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University of California-
Davis researchers comparing long-term farming systems found
that organic safflower yields equaled conventional safflower
over 10 years.
–Photo courtesy of University of California-Davis |
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Designing a farming system to tie together principles of sustainability
and productivity is complex. Organic farmers must consider how the
various components of their system - rotations, pest and weed management,
and soil health - will maintain both productivity and profitability.
This section outlines the major principles incorporated into organic
farming systems.
Rotations
Although practices vary from farm to farm and region to region, at the core
of any successful annual organic farming system is the crop rotation. According
to "Cereal-Legume Cropping Systems: Nine Farm Case Studies in the Dryland
Northern Plains, Canadian Prairies, and Intermountain Northwest," productive
rotations:
 Enhance
soil conservation and build soil organic matter;
Provide
weed, disease and insect control;
Enhance
water quality and conservation, biological diversity and wildlife
habitat; and
Ensure
economic profitability for the farming system.
As the main management tool for all aspects of the farming system - including
weeds, pests, insects, soils, and crop production - a well-planned rotation
is more than the sum of its parts, addressing the connections between all of
those factors. For example, successful rotations, according to "Switching
to a Sustainable System" by Fred Kirschenmann:
Include
the use of cover crops to provide fertility, control weeds and
provide habitat for beneficial insects;
Have
a diversity of plant species to encourage natural predators, discourage
pest and disease build-up, and minimize economic and environmental
risk;
Provide
a balance between soil conservation and crop production by adding
organic matter to the soil to both supply nutrients and improve
soil quality properties such as water infiltration and water holding
capacity; and
Provide
weed control by alternating between warm and cool weather plants
and including weed inhibiting plants (such as rye and sorghum).
Newark, N.Y., organic vegetable farmer Elizabeth Henderson, who farms 15 acres,
considers rotations featuring summer and winter cover crops a key component
of her successful system and relies on them to minimize erosion, maintain and
build soil quality, and control pests.
For agronomic crops, a standard organic corn belt rotation of alfalfa, corn,
soybeans and small grain accomplishes multiple functions because:
The
legumes fix nitrogen, providing for the subsequent non-legumes
in the rotation;
Several
pest cycles are interrupted, especially that of the northern and
western rootworm species, which can be devastating to corn;
Several
plant diseases are suppressed, including soybean cyst nematode;
and
Weed
control is enhanced when perennial weeds are destroyed through
cultivation of annual grains; most annual weeds are smothered
or eliminated by mowing when alfalfa is in production.
(From ATTRA's Overview of Organic Crop Production, available at:
http://attra.ncat.org/attra-pub/summaries/organiccrop.html
or call (800) 346-9140.)
For some farmers, switching to an organic rotation may not be more difficult
than expanding upon or changing the timing in an existing rotation. When Lydia
and Dennis Poulsen of Snowville, Utah, decided to convert their 800-acre beef,
hay and small grain operation to organic, making the switch was much easier
than expected.
"An organic dairy was coming and they needed feed," recalled Poulsen.
"We had alfalfa in our original rotation and we were already trying alternatives
to make the ground healthier." Because their alfalfa-wheat-oat hay rotation
fit right into an organic system plan, the only substantial change they made
on their ranch was to plow in alfalfa as green manure for their subsequent wheat
crop, rather than letting the cows mow down the alfalfa in its final year.
Soils
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Jack Lazor of Butterworks
Farm in Westfield, Vt., shows the end product of composted dairy
manure, which he uses to build soil organic matter, during one
of his popular pasture walks.
– Photo by Lisa McCrory |
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Along with developing a successful rotation, ensuring healthy soil
is imperative to a profitable and successful organic system.
"A lot of people don't think of the soil as an ecosystem but,
in fact, it's probably the most complex ecosystem on earth,"
said Ray Weil, a University of Maryland soil science professor.
"A healthy soil should be breathing out carbon dioxide, breathing
in oxygen. It should hold and absorb water so the plants can survive
between rains. It should resist erosion."
By contrast, a less healthy soil can wash away and pollute surface waters.
From a production standpoint, poor quality soil can limit plant growth and vigor.
