The nature of soil acidity with regard to its quantitative determination

The acidity of mucks and peats poor in alkali and alkali-earth bases can not be considered on the same basis as rock-derived soils. The organic contents of peats and mucks possess acid, or base fixing, properties. It is a mooted point whether such acidity is caused by adsorption or by true acids. Considering rock-derived soils--Altho salts of a number of organic acids have been isolated from soils, no one definite free organic has ever been extracted, as of record. If all of the organic carbon in many soils was considered as being a constituent of a definite organic acid, the hypothetical acid so calculated would be equivalent to only a fraction of the amount of acidity determined by different methods of procedure. In practice, certain salts produce a decrease of soil acidity (sodium nitrate, potassium nitrate, etc.), tho in the laboratory treatments during short periods followed by extractions, the reverse may be true; while the addition of certain other neutral salts produced an increase in acidity in both laboratory and field due to removal of native bases or amphoteric elements. Removal, or adsorption, of dissolved bases by soils appeared to be a chemical function of acid silicates, principally alumino-silicates, the extent of whose hydration is a controlling factor in initial intensity and continuity of reaction. The acidity of soils is, in the main, induced by the loss of calcic and magnesic inorganic salts, derived originally from the hydrolysis of the alkali-earth siliceous complexes, thereby increasing the acid properties or amount of acid silicates. Where the base and its combined radical are added, in H2O solutions, to soils, and in equivalence, with reference both to mass and degree of dissociation, the adsorption of basic ions may be considered as of near equivalence. But when alkali-earth carbonates (CaCO3 and MgCO3) are subjected to moist and intimate contact with acid soils, the active masses will vary in amount and degree of dissociation, while the precipitated product of the reactions will vary in their solubility, or tendency toward reversion thru hydrolysis and recarbonation; hence, the difference in attaining and maintaining equilibria and the disparity in the extent of the reactions, which will vary markedly from chemical equivalence in a given time. Silicic acid, in mass, will progressively hydrolyze and continue to decompose calcium and magnesium carbonate when the liberated CO2 is removed from solution. This acid will pass from the solid to solution phase yielding H-ion concentration and is capable of effecting and inversion of cane sugar. After intense alakli treatments and the removal of excess of hydrates and after intense heating, pure silica, silicates, and titanium oxid will, on the addition of H2O, hydrolyze and act as acids towards the alkali-earth bases. Many acid soils will yield aqueous extracts, alkaline to some of the common indicators, but showing H-ion concentration by electrometric or colorimetric methods. The H-ion concentrations of acid soils are not generally considered as being of such intensity as to be of direct detriment to higher plant life, tho they may effect the growth of bacteria and fungi. The injurious effect of acidity may be attributed, in some instances, to aluminum and other toxic salts, but, in general, more particularly to the diminished supply of available calcium from the depleted lime content of the soil, as influencing the adaptability of the media for biological development and the meagerness of the lime as plant food, or as an essential regulatory component of the plant juice. The formation of organic acids and the generation of mineral acids, such as nitric, in soils may be conceded; but their occurrence within the soil seems to be of but brief duration, because of neutralization by native or applied basic materials. The reactions between soils and alkali-earth carbonates are characterized by a more intense initial activity, with a continued and lesser int