Medicinal and Aromatic Plants—Industrial Profiles


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part of The Gordon and Breach Publishing Group.

ROBERT T.COLTON AND G.JOHN MURTAGH
68
big advantage of providing a uniform stand of plants will become more important once
elite, high yielding, high quality selections begin to be released from the breeding program.
A successful micro propagation protocol has been developed using coppice shoots (List et
al. 1996).
Plant Population and Row Spacing
Leaf yield is strongly influenced by plant density, with the highest yield per hectare being
obtained at the densest planting (Small 1981b). Small’s highest density was 23,000 trees/ha
but subsequent work showed that the trend to higher oil yields continued to at least 36,000
trees/ha (Peak 1982). Industry experience in both NSW and Queensland supports a population
of about 35,000 as being optimum. These high plant populations achieve full ground cover
more quickly after harvest and compete better with weeds by shading.
Row spacing and planting layout are largely determined by the size of the tractors, mowers,
cultivators, sprayers and harvesters likely to be used in the plantation. Single rows at 75–
100cm intervals or twin rows on 1.5m beds, giving elevated rows with an effective 75cm
spacing, are common and can accommodate most machinery. In-row plant spacings to achieve
35,000 plants/ha for these row spacings are: 75cm rows–38cm apart, 100cm rows–28cm
apart, 1.5m beds–38cm apart.
Planting
Cell grown seedlings can be transplanted at almost any time of the year provided soil moisture
is adequate or irrigation is available. In practice, spring is preferable as it avoids the cold
weather and frost risk of winter and the very wet soils and possible heat waves of summer
and autumn.
Because spring is normally very dry, irrigation is essential to ensure good establishment.
This is particularly so with open rooted seedlings as the risk of plant losses is higher, especially
if periods of drying winds and high temperatures occur. (Colton and Murtagh 1990).
Seedlings are planted with a normal seedling transplanting machine (
Plate 7
) which can
place a band of fertiliser under the plants and can apply a quantity of water to each plant.
Pre-emergence herbicide is usually applied immediately after transplanting followed by
irrigation (
Plate 8
). Seedling establishment is enhanced if the soil is kept moist for the first
4–6 weeks or until rain falls.
Field Preparation
The amount and type of land preparation needed will depend on previous land use, soil type
and topography. It may involve drainage, levelling and the break up of compacted layers in
addition to normal weed control and topsoil preparation for transplanting (Colton and
Murtagh 1990).
A good surface drainage system is important, particularly on low lying heavy soils to
allow timely access to fields for harvesting and other operations following periods of heavy
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

CULTIVATION
69
rainfall or flooding. Levelling land to a uniform grade will facilitate drainage. It is also
essential if flood irrigation is being considered. A system of drains big enough to remove
the excess water from a 200mm rainfall event within two days is warranted, in higher rainfall
coastal areas.
Compacted layers are quite common, particularly on heavier soils which have been
cropped or have had heavy machinery over them while they were wet. These hard layers
inhibit root development and restrict moisture infiltration and will reduce the growth rates
of tea tree. Deep ripping to the bottom of the compacted zone will overcome the problem,
but it can re-occur quickly if heavy equipment is used when the soil is saturated.
On sites where major drainage work and levelling is required, preparation should begin
up to one year before the anticipated transplanting time. Where less preparation is necessary,
the lead time can be much shorter but a rushed preparation can be counter productive.
When fields are ready to plant, the top 10cm of the soil should be well prepared, moist,
free of clods and trash and weed free. In this condition, pre-emergence herbicides can work
effectively and seedlings will get away to a good start. Tea tree seedlings do not compete
well with weeds and rely on pre-emergence herbicides or other forms of weed control for
2–3 months after planting.
IRRIGATION
Irrigation is normally necessary in the period after planting to ensure that plants establish
quickly and to minimise losses, particularly if soil and weather are less than ideal. Open
rooted seedlings are unlikely to become established unless they are irrigated regularly for
the first few weeks or there is regular rainfall.
Once plants are well established, the need for irrigation will depend on location, soil
type, depth to watertable, seasonal rainfall incidence and the frequency of below average
rainfall years.
Tea tree is a drought resistant plant and can survive in very dry conditions (Murtagh
1996a). Day to day growth is fed from its root mass which is found in the top 40–50cm of
the soil but survival depends on the deep sinker roots when the top layers of the soil dry out
(Drinnan 1997b). Where the sinker roots reach ground water and the average rainfall exceeds
1,000mm/year irrigation may not be economic.
Moisture stress causes cessation of growth and if severe and prolonged, it will cause
leaves to drop. This represents a loss of oil and a loss of income.
Drinnan (1997b) showed that in the light sandy soils at Mareeba, water stress for periods
of more than 2–4 weeks reduced oil concentration. Concentrations were highest when soils
were continuously moist but not too wet. Soils which were heavier, higher in organic matter
or mulched stayed moist and kept oil concentrations higher. Frequent irrigation achieved
the same results. Murtagh (1991b) found that on the heavier, moisture retentive soils in the
Lismore-Casino area irrigation had no effect on oil concentration.
Drinnan (1997b) found that in North Queensland trees were using 5–9 mm of water per
day, which is about 0.8–1.0 times the pan evaporation rate, in the period leading up to
harvest. In that environment annual moisture requirement was about 1,400mm per year,
which equates to 14ML/ha. Allowing for adequate rainfall for three months actual irrigation
requirement is about 10.5ML/ha.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

