124 Journal of Agricultural Research vot. xvaii. No. 3 



calcite. The number of aerobic organisms was increased by liming, 

 which is evidence that in general those conditions that are favorable 

 to plant growth are also favorable to bacterial activity. 



On the yellow clay the magnesite caused greater bacterial growth, 

 while on the black sand the calcite caused the greater increases. The 

 bacterial diflferences between the magnesite and calcite results on these 

 two soils are probably partly due to the relative availability of the plant 

 food present. The magnesite, which increases soluble soil constituents 

 more than calcite, gave the greater increases on the yellow clay — low in 

 available plant food — and the lesser increases on the black sand — 

 relatively richer in available plant food. The heavy application of 

 magnesite unhindered by clay, with which it would form insoluble 

 compounds, caused too high a concentration of soluble salts on the 

 black sand. The black sand, though less compact, was high enough in 

 organic matter to contain normally the more anaerobes. 



The crop results do not point to any particular ratio between calcium 

 and magnesium which could be called optimum for either soil or crop. 

 This is in accord with the results of Waynick (8) and others. 



It is not possible with the data at hand to determine how much the 



injurious action of the high magnesite application on the black sand was 



due to an unfavorable calcium-magnesium ratio and how much was due 



to the high concentration of soluble magnesium salts; but, in view of 



the fact that the black sand soil still gave an acid reaction after the 



heaviest magnesite application, it is evident that the crop injury was 



not due to alkalinity. 



SUMMARY 



(i) Pot experiments were conducted on two very acid soils of different 

 types, using the natural carbonates, calcite, dolomite, and magnesite, in 

 varying amounts. Wheat, red clover, and blood turnip beets were grown 

 in succession. 



(2) After being cropped 10 months under optimum moisture conditions 

 the soils were tested for soluble salts, nitrates, nitrification, carbon dioxid, 

 acidity, and both aerobic and anaerobic bacteria. 



(3) Although both soils originally contained twice as much magnesium 

 oxid as calcium oxid, still calcite, dolomite, and magnesite, in both quan- 

 tities used, produced, with one exception, good crop increases on both 

 soils. The 6-ton aupHcation of magnesite on the black sand soil killed 

 the crops. 



(4) Good crop increases were obtained with carbonate applications 

 which produced ratios of calcium oxid to magnesium oxid varying from 

 2:1 to 1 :5.3 on the yellow clay soil and from 3.4:1 to i :4 on the black 

 sand. The 6-ton application on the black sand which caused crop failure 

 gave a ratio of i calcium oxid to 7.9 magnesium oxid. 



(5) Wheat, red clover, and beets responded differently toward calcium 

 and magnesium carbonates. With the medium applications beets were 



