3i0 TALKS ON MANURES. 



Labor would bo saved by not cultivating the land. Manure 

 would be saved by substituting vegetation which grows under 

 or above ground, almost all the year round. And, by feeding 

 the siock with cake, the necessary fertility would be obtained 

 at the lowest possible cost. 



It is probable that the land would require this treatment to 

 be rei^eated for several >ears, before there would be a fair 

 growth of gr ss. The land might then be broken up and one 

 grain crop be taken, then it might again be laid down to grass. 



Hitherto, I have considered a case where fertility is almost 

 absent from the land, this, however, is an exception, as agri- 

 culture generally is carried on upon soils which contain large 

 stores of fertility, though they may be very unequally distribu- 

 ted. By analysis of the soil we can measure tlie total amount 

 of fertility which it contains, but we are left in ignorance in re- 

 gard to the amount of the ingredients whicli are in such a form 

 that the crops we cultivate can make use of them. 



At Rothamsted, among my experiments on the growth of con- 

 tinuous wheat, at the end of forty years, the soil supplied with 

 salts of ammonia has yielded, during the whole time, and still 

 continues to yield, a larger produce than is obtained by a liberal 

 supply of phosphates and alkaline salts without ammonia. 



When we consider that every one hundred pounds of wheat 

 crop, as carted to the stack, contains about five per cent, of 

 mineral matter, and one per cent, of nitrogen, it is iijipossible 

 to avoid the conclusion that my soil has a large available bal- 

 ance of mineral substances which the crop could not make use 

 of for want of nitrogen. The crop which has received these 

 mineral manures now amounts to from twelve to thirteen 

 bushels per acre, and removes from the land about sixteen 

 pounds of nitrogen every year. 



Analyses of the soil show that, even after the removal of 

 more than thirty crops in succession, without any application 

 of manure containing ammonia, the soil still contains some 

 thousands of pounds of nitrogen. This nitrogen is in combina- 

 tion with carbon ; it is very insoluble in water, and until it be- 

 comes separated from the carbon, and enters into combination 

 with oxj^gen, does not appear to be of any use to the crop. 



The combination of nitrogen with oxygen, is known as ni- 

 tric acid. The nitric acid enters mto combination with the 

 lime of the soil, and in this fonn becomes the food of plants. 



From its great importance in regard to the growth of plants, 

 nitric acid might b-^ called the main spring of agriculture, but 



