IMPORTANCE OF ORGANIC MATTER IN SOIL 21 



their choice for cocoa cultivation is consequently un- 

 desirable unless ample means are available for supplying 

 the deficiency by the application of heavy dressings of 

 humus-producing materials, such as animal or vegetable 

 matter. 



The most favourable soils for cocoa cultivation are 

 those which have been enriched by the yearly leaf-fall 

 in forest regions, or by alluvial deposits impregnated 

 with various organic matters. The striking development 

 of the San Thome cocoa industry is a good example of 

 the adaptability of such soils for the growth of cocoa. 

 All the best plantations are situated on land cleared of 

 forests, where the leaves annually shed have been con- 

 verted by natural agencies into a rich, black, vegetable 

 mould, in many cases more than a foot deep. These 

 lands have been, and are still being, enriched with valuable 

 fertilising materials carried down by the tropical rains 

 from the neighbouring hills. It is mainly from this 

 rich, upper layer of soil that the trees derive their nutri- 

 tion by means of a veritable network of fibrous roots, 

 for the sub-soil is frequently found to be composed of a 

 sandy clay. Experiments conducted at the Minnesota 

 Agricultural Experiment Station to test the retentive 

 power for moisture of various soils, show that 100 pounds 

 each of sand, clay, and humus are able to retain 25 to 

 30 pounds, 40 to 50 pounds, and 180 to 190 pounds of 

 water respectively. Humus improves both the physical 

 and biological condition of a soil by rendering it more 

 porous. 