ROBERT T.COLTON AND G.JOHN MURTAGH
70
In the light sandy soils of the Mareeba-Dimbulah area irrigation is essential during
most of the year. Evapo-transpiration on fully grown trees ranges from about 4mm/day in
June–July to 8–9mm/day in October–November. Peak demand in spring requires about
60mm of water per week, normally applied by sprinkler in 3–4 applications. When trees
are half grown (12 weeks after harvest) water requirements are about half those of fully
grown trees.
In northern NSW, where tea tree is grown along the high rainfall coast on moisture
retentive soils the need for irrigation is more tactical and its economics need to be considered
on a case by case basis.
In spite of the relatively favourable water relations on many plantations evapotranspiration
typically exceeds median monthly rainfall in 5–12 months of the year, and trees must survive
or grow on deep subsoil moisture if it is available.
Murtagh (1991b), in a three year study, identified three growth phases in tea tree during
the dry spring period, each with a different response to irrigation. The trees had access to
deep subsoil moisture. Early in the growing season (August–September), growth was slow
and the absolute response to irrigation was small. Cool temperatures appeared to restrict
growth and to reduce the availability of water by increasing the internal resistance of plants
to water uptake.
A strong flush of growth commenced about mid-October and over the next month growth
was rapid, with little regard to the total water potential in the shoots or in soil water content.
Although an irrigation response was obtained during this phase, it was reduced by the
relatively small response in shoot water potential to irrigation. During the remainder of the
dry season however growth rates were strongly related to the water potential in flush shoots
and there was a strong response to irrigation during December to February, when air humidity
was high.
The spring flush of growth occurs during the normal dry period and this coincidence is
the most important factor which reduces the need for irrigation under NSW north coast
conditions. Response to irrigation will be site and soil type specific with drier sites being
more responsive. Responses are unlikely where subsoil is kept moist by groundwater.
The economics must be considered carefully as irrigation infrastructure and operating
costs are expensive. For example, Reilly (1988) estimated the cost of installing spray irrigation
would add 25% to the capital cost of plantation establishment, excluding land.
NUTRITION
There has been very little research into the nutritional requirements of plantation tea tree
and there is no published information on the subject.
This lack of information is not surprising considering that plantations were first established
only 15 years ago and most are less than 10 years old. Many on the NSW north coast are
planted on alluvial soils which are reasonably fertile. Early trial work by growers and research
workers found tea tree to be generally unresponsive to added fertiliser on these soils. A
typical result was achieved on two soils in the Casino district in 1994. On a flood plain
alluvial and a peat soil, Clarke (1995) found no response in either biomass production or oil
concentration when rates of up to 150kg/ha of nitrogen, with generous basal dressings of
phosphorus and potassium, was applied to young trees.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

