No. 4.] THE GRASS CROP. 255 



benetit the supply of the most essential article of plant food. 

 The ])cneficial effect usually ceases after a few applications 

 of from four hundred to five hundred pounds per acre ; the 

 lands are more exhausted after its exclusive use as a manure 

 than before. 



Gyi)sum, or plaster, aids in the absorption of the ammonia 

 compounds of the air ; it counteracts the tendency of a clay- 

 ish soil to become hard and impervious in dry weather; it 

 assists, like salt, in the general diffusion of potash and phos- 

 phoric acid present, by causing favorable transformations of 

 existing compounds. A few repeated applications of from 

 six hundred to seven hundred pounds per acre usually termi- 

 nate its good services, which are frequently marked rather 

 by a more liberal growth of clover and of leguminous plants 

 in general than by that of grasses. Aside from lime and 

 sulphuric acid, nothing is added to the future fitness of the 

 soil, as far as essential articles of plant food are concerned. 

 Gypsum, as a sole manurial matter used on grass lands, 

 assists in bringing nearer the time of their failure as a 

 remunerative fodder source. 



Air-slacked lime, lime-kiln ashes and various other kinds 

 of lime refuse are noted for their good influence on grass 

 lands ; they assist in producing a favorable decomposition of 

 organic matter by neutralizing accumulated organic acids and 

 securing thereby conditions favorable to the action of a ben- 

 eficial microbic life in the soil. They aid in the disintegra- 

 tion of potash containing silicious soil constituents, and 

 render thereby inherent sources of plant food more available ; 

 they improve the general physical conditions of a compact, 

 clayish soil by rendering it more mellow and permeable. 

 As a direct addition of plant food they are only in excep- 

 tional cases of real importance ; they are in the majority of 

 cases worthless upon a calcareous soil. 



Marls and clayish marls, free from any perceptible amount 

 of potash and phosphoric acid, act in the main similarly to 

 the previously mentioned lime refuse. Earthy composts of 

 various descriptions, if applied in large quantities, frequently 

 act very beneficially on exposed portions of the upper part 

 of grass roots by protecting them against an undesirable ex- 

 posure to light and atmosphere, there1)y fovoring the forma- 



