Critical Analysis: SAEF Hydroponics

 Introduction:

Based on Ebb-and-Flow irrigation, which has been around for almost a century, SAEF hydroponics is one of the more recent forms of hobby and commercial hydroponic crop production. Its origins lie in attempts to help greenhouse growers leverage common, existing benching and irrigation hardware to diversify into new crops effectively while matching or exceeding the performance of conventional hydroponic systems. Ebb-and-flow benches, often on rolling frames or static frames with rollers, are widely used in high tech plant nursery greenhouses and are used to sub-irrigate nursery flats or potted plants uniformly using minimal hardware. Through recent experimentation and the establishment of small pilot greenhouse and vertical farms around the world, this base irrigation hardware has proven itself capable of operating as a hydroponic system with relatively simple additions and adjustments, resulting in the name SAEF (pronounced like “safe”) hydroponics being coined in 2014.

Using SAEF Systems:

SAEF hydroponics may refer either to the first generation Shallow Aggregate Ebb-and-Flow or to the second generation Shallow Aero Ebb-and-Flow cultivation methods. 

The use of aggregate is more appropriate for smaller scale systems and/or longer cycle plants, and while it allows for less frequent irrigation (due to moisture holding capacity) it allows for evaporative water loss and provides no insulation for efficiency solution chilling. Using an aggregate with a fairly large particle and average pore size allows for exceptional drainage and maximal passive aeration of the root zone. Aggregate use, however, also increases the amount of labor necessary to transplant seedlings into the finishing system and sanitize the system in between crop cycles. 

The use of insulative rafts is more appropriate for larger scales and/or shorter cycle plants, but it can accommodate longer cycle plants if appropriate root pruning is performed as needed and if risers (1 to 2 cm) are added to the bottom of the rafts. Rafts allow for system sealing, effectively eliminating evaporative water loss, and they contribute to system insulation, significantly increasing the efficiency of root zone cooling. The ability to effectively control root zone temperatures with minimal energy plays a vital role in the viability of hydroponic farms (including off grid farms using renewable energy sources) in hot and humid climates, where evaporative cooling is ineffective and heat stress can be most efficiently and effectively alleviated by precise root zone cooling.

With NFT or DFT hydroponics, the choice generally has to be whether to maximize greenhouse space usage efficiency (such as in full floor, end-to-end automated systems) or to sacrifice this for the sake of complete and ergonomic crop access (static aisles between each system section). Maximizing space usage efficiency normally poses a risk of crop infestations and infections going undetected and causing severe economic damage if pest and pathogen exclusion and prevention protocols lapse, while maximizing crop access can mean sacrificing up to 60% of greenhouse floor space to access aisles. Putting SAEF systems on rolling greenhouse benches allows the operator to enjoy both of these advantages simultaneously, as the majority of floor space can be covered while aisles are created only where they are needed for immediate crop scouting or other activities.

Just like aeroponic systems, SAEF systems are not intended to run continuously (unless growing aquatic plants with very low drought tolerance). They are instead designed to pulse irrigate periodically, though SAEF systems do so with much less pressure (energy) and far fewer components (including those that create the risk of clogging). The grower then has the opportunity to determine the irrigation frequency and duration and even run different irrigation programs during the day and night. This means that even more energy can be saved, relative to conventional systems, and that plant roots can be spared from excessive osmotic pressure when they are not translocating as much water.

Another feature of precision pulse irrigation is that root tissues can be hardened. Borderline deficit irrigation strategies can serve to limit the size of plant roots, thereby avoiding unwanted overgrowth and tangling while imparting plants with a more drought tolerant physiology. Whereas plants in NFT systems (accustomed to continual water supply) can reach the permanent wilting point and plants in DFT can suffer oxygen deprivation and roots die back within 1 hour and 3 hours of a power outage or pump/compressor failure, respectively, plants grown in SAEF systems have been demonstrated to be mostly unaffected over 12 hours after such an event, providing an additional safeguard against crop damage and loss.

What SAEF Looks Like in Nature:

In nature, the vast majority of plants are irrigated by recurring cycles of rain with dry periods in between. As rain falls, the water table rises and increases the moisture content in the plant root zone. When the rain stops, the water table recedes, pulling air back into all pores sufficient in size to drain. SAEF hydroponics works the same way, except it keeps the leaves dry by sub-irrigating the root zone. These wet and dry cycles simulate natural plant irrigation and drive optimal growth rates.

Advantages of SAEF:

-Irrigation can be very precise and there is no need for active aeration to raise solution dissolved oxygen concentration.

-System is generally lightweight due to shallow irrigation and thermally stable due to insulation.

-System is highly efficient with water and fertilizer usage and minimizes the risk of clogging and system failure.

-Pulse irrigation allows root hardening and drought tolerance, helping avoid permanent wilting in the event of a power outage.

Disadvantages of SAEF:

-System currently requires customizing rafts for a perfect fit.

-Optimal performance requires perfect leveling.

-Formats are generally limited to horizontal layers.

-Method is one of the newest and least tested.

Conclusions and Future Directions:

SAEF hydroponics is still in its infancy, but ventures into this new territory are showing serious promise in overcoming the reasons many hydroponic farms across the world fail to make a profit due to their inability to maximize operational efficiency or pivot into alternative crops when changing markets demand they be more agile. While traditional hydroponic systems were designed for northern latitudes and perform best under high environmental controls and high input conditions, SAEF hydroponics is opening up new possibilities in underserved and more challenging geographies where these have failed to take hold. While it is by nature a generalized system, research into specific practices, conformations, and components will further contribute to its ability to be set up for specialized operations catering to certain high value crops or target climates. As concerns for sustainability increase globally and more farms are planned to operate on renewable energy grids and closed loop water generation systems, maximizing power and water usage efficiency ensure lower operating expenditures overall and thereby faster return on investment periods. With several new hydroponic greenhouse farms making use of SAEF hydroponics currently planned in the Caribbean, Africa, and SE Asia, time will tell the extent of the scale and impact this methodology will reach.