278 University of Calif ornia Publications in Agricultural Sciences [Vol.3 



This holds, of course, for the other soils as well as for the greenhouse 

 soil, indeed, more markedly so. The phosphorus content of the soil 

 extract is certainly not increased, in the two determinations made, by 

 the treatment of the soil under consideration. In fact, while it is 

 difficult to appraise it as such, there seems to be a slight depression 

 in the amount of the phosphorus present in the soil extracts of the 

 treated, as against those of the untreated soils. The magnesium is 

 affected in the greenhouse soil similarly to the manner in which it 

 was influenced in the other soils, but, as in the case of the potassium, 

 the results are much more emphatic. It is quite evident that large 

 amounts of magnesium go into solution through the influence on the 

 soil of CaC0 3 throughout the period of the experiment, but especially 

 in the periods of the first two samplings. CaS0 4 , on the other hand, 

 only increasas the amount of magnesium when employed at the smaller 

 application and then only in the period of the first sampling. With 

 the larger application of CaS0 4 . in the first sampling and with both 

 applications in the second sampling, there seems to be evidence of a 

 depression in the magnesium content of the soil extract. In the third 

 sampling, the CaS0 4 treated soils seem to behave like the control and 

 furnish another instance of the phenomenon noted above in the case 

 of the other soils. The sulphur content of the soil extract is more 

 markedly affected by the treatment in question in the case of the green- 

 house soil than any other constituent thereof which we have deter- 

 mined. That is, perhaps, not surprisingly so in the case of the CaS0 4 

 treatment, but it is to be particularly remarked how very great such 

 increases are even with the CaC0 3 treatment. Unlike the eases of the 

 other constituents of the soil extract, moreover, that of the sulphur 

 shows the effect of treatment even at the third sampling. 



General Discussion 



From a general survey of our results, a few facts stand out clearly. 

 Of the seven ions which we have determined in the extracts of the 

 soils treated with CaC0 3 or with CaS0 4 , all, with possibly one excep- 

 tion — phosphorus — are affected by the treatment in one or more of the 

 three soils, in the directions either of increase or decrease in amount 

 in the soil solution. The ions are not all affected by the treatment in 

 any one soil, however. It appears that the nature of the soil minerals, 

 as well as the organic matter content of the soil, and hence probably 

 the partial carbon dioxide pressures, are important factors in deter- 



