Research

computerised water conditioning for NFTComputerised – Water conditioning for NFT

 

Various ‘Water Conditioning Units’ are marketed these days to the hydroponics industry. Dr Lynette Morgan put one unit to the test on an NFT lettuce crop, and came up with some interesting results.

  

Introduction

There are many ‘high tech’ products appearing on the market these days, which may or may not have a useful role to play in increasing yields and quality from hydroponic systems. Since science does not yet fully understand all aspects of plant physiology, particularly at a physical and molecular level, and new aspects of crop growth are still being researched, then there exists a wide scope to increase the efficiency of our hydroponic food production.

One area which is the subject of a great deal of scientific research is plant nutrition. This, combined with other aspects of hydroponic production such as water quality and mineral uptake, are important areas where new developments are currently taking place. At Suntec Hydroponics in New Zealand, a scientific trial was recently conducted to evaluate the effectiveness of a computerised water conditioner (distributed by CALCLEAR P/L in Australia) on NFT grown lettuce crops. The trials yielded some interesting results, which could be beneficial to hydroponic producers.

These types of computerised water conditioners, which have their origins in aeronautical technology, have been used for some time now, both in commercial and domestic situations, to soften hard water and remove lime scale from pipes and other equipment, without the use of chemicals. An early indication that these water conditioner units may be of use in the hydroponic industry was when hydroponic lettuce farms in the Sydney area noticed that within a ten day period, blockages that were caused by algae attached to limescale in the system had been dislodged by the effect of the conditioner units. The trials we carried out at Suntec have revealed that these units have other, more significant effects on lettuce plant growth, one of which includes reducing the incidence and severity of the physiology disorder ‘tip-burn’.

The Experiment

Hydroponic producers commonly use a variety of water sources for nutrient formulations. Rain water is usually considered to be the optimum water source for hydroponics by most growers and consultants, however many producers are forced to use bore water of less acceptable quality.

The composition of the water source can cause serious problems in hydroponic production, where the nutrient is constantly recirculated. This is because, as the solution is taken up by the plants and more water is added, elements which are not essential for plant growth tend to accumulate, eventually producing toxic levels. For this reason, and because the CALCLEAR computerised water conditioner units have a beneficial effect on mineral water sources, we ran this trial using two water sources – rain water and water from a bore, which would normally be considered as unsuitable for hydroponic lettuce production.

One of the other major objectives of these trials was to determine if the water conditioner units would reduce the occurrence and severity of tip-burn, which many growers encounter during the warmer months of the year. Tip-burn is a browning and drying of the leaf margins, often occurring as the heads reach harvest. This disorder is more prevalent on butter head cultivars and can results in the loss of a large percentage of a crop. Tip-burn is a calcium transport problem within the plant and is not caused by inadequate levels of calcium in the nutrient solution. Tip-burn damage occurs when the foliage is losing water into the air faster than the roots can take it up or, in high humidity and low water loss conditions, when the transpiration stream is restricted and thus tip-burn results.

There are many theories behind why such a calcium transport problem exists – most are based on the structure and conductance properties of the xylem tissue which carries the calcium in the transpiration stream, but it seems that internal plant properties and environmental conditions play a major role. In hearting lettuce, such as butter head, transpiration of the expanding leaves within the head is limited by surrounding leaves, especially under high humidity conditions, and tip-burn can be severe on these crops if allowed to stand too long before cutting.

The lettuce crops in these trials where monitored for a wide range of other yield and quality factors, to determine firstly what benefit the computerised water conditioners may have on crop growth, and secondly the scientific explanation for any such results.

Materials & Methods

There were four treatments in these trials, which were replicated in a ‘complete randomised block, split/split plot’ experimental design. While this required an NFT system to be built which comprised four separate tanks, pumps, associated gullies and pipes, it was imperative that the correct scientific procedures and design were carried out, so that the data obtained was completely unbiased and would stand up to scientific scrutiny.

Quite often we read reports of new products which have been tested simply by handing them over to commercial growers to have a ‘try’, with the results being reported in detail. Unfortunately, unless the trial has been replicated and run on a properly designed system, with a comparison to a control standard and appropriate statistical analysis, then these types of trials have little scientific merit. It’s a good idea if you are looking at the information provided by manufacturers, to find how their ‘scientific’ trials were carried out and whether they were properly run – ‘scientifically proven’ doesn’t always mean what you expect.

