8.3: Ecological Principles for Agriculture

Approaching agriculture and soil management from an ecological point of view means first understanding the characteristics that comprise resilient and relatively stable natural systems. Then, let’s take a look at overall strategies that can contribute to similar resilience and health of crops, animals and farms. Finally, 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 crop losses:

• Insect damage can be reduced by avoiding excess inorganic nitrogen levels in soils by using precision 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 insects and diseases (such as fungal diseases of roots) can be decreased by lessening soil compaction.
• The 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 infection by beneficial mycorrhizal fungi. Most cover crops, especially in reduced tillage systems, help keep mycorrhizal fungi spore counts high and promote higher rates of colonization by the beneficial fungi in the following crop.
• Parasitic fungal and nematode infections can be suppressed by selected cover crops.
• Weed seed numbers are reduced in soils that have high 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 soil surface, where they are accessible to predation by other organisms, such as rodents, ants and crickets.
• Residues of some cover crops, such as cereal rye, produce chemicals that reduce weed seed germination.

Ecological crop and soil management practices can be grouped under one or more of three strategies:

• grow healthy plants with strong defense capabilities
• suppress pests
• enhance beneficial organisms

These overall strategies are accomplished by practices that maintain and enhance the habitat both aboveground and belowground. And as the field habitat improves, so does the environment in general: less pollution of groundwater and surface water and more wildlife habitat in and surrounding the field.

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. In other words, it requires forethought and good planning.

Many natural, relatively undisturbed, systems are generally stable, and when disturbed by natural forces such as fire, wind or excess rain they are able to bounce back fairly rapidly. In other words, they are resilient. These resilient systems tend to have similar general characteristics:

Efficient. Natural systems have energy flows that efficiently use resources. 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.

Diverse. High biological diversity, both aboveground and in the soil, characterizes many resilient natural ecosystems in temperate and tropical regions. It provides nutrients to plants, checks on disease outbreaks, etc. For example, a diversity of plants—trees versus understory, grasses versus legumes—captures and supplies different resources. And competition for resources and specific antagonisms (such as antibiotic production) from the multitude of soil organisms usually keeps soilborne plant pathogens from causing diseases in a natural grassland or forest.

Self-sufficient. A consequence of efficiency and diversity in natural terrestrial ecosystems is that they become mainly self-sufficient, requiring only inputs of sunlight and rainfall.

Self-regulating. The great diversity of organisms decreases the risk of outbreaks (or huge population increases) of pathogens or insects severely damaging plants or animals. In addition, plants have a number of defense mechanisms that help protect them from attack.

These ecological characteristics provide a good framework for sustainable management of fields and farms, but we must also recognize that crop production (and even urban landscaping for that matter) is a process that greatly disturbs natural ecosystems in order to favor one or a few organisms (crop plants) over the competing interests of others. And systems are also disturbed in other ways to be able to produce crops. Routine management practices that occur during the season cause disturbances even if you have invested heavily in preventive management. For example, irrigation is frequently needed for high-value crops such as fresh market vegetables, even in humid regions. Some practices have little direct disturbance, such as scouting for pests and beneficial insects 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 reduce crop losses.

With currently available pesticides, the temptation exists to simply wipe out competitors—for example through soil fumigation or broad-spectrum herbicides like glyphosate—but this creates dependency on purchased materials from off the farm and weakens the overall resilience of the soil and cropping system. It also promotes genetically induced resistance to these chemicals and makes them less effective in the long run. The goal of ecological crop and soil management is to be proactive and preventive by creating conditions that help grow healthy plants, promote beneficials and suppress pests, and thereby minimize the extent of reactive management (which responds to unanticipated occurrences). The discussion below and in the rest of this book focuses on ways to maintain soil health and to enhance habitat in order to promote one or more of the three strategies listed above.