582 Journal of Agricultural Research voi. x. No. n 



arid and semiarid regions, however, with slight rainfall, under conditions 

 of irrigation, little or no drainage can take place. The injurious com- 

 pounds are then likely to accumulate in the soil. It seems to the writer 

 that the accumulation of such combination of salts and organic matter 

 as are here described should be dreaded. Such formations as these might 

 well be considered the secondary stage of alkali accumulation, described 

 in the first part of this paper. 



It is an old adage in greenhouse work, "Water the pots until the water 

 runs out of the bottom. " In other words, to get the best results a little 

 drainage is always necessary. In irrigation agriculture, however, when 

 there is a scarcity of water, enough is not usually applied to cause any 

 drainage, even when there is a porous soil with sandy or open subsoil. 

 Under these conditions, if the winter rains are not heavy enough to pro- 

 duce the desired effect, the injurious products of decomposition are likely 

 to accumulate year after year until they reach an amount that will seri- 

 ously interfere with agriculture. 



It seems to be a fact that good Citrus crops usually follow heavy winter 

 rains. The rejuvenation, or "coming back," of many orchards may 

 well be attributed to this. This was particularly noticeable in the River- 

 side area in the season of 1916 after the unusually heavy rains of the pre- 

 ceding winter. The groves probably did not "come back" on account 

 of any change in the cultural treatment, as was thought by many, but 

 on account of the removal of injurious compounds from the soil. 



PROTECTIVE ACTION OF SODIUM CHLORID AND SODIUM SULPHATE 

 UPON THE ORGANIC MATTER OF THE SOIL IN PRESENCE OF SODIUM 

 CARBONATE 



It has already been shown that sodium chlorid and sodium sulphate 

 both have a slight solvent action upon the organic matter of the soil. 

 This is especially true of sodium sulphate. In the presence of sodium 

 carbonate, however, a remarkable phenomenon is to be observ^ed. Both 

 salts tend to reduce the solvent action of sodium carbonate. 



The solvent action of sodium carbonate, which is far greater than that 

 of the other sodium salts, is due in all probability to the ionized OH 

 radical. Sodium carbonate being a strong base combined with a weak 

 acid has a decided tendency to hydrolyze — that is, to combine with water 

 in the following manner : NajCOg + H20<=^2NaOH + H2CO3. The sodium 

 hydrate formed in this reaction will in turn ionize into Na and OH. The 

 sodium hydrate formed by the hydrolysis, then, is directly responsible 

 for its caustic action upon the organic matter of the soil, and its degree 

 of ionization is a measure of it. 



By introducing a salt with a common ion into a weak solution of sodium 

 carbonate the ionization may be so forced back as no longer to show 

 color with phenolphthalein. The sodium carbonate as such will still 

 remain in solution, but will not be hydrolyzed. In this way sodium 



