At the same time, it may be possible to manipulate the system to determine precisely what levels of a particular nutrient can contribute to the highest rooting and, more importantly, allow forest nursery managers to maintain these levels in a practical way. The main objectives of the present work were to obtain and compare cuttings and rooting yields from hydro-ram ets in different hydroponic substrates and systems and to investigate the possible roles of essential nutrients on these parameters. In both the ebb and flow system and the aeroponic system (where there was no substrate), only the clone had a significant effect on rooting.
INTRODUCTION
LITERATURE REVIEW
Total number of established and rooted cuttings from hedge plants grown in the ebb-and-flow system (p<0.05). Total number of established and rooted cuttings from hedge plants grown in the three hydroponic systems (NFT, ebb-and-flow, aeroponic) (p<0.05).
LITERATURE REVIEW
The benefits of hyd ropon ics
Periodically, depending on the climatic and environmental conditions, the tables are flooded and then drained to allow plant roots to aerate. The movement of the nutrient solution can be seen in Figure 6. The very light, soft particles that are formed will retain water up to 50% by volume (Table 8) (Carruthers, 1998). e) The term Leca is derived from the initial letters of the words Light Expanded Clay Aggregate.
The nutr ient environment
Nutrient elements are not taken up from a nutrient solution in the same proportion in which they are present (Schwarz, 1995; Carruthers, 1998). Maintaining the balance between Ca and other nutrients by applying low but sufficient N (180 ppm), sufficient but not too high K (400 ppm) and avoiding depletion of P (>5 ppm) in the feed. The presence of ammonium in the root zone solution is beneficial when root zone temperatures are low.
The differences in sensitivity between plants to ammonium toxicity are due to the differences in the sugar concentration in the root. After this period, samples of the nutrient solution were collected and analyzed and the results indicated that the ratios of K:Ca,Mg:Ca and P:(Sot +NO)') in the reference nutrient solution should be higher than the values for the nutrient solution. At concentrations higher than 800 ppm, CO2 increased leaf area and chlorophyll density to a lesser extent. Addition of NaCl to the nutrient solution caused a significant reduction in the total yield and total fresh shoot weight of the plants in all cases.
By conducting analyzes of both plant tissue and nutrient solutions, plant physiological disturbances and imbalances of different mineral elements in the nutrient solution can be compared and correlated (Resh, 1998b). It is possible to control changes in the nutrient solution once precise relationships are established between fluctuations in mineral elements in the plant tissue and those in the nutrient solution (Resh, 1998b). Cu and B, depending on whether leaf samples or whole cuttings were analyzed for nutrient content. 2003) reported that there were large differences in the.
MATERIALS AND METHODS
The nutrient solution was identical for all hydroponic systems. The commercially available fertilizers Hydroponica'f and Agrisol®: Plant calcium (Table 17) were used. The cuttings used as rootstocks in the ebb and flow table were left in the Unigro® 128 stakes throughout the study period. Odd cyclic timers were fitted to the individual units. The timer for the device was set to run for 25 minutes with a three hour off time interval.
Plants to be used as hedge material were removed from the inserts and planted in each substrate type, with the exception of the true NFT gutter which held the plants in the inserts with no supporting substrate. The room was approximately 195mm high and was kept dark (rubber skirting boards). The humidity in the room was kept high. Inserts were adjusted to hold the plants in place and ensure optimal darkness and humidity in the room (Figure 17c).
After cuttings had been in the curing downtunnel for 25 days (75 days since placement), the plants were destructively harvested. Nutrient solution samples (500 mL) were taken from individual tanks containing the nutrient solution used to feed the stock plants in the NFT system. Fourteen days later when the tanks had to be emptied and refilled, samples were taken again. The samples were kept in glass Schott bottles and sent by courier to the ARC (Agricultural Research Council) laboratory in Nelspruit to determine specific nutrient levels.
R ESULTS AND DISCUSSION
Harvest 3
The results were compared to determine if there was a change in nutrient content between harvests in the hedge plants. In the present study, although there was no significant difference in plant Mg levels for plants in most substrates (except NFT and Rockwool®) (Figure 22), the roots (Figure 21) were higher at the higher levels of Mg- plant concentrations. Plant Fe concentration (Figure 23) decreased significantly from harvest I to harvest 3 in plants grown in the NFT, Rockwool®, leca, sand, P:Vand peat substrates, but increased significantly in plants in gravel and perlite.
