Suggested Crop Start Procedure
Before starting planting out, put a 1000 litres or so of water into the sump or less if this is a small of trial system, you require enough water so that the pumps do not run dry before water is returning back into the sump through the return pipe. Start the circulating pump. Watch the water level in the sump and add more water if the sump is going to be pumped dry before water starts running back into the sump from the return pipes. Note the water meter reading (water meters may not be needed if this is just a temporary trial system) before starting to the fill the sump and with sufficient water in the sump to complete the circulation, the difference between these two meter readings is the minimum solution volume you will need to operate the NFT system. Allow this water to circulate through the system for 3-4 hours. This will give you time to check the system for leaks and to make sure that everything is running as it should be. Check the flow rates from individual leader tubes, it should be at least 2 litres per minute per gully and adjust the bypass valve to the sump to get this flow rate. This water will rinse away any impurities (dust and lubricants on the plastics), and should be dumped at the end of 3-4 hours circulation.
Plants propagated in paper pots, peat pots or rockwool cubes are planted by simply standing out at the required spacing on the wet chux cloth in the gullies. Four inch square 'Pete' pots have drainage holes in their bottoms, but three inch peat pots have no drainage holes. It is best to tear off one bottom corner of these pots to provide drainage before setting out in the gullies. Plants raised in multipot trays (large cell trays) or plastic pots are fine for NFT, provided that the plants have a good root ball at planting time. The pots can be filled with any normal propagating media such as peat, peat pumice mix or bark, bark - peat mix or a bark - pumice mix. Carefully remove the plants from the cell trays or pots, keeping the root ball intact and stand on the chux cloth at the required spacing. Avoid root damage as much as possible and never try to wash the roots free from potting mix. When all the plants are in place fold the edges of the gullies up over the top of the paper or peat pots or over the top of the root balls of plants ex pots and staple with a one staple between each plant.
Making up the initial NFT solution..
Read the water meter and then run the volume of water required for circulation into the sump and then set the Jobe valve float to maintain this water level. Shut the valves controlling the flow to the header pipes and open the bypass valve fully. Start the circulating pump so that the water is circulating through the header and sampling pot and back into the sump through the bypass line. An initial solution CF of 20 is required (for tomatoes) and the feed recipe sheet provided indicates what dilution rate is required to get this CF. If the recipe sheet shows that a dilution of 1 in 200 is required for a CF of 20, then add 5 litres of A solution and 5 litres of B solution for each 1,000 litres of water in the sump and then switch on the pH and CF meters or the controller. The CF in the circulating solution should be about 20, but if less then add a little more A & B solution to bring the CF to 20. The pH will generally be reduced by adding the A & B solutions, but if it is over pH 6.1 then add a little of the acid mix. Do not overdose the acid, add acid in doses of about 100ml per 1000 litres in the sump. When the solution is thoroughly mixed and the CF and pH are correct open the valves to the header pipes and close down the bypass valve to give 2 litres/minute flow down each gully. Allow the solution to circulate through the gullies for about half an hour immediately after planting and then shut down the circulating pump.
It is better to use intermittent flow for a few weeks after planting, and to delay using continuous flow. The potting media in peat or paper pots or in the root ball can get too wet and deprive the roots of oxygen with a consequent increased risk of root diseases. Intermittent flow which allows the potting mix to dry somewhat between watering cycles helps to avoid these problems. Judicious use of intermittent flow also helps to control the growth and prevents tomatoes from becoming too vigorous and overly vegetative in the their growth, and promotes earlier flowering and fruit setting.
In the few days immediately after planting running the circulation pump for about half an hour each day is quite adequate. Check the CF and pH during each run and add A & B solution (using equal volumes of A & B solution) and acid as necessary to keep the CF at 20 and the pH between 5.3 and 5.9 for tomatoes.The Jobe valve will automatically add water to the system to keep the volume constant. The plants requirements for watering will gradually increase as they grow, and they need to be watched carefully. Growth should be steady, with reasonably dark leaf colour.
It will be necessary to increase the frequency of watering as the plants grow. Water should be given on any day as soon as the plants show the first signs of drying out. Watering this way, that is when the plants show signs of needing watering, will automatically result in steady increase in watering frequency, from once a day to twice and then three and four times per day. If more than four waterings per day are required, then it is best to change to continuous flow. By this time there should be strong root mat developed in the gullies and outside of the root ball in the media.
The initial root development is usually under the chux cloth, and root development should be carefully monitored. Root growth should be rapid and obvious within a few days after planting. If the roots under the chux cloth do not extend to more than 100 to 150mm within 10 days after planting check the roots carefully for root disease. Root disease is usually apparent as brown tips on the roots under the chux cloth. Roots extended out from under the chux cloth onto the bare plastic of the gully (which dries between waterings) may show dead tips because of drying and this is not an indication of root disease. If there evidence of root disease and root growth is slow then contact your advisor for help.
Solution management with continuous flow.
The CF can be increased once continuous flow is being used. Increase the CF to 25 and then upto 30 in winter. Keep the pH below pH 6.3 at all times as there is some risk of calcium phosphate precipitation at higher pH. If using an automatic controller set the pH control to pH 5.9. The solution in the sump is often covered with foam for two to three weeks after planting. This is not of any concern, and appears to be due to the break down of the chux cloth.
A certain amount of potting media will be washed back into the sump soon after planting. It is important to have a filter over the end of the return pipe to catch this debris, which might otherwise cause the foot valves on the pump suction lines to stick open, with consequent loss of prime when the pumps are started. A nylon stocking over the end of the pipe is as good a filter as anything else. The solution recipe recommended for use after planting should be low in manganese as manganese is usually leached out of the potting media and gives high manganese levels in the solution. Initial recipes are usually relatively high in nitrogen and relatively low in potassium, but once the first fruit are set the crop demand for potassium increase sharply. Solution analysis once month after planting and at monthly intervals thereafter is recommended. Some growers like to dump about 3-4 weeks after planting to get rid of debris in the solution. This dump also removes any high nutrient levels due to leaching from the potting media. If you are going to dump and wish to analyse the solution then take a solution sample for analysis prior to dumping.
High solution temperatures promote root growth, but result in strong, leafy and relatively unfruitful tomato plants. A solution heating thermostat setting of about 180 is recommended with the aim of keeping night solution temperatures in the range of 18-200. Day temperatures will be higher than this depending on the amount of heating of the solution by sunshine.
Revised October 1999. ©R.A.J.White October 1999