CULTIVATION
71
Australian natives are regarded as being generally unresponsive to fertilisers. Weiss
(1997) reported the application of fertilisers to established eucalypts to be unprofitable and
indicated that the few results from fertiliser trials had shown no significant increase in
either oil or foliage yield. Diatloff (1990) found that three species of Leptospermum were
not responsive to nitrogen fertilisation in either plant growth or oil concentration.
However, there is plenty of evidence of eucalypts responding to applied nutrients,
particularly when grown on lower fertility soils and where there was adequate soil moisture
(Cromer 1996).
As NSW tea tree plantations age, particularly on the less fertile soils, tree growth is
slowing and fertiliser responses are becoming more common. The infertile coastal podzols
(red and yellow podzolics) and the peat soils are among the first to respond. These soils
have very low cation exchange capacities, very low phosphorus levels and often potassium
levels are not adequate for high yielding field crops. Peat soils have excellent physical
properties but contain very low levels of plant nutrients, especially potassium, and are
commonly low in copper. (Clarke 1997).
Many of these soils also suffer from nutrient imbalances as a result of low pH, low
calcium or salinity problems. Using soil tests to identify these problems and correcting
them with lime, dolomite or gypsum is proving to be a critical first step in developing a
good nutrition program.
On these soils, trees are responding to annual rates per hectare of nitrogen 70–100kg,
phosphorus 15–20kg, and potassium 35–45kg as well as a range of trace elements. On the
relatively fertile river and floodplain alluvials, where trace elements are not normally
deficient, growers are starting to apply NPK fertilisers at moderate rates of: N 60–80, P 10,
K 20kg/ha, to maintain soil fertility (Clarke 1997). Application occurs after harvest and in
several other split dressings during the main growth period of late October to March. Industry
experience is that tea trees respond much better to small amounts of fertiliser applied regularly.
Some growers are reporting growth responses from regular applications of commercial
foliar nutrient preparations.
It is desirable that nitrogen be in a slowly available form if possible, so that it is less
prone to leaching and denitrification losses during the wet season. Nutrient fortified,
composted spent leaf is an ideal slow release fertiliser which also maintains organic levels
of soils. (Clarke 1997).
In the Mareeba-Dimbulah area of north Queensland, where tea tree is being grown in
light, infertile, sandy soils formerly used to grow tobacco, plantation yields are uneconomic
if trees were not fertilised regularly. Compared to unfertilised trees on these fully irrigated
plantations, adequate nutrition lifts biomass production by about 50% and lifts oil
concentration from 5% to 7% in dry leaf. (Drinnan 1997b).
Commercial practice in these plantations is to apply a complete fertiliser in two
applications in each regrowth cycle, with additional nitrogen and potash applied every 4–
6 weeks. Fertiliser is broadcast and watered-in early in the cycle, while trees are small
and is applied through the sprinkler irrigation once regrowth becomes tall. In each regrowth
cycle of 8–9 months typical applications (kg/ha) are: N 150–200, P 20–25, K 150–200
(Drinnan 1997b).
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

ROBERT T.COLTON AND G.JOHN MURTAGH
72
Leaf Tissue Nutrient Levels
There are few published data on tea tree leaf tissue nutrient levels. Limited studies in north
Queensland (Drinnan 1997b) and northern NSW (Virtue, Murtagh and Lowe 1997) show
that tea tree leaf tissue levels are similar to other important native species, at least for the
major nutrients (Table 4). Drinnan (1997a) also showed that unfertilised trees growing in
infertile sandy soil and exhibiting nutrient deficiency symptoms, had N and K levels in
leaves which were only half those found in healthy, productive trees. P levels were similar
whether trees were fertilised or not but several trace elements particularly copper (Cu), zinc
(Zn) and iron (Fe) were much lower in unfertilised trees (Table 5).
Mycorrhizal Associations
Mycorrhizae are beneficial, soil borne fungi which develop symbiotic associations with
plants. The fungal hyphae of mycorrhizae extend the root surface area of plants to
Table 4 Optimum/normal nutrient levels in leaves of four native tree species
Sources: 1. Drinnan et al. (1997); 2. Reuter et al. (1986); 3. Judd et al. (1996); 4. Incitec
Analysis Systems. Interpretation Chart No. 256. October 1996.
Table 5 Leaf nutrient levels in fertilised and unfertilised
tea tree at Mareeba
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

CULTIVATION 73
increase water and nutrient uptake, particularly the uptake of phosphorus (Mengel and
Kirkby 1987).
The fungus enhances the uptake of phosphorus, nitrogen and trace elements in forest
trees and is most effective in increasing the growth of eucalypts in soils that are deficient in
phosphorus and nitrogen. Forest trees take up nutrients mostly from the surface soil where
fine roots and fungal hyphae are most abundant and nutrients and organic matter are
concentrated (Grove et al. 1996).
Mycorrhizal associations have been observed in a number of myrtaceous species including
Melaleuca spp. (Khan 1993). They have also been observed in M. alternifolia in northern
NSW (Virtue 1997).
Mycorrhizae are likely to be active in most northern NSW plantations as these occur, for
the most part, within areas where tea tree occurs naturally.
Effluent Nutrient Removal
Tea tree is an attractive candidate for effluent reuse on agricultural crops because of its wide
adaptability in warm environments, perenniality, tolerance of wet conditions, annual “cut
and carry” harvest, and high economic return (Murtagh 1996c). Its ability to accumulate
high levels of phosphorus (P) in leaves without any reduction in growth can provide an
economic method of stripping P from effluent and waste water.
Bolton and Greenway (1995) found that tea tree thrived when irrigated with standard
secondary treated effluent, containing 5mg/L of nitrogen and 6mg/L of phosphorus. They
found that accumulated P levels in leaves were higher (up to 11mg P/g DW) than in leaves
of effluent-fed Phragmites australis (1.7mg P/g DW), a species regularly used as a
constructed wetland macrophyte. The regular harvesting of tea tree for oil provides a
renewable and economical sink for the removal of phosphorus from effluent waters.
YIELD CHARACTERISTICS
Plant Composition at Harvest
Trees will be from 1–2m high at harvest, depending on growing conditions and the interval
from last harvest. This height will be achieved in north Queensland every 8–9 months but
will take about 12 months in northern NSW. At the first harvest trees will have a single,
thicker stem and will not be so easily cut as at subsequent harvests, when they will have
several thinner stems.
Harvested biomass contains 40–45% dry matter but can range from 30–55%. The dry
harvested plant is about one third oil bearing leaf in average sized trees but ranges from
27% in big trees (which are more woody) to 40% in smaller trees (Colton and Murtagh
1990).
In plantations having an optimum plant population of about 35,000 plants/hectare
harvested biomass could average about 20–25t/ha fresh weight under good growing
conditions, but could range from 10t/ha in poor growing conditions to 35t/ha under excellent
growing conditions (
Table 6
). This yield range equates to 4–14t/ha dry biomass and 2–5t/ha
of dry leaf.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

