68 1 



As ;i rule the different plants in a class ot" crops resemble each 

 other in this respect. Thus, the cereals or gramineous crops have 

 a small capacity for assimilating nitrogen, therefore they require a 

 liberal supply of nitrogenous manure. The leguminous crops such 

 as beans, peas clover, etc., have a small capacity for potash, and 

 require a good supply of potash. Roots generally have a small 

 capacity for assimilating phosphoric acid, and require a phosphatic 

 manure. 



When the soil is cropped, the crop abstracts a certain amount 

 of the substances necessary to the nutriment of plants, which, if 

 carried away, will impoverish the land to the extent of the amount 

 of the different elements of nutrition that the crop has abstracted 

 from the soil. To maintain the fertility of the soil, that which was 

 abstracted from the soil must be put back into the soil, such as in 

 green manuring where the crop is ploughed into the soil, or it must 

 be made up by the addition of artihcial manures. 



Before we can put in an amount equivalent to what was 

 abstracted we must first know what has been abstracted and the 

 amounts. That we get by an analysis of the ash of the crop. 



The tables I. and II. will give some idea of what the different 

 crops extract from the soil. 



TAHLK I. The composition of the ash of plants in per centage 

 (excluding carbonic acid) : 



