Organic Agriculture.
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ORGANIC AGRICULTURE NURTURES SOIL
BIODIVERSITY
Scientific research has demonstrated that organic agriculture significantly
increases the density and species of soil's life. Suitable conditions for
soil fauna and flora as well as soil forming and conditioning and nutrient
cycling are encouraged by organic practices such as: manipulation of
crop rotations and strip-cropping; green manuring and organic
fertilization (animal manure, compost, crop residues); minimum tillage;
and of course, avoidance of pesticides and herbicides use.
Benefits of organic management on soil biological activity are
summarized below1:
• Abundant arthropods and earthworms. Organic management
increases the abundance and species richness of beneficial arthropods
living above ground and earthworms, and thus improves the growth
conditions of crops. More abundant predators help to control harmful
organisms (pests). In organic systems the density and abundance of
arthropods, as compared to conventional systems, has up to 100% more
carabids, 60-70% more staphylinids and 70-120% more spiders. This
difference is explained by prey deficiency due to pesticide influence as
well as by a richer weed flora in the standing crop that is less dense than
in conventional plots. In the presence of field margins and hedges,
beneficial arthropods are further enhanced, as these habitats are
essential for over-wintering and hibernation. The biomass of earthworms
in organic systems is 30-40% higher than in conventional systems, their
density even 50-80% higher. Compared to the mineral fertilizer system,
this difference is even more pronounced.
• High occurrence of symbionts. Organic crops profit from root
symbioses and are better able to exploit the soil. On average, mycorrhizal
colonization of roots is highest in crops of unfertilized systems, followed
by organic systems. Conventional crops have colonization levels that are
30% lower. The most intense mycorrhizal root colonization is found in
grass-clover, followed by the vetch rye intercrop. Roots of winter wheat
are scarcely colonized. Even when all soils are inoculated with active
micorrhizae, colonization is enhanced in organic soil. This indicates that,
even at an inoculum in surplus, soil nutrients at elevated levels and plant
protection suppress symbiosis. This underlines the importance of
appropriate living conditions for specific organisms.
• High occurrence of micro-organisms. Earthworms work hand in
hand with fungi, bacteria, and numerous other microorganisms in soil. In
organically managed soils, the activity of these organisms is higher.
Micro-organisms in organic soils not only mineralize more actively, but
also contribute to the build up of stable soil organic matter (there is less
untouched straw material in organic than in conventional soils). Thus,
nutrients are recycled faster and soil structure is improved. The amount of
microbial biomass and decomposition is connected: at high microbial
biomass levels, little light fraction material remains undecomposed and
vices versa.
• Microbial carbon. The total mass of micro-organisms in organic
systems is 20-40% higher than in the conventional system with manure
and 60-85% than in the conventional system without manure. The ratio of
microbial carbon to total soil organic carbon is higher in organic system
as compared to conventional systems. The difference is significant at 60
cm depth (at 80 cm depth, no difference is observed). Organic
management promotes microbial carbon (and thus, soil carbon
sequestration potential).
• Enzymes. Microbes have activities with important functions in the
soil system: soil enzymes indicate these functions. The total activity of
micro-organisms can be estimated by measuring the activity of a living
cell-associated enzyme such as dehydrogenase. This enzyme plays a
major role in the respiratory pathway. Proteases in soil, where most
organic N is protein, cleave protein compounds. Phosphatases cleave
organic phosphorus compounds and thus provide a link between the
plant and the stock of organic phosphorus in the soil. Enzyme activity in
organic soils is markedly higher than in conventional soils. Microbial
biomass and enzyme activities are closely related to soil acidity and soil
organic matter content.
• Wild flora. Large organic fields (over 15 ha) featured flora six times
more abundant than conventional fields, including endangered varieties.
In organic grassland, the average number of herb species was found to
be 25 percent more than in conventional grassland, including some
species in decline. Vegetation structure and plant communities in organic
grassland are more even and more typical for a specific site than in
conventionally managed systems. In particular, field margin strips of
organic farms and semi-natural habitats conserve weed species listed as
endangered or at risk of extinction. Animal grazing behaviour or routing
activity (e.g. pigs) was found important in enhancing plant species
composition. Weeds (often sown in strips in organic orchards to reduce
the incidence of aphids) influence the diversity and abundance of
arthropods and flowering weeds are particularly beneficial to pollinators
and parasitoids.
• High-energy efficiency. Organic agriculture follows the ecosystem
theory of closed (or semi-closed) nutrient cycle on the farm. Organic land
management allows the development of a relatively rich weed-flora as
compared to conventional systems. Some "accompanying plants" of a
crop are desired and considered useful in organic management. The
presence of versatile flora attracts beneficial herbivores and other air-
borne or above-ground organisms. Their presence improves the
nourishment of predatory arthropods. When comparing diversity and the
demand of energy for microbial maintenance (as indicated by the
metabolic quotient), it becomes evident that diverse populations need
less energy per unit biomass. A diverse microbial population, as present
in the organic field plots, may divert a greater part of the available carbon
to microbial growth rather than maintenance. In agricultural practice this
may be interpreted as an increased turnover of organic matter with a
faster mineralization and delivery of plant nutrients. Finally, more organic
matter is diverted to build-up stable soil humus.
• Erosion control: Organic soil management improves soil structure
by increasing soil activity and thus, reduces erosion risk. Organic matter
has a positive effect on the development and stability of soil structure.
Silty and loamy soils profit from organic matter by an enhanced
aggregate structure. Organic matter is adsorbed to the charged surfaces
of clay minerals. The negative charge decreases with increasing particle
size. Silt is very susceptible to erosion since it is not charged, but organic
matter layers on the silt surface favor aggregates with silt too.
MAINSTREAMING ORGANIC AGRICULTURE
In line with the Convention on Biological Diversity, organic agriculture can
enhance the value of biological diversity by linking conservation efforts
with social and economic benefits. Decision III/11 on Conservation and
Sustainable Use of Agricultural Biological Diversity "encourages the
development of technologies and farming practices that not only increase
productivity, but also arrest degradation as well as reclaim, rehabilitate,
restore and enhance biological diversity and monitor adverse effects on
sustainable agricultural biodiversity" such as "inter alia, organic farming".
Target 12 of the Global Strategy for Plant Conservation of the Convention
on Biological Diversity (i.e., "30 per cent of plant-based products derived
from sources that are sustainably managed") identifies organic
agriculture as a main indicator to monitor progress towards this target.
Organic agriculture meets precise standards which are verified through
certification; in 2002, the International Federation of Organic Agriculture
Movements has included "organic ecosystems", with specific biodiversity
parameters, within its International Basic Standards for Organic
Production and Processing.
Improved awareness on the potential of organic agriculture to provide
food while conserving biodiversity offers both a practical option to
implement commitments made by governments to the Convention on
Biological Diversity as well as more coherence to national policies (and
related support) to agriculture and environment schemes.