Copper concentrations (Figure 23) were significantly decreased in plants on Rockwool® and non-significantly decreased in plants on NFT and sand substrates. Manganese levels (Figure 23) increased significantly in those grown on gravel and perlite, but decreased significantly in plantings on other substrates. Furthermore, the rooting percentage for plants grown on rockwool in harvest three was lower than for those from harvest 2, which had the highest rooting percentage (Figure 21).
In the current study, coppices of the plants in the gravel had the best rooting overall (Figure 21). There seemed to be no correlation between plant B concentration and rooting. Marien (1991) found that mother plants play a predominant role in the quality of the next generation of cuttings and that special attention should be paid to the fertilization of these mother plants. In contrast, magnesium and Na concentrations increased in the coppice of plants grown in all substrates (Figure 24), except Na levels in the plants grown in perlite (Figure 24).
Ebb-and-flow technique
- Plant analyses: comparison of systems
Figure 29: Total number of cuttings placed and rooted from hedge plants grown in the ebb and flow system (p <0.05). Clone type had a significant effect on the percentage of cuttings that rooted from hedgerows in the ebb-and-flow system (p < 0.001) (Figure 30). Similar to the NFT and ebb and flow systems, cuttings of the same three cold-tolerant clones were planted in the aeroponic system as hedge plants.
The plants in the ebb and flow system produced significantly greater numbers of cuttings to be placed for all three clones compared to those of the aeroponic system. Plants in the NFT system had significantly higher Ca concentrations compared to plants grown in the other two systems (Figure 35). NHEO, plants in the NFT system showed significantly higher levels of Fe compared to plants in the ebb-and-flow system.
ForclonesGN107 and NHOO, plants in the aeroponic system had the highest Cu concentration followed by those in the NFT and ebb-and-flow systems, respectively (Figure 36). For clone GN156, plants in the ebb-and-flow system had the highest Cu concentration followed by plants in the aeroponic and NFT systems, respectively (Figure 36). Parent plants in the NFT system gave the next highest concentrations, which were significantly higher than those in the ebb-and-flow system.
COST-BENEFIT ANALYSIS
V Peat
The highest number of root plants produced were from mother plants kept in perlite (6,700), leca (5,943) and peat (5,798) substrates/systems, while the cheapest root plants to propagate were from mother plants grown in gravel (R 1.97 per , sand (R2.05 per plant) and P:V(R2.2 1 per plant) substrates/systems. On the other hand, the results from these three systems show that the total number of rooted plants was low, and the total cost per plant was high. In this case, the low number and high cost of the rooted may negate the savings achieved in down payment costs. After the aeroponics, ebb and flow, and NFT systems had sand- , the burial ground peat systems the lowest initial capital cost (R43,061, R43,083 and R43,147 respectively), the sand and gravel systems have low costs per plant and the peat system has a high number of rooted plants.
These systems are similar in terms of initial outlay costs, with only the cost of the substrate making the slight difference. Plants in the perlite system produced the highest number of rooted cuttings at a cost of R3.64 per plant. The work reported in this thesis aimed to optimize the production of GN hybrid cuttings in the hydroponic systems.
As discussed (Section 4.1.1), the effect of season, hedge maturity, or both, on rooting percentage had a greater effect than clone, and this should be considered in the design of future experiments. The cuttings with the highest percentage of rooting were from parent plants grown on the gravel substrate, but the plants that produced the highest number of cuttings to set were grown in the ebb-and-flow system. It was difficult to determine which elements played a key role in the rooting process, but evaluation of this evidence provided some information.
Fertiliser
Mondi Forests has installed two hydroponic systems in the past two years, based on the hydroponic systems used by Brazilian companies. A small CTE propagation system was first installed at the Mountain Home Nursery in Hilton. A second, much larger and more extensive system was installed for the propagation of subtropical eucalyptus at the KwaMbonambi nursery near RichardsBay. Subsequently, a deionization unit has now been installed at the KwaMbonambi hydroponic project with the aim of improving water quality before adding acids and fertilizers to formulate a nutrient solution. Since installing this unit the pH of the solution has dropped. easier to manage and the plants respond well.
Two other possible sources of problems at KwaMbonambi's installation were also discovered in the meantime: the frequency of irrigation and design of the beds. This was due to a slight change in the original design of the one at Mountain Home Nursery that was implemented to use less water. The systems were ebb and flow systems and the depth of the bed was reduced in the KwaMbonambi design.
This, together with the high frequency of irrigation, appears to cause rotting and subsequent death of the roots. This fertilizer is eucalyptus specific and although there have been some changes in nutrient composition and elemental ratios, further research will be needed to determine its efficacy. Research into diseases and disease control in hydroponic systems is being explored at the University of Pretoria's Tree Patholog y Co-operative Program.
