8.4: Ecological Crop and Soil Management

We’ll discuss ecological crop and soil management practices as part of a general framework (Figure 8.2). The heart of the matter is that the strength of the system is enhanced by creating improved habitat both aboveground and in the soil. Although it is somewhat artificial to talk separately about aboveground and the soil habitat—many practices help both at the same time—it makes 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: 1) growing healthy plants with strong defense capabilities in healthy soils, 2) suppressing pests, and 3) enhancing beneficial organisms.

Figure 8.2. A whole-system approach to soil and crop management at the field level. Modified from Magdoff (2007).

Aboveground Habitat Management

There are numerous ways that the aboveground habitat can be improved:

• Select crops and varieties that are resistant to local pests (in addition to having 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, use blends of two or more varieties (cultivars) of the same crop. For example, combining one variety that is susceptible to a pest or drought but has a higher yield potential with one that’s resistant and resilient has 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 seems to provide some protection. Perhaps there are possibilities for intercropping with rows of different crop types such as sunflowers with soybeans or peas.
• 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. The push-pull system practiced in East Africa goes a step further by planting the low-growing legume Desmodium within corn rows as a repellent plant for stem borers (push), and grasses along the field perimeter to attract the adult insect moths (pull), while also providing nitrogen and suppressing weeds.
• 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 nitrogen 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 southern United States 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, while also breaking up natural soil aggregates. (The use of practices that reduce erosion is critical to sustaining soil productivity.) Some of these practices, such as the 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.

Belowground Habitat Management

The general practices for improving the soil as a place for crop roots and beneficial organisms are the same for all fields and are the focus of our discussions in the next chapters. The real questions: which ones are best implemented, and how are they implemented in a specific situation (farm or other)? The approaches and practices are discussed in detail in Part 3 of this book, but Table 8.1 summarizes these management approaches and refers the reader to the appropriate chapters. In the final chapter (24) we discuss how all these considerations can be put together into an integrated soil health management approach.

Ch 12.Table 8.1 Management Goals, Approaches and Practices of Soil Health
OVERALL GOALS grow healthy plants, suppress pests, enhance beneficial organisms, all while improving the surrounding environment
Management Approaches and Practices	Where Discussed
Minimize soil disturbance and reduce compaction using reduced tillage, better rotations, controlled field traffic, staying off wet soils, compaction remediation, etc.	Chapters 11 (rotations), 14 (reducing runoff and erosion), 15 (addressing compaction), 16 (reducing tillage), 22 (urban soils)
Keep soil covered with crop residue, rotations with perennial forages, and by growing cover crops, which also helps to maintain continual presence of living roots in soil.	Chapters 10 (cover crops), 11 (rotations), 16 (reducing tillage)
Maximize biodiversity in soil and aboveground through more complex rotations, frequent cover crops, integrated livestock and crop farming, and applying different types of organic matter amendments such as animal manures and composts.	Chapters 10 (cover crops), 11 (rotations), 12 (livestock-crop integration), 13 (making and using composts)
Manage water to promote timely fieldwork and crop needs.	Chapters 14 (reducing runoff and erosion), 15 (preventing and lessening compaction), 17 (irrigation and drainage)
Maintain pH within desired range and nutrients at levels that supply plants with sufficient amounts but without excess loss to the environment by routinely testing soils and applying nutrients, lime and other amendments based on results, frequently using cover crops, addressing salt problems, and integrating livestock and crop farming.	Chapters 18 (nutrient management), 19 (managing nitrogen and phosphorus), 20 (nutrients, CEC, alkalinity, and acidity), 21 (soil tests and their interpretation), 23 (use soil health testing)

A Difficult Pest: Symphylans

Throughout this publication we emphasize the importance to soil health of organic matter and biodiversity, as well as of developing and maintaining good soil structure. However, there is a soilborne arthropod that thrives in soils with good organic matter content and that can cause major damage to a wide variety of crops. Symphylans, which are white and look like a centipede, feed mainly on root hairs and rootlets. They can move around easily with favorable soil structure, lots of old root channels and connecting pores. They occur usually with a spotty, circular distribution within certain parts of fields, and are more of a problem in certain geographic locations. Potatoes and beans appear to be less damaged by the pest, and it has been found that transplanted tomatoes do better than direct seeded ones when symphylans are present. While it is not established that other cover crops help reduce infestations, a spring oat cover crop may lessen damage to a subsequent crop. Increasing the planting density of squash has been shown to help maintain yields in the presence of the pest, though some thinning may be needed. Although some synthetic chemical controls are available, a lot more needs to be learned about how to manage this pest in ecologically sound ways. Care is essential when importing organic amendments: You do not want to introduce this pest by accident. And although there are organisms such as beetles, predatory mites and centipedes as well as fungal pathogens that feed on symphylans, a biologically active soil is not thought to be an adequate defense against this crop-damaging organism.

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 pathogen is more likely to become dominant, necessitating a reactive approach. A long-term strategy of building soil and plant health should reduce the need to use short-term cures.