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A MODIFIED PERMEABILITY TEST FOR MEASURING THE COHESION OF SOIL CRUMBS
Author(s) -
DETTMANN MARGARET G.,
EMERSON W. W.
Publication year - 1959
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1959.tb02344.x
Subject(s) - arable land , cohesion (chemistry) , soil water , permeability (electromagnetism) , soil test , soil science , soil structure , materials science , chemistry , mathematics , environmental science , agriculture , ecology , biochemistry , organic chemistry , membrane , biology
Summary The technique previously described (Emerson, J. Soil Sci. , 6 , 160, 1955) has been improved. A I‐cm. thickness of soil crumbs of standard size (1–2 mm. diameter) is supported on a 1‐cm, layer of glass spheres (0·5–1 mm. diameter), and the permeability measured by percolation of 0·05 N NaCl‐the so‐called ‘initial’ test. Then 3 litres of the same solution are percolated in 24 hours, after which the permeability measurement is repeated—the ‘final’ test. The ratio, K 2 /K 1 , of final and initial permeabilities of the crumbs is regarded as a measure of soil cohesion. The technique has been applied to a wide range of soils, on some of which other structural tests had already been made. The results, in four tables, show: (a) a continuous arable system produces very bad structure; (b) a short‐term ley produces an improvement‐as does wheat‐and some of the improvement is detectable after a subsequent year in arable cultivation; (c) attainment of maximum stability is very slow, for 100 years in grass may not be enough; (d) farmyard‐manure residues increased crumb stability on a clay soil, but not on a sand;(e) a ley, and lucerne too, produces a greater increase than root crops. Limitations of the test are: (a) It should not be used unless the soil acidity is approximately the same for all samples. Very acid clay (pH 4 to 5), known to possess a very poor structure, gives a value of K 2 /K 1 close to unity. (b) It may not be safe to compare soils of differing clay content. A poorly structured sandy loam (12 per cent. clay) gives a much higher value of K 2 /K l than a clay loam (31 per cent. clay) that field experience would assess as having the better structure.