Approaching agriculture and soil management from an ecological point of view means first understanding the characteristics that comprise strong natural systems. Let’s take a look at overall strategies that can contribute to similar strength of crops, animals, and farms. Then we’ll briefly discuss practices that contribute to creating vital and strong agricultural systems (discussed in more detail in later chapters).
MANAGING SOILS AND CROPS TO MINIMIZE PEST PROBLEMS
It is well established—and known by most farmers—that crop rotation can decrease many disease, insect, nematode, and weed pressures. A few other examples of management practices that reduce pest pressure follow:
- Insect damage can be reduced by avoiding excess inorganic nitrogen levels in soils by using better nitrogen management.
- Adequate nutrient levels reduce disease incidence. For example, calcium applications have reduced diseases in crops such as wheat, peanuts, soybeans, and peppers, while added potassium has reduced the incidence of fungal diseases in crops such as cotton, tomatoes, and corn.
- Damage from insect and disease (such as fungal diseases of roots) can be decreased by lessening soil compaction.
- Severity of root rots and leaf diseases can be reduced with composts that contain low levels of available nitrogen but still have some active organic matter.
- Many pests are kept under control by having to compete for resources or by direct antagonism from other insects (including the beneficials feeding on them). Good quantities of a variety of organic materials help maintain a diverse group of soil organisms.
- Root surfaces are protected from fungal and nematode attack by high rates of beneficial mycorrhizal fungi. Most cover crops help keep mycorrhizal fungi spore counts high and promote higher rates of infection by the beneficial fungi.
- Parasitic nematodes can be suppressed by selected cover crops.
- Weed seed numbers are reduced in soils that have a lot of biological activity, with both microorganisms and insects helping the process.
- Weed seed predation by ground beetles is encouraged by reduced tillage and maintenance of surface residues. Reduced tillage also keeps the weed seeds at the surface, where they are accessible to predation by other organisms, such as rodents, ants, and crickets.
- Residues of some cover crops, such as winter rye, produce chemicals that reduce weed seed germination.
Ecological crop and soil management practices can be grouped under one or more of three overall strategies:
- grow healthy plants with strong defense capabilities
- stress pests
- enhance beneficial organisms
These overall strategies are accomplished by practices that maintain and enhance the habitat both above ground and in the soil. Ecological approaches call for designing the field and farm to take advantage of the inherent strengths of natural systems. Most of this is done prior to, and during, planting a crop and has the goal of preventing problems from developing by contributing to one or more of the three overall strategies. However, there are also routine management practices that occur during the season even if you have done a lot of preventive management. For example, irrigation is frequently needed for high-value crops such as fresh market vegetables—even in humid regions. Also, scouting for pest problems and beneficials should be part of routine management during the season. If an unanticipated problem, such as an insect outbreak, arises, remedial action, such as applying the most ecologically sound pesticide or releasing purchased beneficials into the field, may be required to save the crop.
Ecological principles provide a good framework for sustainable management, but we must also recognize that crop production is inherently an “unnatural” process because we favor one organism (the crop plant) over the competing interests of others. With currently available pesticides, the temptation exists to simply wipe out competitors—for example through soil fumigation— but this creates dependency on purchased materials from off the farm and weakens the overall resiliency of the soil and cropping system. The goal of ecological crop and soil management is to minimize the extent of reactive management (which reacts to unanticipated occurrences) by creating conditions that help grow healthy plants, promote beneficials, and stress pests. The discussion below and in the rest of this book focuses on ways to maintain and enhance habitat in order to promote one or more of the three strategies listed above.
STRONG ECOSYSTEM CHARACTERISTICS
Efficiency. Efficient energy flows are characteristic of natural systems. The sun’s energy captured by green plants is used by many organisms, as fungi and bacteria decompose organic residues and are then fed upon by other organisms, which are themselves fed upon by others higher up the food web. Natural ecosystems also tend to be efficient in capturing and using rainfall and in mobilizing and cycling nutrients. This helps to keep the ecosystem from “running down” because of excessive loss of nutrients and at the same time helps maintain the quality of the groundwater and surface waters. Rainfall tends to enter the porous soil, rather than run off, providing water to plants as well as recharge to groundwater, slowly releasing water to streams and rivers.
Diversity. High biological diversity, both above ground and in the soil, characterizes many natural ecosystems in temperate and tropical regions. It provides nutrients to plants, checks on disease outbreaks, etc. For example, competition for resources and specific antagonisms (such as antibiotic production) from the multitude of soil organisms usually keep soilborne plant diseases from severely damaging a natural grassland or forest.
Self-sufficiency. A consequence of efficiency and diversity in natural terrestrial ecosystems is that they become self-sufficient—requiring only inputs of sunlight and rainfall.
Self-regulation. Because of the great diversity of organisms, outbreaks (or huge population increases) of diseases or insects that severely damage plants or animals are uncommon. In addition, plants have a number of defense mechanisms that help protect them from attack.
Resiliency. Disturbances, such as climate extremes, occur in all ecosystems—natural or not. The stronger ones are more resistant to disturbances and are able to bounce back more quickly.
—MODIFIED FROM MAGDOFF (2007).