140 INFLUENCE OF SALTS ON THE SOIL 



added where ammonium sulphate is being used as a fertilizer. Lip- 

 man's work showed that calcium carbonate stimulated nitrification 

 more than did gypsum, that sodium chlorid was injurious to nitrify- 

 ing organisms, and that ferrous sulphate in amounts from 10 to 100 

 mg. per 100 gm. of soil was without effect. Later, he and Brown 

 decided that both ammonification and nitrification were promoted 

 by magnesia lime to a more marked extent than they were by non- 

 magnesia lime. This, however, was to a certain extent dependent 

 upon the treatment and crop growing on the soil. Both ammonifi- 

 cation and nitrification were accelerated by sodium nitrate. In a 

 more recent work Lipman, Brown, and Owen found that small 

 applications of calcium carbonate stimulated bacterial activity, 

 whereas large applications had a detrimental effect upon ammonifi- 

 cation. 



In Owen's experiments, magnesium carbonate was more efficient 

 in promoting ammonification and nitrification than was either 

 calcium or potassium carbonate. According to Engberding ammo- 

 nium sulphate, sodium nitrate, potassium nitrate, and caustic lime 

 all increase the bacterial content of the soil, but decrease its nitrogen- 

 fixing powers. Kruger's work indicated that calcium carbonate 

 was more effective in promoting nitrification than was lime, the 

 reverse being true with regard to the putrefactive bacteria. The 

 formation of ammonia from peptone was especially favored by 

 calcium carbonate. Lyon and Bizzell found that lime favored 

 nitrification, as did also certain nodule-bearing legumes. Fischer 

 concluded that the presence of calcium carbonate in a nutritive 

 solution favored the formation of protein nitrogen, but magnesium 

 carbonate lessened the transformation of ammonia into protein 

 nitrogen. Calcium oxid, however, exerted a much greater influence 

 upon, soil bacteria than did calcium carbonate. 



Kellermann and Robinson's results are of especial interest as 

 they indicate that magnesium carbonate, applied in amounts 

 exceeding 0.25 per cent, to a soil fairly high in magnesium carbonate, 

 positively inhibited nitrification, whereas calcium carbonate up to 

 2 per cent, favored it, thus indicating that the lime-magnesia ratio 

 is of great importance with regard to bacteria as well as the higher 

 plants. These results have been confirmed by C. B. Lipman and 

 Burgess in whose experiments magnesium carbonate was highly 

 toxic both in soil and in solution to Azotobacter chroococcum, while 

 calcium carbonate was never toxic even in quantities up to 2 per 

 cent. Furthermore, calcium carbonate exerted a protective influ- 

 ence against the toxic properties of magnesium carbonate. The 

 optimum ratio varied, depending upon the medium. 



Peck studied the influence of a number of salts upon bacterial 

 activity when applied to the soil, with the result that the carbonate, 

 sulphate, and phosphate of calcium were found to stimulate ammoni- 