The Treatments

The four treatments designed to test the water conditioners were:

  1. A rain water-based nutrient (lettuce formula) – this is the control treatment against which comparisons are made.
  2. A rain water-based nutrient (lettuce formula) with a CALCLEAR digital water conditioner unit attached.
  3. A bore water-based (lettuce formula) nutrient solution – control treatment.
  4. A bore water-based (lettuce formula) nutrient solution with a CALCLEAR digital water conditioner unit attached.

The Objectives

The objectives of these two trials were to determine the effect of the CALCLEAR computerised water conditioner (Digital units) on two successive crops of hydroponic lettuce, grown in both rain and bore water-based systems, by assessment of the following variables:

  1. Total and marketable yield.
  2. Nutrient uptake and accumulation within plant tissue.
  3. Incidence and severity of foliar tip-burn under unfavourable environmental conditions.
  4. Flavour, by occurrence of bitter components in harvested crops.
  5. Shelf life of the harvested crop.
  6. Colour intensity of red coral lettuce.
  7. Nutrient and foliar mineral analysis, including monitoring of sodium levels.
  8. 8. Effect on conductivity and pH levels of each treatment.
  9. Incidence of botrytis disease on the winter grown crop.
  10. Crop timing.
  11. Examination of plant xylem tissue.
  12. Incidence of premature plant bolting.

The System

The NFT system consisted of four treatment tanks, each with its own pump and delivery supply and return system. The crop was divided into three replications, with one gully of each of the four treatments in each replication. Each treatment had 3 randomised gullies, with each gully having a randomised block of 16 plants (48 plants per treatment, per planting). The summer crop consisted of the Butter head variety ‘Buttercrunch’ and the winter crop consisted of both ‘Buttercrunch’ and a red coral variety ‘Lollo Rossa’.

All plants were raised in a sterilised bark media for 3 – 5 weeks, when they were transplanted into the NFT system. Seedlings of the same size were selected for inclusion in the trial and randomly assigned a treatment. The CALCLEAR digital units were installed as instructed by the manufacturer, by fitting the unit onto the flow of the NFT system, ensuring that the antennae wound around the flow pipe were at least one metre from the electric pump motor. These units were in operation 2 days after transplanting the seedlings.

All nutrient solutions had the conductivity maintained within the 18 – 22 (1.8 – 2.2 mS/cm) range for the life of the crop. Pest (aphid and whitefly) control was carried out as required on both crops. The summer-grown crop was planted on 6th February 1998 and all treatments harvested on 8th April 1998. The following crop was planted on 24th April 1998, with harvest occurring on 13th July and 8th August 1998. Both crops were grown under standard greenhouse conditions, with air and solution temperatures monitored on a daily basis.

 

Crop Measurements

During each crop, the solution conductivity and pH was monitored and adjusted, so that all treatments were consistent with each other. A complete solution analysis was carried out on three occasions for each crop, to ensure no mineral deficiencies occurred during crop production (i.e to ensure adequate nutrients were present in the solutions, and to determine any effect of the conditioner units on mineral content over time). A foliar mineral analysis was carried out at the completion of each crop to determine if any differences in mineral accumulation had occurred between treatments (Both solution and foliar mineral analysis was carried out by R. J. Hill Laboratories in New Zealand).

Top: Monitoring of the (summer) water conditioning NFT lettuce trial
Below, Left to Right: The first sign of tip burn, Area of tip-burn growing in size and severity, More servere tip burn.

Data Collection

Crop 1 (Jan – March 1998)

During crop development, the incidence and severity of tip-burn was recorded by means of a photographic scale chart. This allowed each plant to receive a score of 1-6 depending on the severity of foliar tip-burn encountered, with 0 indicating no tip-burn present and 6 indicating severe tip-burn on an unmarketable plant. It should be noted that the conditions during this summer crop were extremely conducive to the development of tip-burn – i.e high temperatures and humidity levels. The objective was also to provide cultural conditions (through use of a susceptible cultivar and moderately high CF levels) that could help induce tip-burn in this crop, in order to fully evaluate the potential of the units in tip-burn reduction.

At harvest, all treatments were assessed for external tip-burn and internal tip-burn, as occurred inside the heart leaves of each head – this was given a score of 1 – 6 and the portion of leaves with no tip-burn damage was weighed. Flavour was assessed by detection of the bitter component, by sensory evaluation of three of the inner leaves of each head. Total head weight was recorded for each plant and recordings of both fresh and dry weight taken.

