There is little doubt that organic farming methods improve bio-diversity and long term sustainability.
The benefits to farmers include:
Lower costs
Improved soil conditions
More species of plants
More species of animals
More species of helpful insects
From Wikipedia:
Organic farming and biodiversity
The effect of
organic farming
has been a subject of interest for researchers. Theory suggests that
organic farming practices, which exclude the use of most synthetic
pesticides and fertilizers, may be beneficial for biodiversity.
This is
generally shown to be true for soils scaled to the area of cultivated
land, where species abundance is, on average, 30% richer than that of
conventional farms. However, for crop yield-scaled land the effect of
organic farming on biodiversity is highly debated due to the
significantly lower yields compared to conventional farms.
In ancient farming practices, farmers did not possess the technology
or manpower to have a significant impact on the destruction of
biodiversity even as mass-production agriculture was rising.
Nowadays,
common farming methods generally rely on pesticides to maintain high
yields. With such, most agricultural landscapes favor mono-culture crops
with very little flora or fauna co-existence (van Elsen 2000). Modern
organic farm practices such as the removal of pesticides and the
inclusion of animal manure,
crop rotation, and multi-cultural crops provides the chance for biodiversity to thrive.
Benefits to biodiversity
Nearly
all non-crop, naturally occurring species observed in comparative farm
land practice studies show a preference in organic farming both by
population and richness.
Spanning all associated species, there is an average of 30% more on
organic farms versus conventional farming methods, however this does not
account for possible
loss of biodiversity due to decreased yields.
Birds, butterflies, soil microbes, beetles, earthworms, spiders,
vegetation, and mammals are particularly affected. Some organic farms
may use less pesticides and thus biodiversity fitness and population
density may benefit.
Larger farms however tend to use pesticides more liberally and in some cases to larger extent than conventional farms. Many weed species attract beneficial insects that improve soil qualities and forage on weed pests.
Soil-bound organisms often benefit because of increased bacteria
populations due to natural fertilizer spread such as manure, while
experiencing reduced intake of herbicides and pesticides commonly
associated with conventional farming methods.
Increased biodiversity, especially from soil microbes such as
mycorhizzae, have been proposed as an explanation for the high yields
experienced by some organic plots, especially in light of the
differences seen in a 21-year comparison of organic and control fields.
Impact of increased biodiversity
The
level of biodiversity that can be yielded from organic farming provides
a natural capital to humans. Species found in most organic farms
provides a means of agricultural sustainability by reducing amount of
human input (e.g. fertilizers, pesticides).
Farmers that produce with organic methods reduce risk of poor yields by
promoting biodiversity. Common game birds such as the ring-necked
pheasant and the northern bobwhite often reside in agriculture
landscapes, and are a natural capital yielded from high demands of
recreational hunting.
Because bird species richness and population are
typically higher on organic farm systems, promoting biodiversity can be
seen as logical and economical.
Highly impacted animal species
Earthworms
Earthworm
population and diversity appears to have the most significant data out
of all studies. Out of six studies comparing earthworm biodiversity to
organic and conventional farming methods, all six suggested a preference
for organic practices including a study at the pioneering Haughley farm
in 1980/1981 that compared earthworm populations and soil properties
after 40 years.
Hole et al. (2005) summarized a study conducted by Brown (1999) and
found nearly double the population and diversity when comparing farming
methods.
Birds
Organic
farms are said to be beneficial to birds while remaining economical.
Bird species are one of the most prominent animal groups that benefit
from organic farming methods. Many species rely on farmland for
foraging, feeding, and migration phases. With such, bird populations
often relate directly to the natural quality of farmland.
The more
natural diversity of organic farms provides better habitats to bird
species, and is especially beneficial when the farmland is located
within a migration zone. In 5 recent studies almost all bird species
including locally declining species, both population and variation
increased on organic farmland,.
Making a switch from conventional farming methods to organic practices also seems to directly improve bird species in the area.
While organic farming improves bird populations and diversity, species
populations receive the largest boost when organic groups are varied
within a landscape. Bird populations are increased further with optimal
habitat for biodiversity, rather than organic alone, with systems such
as Conservation Grade.
Butterflies
A
specific study done in the UK in 2006 found substantially more
butterflies on organic farms versus standard farming methods except for
two pest species. The study also observed higher populations in
uncropped field margins compared with cropland edges regardless of farm
practice. Conversely, Weibull et al. (2000) found no significant differences in species diversity or population.