ROBERT T.COLTON AND G.JOHN MURTAGH
74
Oil concentration can also vary. In freshly harvested biomass, which contains stems,
twigs and leaf, it can range from 5–13mg/g. In dry leaf the range is 30–80mg/g (3–8%)
with 50–60mg/g being fairly typical (Table 7).
Oil Yield
A medium oil concentration of 55mg/g and an average biomass production of 4t/ha of dry
leaf will result in an oil yield of about 200kg/ha per harvest (Table 8). On the NSW north
coast, where crops are harvested annually this yield becomes the annual yield. In north
Queensland where crops are harvested every 8–9 months, this per harvest figure becomes
260–300kg/ha per annum.
In practice, both NSW and Queensland growers are averaging about 180–200kg/ha/
harvest, with some achieving up to 250kg. Combinations of above average management
and more productive sites are resulting in oil yields of 250–300kg/ha/harvest. However,
restricted growth caused by weeds, poor soil or dry conditions can easily reduce oil yields
to 100–150kg/ha/harvest.
In new plantations, full yields are not achieved until year 3 (Small 1986). Oil concentration
is normally lower at the first harvest (Drinnan et al. 1997).
Table 6 Typical biomass yield (t/ha) under different
growing conditions
Table 7 Typical oil concentrations in different plant fractions
Table 8 Oil yield with different combinations of growth rate and oil concentration
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

CULTIVATION 75
HARVESTING
When to Harvest
The aim is to harvest when trees have reached their maximum leaf yield and leaves contain
their maximum oil concentration. However these two factors do not necessarily reach their
peaks at the same time of the year.
In a four year, month of harvest study Murtagh (1996b) showed that in NSW biomass
yields are highest when annual harvests occur between July and September and lowest
when harvests occur in May. The yield advantage of winter—early spring harvests results
from the fact that the most efficient regrowth period (4–6 months after harvest) coincides
with the best growing months (January–March) when temperature, moisture and humidity
are closer to optimum.
Regrowth is always slower in the three months following harvest because light
interception, and hence photosynthesis, are limited by the plants’ small leaf area. (Murtagh
1996b). With July–September harvests, this period of slower growth mainly coincides with
the cooler, drier spring period.
Murtagh and Smith (1996) found that oil concentration in northern NSW varies
significantly from month to month and between years but tends to be lowest in the July-
September period. Drinnan (1997b) supports these findings, reporting the highest oil
concentrations over summer and the lowest in late winter—spring in north Queensland.
Harvesting at different times has very little effect on oil quality or composition (Murtagh
and Smith 1996; Drinnan 1997a).
When total biomass and oil concentration are combined they tend to balance out, leaving
no clear cut advantage for any one month of harvest. However, in years when oil concentration
is particularly low during July–September harvesting should be delayed. In frost prone areas
April–June harvests are not advisable as new coppice growth is readily damaged. On heavier
soils prone to waterlogging summer harvesting may be inadvisable, to avoid soil compaction.
A crop is ready to harvest once its canopy is fully developed and trees have reached
maximum leaf yield (
Plates 9

11
). Once trees have reached this stage they tend to start
losing lower leaves and stems begin to thicken (Colton and Murtagh 1990). Delaying harvest
beyond this point increases harvest costs and reduces distillation efficiency for no additional
oil yield. Tree size will vary with growing conditions but 1.5–2m is a common height for
trees ready to harvest in well grown plantations.
This stage is reached after 8–9 months regrowth in north Queensland, about 12 months
in the NSW Northern Rivers, and may take up to 15–18 months in cooler, slower growing
sites further south. The interval from planting to the initial harvest is likely to be from 3–6
months longer than the interval between subsequent harvests. At the initial harvest, trees
will have single stems which will thicken if harvest is delayed unduly and can quickly
exceed the cutting capacity of the harvester.
Harvesting Equipment
Harvesting involves cutting the whole tree about 150mm from the ground, chopping the
material into 10–30mm lengths, and blowing it into field bins for transport to the distillery
(Plate 11).
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,

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