PLANT INDUSTRY 383 



methods the proportion of cropping years to fallow years can be 

 reduced from 1:7 to 1:2. 



In Southern Nigeria the establishment of Native Administrations 

 is of more recent date than in the Northern Provinces, and until 

 about 1930, it was not found possible to enlist their co-operation 

 in agricultural extension work through the medium of demonstra- 

 tion plots and schools. As soon as the best technique for maintain- 

 ing fertility in each area has been established, however, the methods 

 of extension work now in existence should make it rapidly popular. 



In the Northern Provinces of Nigeria the single rainy season 

 renders the production of two crops during the year impossible, 

 and therefore any attempt to introduce green manuring would be 

 doomed to failure. In certain areas, for example in the neighbour- 

 hood of Kano, an intensive fixed cultivation is already practised 

 and provides an interesting example of a native system especially 

 suited to the environment. Permanent cultivation throughout the 

 Northern Provinces will come eventually through the development 

 of mixed farming, a subject which is considered later. 



ROTATION OF CROPS 



Green manuring has been the subject of experiments also in the 

 Northern Territories of the Gold Coast, where, since 1929, large 

 increases in crops have resulted from special rotational systems 

 which include green manure. Thus a five-year rotation consists 

 of (i) yams, (2) Bengal bean {Mucuna) as a green manure which 

 is dug in, (3) cotton, (4) Guinea corn, (5) maize and groundnuts 

 interplanted. This has given excellent experimental results, as 

 also has a three-year rotation consisting of (i) yams, (2) Bengal 

 bean, (3) maize and groundnuts. The usual native cultivation in 

 this area involves two years' cropping followed by five or six years' 

 fallow^, but near the villages, where cultivation has been continuous 

 for long periods, soil fertility has been much reduced. It is con- 

 sidered that the new rotations may be of value in native farming 

 in the future, but at present land is so abundant, except close to the 

 villages, that farmers would regard it as waste of a year's crops to 

 plough in the beans. 



In the North Mamprusi region very diflferent conditions prevail 

 from those just described, as shown by a recent survey undertaken 



