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Criticisms and Frequent Misconceptions about Organic Agriculture: The Counter-Arguments |
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Misconception Number 12: In tropical developing countries, the surplus of organic matter that can be returned to the soil is too small and mineralization of organic matter is too quick to provide sufficient nutrient inputs to the plants. Therefore, the only way to avoid depletion of agricultural soils is to provide them with regular synthetic fertilizer inputs.
Summary of Counter-Arguments:
- Organic matter is crucial to soil fertility. Synthetic fertilizers are not substitutes for organic matter.
- Organic agricultural techniques enable farmers to maximize production and use of organic matter.
- The use of various non-chemically processed mineral fertilizers (such as rocks) is allowed in Organic Agriculture if necessary to complement nutrient inputs from organic matter sources.
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Details of Counter-Arguments:
The agronomic importance of organic matter cannot be overemphasized and
accelerated degradation of soil organic matter in tropical areas is indeed
a challenge in the aim of obtaining high productivity, but synthetic
fertilizers are no substitute for organic matter. Organic matter
contributes substantially to nutrient supply, cation exchange capacity
(CEC), and favorable soil structure. A
loss of soil organic matter due to unsustainable agricultural practices
mines the soil fertility in a way for which mineral fertilizers can not compensate.
In soils that are depleted of organic matter, application of single compound
mineral fertilizers remains ineffective because the low CEC of the soils and
limited availability of other nutrients (e.g., micronutrients) often
become the limiting factors.
In addition, synthetic fertilizer use has not been proven as an
economically sustainable way of improving soil fertility and yields in
Africa and parts of Asia, partly because it is too expensive and risky to
use for poor farmers faced with poor infrastructure and risky rainfall
patterns, and partly because relying on synthetic fertilizers might work
in the short term, but it depletes the soils in the long term. Therefore, it is crucial to improve the use of locally available resources
and to build soil organic matter content as much as possible.
The production of organic matter is generally not a constraint in
the semi-humid or humid tropics. In fact, the humid tropics have more potential for organic matter
production than temperate regions due to year-around plant growth. However,
the availability of organic matter resources for agriculture might be
reduced by other competing uses such as fuel and house construction.
Appropriate technologies, such as solar cookers, are yet to be developed
and disseminated to reduce this competition.
The production of organic matter is mainly a constraint in arid and
semi-arid tropics, where the low availability of water limits plant
growth. Despite these constraints, farmers in these areas sometime waste
organic matter by burning crop residues. They may also not use all
available organic matter that could be added to the soils through mulching
or other techniques. In many farming
systems with livestock, the manure deposited in the night kraals (or
in stables in the case of zero grazing) is often not returned to the
cultivated fields, but left to decompose in a small area. With improved
transportation and targeted application techniques (such as planting pits
often promoted in African organic projects), this manure resource could
contribute to building soil organic matter. Organic agriculture, through the emphasis on building soil
fertility with organic matter inputs, can help farmers make better use of
existing organic matter sources.
In the semi-arid Great Plains of
Colorado, organic management has enabled
increases in the organic matter content of soil and has maintained or
increased the stocks of macro and some micro nutrients available to the
plants. [1] Although there are
many examples of such promising results, more research is
needed on organic techniques that can help increase production of organic
matter on the farm, especially in dry areas. Some studies have shown
that there are promising leguminous plants that can be cultivated in very
dry conditions, for instance during the dry season in semi-arid regions,
and produce a substantial amount of organic matter and serve to fix nitrogen.
One example of this is the Jack beans (Canavalia
ensiformis) that will grow where either the climate is so dry or the
soils so poor that virtually nothing else will grow. [2]
This plant and other leguminous crops (e.g., Crotalarias and Mucuna)
provide especially large amounts of biomass that can be used as reliable
supplies of organic matter.
The degradation of organic matter is determined by the quality of
the added material, the soil water content, and the soil temperature. In
semi-arid areas degradation is often delayed due to low soil water
content. Many organic materials are rather recalcitrant to degradation,
including phenol- and tannin-rich, leguminous tree leaves. Moreover, the use of certain organic techniques can
help address the problem of quick mineralization. For instance, the
use of hedgerows can slow down mineralization, due to the lower
degradability of leaves and twigs.
Finally, the use of various
non-chemically processed mineral fertilizers (such as rocks) is allowed in
Organic Agriculture, if they are used with the aim of addressing
long-term fertility needs.
[1] Long-term Organic Farming Impacts on Soil Fertility, by Jessica G. Davis, Jami Daniel, and Lew Grant, Paper presented at the 18th World Congress of Soil Science July 9-15, 2006 - Philadelphia, Pennsylvania, USA.
[2] http://www.agroforestry.net/overstory/overstory29.html.
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