Total, inorganic, organic, and available P were determined for 12 loess‐derived prairie soil profiles. The amount of total phosphorus (TP) is high near the surface, has minimum values from 1 to 3 ft, has maximum values from 3 to 6 ft, and has nearly uniform values below 6 to 7 ft. The higher amounts near the surface are due to organic phosphorus (OP). The amount of OP in the poorly drained soils is about one‐half that in the better drained members of the topo‐sequence. Differences in organic carbon (OC)/OP ratios between the poorly and better drained soils are appreciable, with the poorly drained soils having the higher ratios. Difference in extractable or available phosphorus (AP) within and between profiles may be interpreted when pH, extractable Fe and Al, rooting depth of plants, TP and OC/OP ratios are considered. Phosphorus differences between soils of southeast and southwest Iowa are appreciable. The role of P in soil genesis studies is discussed.

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A study was made to evaluate the degree of horizon development in seven prehistoric Indian mounds of known age in northeastern Iowa. Comparisons were made between the data obtained for the Indian mound soil profiles and two virgin, loess‐derived Fayette profiles from the landscape near the mounds. The parent materials for the mound soils were the leached upper horizons of the soils under and immediately adjacent to the mounds. Morphologically, the mound profiles exhibited pronounced A1 horizons, weak color and structural A2 horizons, and incipient B horizons. Differences in profile development among the mounds were attributed to differences in mound age. The development of soil profiles in the mounds has been the most pronounced during the first 1,000 years. The mounds have reached their greatest present horizon expression in a period of no more than 2,500 years, and are similar in many respects to the Fayette soils which have developed over a period of no more than 14,000 years.