418 EXPERIMENT STATION RECORD. [Vol.40 



between the percentage of inorganic colloid suspension and the percentage of 

 organic carbon or humus in the soil. 



" Native uncultivated soils contained appreciably less colloid suspension than 

 did similar soils which had been under cultivation for a number of years. 

 The (iecomposition of 1 per cent organic matter in soil had no marked effect 

 on the percentage of inorganic colloid suspension; 3 per cenl organic matter 

 in some cases decreased the percentage of colloids. Barley decreased the 

 amount of colloid suspension more than did alfalfa or manure. 



"The addition of ground lime rock appreciably den-eased the percentage 

 of inorganic colloid suspension in the soil when no organic matter was added. 

 When organic matter was added, the flocculating effect of lime was appreciably 

 diminished, especially in clay loam soil. The addition of powdered sulphur 

 and gypsum to soil markedly decreased the colloid content, and organic matter 

 had no appreciable effect in counteracting the flocculating effect of these sub- 

 stances. The addition of sodium nitrate to soil markedly increased the colloid 

 content, and the addition of organic matter appreciably decreased the detioe- 

 culating effect of this compound. The addition of lime, sulphur, sodium nitrate, 

 iron sulphate, ammonium sulphate, and organic matter to soils did Dot funda- 

 mentally change the composition of the inorganic colloid suspension obtained 

 from the soil. The addition of gypsum to soil increased the percentage of 

 silica, calcium, and manganese, and decreased tbe percentage of iron in the 

 colloid suspension. 



" The inorganic colloid suspension contained an appreciably higher per- 

 centage of iron, aluminum, and manganese than the untreated soil. In soils 

 which readily form plowsole the percentage of silica in the colloid suspeusiou 

 was also appreciably higher than in the untreated soil. The percentage of 

 iron and aluminum in colloid suspensions from soils which readily form hard 

 plowsole was higher than in colloid suspensions, from soils which do not form 

 a hard plowsole. The percentage of iron and aluminum in the colloid suspension 

 from a soil was found to be directly correlated with the readiness with which 

 the soil formed plowsole." 



A list of references to literature cited is given. 



Studies on nitrification in natural soils and its importance from an eco- 

 logical point of view, in Sweden, 11. IIessexm.w {Skogsvdrdsf&r. Tidskr., Xo. 

 4-6 (1917), pp. 321-U6, figs. 30; abs. in Intermit. Inst. Agr. [Rome], Internal. 

 Rev. 8oi. and Pract. Agr., 9 (1918), Xo. 6. pp. 662-665; Chem. Abs., 12 (WIS), 

 No. 23, p. 26^6). — The author distinguishes between two kinds of humil'erous 

 soils, one type being described as well aerated by the action of worms and 

 insects and as characterizing deciduous forests and to a lesser degree pine 

 forests on soils rich in inorganic salts, while the other type, comprising dead. 

 decomposed, or decomposing vegetation, is said to occur in ordinary pine 

 forests and frequently to form a series of layers of varying stages of decom- 

 positon clearly defined from the mineral subsoil. Studies were made with 

 soils from different types of forests, and included an examination of the soil 

 samples for nitrifying bacteria, tests of the nitrifying capacity of the dim-rent 

 soils, and determinations of the nitrogen content of trees and plants growing 

 on the various soils at different seasons. Conclusions were reached as follows: 

 The humus of beech woods contained as many nitrifying as denitrifying 

 bacteria distributed throughout the mass, while samples of tins soil forme 1 

 considerable amounts of nitrates. On the other hand, the humus of pine forests 

 with a mossy covering was characterized by the absence of denitrifying organ- 

 isms and of bacteria capable of nitrifying ammonium sulphate. No potassium 

 nitrate was found in the tissues of plants growing on this soil. 



