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The Restoration of a Structurally Degenerated Soil¹

ABSTRACT

Common agricultural practices contribute to the loss of favorable soil structure. On the other hand, certain natural forces appear to contribute to the recovery of porosity and tilth. These include wetting and drying, freezing and thawing, the effects of root growth and decay, and the activity of soil organisms.

In order to learn more about the nature and interplay of these forces, a method was developed for studying structural changes in buried cores of compacted soil. The technique of preparing these with various additives is described. The cores were buried under three types of cover: Forest, grass, and clean cultivation. The additives were fresh organic matter, lime and fertilizer, and an insecticide.

During a 2-year period the following relationships have come to light:

1. A platy structure forms as a result of wetting and drying, and plant roots tend to enter the shrinkage cracks.
   
2. Earthworms and other small invertebrates are active in transporting and mixing the core soil with surrounding soil, particularly with added organic matter.
   
3. Added organic matter results in a rapid increase in aggregate stability, followed, under cultivated conditions, by a seasonally fluctuating decline.
   
4. Changes take place more slowly under forest cover than in an open field.
   

The restorative process appears to be essentially a result of the interaction of physical and biological factors.

¹ Contribution from the Earlham College — Charles F. Kettering Foundation, Soils Research Project, Earlham College, Richmond, Ind. This work was made possible by grants from the C. F. Kettering Foundation. Gertrude Ward has aided in the biological phase of the work and James Thorp has given encouragement and advice. Richard Lawrence contributed substantially in the earlier work and several other student assistants have aided continuously.

² Associate Professor of Physics; Head, Department of Biology; and student Research Assistant, respectively.

Received for publication January 26, 1956. Accepted for publication October 23, 1956.