340 TALKS OX MANURES. 



Labor would be saved by not cultivating the land. Manure 

 would be saved by substituting vegetation waicli grows under 

 or above ground, almost all th 3 yeat- roand. And, by feeding 

 the Suock with cake, tiu necessary fertility would be obtained 

 at the lowest possible cost. 



It is probable that the land would require this treatment to 

 be rep3afced for several >ears, before there would be a fair 

 growth of gr ss. The land might then bo 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 largo 

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

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

 of fertility which it contains, but we are left hi 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 Rothamsbed, among my experiments on the growth of cou- 

 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 impossible 

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

 ance; of mineral substances which the crop could not make uso 

 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 aftar 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- 

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

 c olios separated from the carbon, and enters into combination 

 with oxygen, does not appear to be of any use to the crop. 



The combination of nitrogen with oxyg:n, is known as ni- 

 tric acid. The nitric acid enters into combination with the 

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



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

 nitric a3id might be called the main spring of agriculture, but 



