Issue 39: Needs Based Feeding

Issue 39
March/April – 1998
Story Title: Needs Based Feeding
Author: Roger Fox

Most Hydroponic Systems aim to give plants more water than they need, to avoid transpirational stress. But a new system developed in Australia rations only the exact amount they will use.

Most contemporary hydroponic production systems divide neatly into two categories – recirculating or run-to-waste – according to the nutrient delivery method they use. But a new system developed in Australia fits into neither of these categories, instead using capillary principles to create a new approach.

Melbourne-based company Auto Pot Systems P/L have only recently ventured into the commercial hydroponic market. They are best known for their hobby hydroponic systems, which are based on the concept of making “patio gardening” an almost labour-free activity, to suit busy urban dwellers. At the heart of their hobby systems is a unit called a “Smart Valve”, which automatically regulates the flow of nutrient solution to potted plants via a tap, thus removing the need for labour input.

But according to company directors Jim Fah and Philip Kua, the Smart Valve first needed to be redesigned before it could be applied to use on a commercial scale. Design engineers and material engineers were called in to assist in the redesign process, and the result is the Smart Valve Mark II

“The new one has three parts – the previous version had 18 parts,” Philip Kua explains. “It also now comes with a guarantee of no overflow.

“For the Smart valve to work, air exchange is very important, and with the new one, it’s impossible to clog up the air exchange hole.”

Greenhouse Trials
In aiming to develop commercial-scale systems, the company first needed to establish its own greenhouses for trial purposes. Here the partners were fortunate in having access to land within a few hundred metres of their retail shop, which is located within the Gardenworld Nursery complex at Keysborough in outer Melbourne. Accordingly, in September 1997, two igloo-style greenhouses were constructed (each of 500sqm), and these have become the trial sites for their two new commercial systems.

In one of the houses, a larger modified version of the original Auto-Pot is being used to grow vegetables, including tomatoes, cucumbers and eggplants. Each growing “module” comprises two 10-inch pots and a Smart Valve, with the modules lined up side by side to form rows. In the current plant trial, 1500-1600 plants are being grown within the 500sqm greenhouse area.

“With this demonstration house, we want to show potential growers how it can be done,” Philip explains.

One of the most interesting features of the set-up is that the whole house is being fed by the same simple reservoir system that is used in the hobby version. A simple fertigation unit copes with 1600 plants, and ordinary suburban water pressure is all that is required.

“It uses ordinary suburban water pressure for the whole house. In fact the pressure is cut down – it,s coming out at about 12-15psi. So pressure is not an issue at all – in fact too much pressure is a problem, it starts to burst the pipes.

“And because we work with such small pressure, we get very few plumbing problems.”

But the most unique aspect of the system, according to Jim and Philip, is its entirely “needs-based” feeding method. The Smart valves will only open when the plants in that module require topping up with nutrient; and no additional nutrient will be supplied until all of it has been used up. The technique, therefore, cannot be described as run-to-waste, since no excess nutrient is wasted, and nor can it be described as recirculating. It is, they claim, a new approach to hydroponic growing, which addresses a number of the environmental problems associated with other systems.

“The reason systems need high pressure is because all points open at the same time – you might have 1000 outlets opening at once. Then you need a computer to put it into stations,”Philip explains.

“But this is different. Each of the plants has their own valve and they tell the system when to water. It’s absolutely needs-based and that’s why we can have a big plant next to a small one. You don’t have to organise plant stations on the computer, or move plants around etc. I can decide to put a seedling right next to a mature plant.”

In exploring the market for hydroponic systems in Asia, Jim and Philip have found that a consistent problem is high nutrient temperatures, particularly where long lengths of channel are positioned in full sunlight. Recirculating nutrients get hotter and hotter as they move through such systems, meaning that nutrient cooling is required to operate effectively. Their new approach will, they believe, help to address this and other nutrient related problems.

