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.
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: https://attra.ncat.org/product/organic-crop-production-overview/)
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.
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")