It is important that the nursery industry find alternate methods of applying water to their plants to counteract the current problems of dryland salinity, groundwater contamination, disease spread and water waste.

Australia is the driest continent on earth and as a broad-acre farmer with over thirty five years experience in grain production, I have had closer exposure to the effects of salinity and drought than most.

The application of excess water to our soils raises the water table and brings salt deposits within the reach of the root systems of soil-grown plants. Over-watering or overhead watering leaches nutrients out of containerised plants into the groundwater where it may build up to toxic levels as it has in Holland. (In that country, run-to-waste hydroponic systems have been responsible for an unacceptable build up of nutrient and have been disallowed).

Disease may be spread between plants up droplet splash or by infected water flowing past clean stock. Water falling between plants, and poor spray patterns, are major contributors to water waste and if such water is recycled it adds to running costs by making sterilising necessary and increasing risk of disease.

The System

In 1996, we decided to use Autopot Capillary Watering in our Australian Native Nursery, having tried a flood-and-drain system on a small scale and found it unsatisfactory.

We purchased 120 CapPlus capillary trays from a hydroponic systems manufacturer in Melbourne. These were fitted to a steel bench system in our shadehouse, at waist height, in rows of 10 trays.  The trays measure 1260mm x 750mm and may be clipped together, side by side, or end to end. The use of PVC pipe legs is an option with these trays, but we decided to go for an unobstructed floor area. 

The  system is fed with rainwater from two buildings, which flows into a 50,000 litre Polytank. A pressure pump then transfers water to an underground tank to keep the water cool and give the option of adding liquid fertilizer. (We currently mix our own potting mix and add low P controlled release fertilizer). A float vavle controls the water level in the tank.

A 12-volt diaphragm pump with battery and back-up charger, supplies water to the trays at 10 psi, so that in the event of a power failure the pump continues to run. The pump runs in series with a pressure tank to avoid unnecessary cycling and is capable of supplying all the water requirements of 8,000 to 10,000 native plants on a hot day.

As the water enters the capillary trays it is controlled by the "Smart-valve" fitted into each tray. This allows water to flow until it reaches a preset level, whereupon the valve closes and remains closed until the water is used up. It then reopens and repeats the process.

A capillary mat is stretched across the top of each tray and folded down into two channels that carry the water. By a process of wicking up the water, the whole mat surface becomes damp. It is necessary to pre-wet these mats to start the capillary going as a dry mat will not suck up water and neither will a dry plant. The tray is finally covered with a film of weed mat and the plants sit on top.

Results

To date the 50,000 litre water tank has been adequate to water 8,000 to 10,000 plants during the summer period. From March to September it is also used in our home for domestic purposes. Obviously, periodic rains replenish the tank supply.

Because the system was designed for hydroponic use in a greenhouse, I have made some modifications to improve the operation in the more hostile environment outside. The trays has a much more robust capillary mat fitted. This can withstand washing with a pressure-blaster and has an inbuilt weed mat on top and a plastic film underneath.. This mat is easier to keep clean and prevents roots from growing through the mat.

The Marix that originally covered the capillary mat has been replaced with standard weed-mat that I cut with a hot soldiering iron. This standard mat will withstand scrubbing, pressure blasting and sunlight. It also prevents root penetration, algal growth and water evaporation.

As a precaution, during very hot periods, (up to 43 degrees C), we handwater weekly to keep the moisture in the upper part of the pot. 

The whole system is stripped and sterilised twice yearly between seassons and the mats sprayed with moss and liverwort killer.

Valves do occasionally develop a slow leak, generally a regular drip, but they are easily cleaned and water loss is minimal. Discussion with the manufacturer could see improvements to this smalll problems. 

We grow the majority of our 480 species of plants in 67mm duper square native tubes.  It has been necessary to have special weldmesh racks manufactured to my specifications in order to keep the tubes updright and ensure that the bases fit square on the mat.  These racks have been extremely successful. Specially capillary pots, with holes in the bottom, are used if we have to pot on.

Benefits

The benefits observed to date are listed as follows:-
1. A robust root system that grows toward the moisture source at the bottom of the pot.
2. Impressive plant growth and root development.
3. High plant survival rates (client satisfication).
4. Disease cannot spread between trays as each tray has its own water inlet and reservoir.
5. Apart from the semi-annual cleaning, there is no labour involved.
6. Very cheap to run as water costs are minimal.
7. No water waste at all.
8. The plant uses all nurtient and none runs to waste.

Conclusion

There are alternative capillary systems availbale, but the few I am aware of have a run-to-waste component or else recyling is necessary. Also the risk of root disease spread is much greater with these alternatives.

My only other considered alternative was hand watering, but as my small operation is run by myself and wife when she is available outside working hours, the time required to handwater made my present system my only option.

Capital cost of my system is fairly high, but the running costs balance the equation. It also allows me the opportunity to do other jobs or take time out and most importantly it has no effect on the environment whatsoever!