414 



THE FERTILITY OF SOILS IN THE TROPICS 



away, it is not to be expected that very general recourse 

 to nitrogenous manuring will be necessary. Probably in 

 the near future such treatment will only be required on 

 hillsides damaged by wash and on old tapioca land and 

 possibly coffee land. 



In no case has any relationship been traced between 

 yield and nitrogen content. 



Potash. The same ten soils may be retained as ex- 

 amples throughout; the following table shows the per- 

 centage amounts of potash they contain : 



The quantities present in the clay soils are, as was to 

 be expected, greater. The lowest figure yet obtained for 

 '* available " potash is 0*004 P er cent., and this was from 

 a good yielding estate. No relationship between potash 

 content and fertility has as yet been traced, and it seems 

 likely that in most types of Malayan soil sufficient is 

 always present for the ordinary needs of the tree. In 

 the prevention of the effects of drought, however, arti- 

 ficial potash fertilizing is effective even on a soil con- 

 taining as much as 0*015 per cent. '" available " a. pheno- 

 menon observed in other countries and with other crops. 



Phosphate. With the exception of the peaty soils, 

 which will be dealt with in connection with coconuts, 

 the soils in Malaya are markedly deficient in this element. 

 The percentage of this constituent in the soils whose 

 other analytical characteristics have been given are as 

 follows : 



Phosphate appears, in fact, to be the limiting factor, 

 and in all cases where differences of fertility not ascribable 



