Nov. ], 1919 Carbonates of Calcium and Magnesium on Acid Soils 123 



potassium-nitrate and by the Jones ^ calcium -acetate methods. Bac- 

 terial counts were the average of counts on five plates made after 10 

 days' incubation at 20° C, by the method of Noyes and Voigt.^ 



The quantities of salts, as determined by the electric bridge, were 

 greater with the use of the magnesite than with the calcite. This, to a 

 certain extent, illustrates the comparative solubilities of the calcium 

 and magnesium compounds as well as of other soluble salts resulting 

 from the reactions taking place between these carbonates and the soil 

 constituents. 



The carbon-dioxid determinations show that the decomposition of the 

 added natural carbonates was not complete in any case at the end of 

 10 months. The data tend to confirm, however, Maclntire's statement 

 (6) that magnesium carbonates are more readily decomposed than is 

 calcium carbonate. 



While each soil (Table I) contained approximately two parts of mag- 

 nesium oxid to one part of calcium oxid there was almost twice as much 

 of both calcium and magnesium oxids in the clay soil as in the sandy 

 soil. Six tons of magnesite per million pounds of soil increased the 

 magnesium oxid content by 0.57 per cent. This made the ratios of 

 calcium oxid to magnesium oxid approximately i to 8 for the sandy 

 soil and i to 5 for the clay soil. The 2-ton application of magnesite 

 which was not injurious made the ratio of calcium oxid to magnesium 

 oxid I to 4 for the sandy soil. It might be contended that the sandy 

 soil would have produced crops with a ratio of i to 5 between calcium 

 oxid and magnesium oxid, but it must be remembered that in any case 

 only small portions of the total calcium and magnesium were in solution, 

 and it is quite probable that the clay soil would ofifer more resistance 

 to the injurious action of the magnesium salts than the sand would. 



The 12,000-pound application of magnesite gave 1,320 pounds of 

 soluble salts per million of the black sand and only 624 on the yellow 

 clay. Recent tests by one of the writers (unpublished data) have shown 

 that magnesium carbonate increases the solubility of soil constituents 

 more than calcium carbonate does. Soluble magnesium in quantity 

 has long been known to be detrimental to plant and bacterial develop- 

 ment. This is in accord with both the high soluble salt content and low 

 aerobic bacteria counts on the black sandy soil with the 12,000-pound 

 application of magnesite. 



In a previous paper (7) it has been shown that nitrification occurs in 

 these acid soils and that the amounts of nitrates found in the soils when 

 sampled are largely influenced by the growing crop. Tlie nitrates after 

 incubation are evidence that liming increases the nitrifying power of 

 the soils. In all cases magnesite caused greater nitrification than did 



• Jones, C. H. op. ar. 



" Noyes, H. A., and Voight, Edwin, a technic tok the BAcrERioi.oGicAL bxaminatiom op soils. 

 In Proc. Ind. Acad. Sci. 1916, p. 272-301, 6 fig. 1917. 



