196 EK. W. Ailgard— Objects and Interpretation of Soil Analyses. 
Here the continuous rise of moisture from the subsoil tends to 
keep up the supply to the water roots, while at the same time 
nutrition, as is well-known, continues almost unabated in air- 
dry soils, so long as there is no injurious rise of temperature in 
consequence of that dryness. But that is precisely the point 
where a high moisture-coefficient comes into play, by prevent- 
ing, in consequence of evaporation, a rise of temperature that, 
under similar circumstances would prove fatal to the surface 
roots of the crop in soils of low absorption power. In fact, 
Mayer’s conclusion is at variance with the ordinary experience 
of centuries, repeated every day in the droughty regions of the 
South and of the Pacific coast. It takes more than flower-pot 
experiments to invalidate the universal designation of soils of 
low hygroscopic power, as “ droughty.” ; 
The moisture-coefficient depends in ordinary soils, upon one 
or more of four substances, viz: (in the order of their efficacy), 
humus, ferric hydrate, clay and lime. It varies in cultivat- 
able soils from about 1°5 to 23 per cent at 15° C., and in a satu- 
rated atmosphere. A pure clay rarely exceeds 12 per cent; 
ferruginous clays show from 15 to 21; some calcareous clay 
soils rise nearly as high, while peaty soils rise to 28 per cent 
and even more, but the efficacy of the ferric hydrate depends 
essentially upon a state of fine division. When merely incrust- 
ing the sand-grains, or aggregated into bog-ore grains, it exerts 
little or no influence, although the analysis may show a high 
percentage. Sometimes soils highly colored show but a small 
iron percentage, while yet, on account of very fine diffusion, 
the advantages referred to are realized. : 
From 1% to 40 are ordinary percentages of ferric oxide, 
occurring even in soils but little tinted. Ordinary Oe hae 
a 
ferric hydrate to ferrous salts, most commonl: t 
manifests itself promptly by the “ blighting ” of the crop. B we 
under natural conditions this can rarely occur, because . 
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