1916] SOILS — FEKTILIZEES. 727 



plants possessed a decided ability to obtain calcium and magnesium from sand 

 extracted with strong hydrochloric acid." 



A list of 42 references to literature bearing on the subject is appended. 



Sour soils and liming, W. Frear (Pcnn. Dept. Agr. Bui. 26 J (1915), pp. 

 221).— This bulletin, a revision of Bulletin 61 (E. S. R., 12, p. 027). deals with 

 soil acidity and the use of various limestone products for its correction, the 

 object being to present in logical order the present knowledge on the subject, 

 with special reference to the results of American studies, particularly those 

 made at the Pennsylvania Experiment Station. An extensive set of practical 

 conclusions is included, most of which have been noted from other sources, 

 especially the Pennsylvania Station reports. 



It is concluded that in soil formation the rocks lose much of their basic mate- 

 rials, lime especially, the final result of which is an acid residue, particularly 

 where colloidal minerals and organic residues from decay accumulate. " This 

 acid condition is immediately due to a great variety of materials, some the 

 result of soil weathering, some of crop action, in slight degree of the early 

 products of plant decay ; often, and in much greater degree, of the later, more 

 resistant residues from decay ; and finally to various additions, fertilizers, or 

 substances added for other purposes. When the acidity-producing substances 

 are themselves readily decomposable plant materials, their early destruction 

 usually follows, and their alkaline mineral constituents are released. As a 

 result, their acid effect is only temporary. ^ When, however, the cause is an 

 unsatisfied colloid, mineral or organic, a material but slowly decomposable in 

 the soil, the acid condition is permanent, though variable in degree, as conditions 

 of cropping, cultivation, etc., tend to increase or decrease the acidity. . . . 



" Soil cultivation hastens the decay of organic materials. . . . The tendency 

 of stirring the soil, as by the use of cultivated fallow, should be to reduce 

 acidity. . . . The acid-producing effect of commercial fertilizers is usually not 

 very great. The nitrates tend to leave alkaline residues. The acid phosphates 

 take very little lime to make them neutral or alkaline. Calcium sulphate is, in 

 silty loam soil, of but slight effect, although on clay loams and clays it may be 

 more active. The potash salts, in the amounts ordinarily applied, are not of 

 large influence in this respect. Thomas slag is mildly alkaline in its effect. 

 Ammonium sulphate is the most conspicuous producer of acidity. Its continuous 

 use inevitably tends to produce pronounced acidity in the soil. . . . 



" The kinds of plants occurring on a soil and the manner of their growth 

 usually give the first evidence of [acidity]. Clover failure . . . and the replac- 

 ing of the sweet grasses by plantain, moss, and sorrel, are the common signs. 

 . . . Careful cultivation stimulates soil fermentations. These will, sooner or 

 later, destroy temporary acidity. Mild acidity of a more permanent character 

 may be overcome by the use of nitrate of soda and basic slag, both of which have 

 alkaline residual effects. Where, however, the acidity is pronounced . . . lime, 

 pulverized limestone and leached wood ashes, marls, and oyster shells, burned or 

 raw and pulverized, are the only materials powerful enough and cheap enough 

 for the purpose." 



Lime and its uses in agriculture, R. Harcouet {Ontario Dept. Agr. Bui. 238 

 {1916), pp. 12). — This bulletin deals with soil acidity, the forms and uses of 

 lime in agriculture, and the action of lime in soils. 



Liming and inoculating soils, C. S. Dorchester, T. R. Douglass, and P. O, 

 Taff {lotca State Col. Agr. Ext. Bui. 40 {1916), pp. [41, figs. .3).~The general 

 lime requirements of Iowa soils are discussed. Ground limestone is considered 

 the best kind of lime to use on these soils. Methods of inoculation of soils for 

 legume growing are also briefly described. 



