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Greenhouse management Tomato crop management Management of alternative greenhouse food crops. Crop Nutrition

Immediate Post Planting Care...

General Principles
Objective: to grow a fruitful plant with controlled vigour capable of sustained high yields without susceptibility to disease or pests.

Immediately after planting the roots are confined within the root ball transplanted into the bag, and the water reserves available to the small plants are limited until the roots grow out into the surrounding media. Watering once, twice or perhaps three times a day will be required for the first few days during the summer, depending on the weather. In winter the plants might only require watering once every few days. Each watering should be with only a small volume of water, not more than 200 ml per plant at any time. The roots should be growing actively out into the pumice or sawdust within 5 days in summer and once this starts much greater water reserves are available to the plants.

It is often necessary to restrict the water supply from this time and until the first truss of fruit is set and has started to swell, in order to limit the plants natural tendency to produce strong vigorous growth and to encourage early flowering and strong development of successive trusses of flowers. This is especially the case with tomatoes but less so with Peppers and cucumbers. Manual control of watering is better than using automatic solarimeter control during this phase of development. The plants need to be watched continuously and only watered when the first signs of incipient dryness appear, using waterings of 200 ml per plant. The frequency of watering is likely to vary between once and four times per day, depending on weather conditions. During February, March and early April, when the weather is likely to be hot and dry (In New Zealand), overhead damping either by hand with a hose pipe or by overheads sprinklers will be very helpful in keeping avoiding stress and will assist in keeping the greenhouse cool.

With tomatoes it should be possible to continue to water by manual control until the second truss of fruit is set and at then to change to automatic control. Cucumbers and peppers will normally change to automatic control about 10 - 14 days after planting depending on the time of planting. The plants at this stage should be reasonably short and stocky. This can only be achieved by carefully restricted watering during the early post planting phase. Some growers attempt to control growth by using very high CF feeds, but this is not effective in the absence of controlled watering and can lead to problems of salt build up in the bags. Failure to control growth properly in this early stage may delay and weaken flowering and reduce fruit set and quality, and will encourage stem botrytis infections in thick sappy stems later in the season.

Automatic watering using a solarimeter.
Solarimeters used in NZ are either stand-alone instruments directly coupled to watering controllers or as supplied as an input device for greenhouse environmental control computers. Both work in exactly the same way and are used in exactly the same way. Solar radiation is measured outside the greenhouse, but for most greenhouses 70% of the outside solar radiation is received by the crop inside the greenhouse, and 70 % of the solar radiation reaching the crop is used to transpire water from the crop. Thus solar radiation measurement provides a very good guide to day time water use by greenhouse crops. Solarimeters used in NZ record radiation in several different units, calories/cm2 (cal/cm2), mega Joules/m2 (MJ/m2), Watt-hours/m2 (Wh/m2)or sometimes kilolux hours. The basic relation between energy and evaporation is that 586 calories or 2454 Joules are used to evaporate 1 ml or 1 g of water at 20. Thus evaporation per m2 of greenhouse area for each unit of radiation outside the greenhouse is:

for each cal/cm2 , 10,000(cm2/m2) x 49% = 8.36 ml/m2 586 cal/ml

for each MJ/m2 , 1,000,000 (J) x 49% =200 ml/m2 2454 J/ml

for each Wh/m2, 3,600 (J/Wh) x 49% = 0.72 ml/m2 2454 J/ml

These figures are per m2, and so the amount per plant can be obtained from the plant density. For example with a 100 cal/cm2 and with 2.5 plants /m2 the amount per plant would be 836/2.5 = 334 ml.

Water use for tomatoes is relative to radiation receipt and is proportional to plant height:

Plants height relative water use suggested solarimeter set point cal /cm2
300-600 mm 0.4 160 - 180
600 - 900mm 0.6 120
900 - 1200mm 0.8 90
> 1200mm 1.0 50 - 70

Solarimeter calibration is not precise and the proper set point can only be determined by experience on site. The solarimeter set point only determines how many waterings are given, the volume of water given depends on the time duration of each watering or the volume set for each application.

The microtubes were originally positioned to water the root ball from the pot, when automatic watering starts the microtube should be re- positioned so that it is not watering into the original root ball.

As a general rule waterings should not be less than 150 ml /plant, as small applications increase the variability in delivery between plants, and usually 200 ml per application is about the ideal.

Liquid feeding
New pumice or sawdust bags have very low nutrient concentrations at planting time, and the aim of the feeding programme is to build up a reasonable nutrient concentration in the root zone over the first two to three weeks. Apply liquid feed with every watering using a CF of 20.

No run off is required until nutrient concentrations start to rise in the bags. Start taking weekly pumice or sawdust samples two weeks after planting and measure the CF of the 1:1.5 water extract from the samples.

This CF will initially be low, but once it rises to about CF 6 (30 - 35 in the bag) it is necessary to increase the amount of water so that there is some run off. The feed CF and amount of run off should then be adjusted so that the water extract CF is kept in the range of 8-10 through the summer or autumn, and rising perhaps as high as 12-15 in June, July and August (New Zealand southern hemisphere weather). See the 'Taking pumice - sawdust samples' page for details of the 1:1.5 water extract test for measuring the CF in the bag Media.

Young plants cannot use much potash, and the start recipe should contain little potash with a high calcium and magnesium content. The potash supply needs to be increased as the fruit load increases (especially for tomatoes), and allowed to rise to a maximum about the time the 8th truss is setting. Two recipes are usually supplied before planting, and as soon as the first truss is set with fruit about the size of a 20 coin, change to the a second recipe with increased potash. When the third truss is in full flower send a pumice or sawdust sample for analysis if available to you so a new feed with more potash will be calculated from the analysis results. Further samples and recipe changes will be required at the 5 th and 8 th and 10 th truss stages of growth.

Little work is required on the crop in the first few weeks after planting, and strings should be hung during this quiet period. ReelNZ can be hung on the top wire and enough string paid out for tying up the plants. Dutch hooks require quite a lot of time for unwinding string, and so we recommend using separate strings from the ground to the wire, to avoid this waste of labour. Cut the strings to length in batches of 200 or so strings. The bottom end of the string can be tied around the stem, or placed under the bag (without any tie) or can be fastened to the plant with Ami clips.

Using the clips is probably fastest and uses least labour. If the string is tied, there is the option of making a bight round the stem secured with a reef knot or of using a hitch around the stem leaving a tail for undoing the string later. It is vitally important that the string should not bite into the stem and girdle the stem as it grows. The string length must be sufficient to allow for twisting (each turn around the stem uses about 40 mm of string) and that a sufficiently long tail ( 200 mm minimum) be left above slip knot on the top wire.