42 
analyses made by the Government Laboratory, British 
Guiana, in which the average figures from ten cacao soils 
collected in different islands were as follows: .119% phos- 
phoric acid, 451% potash and .256% nitrogen. These are 
stated to be good cacao soils. Another series of eight soils, 
in which the yield is said to be unsatisfactory, the average 
analysis was phosphoric acid. 054%, potash .063% and ni- 
trogen .127%. Presuming that the samples were taken in 
the usual manner, viz. from the upper 6-2/3 inches of soil, 
which weighs over an average two million pounds per acre, 
the total plant food in the good soils would be 2380 pounds 
phosphoric acid, 9020 pounds potash and 5120 pounds ni- 
trogen and in the poor soils 1080 pounds phosphoric acid, 
1260 pounds potash and 2540 pounds nitrogen. 
Comparing the figures of the unavoidable loss and the ac- 
tual plant food in the soil we find that even the poor soil 
contains enough nitrogen for 202 crops, enough phosphoric 
acid for 255 crops and enough potash for 290 crops. This 
however, is merely a theoretical possibility. Practically, the 
question is not how much actual plant food does a soil con- 
tain but how much plant food is there available or can 
there be made available during the growing season. 
The plant foods removed from the soil by the crops taken 
off represent but a fraction of the actual loss, especially 
in the cacao plantations as they are cultivated today. 
The principal losses are caused by leaching and washing. 
The heavy tropical rains wash away large amounts of 
humus as well as soluble potash and phosphate salts from 
the underlaying soil. The shade trees take up large amounts 
of potash and phosphate as well as nitrogen, except the 
legumes. These elements are again partly returned to the 
soil in the leaves and flowers dropping, but a great deal 
of the plant food is lost before it reaches the cacao roots. 