“We all know the issues of water recycling,” Philip observes. “You’ve got to disinfect it, you’ve got to cool it in Asian countries, you’ve got to monitor pH levels, salt levels and so on. With this, because there is no recirculation, the whole thinking changes.

“We obviously don’t need to sterilise, because the water will not be returning. For hot climates (such as Asia) we don’t have to worry about trying to refrigerate it because its cool, always coming fresh from the supply – unless of course, your mains is hot.”

Auto Pot say that a major benefit of this approach is that the nutrient solution does not require adjusting for conductivity or pH – it only needs total replacement periodically when it becomes depleted. As a result, the plants are always being supplied with the full balance of nutrients and the right pH levels.

The medium being used in the pots is perlite – 2.5 litres per pot – which has the benefit of being very free draining.

According to Philip, the simplicity of nutrient delivery in this system means that running costs are very low. In terms of capital costs, the company quotes a figure of $5 per “growing point”, which they believe is competitive with many dripper-fed and NFT systems. At present, they are manufacturing standard 2-pot modules, but this may change at a later stage.

While a variety of vegetable crops have been grown successfully, the system has not yet been trialled for roses, which would appear to be a suitable candidate for this type of pot culture. According to Philip, the technique has already attracted the interest of some local tomato growers, who are currently using drip-to-waste and are being pressured by local council authorities to stop run-off from their properties. Many, he says, are not keen to convert to recycling systems.

While Auto Pot is manufacturing a standard two-pot unit at present, they may review the design in the future to incorporate something larger. Because the system is modular, Philip says, growers can trial a small area of it and keep adding on.

Capillary Tables
The second of Auto Pot’s new commercial hydroponic systems is based on capillary tables, which are housed in a second demonstration greenhouse. This system has been designed particularly for the production of potted flowering plants and is currently being trialled at 15 nurseries.

The “Capillary Plus” system consists of specially designed 1sqm trays, each of which incorporates one of the new Mk 2 Smart Valves. The modular tray tables can be combined in any configuration, to form any size bench. Jim Fah explains the rationale behind the design.

“You could have one valve to feed the whole table, but then the benching becomes difficult and costs a lot more. One valve per small module is better and then you can form any size of bench you want. The valves are relatively inexpensive.”

The tables are covered with cotton-based capillary matting, over which a fine layer of porous weed mesh is layed – this stops the roots from entering the matting itself. The weed mesh is cheap enough to be disposed of after each crop and replaced.

Nutrient is admitted to the tables via the Smart valves, and runs down the moulded channels. It is absorbed by the capillary mat and drawn up by the roots of the plant. The level of nutrient which enters the trays can be set via the valve, eg. 25mm, 40mm, etc. If required, the system can also be set to dry out for periods, to suit dryland plants or cactus. For general use, the system is set to provide 100-200ml per pot per day. “The plant drives it all,” Jim says. “You don’t need a computer. There is no sterilising between crops and therefore no down-time.”

The Capillary Plus system has so far been trialled with a range of flower crops, including gerberas, cyclamens and tuberous begonias, on around 15 nurseries, including large production nursery Walls Floriana. Results, according to Jim, have been very good, with the plants surviving one of the hottest summers Melbourne has experienced.

As well as attracting much interest from wholesale nurseries, the Capillary Plus is also showing potential for use in retail nurseries, as a method of displaying potted stock to the public – without the need for overhead watering and the flower damage that goes with it. In addition, Jim Fah is currently developing a propagation unit, which uses the same capillary trays with a heat unit fitted underneath. Germination trials to date have been most successful.

Like the plant modules in the other trial greenhouse, the operation of the Capillary Plus hinges on the plant driven demand of the Smart Valve. This is where Jim and Philip see their systems as offering something unique, especially in terms of reducing water useage and run-off.

“The valves are driven by the plants, so we don’t have to adjust it for whatever plants we put in here – it doesn’t matter if it’s summer or winter. Also, it doesn’t waste a drop of water – whatever comes in is used up before more comes in.”

With water use restrictions growing and cost rising, that’s a line that will resonate with many growers.