51 8 Journal of Agricultural Research voi. xv, N0.9 



The decomposition of i per cent organic matter in soil had no marked 

 effect on the percentage of inorganic colloid suspension; 3 per cent 

 organic matter in some cases decreased the per cent of colloids. Barley 

 decreased the amount of colloid suspension more than did alfalfa or 

 manure. 



The addition of ground lime rock appreciably decreased 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 de- 

 creased the colloid content, and organic matter had no appreciable effect 

 in counteracting the flocculating effect of these substances. 



The addition of sodium nitrate to soil markedly increased the colloid 

 content, and the addition of organic matter appreciably decreased the 

 deflocculating effect of this compound. 



The addition of lime, sulphur, sodium nitrate, iron sulphate, ammo- 

 nium sulphate, and organic matter to soils did not fundamentally change 

 the composition of the inorganic colloid suspension obtained from the soil. 



The addition of gypsum to soil increased the percentage of silica, cal- 

 cium and manganese, and decreased the percentage of iron in the colloid 

 suspension. 



The inorganic colloid suspension contained an appreciably higher per- 

 centage of iron, aluminium, and manganese than the untreated soil. 



In soils which readily form plowsole the percentage of silica in the col- 

 loid suspension was also appreciably higher than in the untreated soil. 



The percentage of iron and aluminium 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 aluminium in the colloid suspension from 

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

 the soil formed plowsole. 



LITERATURE CITED 

 (i) Ashley, Harrison Everett. 



1909. THE COLLOID MATTER OF CLAY AND ITS MEASUREMENT. In U. S. Geol. 



Survey Bui. 388, 65 p., 9 fig., i pi. References, p. 59-62. 



(2) BreazealE, J. F. 



1917. FORMATION OF "BLACK ALKALI " (SODIUM CARBONATE) IN CALCAREOUS 



SOILS. In Jour. Agr. Research, v. 10, no. 11, p. 541-590, 26 fig., pi. 62 

 Literature cited, p. 589. 



(3) — 



1917. QUALITY OF RIVERDALE IRRIGATION WATER. In Cal. CitTOgraph, V. 2. 



no. 4, p. 14. 



(4) FRAPS, G. S. 



1914. AMMONIA-SOLUBLE INORGANIC SOIL COLLOIDS. Texas Agr. Exp. Sta. 

 Bui, 165, 8 p. 



