[ 5" ] 



but if the soil is left ploughed up and bare for a few days 

 and if heavy rainfall takes place, the same soil may show 

 less than Jg-th per cent, of available nitrate. Loss by 

 drainage may come up to as much as 80 or 100 Ibs. of N. per 

 acre, but this is not what ordinarily takes place even in 

 lands swamped with water such as the rice fields of Bengal 

 are. The chief protection against the loss of nitrates and 

 indeed of all soluble plant-food is the generation of vegetable 

 and animal life, visible and microscopic, at the beginning 

 of the rainy season. When the rainy season actually com- 

 mences, fields which are not under crops, have a luxuriant 

 growth of weeds and minute vegetation and also of 

 animals large and small. The animal and vegetable life 

 growing rapidly in the soil throughout the rains prevent to 

 a great extent the washing away of fertility. The question 

 of loss of nitrate and other soluble food-materials by drain- 

 age is very complicated, but the loss is not so very great in 

 the tropics owing to the rapid propagation of vegetable and 

 animal life of all sorts which helps to convert soluble nitrates 

 &c. into comparatively insoluble protoplasmic bodies. 



819. Absorptive power of soils. To understand how the 

 utilization of phosphates, potash, lime and other food-rr.ate- 

 rials by plants is governed, it is necessary to get an idea of 

 what is called the absorptive power of soils. It is not alto- 

 gether a chemical process. It is both physical and chemical. 

 Bases and salts are partly absorbed by the soil as a whole 

 and partly decomposed. Cut off the bottom of a large bottle 

 and place the bottle vertically with its mouth downwards, the 

 mouth being secured with a plug of cotton wool. Fill the 

 bottle with clay loam slightly dampened with water. Then 

 pour dilute ammonia water in small quantities until the liquid 

 begins to drop from the lower end. It will be found that this 

 liquid is little more than mere water. In this way, consider- 

 able quantities of ammonia are absorbed by clay. If you repeat 

 the above experiment with K? SO solution instead of ammonia 



