Healthy Soils, Healthy Crops - A video series released by South Carolina that focus on soil health and some of the conservation practices that improve soil health, and activities that benefit from improved soil health. Precision agriculture is also highlighted.
The Papers of John E. Weaver - A great collection of papers on root development of crops, prairie grasses and forbs, trees, soil erosion and lots of other subjects. Old papers from 1915-1968 but very detailed experiments with great references and pictures. University of Nebraska Lincoln Web site.
Development and Activities of Roots of Crop Plants: A Study in Crop Ecology, John E. Weaver, May 1922
The Living Network in Prairie Soils – Great section on the soil forming process and pictures of prairie grass roots.
Relative Efficiency of Roots and Tops of Plants in Protecting the Soil from Erosion, J. E. Weaver, October 1935. Probably the original rainfall simulator experiment, comparing erosion on crop (winter wheat), alfalfa and native range.