Permeability and Intake Rates of Medium Textured Soils in Relation to Silt Content and Degree of Compaction

From 1948 through 1953, percolation rates were determined for 215 medium textured layers of soil from farmland in Arizona, Colorado, New Mexico, and Utah. Knowledge of the differences in percolation rates are helpful in establishing soil treatment units. This knowledge helps to indicate those areas most apt to be damaged by overirrigation, feasibility of reclamation of saline and alkali affected soils and to design effective drainage systems. Water‐intake rates for these layers of soil at field moisture were determined for the first 2 hours. In many cases they were compared with either irrigation intake rates or infiltrometer values. Thus, it was possible to locate not only limiting layers but also to develop clues for soils with different intake rates. The results were helpful in grouping soil units which have similar requirements for irrigation layout and tillage practices. Medium textured soils, containing less than 2.5% organic matter, but more than 40% silt, behaved like silt loams and tended to have slow permeability and intake rates. In contrast, medium textured soils which contained less than 40% silt had moderate permeability and moderate intake rates unless they were compact and had few effective pores. Both permeability and intake rates varied with compaction of the soil. Three degrees of compaction or bulk density appeared to be significant. However, the limits for classes of bulk density were higher for sandy loams, sandy clay loams, and loams containing less than 40% silt than for the loams and silt loams containing 40% or more silt. Direction of natural breakage, especially in firm soils, and the number of effective pores per square foot were also important clues in evaluating permeability and intake rates. Each of these clues must be considered with reference to the others.