Soil types on gently rolling or nearly flat uplands and terraces in Nebraska, Kansas, and Minnesota were very homogeneous in N content, those on broken lands or on flood plains were heterogeneous. On gently rolling Carrington silt loam the HC/N ratios at 0-6 in. were 39.0-49.5, but on the highly rolling or bluff lands in eastern Neb. the Knox type varied from 44.2 to 77.8, averaging 57.4. The graphical relation of N content to rainfall is apparently a curve. After reducing stabilized Neb. virgin grassland soils to a comparable texture basis of a hygroscopic coefficient of 10, the following comparison of N contents in the 0-12 in. layer may be made: Eastern Neb. with precipitation of 30 in., 0.196% N; Central with 24 in., 0.188% N; West Central with 19 in., 0.157%; and Western with 16 in., 0.139%. This is a ratio of 100:96:80:71. In soil classification and mapping, the most important things to stress are textural uniformity, rainfall, and topography, in the order named.