134 SCIENCE IN AFRICA 



of soils in Nigeria is enormous, as would be expected in a country 

 ranging in altitude from sea-level to over 13,000 feet, and in rain- 

 fall from over 300 inches annually in the Gameroons to under 

 25 inches in the north. The pH, for instance, was found to range 

 from 9 (very alkaline) in the limestone region near Lake Chad to 

 under 4 (very acid) in the pleistocene area in the south of Benin 

 Province. The practical results which can be expected from an 

 understanding of soils are shown by the fact that, in certain very 

 acid soils with a pH of 4-0-4-3, a small dressing of lime (sufficient 

 to raise the pH to 4-8 or 5-0) increased the yield of maize appreci- 

 ably, but heavier dressings had a definitely depressing effect on 

 the green manure crops. As another example, which is a most 

 significant discovery, it has been established on the experimental 

 stations of the agricultural department at Zaria and Kano that 

 small applications of farmyard manure — one to two tons per acre 

 compared with the usual ten tons per acre in England — produce 

 astonishing responses in increased yields of guinea corn and cot- 

 ton. Hartley and Greenwood (1933) have done important work 

 on this. 



The trend of recent work in Nigeria is to indicate that, both in 

 the humid and semi-arid regions, the lack of mineral plant food, 

 particularly phosphorus, is a more important factor than the 

 lack of nitrogen; but nitrogen and humus appear to become 

 more important again in the very dry areas. The mere fact that 

 in the humid tropics good crops are obtained immediately after 

 clearing old bush may be largely due to an accumulation of 

 mineral matter which is set free by the rapid oxidation of the 

 humus rather than to nitrogen derived from the humus. For in 

 Nigeria it is found that, in soils under high bush or forest, the base 

 status and pH are high at the surface, but diminish rapidly with 

 depth; whereas on a soil which has long been under continuous 

 cultivation this is not the case. 



In the Gold Coast the agricultural chemist has, since 1931, been 

 able to devote most of his time to work on the soils. Attention is 

 being given mainly to cultivated lands, but work is resulting in a 

 general classification. Already several hundred samples have been 

 examined, and the work aims at a soil survey of all cultivated 

 lands, which should be ready soon. A map showing the results 



