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What is Neem?
Introduction
The Neem tree is
indigenous to India. Indians have revered the neem tree for a very
long time. To millions of Indians neem has miraculous powers. For
centuries people of India have used neem twigs for cleaning their
teeth, treated skin infection with neem leaf juice, used it as a
tonic and kept away bugs with different neem extracts. It also
formed part of several rituals. The tree has been used in curing so
many ailments that it has been called "the village pharmacy".
Distribution
Nim or Neem, Azadirachta indica A.Juss belongs to the sub family
: Meliodeae; order: Meliales. It is believed that Neem originated in
Asia and Burma. However the exact origin is uncertain. Some believe
it to be native to the whole Indian subcontinent whereas others are
of the opinion that it belongs to dry forest areas throughout all of
South and Southeast Asia including Pakistan, Sri Lanka, Thailand,
Malaysia and Indonesia.
Neem is now widely distributed in many
countries of the world by cultivation. Indians migrating to African
countries introduced neem into that continent. Neem grows abundantly
between Somalia and Mauritania. Neem has also been introduced into
Fiji Islands and from there it has spread to other South Pacific
islands. Neem is also cultivated in the West Indies, Australia and
some countries of Central and South America. Neem is grown in
Southern Florida and is being established in Southern California and
Arizona in the United States.
In India neem is seldom found in the
forest. It is mostly grown as an avenue or shade tree and in variety
of habitats. Neem is seldom leafless - one of the reasons why it is
prized in India. The Indian subcontinent has nearly eighteen million
neem trees. Most of them line the roadsides or are found clustered
around markets or backyards and provide great relief from the sun.
Neem grows to height of about 20 meters and a girth of 25 meters. It
grows well on dry, stony, clayey and saline soils. It has a strong
root system that extracts nutrients and moisture from poor soils.
Neem grows upto about altitude of 1,500 meters. It can withstand
high temperatures but cannot survive frost.
Agronomy
The compound leaves of neem appear smooth. However, closer
examination of young leaves near the shoot apex will reveal the
presence of resin secreting glands. The lower portions of the leaf
stalk are covered with extra floral nectaries that attract ants.
Damaged tissues of the stem secrete gum. Occasionally a milky white
secretion is noticed from stems prior to flowering and production of
new leaves. It is also well known that the green unripe fruits
secrete a milky white latex, very bitter in taste because of some
limonoids, but apparently free from azadirachtin.
The neem tree flowers
between January and May in India although occasional flowers can be
found on trees during other months, particularly, August-September.
Trees in the southwest bloom first and there is a progression in the
blooming period from the south to north. Flower buds of neem open in
the evening and they are more scented at night and also secrete
nectar that attracts a variety of pollinators. Neem honey is very
popular and this has no azadirachtin.
Neem tree takes
considerable abuse. It can withstand pollarding (repeated topping at
heights above 1.5m) and coppicing (repeated topping at near ground
level) very well. This is possible because of the root system which
is large enough to feed a full grown tree.
A neem tree normally starts fruiting after 3-5 years. In about 10
years it becomes fully productive. From the tenth year onwards it
can produce upto fifty kilograms of fruits annually. It’s lifespan
is about two centuries.
|Neem is easily propagated by seeds. However, the seeds are viable
only for about three weeks after harvest under normal conditions of
storage. Stem and root cuttings can also be used to propagate neem.
Neem tree grows almost anywhere in the low land tropics. Its
performance is best in areas which have an annual rainfall of 400 -
1,200 mm. Even if the maximum shade temperature soars past 50 C it
thrives well. However, it cannot withstand freezing or cold for
long. It grows from sea level up to heights of 1000m. The tap root
of this tree is nearly twice the height of the tree.
Neem grows well in dry infertile sites. It performs well even where
soils are sterile, strong and shallow. Neem also grows well in acid
soils. It is believed that fallen neem leaves which are slightly
alkaline (pH 8.2) are good for neutralizing acidity in the soil. The
neem tree however, cannot withstand waterlogging.
Neem grows rapidly and yield timber for five to seven year. Weeds do
not affect its growth and it can dominate almost all competitions.
Chemistry of Neem
Neem plants, as do all other plants, contain several thousands
of chemicals. Of special interest are the terpenoids that are unique
to neem and some related members of this family. More than a hundred
terpenoids are known from different parts of the neem plant. Of its
biological constituents, the most active and well studied compound
is azadirachin. However, in most traditional preparations of neem as
pesticide or medicine a mixture of neem chemicals are present and
provide the active principles. Several different kinds of
azadirachitins (A to K) have been isolated,the most abundant of
which is Azadirachtin-A.
The neem terpenoids are
present in all parts of the plant, in the living tissues. Recently,
the site of synthesis and accumulation of the neem chemicals has
been identified as secretory cells. Secretory cell are most abundant
in the seed kernels. The secretory cell can be seen with iodine
solution. The bulk of the kernel is actually a pair of cotyledons of
the seed. In general, the kernels contain about 30-40 % oil.
Triterpenoid content of the kernels is about 2.5 to 3%. The
azadirachtin content in the kernels may vary from 0.2 to 0.6%.
Besides the terpenoids, neem also contains more than 20 sulphurous
compounds responsible for the characteristic smell of crushed seeds
and neem oil. The gum of neem contains different kinds of sugars.
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