The percentage of heads considered marketable was also recorded (i.e. no incidence of tip-burn and of an acceptable size, shape and weight). The number of plants with premature bolting was recorded, with bolting being defined as elongation of the stem and ‘spiralling’ of the leaves within the head.

Crop 2 (April – July 1998)

Due to the growth period of this crop being winter, no tip-burn was encountered on any treatments. Crop two consisted of two cultivars – Green Butterhead and Red Coral. Red coloration was assessed on the Red Coral variety during growth and at the time of harvest, by means of a computer-generated colour chart. At the time of harvest, total and marketable yield was recorded as weight per head, along with flavour (bitter component) and shelf life.

Shelf life was assessed by placing each head of marketable quality into a ‘lettuce sleeve’ with roots intact, as would be done in a commercial operation. Each head was weighed after packing and the weight and quality loss recorded on a daily basis, until unacceptable shelf life was reached. This was determined as being the loss in quality that would result in an unmarketable product (i.e. unacceptable wilting, foliar browning, disease incidence or other disorders).

An examination of the xylem structural development was carried out on this crop by placing a number of plants from both treated and untreated gullies in a solution containing red dye. As water was taken up by the plant, the xylem tissues were stained and could be observed.

Statistical Analysis

All data was analyzed according to the experimental design, as well as an analysis of data frequencies within each treatment. Results were reported as:

  1. Those which were statistically significant at the 5% probability level from an analysis of variance.
  2. Those where means were separated by one or more standard errors across all treatments.

 

Results

Crop 1 – Summer

For both the rain and bore water treatments, the conditioner units had a noticeable advantage in increasing the number of leaves which were free of tip-burn, thereby improving marketable yield even though fresh weights were similar. So while the fresh weight of the bore water treatments was similar, the important variable – the tip-burn free portion – was significantly higher in the bore water, conditioned treatment.

Many of the lettuce heads in the bore and rain water treatments with no conditioner unit attached, were unmarketable, due to the occurrence of severe tip-burn on both outer and inner leaves. In contrast, many of the conditioner treatment heads in both rain and bore water solutions were tip-burn free and of a good marketable size. In the rain water samples, a higher total fresh weight was recorded in the water conditioner treatments, as well as a large difference in the occurrence of tip-burn free leaves in the inner heart.

Figure 1. Effect of water source and CALCLEAR treatment on the incidence and severity of external tip-burn in the summer crop.

Figure 2. Effect of water source and CALCLEAR treatment on the relationship between foliar calcium levels and foliar tip-burn in the summer crop.

Figure 3. Effect of water source and CALCLEAR treatment on bitter taste of Buttercrunch lettuce in the summer crop.

Tip-burn

Figure 1. shows the level of tip-burn encountered in the crop treatments during the crop cycle. The tip-burn scale ranges from 1 to 5, with a score of 1 being slight tip burn and 5 being severe tip burn symptoms. Note that before 30 days, no tip-burn was encountered in any of the treatments. This was as expected, since tip-burn is known to occur as the plants reach maturity and form heart leaves.

The marketable threshold is the point at which a lettuce head becomes unmarketable due to the severity of tip burn symptoms, with any damage greater than a very slight browning of the margins of the outer leaves considered unmarketable. At the time of harvest, most of the conditioner-treated heads were of marketable maturity, with many of them having no tip-burn or only slight browning of the outer leaf margins. However, the untreated heads in both the bore and rain water had a greater degree of tip-burn, often on all leaves both inside and outside of the heart, making the large percentage of these plants unmarketable. Water source had no significant effect on the incidence or occurrence of tip-burn in this crop, indicating again that tip-burn occurrence is independent of solution pH and nutrient content.

While treatment with the conditioner units lessened the occurrence of internal tip-burn in both water sources, the greater effect was on the incidence of external tip-burn occurring on the outer leaves. Internal tip-burn was considered an important variable to measure in conjunction with external tip-burn, as lettuce heads can be sold with the producer not having any idea that the inner heart leaves are affected with tip-burn. Quite often, the only time that it is discovered that a crop has suffered from tip-burn is when the consumer pulls apart the head – a fact which must be a concern for the producer.

This assessment was carried out a week after the plants reached harvestable maturity, so that differences in the ability of the heads to ‘hold’ in an acceptable condition could be examined. Tip-burn tends to increase in severity at a much greater rate as the plants become over mature. Even at this later stage of harvest, the conditioner-treated plants had a lesser incidence of both external and internal foliar tip-burn. Internal tip-burn was measured by dissecting the inner heart leaves of each plant and separating them into the those effected by tip-burn and those unaffected. This result is attributed to the increase in xylem conductance in the plants treated with the conditioner units – this was later proven in the winter crop.