Spiders
Ten
studies have been conducted involving spider species and abundance on
farm systems. All but three of the studies indicated that there was a
higher diversity of spider species on organic farms, in addition to
populations of species. Two of the studies indicated higher species
diversity, but statistically insignificant populations between organic
and standard farming methods.
Soil Microbes
Out
of 13 studies comparing bacteria and fungus communities between organic
and standard farming, 8 of the studies showed heightened level of
growth on organic farm systems. One study concluded that the use of
“green” fertilizers and manures was the primary cause of higher
bacterial levels on organic farms.
On the other hand, nematode
population/diversity depended on what their primary food intake was.
Bacteria-feeding nematodes showed preference towards organic systems
whereas fungus-feeding nematodes showed preference for standard farm
systems.
The heightened level of bacteria-feeding nematodes makes sense
due to higher levels of bacteria in organic soils, but the
fungus-feeding populations being higher on standard farms seems to
contradict the data since more fungi are generally found on organic
farms.
Beetles
According
to Hole et al. (2005), beetle species are among the most commonly
studied animal species on farming systems. Twelve studies have found a
higher population and species richness of carabids on organic systems.
The overall conclusion of significantly higher carabid population
species and diversity is that organic farms have a higher level of weed
species where they can thrive.
Staphylinid
populations and diversity have seemed to show no specific preference
with some studies showing higher population and diversity, some with
lower population and diversity, and one study showed no statistical
significance between the organic and conventional farming systems.
Mammals
Two
comparative studies have been conducted involving mammal populations and
diversity among farm practices. A study done by Brown (1999) found that
small mammal population density and diversity did not depend on farming
practices, however overall activity was higher on organic farms.
It was
concluded that more food resources were available to small mammals on
organic farms because of the reduction or lack of herbicides and
pesticides.
Another study conducted by Wickramasinghe et al. (2003)
compared bat species and activity. Species activity and foraging were
both more than double on organic farms compared to conventional farms.
Species richness was also higher on organic farms, and 2 of the sixteen
species sighted were found only on organic farms.
Vegetation
Approximately
ten studies have been conducted to compare non-crop vegetation between
organic and conventional farming practices. Hedgerow, inner-crop and
grassland observations were made within these studies and all but one
showed a higher weed preference and diversity in or around organic
farms.
Most of these studies showed significant overall preference for
organic farming preferences especially for broad-leafed species, but
many grass species showed far less on conventional farms likely because
pesticide interaction was low or non-existent.
Organic farm weed
population and richness was believed to be lower in mid-crop land
because of weed-removal methods such as under sowing.
Switching from conventional to organic farming often results in a
“boom” of weed speciation due to intense chemical change of soil
composition from the lack of herbicides and pesticides. Natural plant
species can also vary on organic farms from year-to-year because crop
rotation creates new competition based on the chemical needs of each
crop.
Farmers’ Benefits from Increased Biodiversity
Biological
research on soil and soil organisms has proven beneficial to the system
of organic farming. Varieties of bacteria and fungi break down
chemicals, plant matter and animal waste into productive soil nutrients.
In turn, the producer benefits by healthier yields and more arable soil
for future crops.
Furthermore, a 21-year study was conducted testing the effects of
organic soil matter and its relationship to soil quality and yield.
Controls included actively managed soil with varying levels of manure,
compared to a plot with no manure input.
After the study commenced,
there was significantly lower yields on the control plot when compared
to the fields with manure. The concluded reason was an increased soil
microbe community in the manure fields, providing a healthier, more
arable soil system.
Detriments to biodiversity through organic farming
Organic
farming practices still require active participation from the farmer to
effectively boost biodiversity. Making a switch to organic farming
methods does not automatically or guarantee improved biodiversity.
Pro-conservation ethics are required to create arable farm land that
generates biodiversity.
Conservationist ideals are commonly overlooked
because they require additional physical and economical efforts from the
producer.
Common weed-removal processes like undercutting and controlled burning
provides little opportunity for species survival, and often leads to
comparable populations and richness to conventionally managed landscapes
when performed in excess.
Another common process is the addition of
biotopes
in the form of hedgerows and ponds to further improve species richness.
Farmers commonly make the mistake of over-using these resources for
more intense crop production because organic yields are typically lower.
Another error comes from the over-stratification of biotopes. A series
of small clusters does not provide adequate land area for high
biodiversity potential.
Here is the Wikipedia
page