Special Reports/Organic Farming
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Living with
organic inputs
By Abdul Waheed,
A. Hannan & DrA.M.Ranjha
HEALTHY
soil is a combination of minerals, rock, water, air, organic
matter (plant and animal residue), micro-organisms,
including bacteria, fungi, protozoa and a variety of insects
and worms. In healthy soil this intricate web carries out a
process that continually replenishes the soil and maintains
long-term soil fertility.
Before the use of chemical fertilisers, the earth and
animals worked together to enhance fertility of the soil.
Through the decomposition of raw, natural proteins such as
bone, blood, fish and feathers, soil received the nutrients
needed to maximise fertility. When used with reference to
fertilisers, the word organic generally means that the
nutrients contained in the product are derived solely from
the remains or are a by-product of an organism. Cottonseed
meal, blood meal, fish emulsion, manure and sewage sludge
are examples of organic fertilisers. Urea is a synthetic
organic fertiliser.
There has been much controversy over organic versus
inorganic fertilisers. It is important to realise that
plants do not differentiate between organic and inorganic
fertilisers. Their tiny root hairs can absorb only nutrients
that have been broken down into inorganic, water-soluble
forms. It makes no difference to your tomato plant if the
atom of nitrogen it is absorbing has come from a compost
pile or a fertiliser factory. There are, however, advantages
and disadvantages to each form of fertiliser, organic and
inorganic. The primary advantage of using packaged
commercial fertiliser is that nutrients are immediately
available to plants. As well, the exact amounts of a given
element can be calculated and given to plants.
Commercial fertiliser, especially nitrogen, is easily washed
below the level of the plant's root system through leaching
of rain or irrigation. An application which is too heavy or
too close to the roots of plants may cause "burning"
(actually a process of desiccation by chemical salts in
fertiliser). As well, heavy applications of commercial
fertilisers can build up toxic concentrations of salts in
the soil, thus creating chemical imbalances. If organic
materials are readily available and cheap, the expense of
the commercial fertiliser should also be considered.
There is less danger of over-fertilisation by adding
decomposed organic material to a garden. It provides a slow
release of nutrients as micro-organisms in the soil break
the organic material down into an inorganic, water soluble
form which the plants can use. The addition of organic
material improves soil structure or "workability" immensely.
It also vastly improves the water-holding capacities of
sandy soils, a distinct advantage in arid climates such as
ours.
Organic fertiliser is not immediately available to plants.
As noted above, this "slow- release" feature can be an
advantage. However, if there is an immediate need for
nutrients, organic fertiliser cannot supply them in a hurry.
Furthermore, information on the amount of nutrients and the
exact elements in an organic fertiliser such as manure is
not readily available to the home gardener. In contrast,
when you apply manufactured inorganic fertiliser you know
the kinds and amounts of the elements it contains, and this
allows you to be more precise in meeting a plant's
nutritional needs.
The possibility of nitrogen depletion is another drawback of
organic fertilisers. Because of complex bacterial action,
the addition of a large amount of organic material can cause
a temporary nitrogen depletion in the soil and therefore in
plants.
Compared to synthetic fertiliser formulations, organic
fertilisers contain relatively low concentrations of actual
nutrients, but they perform important functions which the
synthetic formulations do not. They increase the organic
content and consequently the water-holding capacity of the
soil. They improve the physical structure of the soil which
allows more air to get to plant roots. Where organic sources
are used for fertiliser, bacterial and fungal activity
increases in the soil. Mycorrhizal fungi, which make other
nutrients more available to plants, thrive in soil where the
organic matter content is high. Organically derived plant
nutrients are slow to leach from the soil making them less
likely to contribute to water pollution than synthetic
fertilisers.
Some organic fertilisers are high in one of the three major
nutrients (nitrogen, phosphorus, or potash,) but low or zero
in the other two. Some are low in all three macronutrients.
A few organic products can be purchased "fortified" for a
higher nutrient analysis. The ingredients used to fortify
organic fertilisers are organic materials; for example, rock
phosphate to increase phosphorus, or greensand to increase
potash.
Organic fertilisers depend on soil organisms to break them
down to release nutrients; therefore, most are effective
only when soil is moist and warm enough for the
micro-organisms to be active. Nutrient release by microbial
activity, in general, occurs over a fairly long time period.
