66 THE BANANA 



as a result of continual alterations in the concentration 

 of the soil waters.* 



HUMUS 



For bananas it is important that there should be decayed 

 vegetable matter, " humus," in the soil. According to 

 Voelcker, " the principal effects of humus on the soil are 

 of a physical character, and it exercises particular benefit 

 through its power of retaining moisture. Humus, how- 

 ever, has a distinct chemical action, in that it forms 

 combinations with iron, calcium, and ammonia. It thus 

 becomes one of the principal sources of supply of the 

 nitrogenous food of plants, and a soil rich in humus is one 

 rich in nitrogen." 



FARMYARD MANURE 



Farmyard manure is to a large extent composed of 

 humus, and contains all the constituents required by 

 crops ; but the physical condition of the soil is also im- 

 proved by its use, inasmuch as the land is kept porous, and 

 air is allowed free access. It may be spread fresh on the 

 banana fields and ploughed in at any time. The great 

 difficulty is to get enough of it, but whatever there is 

 should be applied as soon as the plants are put in, or, 

 generally speaking, at the earliest stage possible in the life- 

 history of the plant or ratoon. Green manuring should 

 be used as a substitute, if farmyard is not available, 

 (See paragraphs on Mulching, p. 33.) 



LIME 



The use of lime is of the greatest importance, as it 

 increases fertility, chiefly by improving the physical 

 texture of the soil. 



It is natural to suppose that any soil derived from 

 limestone must have abundance of lime in it. But natural 

 agencies, chiefly the carbonic acid and water in the soil. 

 * Agric. News, xii. 104 {1913). 



