Building Soils for Better Crops, Third Edition

Ecological Crop and Soil Management

Overview
A whole-system approach to soil and crop management at the field level. Modified from Magdoff (2007).

We’ll discuss ecological crop and soil management practices as part of a general framework for approaching ecological crop management (figure 8.4). The heart of the matter is that the strength of the system is improved by creating improved habitat both above ground and in the soil. Although it is somewhat artificial to talk separately about aboveground and soil habitat—many practices help both at the same time—it should make many issues clearer. Not all of the aboveground discussion refers directly to management of soil, but most does. In addition, the practices we’ll discuss contribute to one or more of the overall strategies: (a) growing healthy plants with strong defense capabilities, (b) stressing pests, and (c) enhancing beneficial organisms.

Aboveground Habitat Management

There are numerous ways that the aboveground habitat can be improved to help grow healthy plants, stress pests, and enhance beneficial organisms:

  • Select crops and varieties that are resistant to local pests (in addition to other qualities such as yield, taste, etc.).
  • Use appropriate planting densities (and companion crops) to help crops grow vigorously, smother weeds, and (with companion crops) provide some protection against pests. In some cases, blends of two or more varieties of the same crop (one susceptible to a pest but with a higher yield potential, and one that’s resistant) have shown potential for increasing total yields for wheat and rice. Even though the farmer is growing the same crop, increased genetic diversity due to using different varieties (cultivars) seems to provide some protection. Perhaps there are possibilities for growing mixes of other crops as well.
  • Plant perimeter (trap) crops that are more attractive to a particular pest than the economic crop(s) growing in the middle of the field and so can intercept incoming insects. (This has been successfully practiced by planting blue Hubbard squash on the perimeter of summer squash fields to intercept the striped cucumber beetle.)
  • Create field boundaries and zones within fields that are attractive to beneficial insects. This usually involves planting a mix of flowering plants around or as strips inside fields to provide shelter and food for beneficials.
  • Use cover crops routinely for multiple benefits, such as providing habitat for beneficial insects, adding N and organic matter to the soil, reducing erosion and enhancing water infiltration into the soil, retaining nutrients in the soil, and much more. It is possible to supply all of the nitrogen to succeeding crops by growing a vigorous winter legume cover crop, such as crimson clover in the South and hairy vetch in the North.
  • Use rotations that are complex, involve plants of different families, and, if at all possible, include sod crops such as grass/clover hay that remain without soil disturbance for a number of years.
  • Reduce tillage. This is an important part of an ecological approach to agriculture. Tillage buries residues, leaving the soil bare and more susceptible to the erosive effects of rainfall, and at the same time breaks up natural soil aggregates that help infiltration, storage, and drainage of precipitation. (The use of practices that reduce erosion is critical to sustaining soil productivity.)

Some of these practices—use of cover crops and more complex rotations and reducing tillage—will also be mentioned below under “Enhancing Soil Habitat” and discussed in detail in later chapters.

Enhancing Soil Habitat

The general practices for improving the soil as a place for crop roots and beneficial organisms to thrive are the same for all fields and farms and are the focus of our discussions in the next chapters. However, the real questions are which ones are best implemented, and how are they implemented on a specific farm? These questions can only be answered by knowing the specific situation as well as the resources available on the farm. However, many practices are outlined below that may make the soil a better environment for growing healthy plants, stressing pests, and enhancing beneficial organisms:

  • Add organic materials—animal manures, composts, tree leaves, cover crops, rotation crops that leave large amounts of residue, etc.—on a regular basis (see chapters 10, 11, 12, 13).
  • Use different types of organic materials because they have different positive effects on soil biological, chemical, and physical properties (chapter 9).
  • Keep soil covered with living vegetation and/or crop residues by using cover crops, sod crops in rotation, and/or reduced tillage practices (chapters 10, 11, and 16). This encourages water infiltration, reduces erosion, promotes organisms that feed on weed seeds, and increases mycorrhizal numbers on the roots of the following crops.
  • Reduce soil compaction to a minimum by keeping off fields when they are too wet, redistributing loads, using traffic lanes, etc. (chapter 15).
  • Use practices to supply supplemental fertility sources, when needed, that better match nutrient availability to crop uptake needs (chapters 18, 19, 20, 21). This helps to reduce both weed and insect damage as well as pollution of surface and groundwaters.
  • For soils in arid and semiarid climates, reduce salt and sodium contents if they are high enough to interfere with plant growth (chapter 20).
  • Evaluate soil health status (chapter 22) so that you can see improvement and know what other soil improving practices might be appropriate.
  • Use multiple practices that improve the soil habitat (chapter 23). Each one may have a positive effect, but there are synergies that come into play when a number of practices—such as reduced tillage and cover crops—are combined.

CONFLICTING DISEASE MANAGEMENT ADVICE?

In this book we promote reduced tillage and retention of crop residues at the soil surface. But farmers are often encouraged

to incorporate crop residues because they can harbor disease organisms. Why the conflicting advice? The major difference is in the overall approach to soil and crop management. In a system that involves good rotations, conservation tillage, cover crops, other organic matter additions, etc., the disease pressure is reduced as soil biological diversity is increased, beneficial organisms are encouraged, and crop stresses are reduced. In a more traditional system, the susceptibility dynamics are different, and a disease organism is more likely to become a dominant concern, necessitating a reactive approach. A long-term strategy of building soil and plant health reduces the need to use short-term cures.

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