54 MANURING 



quantity supplied was unrecovered. By far the greater 

 proportion of the unrecovered nitrogen was lost in the 

 drainage water. This indicates that much more nitro- 

 genous manures must be added than are actually required 

 by the crop. 



Plants take up from the soil : nitrogen, phosphoric acid, 

 potash, lime, magnesia, soda, oxide of iron, sulphuric 

 acid, chlorine, and silica. Many virgin, tropical soils 

 contain these constituents in adequate quantity and 

 in a sufficiently available condition for the remunerative 

 cultivation of cocoa ; in others there is a deficiency of 

 one or more of these elements ; so that after a few years' 

 cropping the soil becomes impoverished and consequently 

 remains unproductive until the missing elements are 

 restored. 



The value of the soil, therefore, may be estimated by the 

 amount it contains of the ingredient or ingredients which 

 are most lacking in an available condition. A chemical 

 analysis of the soil may demonstrate that all the food 

 elements necessary for plant nutrition are present, but 

 unless they are in such a form as to be soluble in the 

 sap of the root-cells they are of no immediate value to 

 the plant. 



The Economical Application of Manures. The chemical 

 analysis of the soil and of the crop to be cultivated 

 undoubtedly furnishes useful hints in regard to the soil's 

 manurial requirements, but there are other important 

 factors to be taken into consideration, such as the physical 

 and hygienic condition of the soil. 



Not until the cocoa planter has satisfied himself that 

 his soil is satisfactory in these latter respects should he 

 attempt to deal with the manurial problem. 



The economical application of manures is dependent 

 upon a due consideration of the requirements of the 

 cocoa trees, the composition of the soil, the physical 

 condition of the soil, and the composition of the manures 

 applied. 



The plant-food ingredients in which soils are most 

 generally lacking are : nitrogen, phosphoric acid, potash, 

 and less frequently lime. 



Chemical analyses of different parts of the cocoa tree 

 have already been given (chapter iv.). The ingredients 

 used up in the formation of the leaves are in a great 