One potential drawback is that the organic fertiliser may
not release enough of their principal nutrient when the
plant needs it for growth.
Cottonseed meal is a by-product of cotton manufacturing. As
a fertiliser, it produces a somewhat acidic reaction.
Consequently, it is frequently used for fertilising
acid-loving plants such as azaleas, camellias, and
rhododendrons. Formulas vary slightly, but generally,
cottonseed meal contains seven per cent nitrogen, three per
cent phosphorus, and two per cent potash. Nutrients are most
readily available to plants in warm soils, but there is
little danger of burn.
Blood meal is dried, powdered blood collected from cattle
slaughterhouses. It is a rich source of nitrogen, so rich,
in fact, that it may burn plants if used in excess.
Gardeners must be careful not to exceed the recommended
amount suggested on the label. In addition to nitrogen,
blood meal supplies some essential trace elements, including
iron.
Fish emulsion, a balanced, organic fertiliser, is a
partially decomposed blend of finely pulverised fish. A
strong odour is associated with most brands of fish emulsion
fertiliser, but the smell dissipates within a day or two.
Recently, deodorised brands have been developed. Fish
emulsion is high in nitrogen and is a source of several
trace elements. Contrary to popular belief, too strong a
solution can burn plants, particularly those growing in
containers. In the late spring, when garden plants have
sprouted, an application of fish emulsion followed by a deep
watering will boost the plants' early growth spurt.
Manure is a complete fertiliser, but low in amount of
nutrients it supplies. Manures vary in nutrient content
according to animal source and what the animal has been
eating. A fertilizer ratio of 1-1-1 is typical. Commonly
available manures include horse, cow, chicken and sheep (one
should avoid using pig, dog or cat faeces because of the
problems involved with internal parasitic worms which may be
transferred to human beings).
The highest nutritional concentration is found in manure
when it is fresh. As it is old, exposed to weather, or
composted, nutrient content is reduced. However, most
gardeners prefer to use composted forms of manure to ensure
lesser amounts of salts, thereby reducing the chance of
burning plant roots. Because of its low concentration of
plant nutrients, manure is best used as a soil conditioner
instead of a fertiliser. Typical rates of manure
applications vary from a moderate 70 pounds per 1000 square
feet to as much as one ton per 1000 square feet.
Sewage sludge is a recycled product of municipal sewage
treatment plants. Two forms are commonly available—activated
and composted. Activated sludge has higher concentrations of
nutrients (approximately 6-3-0) than composted sludge. It is
usually sold in a dry, granular form for use as a general
purpose, long lasting, non-burning fertiliser. Composted
sludge is used primarily as a soil amendment and has a lower
nutrient content (approximately 1-2-0).
There are some questions about the long-term effects of
using sewage sludge products in the garden, particularly
around edible crops. Heavy metals such as cadmium, sometimes
present in the sludge, may build up in the soil. Possible
negative effects vary with the origin of the sludge and with
the characteristics of the soil where it is used.
When packaged as fertilisers, organic products have the
fertiliser ratio stated on the package label. Some organic
materials, particularly composted manures and sludge, are
sold as soil conditioners and do not have a nutrient
guarantee stated on the package, although small amounts of
nutrients are present.
Whereas positive effects of use of fertiliser on environment
are often overlooked, attention now a days is focussed on
negative aspects. Mineral and organic fertilisers are
considered harmful.
Mineral and organic fertilisers accumulate dangerous or even
toxic substances in soil from their constituents, e.g. Cd
from mineral phosphate fertilisers or from town or
industrial waste products;
They cause eutrophication of surface water, with its
negative effect on oxygen supply (damaging fish and other
forms of animal life);
Nitrate accumulation in ground water, thus diminishing the
quality of drinking water;
They cause unwanted enrichment of atmosphere with ammonia
from organic manures and mineral fertilisers, and with N2O
from de-nitrification of excessive or wrongly placed
nitrogenous fertiliser.
As to contamination of soils with toxic heavy metals, it can
easily be shown that mineral fertilisers make only a rather
small contribution in comparison with, for example, town
wastes. However, as soil fertility must be considered in the
very long term and not only in decades or centuries, the
annual addition should be kept at such a low level that the
enrichment is negligible. Industrial waste products should
always be carefully checked to determine whether they
contain potentially toxic substances, and appropriate
critical limits should be established.
Courtesy: The
DAWN |
Pakissan.com;
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