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| The Neem
Tree (Azadirachta indica A. juss) and its derivatives
have great relevance in organic farming practices.
This remarkable tree has been identified as a renewable
resource for home grown agro-chemicals and nutrients
which are bio - degradable, non-toxic and effective.
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| Long before
synthetic chemicals and commercial insecticides
and fertilizers were available, Neem derivatives
were used in Indian villages to protect and nourish
crops. Scientific research has shown that Neem extracts
can influence nearly 400 species of insects. |
| It is
significant that some of these pests are resistant
to pesticides, or are inherently difficult to control
with conventional pesticides. (floral thrips, diamond
back moth and several leaf miners). Most Neem products
belong to the category of medium to broad spectrum
pesticides, i.e., they are effective over a wide
range of pests. |
| Using
neem derivatives for managing pests is a non-violent
approach to controlling pests. Neem products work
by intervening at several stages of the insect's
life. They may not kill the pest instantaneously
but incapacitate it in several ways. Neem very subtly
employs effects such as repellence, feeding and
ovipositional deterrence, growth inhibition, mating
disruption, chemo-sterilization, etc. These are
now considered far more desirable than a quick knock-down
in integrated pest management programs as they reduce
the risk of exposing pests' natural enemies to poisoned
food or starvation. |
| The action
of Neem products fulfills all priorities among environmental
objectives. This unique tree is perhaps the most
significant example of how nature can combine diverse
functions i.e., the action of de-oiled Neem cake
as a pesticide cum fertiliser. |
| Chemistry
of Neem for Organic Farming |
| Neem
plants, as do all other plants, contain several
thousands of chemicals. Of special interest are
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 Azadirachtin. 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 azadirachtin (A-K) have been isolated,
the most abundant of which is Azadirachtin-A. |
| The Neem
terpenoids are present in almost all parts of the
plant, in the living tissues. Recently, the site
of synthesis and accumulation of Neem chemicals
has been identified as secretory cells. Secretory
cells are most abundant in the seed kernels. |
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| Good soil fertility
means good crop yields. Preventing the loss of plant
nutrients from an ecosystem is important for soil-fertility
management. Nitrogen, phosphorus, and potassium
(N,P,K) are the three major elements which determine
soil fertility and should be ideally present in
4:2:1 ratio; aberrations affect fertility and therefore
crop yield. Urea, containing 46% of N, is applied
to crops in the largest amounts; but less than half
of this N, in the form of nitrate, is available
to the crops. |
| The rest is lost
through 'leaching' or by 'volatilization', or by
surface run-off after a heavy shower, (Prasad and
Power 1995). Leaching of soluble nitrates into the
subsoil and, eventually into ground water, is well
known. Nitrate losses of 50 to 70% through leaching
were observed in rice crops in India. |
| Leaching not only
depletes precious nitrate but also takes away clay,
soil, and organic matter, leading to low chemical
soil fertility and low plant-available water reserves.
Ammonia volatilization also can contribute to a
nearly 60% nitrate loss. Loss through volatilization
occurs when the denitrifying bacteria reduce the
nitrate to elemental nitrogen and nitrous oxide
which escape to the stratosphere and cause ozone
depletion and also contribute to greenhouse warming.
On the other hand, nitrate build-up in drinking
water can reduce the blood's ability to transport
oxygen, especially if the nitrates are converted
into nitrites (blue-baby syndrome). Even ruminants
are vulnerable to nitrate or nitrite poisoning,
leading to poor growth rates, reduced milk production,
and increased susceptibility to infections, and
even abortions. |
| One way to minimise
nitrate loss is to apply the urea more than once
in smaller quantities or, alternatively, to use
a slow-release urea which makes the urea available
in the soil for a longer time. Bains et al. (1971)
in field trials in India found that an accetone
extract of neem kernel was an excellent nitrification
inhibitor, even better than sulfur-coated urea.
Ammonia volatilization, urea hydrolysis, and leaching,
were all reduced when urea was blended or coated
with neem cake. |
| Results from several
field experiments show that neem cake coating of
prilled urea increased nitrogen uptake by 4.5 to
19.4%. The increase in rice yield due to neem cake
coating/blending of prilled urea ranged from 1 to
54%, the average being 9.6%. Neem cake coated urea
applied to rice or sugarcane also left a carryover
effect and increased sugarcane yield by 7% in the
ratoon sugarcane crop . |
| Ready-to-use, neem-based
urea-coating agents, such as 'Nimin' (containing
ca. 5% neem bitter tetranortriterpenoids) are now
commercially available in India. Application of
Nimin-coated urea (1 part Nimin: 100 parts urea,
wt/wt) reduced losses of fertiliser N through leaching
and denitrification by 30-35% and increased yields
in treated crops by up to 25% (Vyas et al. 1996).
The bitters in Nimin delay the denitrification process
up to 30 d by either killing nitrifying bacteria
or suppressing their |
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