Changes in Organic Matter and Bulk Density with Depth Under Two Cropping Systems¹

Measurements of soil organic matter and bulk density with depth after 24 years of continuous cotton and continuous lespedeza were significantly different. Continuous cotton resulted in a lower organic matter content in the surface soil than continuous lespedeza, while the soil bulk density under cotton was considerably higher than lespedeza at the 12.7 to 20.3‐cm depth. The maximum compaction that could be given the Norge loam, a Reddish Prairie soil, when subjected to a constant load, was directly related to the amount of organic matter present in the soil. Maximum compaction was extremely sensitive to small changes in organic matter caused by different cropping practices. Data also shows maximum compaction occurs on a Norge loam at a soilwater pressure of 1/3‐bar, or at what is frequently called “field capacity”.