THE SCIENCE OF CATCHCROPS 79 



Ground nuts are chiefly valuable for their 

 fertilising properties. In the United States a 

 yield of from 1,500 to 3,000 Ib. of nuts per acre 

 can be obtained. Ground nuts and coconuts 

 thrive on similar soil. In Tropical Africa the yields 

 are not so high as elsewhere, although the ground 

 nuts produced are more valuable, as they contain 

 a greater percentage of oil. There is always a brisk 

 demand for this class of oil in the European 

 markets, and good shelled nuts realise upon an 

 average about 12 10s. per ton. The oil extraction 

 does not necessitate expensive machinery, and the 

 residue, which contains quite 7 per cent, of nitrogen, 

 furnishes valuable food for cattle, and manure. 

 African unshelled and shelled ground nuts yield 

 32 and 50 per cent, of oil respectively, and oil 

 extracted locally in East Africa has been valued 

 as high as 40 per ton. 



Tapioca and pineapples are very exhausting to 

 the soil, although the former product has long 

 been a favourite, owing to the fact that it always 

 commands a ready market. Popular with the 

 natives as an article of diet, it is, in some regions, 

 used as the basis of the staple food in substitution 

 for rice. As regards the soil- exhausting drawback, 

 that practical authority, Mr. Frederick Knocker, 

 says : ' Tapioca greedily absorbs from the soil a 

 far larger proportion of nourishment than should 

 fall to the lot of a catchcrop, burrowing far and deep 



