II 



to grow and collect food from the air and soil. The late 

 application of these manures, however, is to be avoided, as 

 we shall see later. 



In this connection it is worth noticing that, in the 

 Woburn wheat experiments, ammonia salts appeared not 

 to delay the ripening of the crop so much as nitrate of 

 soda. 



The net effect of the increase of leaf and chlorophyll, and 

 of the lengthened period of growth, is the apparent anomaly 

 that a very large increase of non-nitrogenous material is 

 produced by the use of nitrogenous manures. For example, 

 Sir John Lawes and Sir H. Gilbert estimate a very large 

 gain per acre in carbohydrates (starch, sugar, &c.) from 

 manuring with nitrogen and minerals, as compared with 

 minerals only, in all the chief crops under experiment at 

 Rothamsted. The gain in carbohydrates for each pound of 

 nitrogen in the manure has been as follows, on the average of 

 several plots dressed with nitrogen in different forms and 

 quantities per acre 



TABLE III. 



Carbohydrates 



Crop. per Pound of 'Nitrogen 



in Manure. 



Lb6. 



Wheat 31-0 



Barley 46-3 



Sugar Beet 42-1 



Mangels 29-9 



Potatoes 17-0 



Beans 5-5 



How NITROGEN is TAKEN UP BY PLANTS. 



Like all the substances taken up by the roots of plants, 

 nitrogenous matter is only useful when in a state of solu- 

 tion, for plants have no power of absorbing insoluble 

 material. In this respect, sulphate of ammonia and other 

 ammonia compounds are quite suited to the requirements of 

 plants, being freely soluble in water. 



The three forms of nitrogen in the soil differ in their use- 

 fulness to the plant. Organic nitrogen is for the most part 

 useless, and must be regarded as a reserve which is gradually 

 drawn upon as the nitrogen is converted into other forms. 

 Ammoniacal and nitric nitrogen are, however, both use- 

 ful to plants. Nitric nitrogen is taken up readily, and is 

 often stored up in the plant for a time. Under favourable 

 conditions a suitable temperature and the presence of 

 carbohydrates in the plant being especially necessary it is 

 gradually changed into various organic substances, such as 

 amides and finally albuminoids. 



Ammoniacal nitrogen may also be directly used by plants. 

 Owing to the fact that, under natural conditions, most of a 

 crop's nitrogen, if not the whole of it, is taken up in the 

 nitric form, statements are frequently met with to the effect 



