578 



Journal of Agricultural Research 



Vol. X. No. It 



Table XLI. — Solubility of calcium carbonate in soils 



By subtracting the water-soluble lime extracted from the controls from 

 the lime recovered from soil to which calcium carbonate had been added, 

 a difference is obtained, representing the effect of the application of cal- 

 cium carbonate. In the same way are subtracted the bicarbonate deter- 

 minations and a difference secured, also representing the effect of the 

 calcium carbonate. It will be seen that there is a regular increase in the 

 case of the total water-soluble lime, and, first a rise, then a drop, in the 

 case of the bicarbonates. The calcium carbonate has gone into solution 

 but is not present as a carbonate or bicarbonate. The presence of sodium 

 chlorid in the higher concentrations seems to be forcing back the solu- 

 bility of calcium as a bicarbonate. This is also true with sodium nitrate 

 and sodium sulphate. 



ALKALI CRUSTS IN IRRIGATED REGIONS 



In many of the irrigated districts in southern California, especially 

 around Riverside and Corona, the so-called crusts or efflorescence of alkali 

 salts is frequently noticed on the surface of the soil. These crusts appear 

 after each irrigation as a light, fluffy, brown efflorescence, particularly 

 along the edge of the irrigation furrow. They are not crusts, except in 

 the popular conception of the term, in that they do not harden the surface 

 of the soil ; they are also to be distinguished from the black, gummy crust 

 formed by black alkali, and from the crystalline crust of the other sodium 

 salts constituting white alkali. 



They are usually dissolved by each irrigation and carried down into the 

 soil only to be returned to the surface in a few days by the upward move- 

 ment and evaporation of the water. This upward and downward move- 

 ment is continued throughout the season until the crusts are finally dis- 

 solved by the winter rains and carried down to some depth into the soil 

 or off by drainage. Unless the winter rains are unusually heavy, the 

 crusts usually appear again in the spring after the first irrigation. Both 

 the crusts themselves and their water extracts are extremely toxic to 

 Citrus seedlings, the toxicity being entirely out of proportion to the 

 known toxicity of the inorganic salts that make up the solution. 



