Professional Development Program






PAGE 47 / 102

Unit 2: Applying Ecological Principles

Our roadmap for Unit 2 leads us through sections on Sustainable Crop Production and Sustainable Livestock Production. These sections each begin with the concept of creating optimum conditions for plant and animal health. This is a foundational concept in sustainable agroecosystem management and lays the groundwork for the discussion of production strategies (key practices) contained in each section.  Before we begin our exploration of management goals and key practices, let’s review the main take-home lessons for agroecosystem managers that we covered in Unit 1. Click on the ecological principles below for a brief summary:
1. Ecosystem characteristics are determined by place.
2. Ecosystems are organized, integrated networks of species and populations.
3. Ecosystem health and function are dependent upon the continuous flow and cycling of energy and nutrients.
4. Though ecosystems are dynamic and change over time, they are inherently stable.

Location and related climatic factors (e.g., soil type, temperature ranges, amount and distribution of rainfall, length of growing season) place limits on what kind of agriculture can be practiced in particular regions. Humans can modify those constraints to some extent—for example with irrigation or by constructing drainage systems—but there are costs associated with those kinds of changes. To enhance agricultural sustainability, agroecosystem managers recognize and work within their environmental limitations, but at the same time take advantage of technological advances that address ecosystem constraints in order to gain a competitive edge in the marketplace.

All farms and ranches can be viewed as a type of ecosystem. As such, they are organized, not chaotic, and have an inherent structure based on the interrelationships of the various species and populations within the system. An agroecosystem’s structure can be studied and described in terms of its component parts and the interactions that occur among and between those parts. In agroecosystems, crop plants, animals, weeds, pest organisms and microorganisms interact with each other to varying degrees and with different impacts. Understanding these interactions allows agroecosystem managers to develop production practices that are cost effective and in keeping with sustainability goals. Enhancing and managing the diversity of relationships within the ecosystem can reduce the need for external inputs, capitalize on the ecological processes that support the functioning of the agroecosystem and limit negative environmental impacts.

Like all ecosystems, agroecosystems are dependent on the continuous flow and cycling of energy and nutrients. As energy is transferred from one organism to another, much of it is lost to heat. Compounding this inherent inefficiency, additional energy inputs (e.g., fuel, nutrients, electricity, etc.) are required in order to grow, harvest, process and market the end product. So an important task for agroecosystem managers is to try and manage the energy and nutrient cycles to be as efficient as possible. In this context, sustainability goals might include reducing the quantity of purchased fertilizer applied to the field; or if fertilizer has to be applied, making sure that most of those nutrients are taken up by the crop and not lost to the soil. Likewise, farmers and ranchers are increasingly looking for ways to improve the energy balance within their systems, both for environmental and profit reasons.

Ecosystems are remarkably stable, despite the many internal and external forces that work upon them over time. This characteristic of ecosystems is often described as dynamic equilibrium. A key question for agroecosystem managers is whether that dynamic equilibrium can be enhanced or capitalized on to improve production, environmental benefits and profits: Both research and experience show that it can be. The goal in sustainable farming and ranching is to develop an agroecosystem that is strong enough to withstand or recover quickly from shocks or disturbances (resistance and resilience).

PAGE 47 / 102