff, “Automated Irrigation Techniques”. “Asociacion del Riego Sostenible”. Available at: https://www.youtube.com/watch?v=IwWU9BxVJZ0/ (Accessed: 29 January 2021).