When a complete foliar mineral analysis was carried out on all treatments, it was found that the conditioner-treated plants had higher foliar calcium levels than the untreated plants (Figure 2.). This effect was more pronounced in the bore water conditioner-treated plants, but occurred to a lesser extent in the rain water conditioner-treated plants. However, while the foliage had accumulated higher calcium levels, this was not due to differences in calcium levels in the individual solutions. There was no correlation found between the calcium levels in the nutrient solution (with a nutrient analysis taken at the same time as the foliar mineral analysis and on two previous occasions) and those accumulated in the leaves. This suggests that the conditioner units improve uptake and transport of calcium, thus reducing the severity of tip-burn, and may also improve the utilisation of calcium in plant cell development. A general correlation was found between leaf calcium content and tip-burn, as assessed by the visual scale. Levels of all the other elements, as assessed by foliar mineral analysis, were unaffected by water conditioner treatment.

Flavour

At the time of harvest, each treatment was assessed for flavour (by sensory evaluation panellists), examining the bitter component of the inner heart leaves, which is the major flavour problem encountered in lettuce crops. Lettuce plants under stress, such as those grown rapidly at high solution conductivity levels, or those grown slowly under winter conditions, often develop bitter flavours.

Figure 3. shows the severity of plants with bitter flavours of the inner heart leaves. A score of 0 was given for those with no bitter flavours, with a score of 2 being considered inedible. Both the rain and bore water conditioner-treated plants had significantly lower incidence of bitter flavours than the untreated water samples. This result may be due to the increased nutrition and lower incidence of tip-burn on the conditioner-treated plants, resulting in plants which were essentially under less stress, and thus receiving less of a ‘check’ to growth than the untreated crop. It is also possible that the conditioner-treated solution works to some extent to reduce the polymerization of glucose molecules into starch crystals, allowing a higher concentration of free sugars within the plant cells, therefore conferring a better taste.

Crop 2 – Winter

The water conditioner treatment resulted in significantly improved fresh weight and marketability for the Buttercrunch lettuce grown in the rain water solution. Marketability of Buttercrunch was assessed mostly by the degree of heart formation which had occurred at harvest and secondly by weight.

For the winter crop, where nutrient uptake and transpiration were unlikely to be limiting and where no apparent differences in solution conductivity, pH or leaf nutrient levels occurred, it is difficult to find an explanation for the significant improvement in fresh weight, in terms of mineral uptake. It remains a possibility that the conditioner units are able to influence translocation and metabolism within the plant, and may be able to enhance the photosynthetic system in some way. There is some evidence that they influence the mobilisation of sugars and prevent starch accumulation in leaf tissue. Early growth (as measured by leaf span) was better in the conditioner-treated rain water gullies for Buttercrunch lettuce, although little or no difference occurred in the bore water treatments.

Other evidence suggests that the water conditioner units may also confer some advantage in the areas of improved appearance (colour and size) in red coral lettuce, greater shelf life, reduced occurrence of summer premature bolting and faster growth rates, but further crop trials would need to be run over a number of seasons to determine if this data was significant at the five percent probability level (Current data analysis only shows means separated by one or more standard errors).

Examination of Xylem Development & Translocation

Illustration 7 shows the differences in xylem tissues (stained red on a green lettuce leaf) between the conditioner-treated and untreated Butterhead cultivar (from the bore water treatment). Since water and calcium travel in the xylem tissue, this simple procedure allowed the xylem vessels to become stained as the plants transpired and took up water. Xylem vessel development is important for plant growth and final quality, as calcium which travels through the xylem is integral to the development of new cells and retaining the structure of existing cell walls. Thus, higher levels of calcium in many crops results in firmer fruit, longer shelf life, lower incidence of tip-burn and wilting and greater disease resistance.

While the tissue analysis data from this crop did not indicate that higher levels of calcium had accumulated in the conditioner-treated plants, it is obvious that xylem development had benefited. The reason why the increased foliar calcium levels from the summer grown crop were not repeated in the winter grown crop, is probably due to the seasonal differences in growth rates. In summer the plants had maximum light and temperature levels for optimum growth, and the limiting factor was the rate of transport of water and calcium through the xylem tissue. In winter, the limiting factor was not the rate of water nutrient uptake, but the lower light and temperature levels which slowed plant growth significantly. It should also be noted that tip-burn rarely occurs in winter grown crops, thus the plants obviously take up and can transport sufficient calcium in winter anyway, and this process cannot be, and does not need to be, enhanced.

