BBC
Bbc News: Soil Loss Threatens Food Prospects
An informative site that examines the multiple causes of soil erosion and possible remedies.
US Environmental Protection Agency
Epa: Acid Rain
Explore more about acid rain. This is an online experiment to observe "The influence of acid rain on plant growth." Find out how acid rain can damage your plants directly and indirectly.
Wikimedia
Wikipedia: Crop Rotation
Wikipedia provides a definition of crop rotation, including a brief history and examples.
Wessels Living History Farm
Living History Farm: Crop Rotation
A history of crop rotation in the United States. Once an incentive from the New Deal, farmers were paid to plant certain crops or let the soil lie fallow.