SOIL AMENDMENTS 537 



sandy loam soil was found by Kellerman and Robinson l 

 to favor the formation of nitrates up to an application 

 of 2 per cent, which is much more than would ever be 

 applied in practice. It must be kept in mind, however, 

 that this limit does not apply to all soils, as the absorp- 

 tive properties of the soil for lime will determine the 

 maximum application that may profitably be made. 

 Kellerman and Robinson found also that the application 

 of magnesium carbonate in excess of 0.25 per cent in- 

 hibited the formation of nitrates. Kelly 2 also has 

 recently reported that the addition of magnesium car- 

 bonate to the soils with which he experimented resulted 

 in a marked depression of both ammonification and nitri- 

 fication, and that the addition of calcium carbonate did 

 not overcome this depressing influence. 



457. Effect on toxic substances and plant diseases. - 

 Free acids are toxic to most agricultural plants. Some 

 plants are much more sensitive than others. Alfalfa, 

 for example, should have a slightly alkaline medium for 

 its best growth, and any acid is very injurious. Calcium 

 salts, in neutralizing acidity, remove this toxic condition. 

 A liberal application of lime is therefore a precaution 

 against injury of this kind. 



The. presence of soluble calcium, with its effects on the 

 soil, retards the development of certain plant diseases, 

 such as the " finger and toe " disease of the Cruciferse. 

 On the other hand, it may promote some diseases, as, for 

 example, potato scab. 



1 Kellerman, K. F., and Robinson, F. R. Lime and Legume 

 Inoculation. Science, n. s., Vol. 32, pp. 159-160. 1910. 



2 Kelly, W. P. The Effect of Calcium and Magnesium Car- 

 bonates on Some Biological Transformations of Nitrogen in 

 Soils. Univ. of Calif. Pub., Agr. Sci., Vol. 1, No. 3, pp. 39-49. 

 1912. 



