THE FERTILITY OF SOILS IN THE TROPICS 423 



The carrying out of manuring experiments in the 

 northern tropical districts presents many difficulties, and 

 one series of experiments established by the Department 

 of Agriculture and Stock, under my direction, had to be 

 abandoned; another series was started last year in the 

 neighbourhood of the Kamerunga State Nursery, and 

 this has already suffered from very adverse climatic con- 

 ditions, viz., an unprecedented spell of dry weather last 

 year, followed by exceptionally heavy rains this year. 



Several manurial experiments carried out in Southern 

 Queensland, under sub-tropical conditions, gave excellent 

 results, and demonstrated, beyond doubt, that exhausted 

 banana lands may, by thorough cultivation and the aid 

 of heavy dressings of artificial fertilizers, produce crops 

 equalling those obtained from virgin lands. Of course 

 not all exhausted lands may give such good results, 

 as it is of great importance that the soil be in good 

 physical condition and, above all, contain a fair amount 

 of humus. 



As to the class of soil required for banana culture, 

 authorities somewhat differ, but the contradictory state- 

 ments one meets are perhaps more apparent than real, 

 and are largely influenced by local conditions. 



Like all tropical plants, bananas require an abundant 

 and regular supply of moisture, and therefore the soil 

 must possess a good water-holding capacity, but at the 

 same time be well drained, to prevent the water becom- 

 ing stagnant near the surface. 



The manager of the Experimental Garden at Kwai 

 (German East Africa) states [2] : Bananas like moist, 

 swampy flats with a rich, fat soil. Soil rich in humus 

 always yields larg'er crops of bananas than clayey soil. 

 Against this statement, which undoubtedly is due to ex- 

 ceptional local conditions, we must note in Dr. Grote- 

 wold's paper on banana culture [3], that bananas love 

 moisture, but do not thrive in swamps. The soil must 

 also be free from excessive amounts of salt, and flats 

 containing an excess of salt may be made fit for culti- 

 vation by flooding them with water for some time, as 

 practised in Colombia. 



With regard to humus, Henricksen [4] states, that 



