Field clues to soil permeability were investigated at 182 locations from 1947 through 1951. Estimates of permeability were made in the field without prior knowledge of measured percolation rates. Then the estimated permeability class was compared with the measured rate. In case of discrepancy, the profile was re‐examined to see if any signfiicant clues had been overlooked. It was found that permeability could be estimated, with fair precision, from information obtained in the field, in terms of seven classes that are defined in terms of saturated percolation rates.The first step is determination of the type of structure. Then the class of permeability is estimated from four principal clues and one or more of eight secondary clues. Types of structure and structureless conditions found significant are fragmental, platy, nuciform, cubical blocky, prismatic, single grain, and massive. Principal clues are relative dimensions, horizontally and vertically, of structural aggregates; amount and direction of over‐lap of the aggregates; number of visible pores; and texture. Important secondary clues are compaction, direction of natural breakage, silt content, cementation, type of clay minerals, character of coatings on aggregates, degree of mottling and certain features of climate. None of these clues, when taken singly, is a reliable indicator of permeability, but each must be considered with reference to the others.
The purpose of this study was to determine some of the changes that have taken place in the structure of several Corn Belt soils and its influence on tilth, permeability, volume weight, and percent of pores drained.
Samples of soil were examined in the field to determine the type, class, and grade of structure, direction of natural fracture when lumps were broken, and size and number of visible pores. Six to twelve undisturbed soil core samples 3 inches thick and 3 inches in diameter were taken at random from each plot and depth to determine permeability, volume weight, and percent of pores drained at 60 centimeters tension.
Many surface soils that originally were granular or crumb in structure have changed through cultivation and poor management practices to a fine fragmental or massive structure. With these changes in structure the percolation rate decreased from 8.4 inches to 0.2 of an inch per hour, percent of pores drained was reduced from 9.2 to 3.5, and the volume weight increased from 1.1 to 1.31.
The surface crust was the least permeable layer in the upper 18 inches of the soils studied.
Color is one of the first mentioned and most essential Characteristics to be considered in any system of soil classification. Consequently the soil scientist must be able to-correctly interpret colors and describe them go that other investigators, as veil as laymen, can get a clear conception of-his findings. It is further important that different men interpret soil colors alike,
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