THEORIES OF NITRIFICATION. 27 



Costa Rica is offered by Mr. Julio E. Van der Laat. In urging the 

 use of commercial fertilizers, particularly nitrate of potash, this writer 

 propounds the theory that a process of nitrification in the soil is neces- 

 sary in rendering the fertilizer available for the coffee trees. This is 

 thought to be brought about, or at least favored, in two ways: (1) By 

 spreading in the plantations fine earth taken from ditches and pools 

 and (2) by shading. It is declared that the alluvial matter is not a 

 manure, and that its good effects are due to its "richness in nitrifying 

 organisms." The completion of the process of nitrification also requires 

 humidity, and shade is said to have "no other effect or utilit} r than 

 that of maintaining this humidity in the soil and in the atmosphere 

 during the dry season. " While thus admitting that the benefits of shade 

 are entirety indirect, this writer betrays no doubt of its importance: 



The want of shade brings two evils: The soil cracks and injures the smaller roots 

 of the coffee, and, what is still worse, nitrification ceases or is diminished, and the 

 tree is thus deprived more or less completely of its nitrogenous nourishment, and the 

 remainder of the fertilizer fails of its proper effects. 



Shade is, then, an essential condition for the production of large crops; but it 

 should be lofty, to allow free circulation of air, and not excessive, so as not to cause 

 injury during the winter. 



The shade trees should have deep roots, of a kind to draw their nourishment from 

 a stratum of soil different from that in which are spread the roots of the coffee tree. 



This theory of the function of shade probably owes its existence tcr 

 the more or less conscious realization of the fact that the results of the 

 shade culture practiced in Costa Rica required other explanation than 

 that of direct benefits which could be ascribed to a diminution of sun- 

 light. It is by no means impossible that the soil bacteria may be 

 found to play an important role with coffee, as well as in other depart- 

 ments of agriculture, but our knowledge of these organisms is still too 

 slight to furnish more than ground for speculation, while the demon- 

 strated utility of leguminous soiling crops gives great strength to the 

 analogous explanation of the value of the arboreal types of the same 

 family. The idea that the leguminous shade trees do not impoverish 

 the soil because the}" are "deeper rooted" is of course another assump- 

 tion made in support of a method for which the real justification 

 remained hidden. 



Similar ideas appear in Cameron's account of the coffee industry of 

 Coorg district of British India: 



Where the initial mistake has been made of removing the indigenous deep-rooted 

 shade — and it is pretty universal — replanting has been compulsory, as no one now 

 thinks of growing coffee successfully without shade. 



But in addition to losing much valuable time in secondary planting it will be felt 

 that the land is called upon to do double service. This, however, is not the only 

 disadvantage arising from the sudden exposure of forest soil long nurtured under 

 shade. Such treatment causes a revulsion in the chemical action of the soil, and 

 under strong sunlight the valuable process of nitrification is arrested. Possibly this 

 may account for the infertility of long-abandoned coffee lands. It is therefore clearly 