The increase in stained xylem tissue could be a result of several factors. Firstly, the conditioner-treated solution may be affected in such a way that it can be more readily absorbed than the untreated solution, passing through cell membranes at a higher rate. Secondly, the conditioner treatment could have resulted in better development of the xylem vessels during plant growth, remaining free of cellular debris and crystalline obstructions. It was shown that the conditioner units act on all these variables. When untreated plants were placed in treated water, they translocated the red dye; when treated plants were placed in untreated water they too translocated the red dye. However, untreated plants in untreated water did not translocate any red dye during the same time interval.

Left: Leaves of water conditioner treatment plant from the same crop after a few hours in the dye solution. The xylem has been stained red, showing the greater degree of movement in the transpirational stream. Right: Leaves of a control plant (no water conditioner treatment) after a few hours in the red dye solution. The red dye has not moved through the xylem.

Possible Modes of Action of the Water Conditioner Units

From the technical information provided about the units by CALCLEAR (Australia), and the results obtained from these scientific trials, it seems that the computerised water condition units operate by generating a rapidly changing waveform, which is required to achieve ionisation of all the different nutrient salts that are present in water and nutrient solutions. Other devices, such as magnets or coils, which can be used to produce an ionising field, only succeed in affecting a small proportion of the salts in solution. The strong flux field which the units generate in the nutrient supply pipe modifies the calcium carbonate crystal nuclei.

What is suspected actually happens, is that the field generated by the units affects the spin of the electrons within their orbital, causing the ions to be unable to react or combine with other ions in the solution. Thus the nutrients are unable to form crystaline salts with other elements, and may be prevented from forming crystaline structures within the xylem, allowing the plant to transpire more effectively. The increased transpiration has a follow-on effect in improving calcium transport, therefore reducing tip-burn.

Our research suggests these units also influence plant physiology in other beneficial ways, and we are currently undertaking further crop studies on other plant species to verify the results reported here and to examine further the mode of action of the conditioner units

Summary

In summary, the CALCLEAR conditioner units provide several benefits to hydroponic lettuce production. From the results of these trials, their most dramatic influence is on factors in the plant which are likely to respond to improved transpiration, and mobilisation of ions in the xylem. There is some evidence that they also influence plant metabolism.

Any improvement in the yield and/or quality of a hydroponically grown lettuce crop gives a producer an added economic edge in an already very competitive industry, where a high quality product is demanded. The CALCLEAR computerised water conditioning system had already proven to have many beneficial effects on domestic and commercial water supplies, and with the results of these trials, to also be beneficial within a hydroponic application.

This research was carried out by SUNTEC, an independent hydroponic research organisation in New Zealand, by Dr Lynette Morgan PhD and Simon Lennard M.Hort.Sc.

CALCLEAR can be contacted at Level 2/56 York Street, Sydney, 2000, Australia, Telephone (02) 9977 8801, Fax (02) 9977 8805).

References

Battey, N. H., 1990. Calcium Deficiency Disorders of Fruits and Vegetables. Postharvest News and Information Vol 1 no 1, pp 23 – 27.

Bres, W., and Weston, L. A., 1992. Nutrient accumulation and tip-burn in NFT-grown lettuce at several potassium and pH levels. HortScience 27:7, 790 – 792.

CALCLEAR Computerised Water Conditioner – Technical Information.

Cresswell, G. C., 1991. Effect of lowering nutrient solution concentration at night on leaf calcium levels and the incidence of tip-burn in lettuce (var, Gloria). Journal of Plant Nutrition, 14:9 913 – 924.

Economakis, C. D., 1990. Effect of solution conductivity on growth and yield of lettuce in nutrient film culture. Acta Horticulturae 287, 309 – 316.

Morgan, L. S., 1998. Calcium and plant disorders in Hydroponics. Practical Hydroponics and Greenhouses, Issue 38 pp61.

Morgan, L. S. 1999. Hydroponic Lettuce Production. (currently in print). Casper Publications, NSW, Australia.

First Published in Practical Hydroponics & Greenhouses Magazine, January/February 1999. © Copyright Casper Publications.

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