: Here you will find clear descriptions of what you just saw, how they know what they said they knew, why they know it to be trustworthy information. Finally we will ask the question, "So what!" and explore why the information is important.
In this clip from the 2009 public presentation “Agriculture After Norman Borlaug,” Dr. Crews presents a depiction of what agriculture looked like in pre-industrial times— the period of agriculture before fossil fuel-powered equipment was used to manipulate and manage croplands. Dr. Crews describes significant shifts that happened once humans transitioned from hunter-gatherers to becoming farmers of increasing sizes of land, intentionally planting, tending, and harvesting crops for the purposes of food production.
In this clip, Dr. Crews builds upon a simple model of the phosphorus cycle in native ecosystems to illustrate the changes to the phosphorus cycle in soils changed as a result of pre-industrial agriculture. Ecologists often refer to a model like this as a budget because, like a financial budget, it tracks the influx and outflow of resources into a system. Such budgets help us to understand which ecosystems may be receiving different amounts of a nutrient than were previously available or alter ecosystems to grow larger or more productive crops than would have otherwise been possible.
Although Dr. Crews and other agricultural ecologists were not alive to study agriculture practices or impacts during pre-industrial periods, they are able to combine their knowledge of physical processes, such as the forces of erosion and leaching, with artifacts and traces left by civilizations practicing pre-industrial agriculture to come to conclusions illustrated in the simple model. Additionally, some societies around the world still practice agriculture in ways very similar to practices carried out centuries ago, providing more support to these conclusions.
Despite agriculture’s essential purpose to provide a stable food supply, it is often taken for granted. Yet scientific study of agriculture enabled advances that allowed agriculture to keep up with soaring population rates in recent decades. Agricultural ecologists like Dr. Crews study agricultural in an ecological context in order to make additional advances in the productivity of crops while considering the impacts such farming might have on surrounding natural ecosystems.
Reflect on the clip using these questions. Then, record your thoughts in a science journal or discuss them with a friend.
Thinking in Systems:
In the series of videos on phosphorus, Dr. Crews uses the scientific technique of simplifying a complex system to better understanding or communicate it to others. In this activity you will think about how to use a simple model to illustrate a complex system found in your everyday life.
1. Think of a system in your everyday life that sometimes works well and sometimes doesn’t work well or at all.
2. Take a picture of or draw something that represents that system. Put that image in a power point slide, like Dr. Crews did. Alternatively, images and can be added to a science journal.
3. Identify the basic function of the system and basic flows in and out of system. Flows might be money, energy, parts of a product, or something else. Add these flows to your image as arrows. If you have numbers for each aspect, be sure to include these numbers clearly.
4. Identify places in the process where your moving component (energy, money, ect.) might be lost or changed into something new.
5. What processes that happen within the system might affect its functioning? What would slow down or speed up the process? Is there anything that would shut the system down altogether?
6. Think about ways that people, even you, could alter or improve this system to get a desirable outcome. Share your ideas with a friend or in a journal.
Example: Some cities offer a bike-share system to help residents and visitors get around without using cars or buses. In such systems, bikes are the item moving throughout the system (like phosphorus through the air and soil). Although, unlike phosphorus, the bikes (hopefully) do not change form: they move from one area to another within the bike system and under special circumstances (purchase or theft) bikes may join or leave the system altogether.
The complete PowerPoint for this presentation, "Agriculture After Norman Borlaug," is available on the AGCI website. Click the link or search "Tim Crews" on agci.org.
Crews, Timothy E., Kanehiro Kitayama, James H. Fownes, Ralph H. Riley, Darell A. Herbert, Dieter Muller-Dombois, and Peter Vitousek. 1995. “Changes in Soil Phosphorus Fractions and Ecosystem Dynamics across a Long Chronosequence in Hawaii,” Ecology, Vol.76, No. 5 (July, 1995). Ecological Society of America, pp. 1407-1424. http://www.jstor.org/stable/1938144