Commercial Fertilizers. 161 



composed of carbonates of lime, magnesia and potash, with a 

 small quantity of phosphates (% per cent). The ashes from 

 soft woods contain less potash than those from hard woods. Coal 

 ashes have practically no value for fertilizing purposes. Wood 

 ashes have a beneficial action on the mechanical condition of 

 light soils, mainly because of the large amount of lime they con- 

 tain. This binds the soil particles together, thus increasing their 

 capillary action and improving their tilth. On clay soils there 

 is a tendency for wood ashes to cause "puddling." This is 

 avoided by applying an equal quantity of land plaster with the 

 ashes. 



All the materials mentioned with the exception of tobacco 

 stems are soluble in water, so there is no such marked difference 

 in availability as was noted in the case of nitrogenous and phos- 

 phatic fertilizers. 



Indirect fertilizers. There are a number of substances which 

 are beneficial to the land under some conditions, although they 

 add neither humus nor important quantities of plant food. 

 Among such materials are lime, gypsum and common salt. 



Lime. There are very few if any soils, which do not contain 

 sufficient lime to supply the plant. The chief value of lime ap- 

 plications must be as an indirect fertilizer. Its action is three- 

 fold: Mechanical, chemical and biological. Its mechanical ef- 

 fect on heavy soils is to make them less_adJ3siYfi_and more friable 

 and easier to work when dry. On light porous soils its effect is 

 exactly the reverse. It^binda the particles together, increases 

 the cohesive power and improves capillarity. Chemically, its 

 action is important. It acts on insoluble potash compounds, 

 liberating potash. It aids in the decomposition of organic mat- 

 ter. It corrects acidity by combining with the acids present. 

 Its biological action is dependent upon the chemical reactions 

 it induces. Its presence is a necessary condition to nitrification, 

 a biological process. It combines with the nitric acid .formed, 

 producing nitrates. By maintaining the soil neutral, or slightly 

 alkaline, it creates a proper medium for the growth and develop- 