In organic farming systems, the majority of nutrients are supplied from organic
matter additions such as compost, manures and cover crops. These amendments
not only feed the plants, but the soil organisms as well. As soil organic matter
accumulates, soil structure improves, and populations of other important soil
organisms, such as earthworms - which tunnel through the soil, improving aeration
and infiltration - increase. Those organisms break down organic material to
release nutrients at a steady pace so they are available for plant uptake. Soil
microorganisms also hold nutrients in a more stable form so they are less susceptible
to being lost - through leaching, soil erosion or runoff.
The soil is a virtual microscopic zoo of organisms. Soil biologists are just
beginning to tease apart how those organisms function in organic farming systems.
Numerous studies show that organic systems have higher microbial populations
and activity. The long-term SAFS trial in California's Central Valley comparing
organic and conventional farming systems in a tomato, bean, corn and safflower
rotation found significantly higher microbial populations and activity in organic
systems than the conventional ones. New research from North Carolina State University
shows that increases in microbial populations and microbial activity may occur
by the first or second year of the transition to an organic system.
Researchers also are discovering that they can improve fertility in organic
systems by micro-managing the soil fauna. In the SAFS experiment, researchers
studied the role of bacteria-feeding "good" nematodes, small soil
organisms that help make nitrogen available to plants. The researchers found
that by irrigating plots in the fall to improve cover crop germination, the
nematode population increased. This higher beneficial nematode population led
to more nitrogen release from the cover crop in the spring. The nematodes also
stored nitrogen over the winter that might otherwise have been lost.
Cover crops, an essential part of organic systems for soil building and soil
fertility, also benefit the soil by improving soil structure, which in turn
improves water infiltration and water-holding capacity. The long-term systems
trial at UC-Davis proved some of those benefits dramatically, such as 50 percent
higher water infiltration and 35 percent lower runoff in the organic plots.
"Nobody could have possibly predicted such a dramatic difference in the
water runoff and infiltration between the organic and conventional systems,"
said SAFS project leader Steve Temple. "It's given us a new appreciation
of the importance of cover cropping and residue management."
Cover crops planted after a crop is harvested - also known as catch crops -
recover nutrients that would otherwise leach into the subsoil and groundwater.
Cover crops prove invaluable to organic growers who don't have access to affordable
sources of compost and manure. A study of potato production in Idaho found that
legumes such as alfalfa, pea and pea-oat hay could provide 80 to 100 percent
of nitrogen needed for a potato crop, and if harvested for feed or seed, 40
to 60 percent of the required nitrogen for the subsequent crop. Similarly, a
northern California research project showed a nitrogen replacement value of
150 pounds per acre with cover crops.
Carmen Fernholz, who grows organic barley, oats, wheat, flax, corn, soybeans
and alfalfa on his 410-acre west central Minnesota farm, manages a three-year,
four-year or even longer rotation heavily reliant upon cover crops. Without
exception, he underseeds all of his small grains with a legume crop, such as
red clover or annual or perennial alfalfa. After harvesting the small grain,
he allows the underseeded legume cover crop to serve as a green manure - or,
with perennial alfalfa, as a cash crop. The number of seasons for the perennial
alfalfa will depend on the weed and nutrient histories of the particular field.
"Cover crops, coupled with my managed applications of animal manures,
have become the mainstay of my soil nutrient-building management plan,"
Fernholz said. "They are the foundation of my rotation because they supply
a significant portion of the nitrogen needed for crops such as corn and wheat.
They are a reliable, nature-friendly, easily managed fix between my cash crops."
Organic farmers also use manures and composts regularly, especially when they
are accessible and affordable. Many organic farmers make their own compost,
either by using livestock manure from their own operations or from a nearby
source and combining it with straw or wood shavings. Manures and composts provide
many of the same soil-building benefits as cover crops. (Federal regulations
dictate that raw manure may not be applied 90 days prior to harvest if the edible
portion of the crop does not contact the soil, or 120 days prior to harvest
if the edible portion of the crop does contact the soil).
Vollmer, the North Carolina tobacco farmer who converted to organic strawberry
production, ripped into "The Secret Life of Compost" by Malcolm Beck
to learn how to make his own compost. He uses horse manure, wood shavings, oat
straw and any other suitable materials he can find.
Compost provides many other benefits, too. Since transitioning to organic,
said Vollmer, "I'm able to see improvements in the soil - the pH has risen
from 5.2 to 6.7, I don't need to add lime, the water holding capacity has increased,
and there's less soil crusting."
(For more information on soil management, see Building Soils
for Better Crops in "Resources")
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