EESTOEING FERTILITY TO THE SOIL. 341 



being perfectly soluble in water, it is constantly liable to be 

 washed out of the soil. In the experiment to which I have re- 

 ferred above where wheat is grown by mineral manures alono 

 we estimate that, of the amount of nitric acid liberated er.ch 

 year, not much more than one-half is taken up by the crop. 



The wheat is ripe in July, at which time the land is tolerably 

 free from weeds ; several months, therefore, occur during 

 which there is no vegetation to take up the nitric acid ; and 

 even when the wheat is sown at the en:l of October, much ni- 

 tric acid is liable to be washed away, as the power of the plant 

 to take up food from the soil is very limited until the spring. 



The formation of nitric acid, from the organic nitrogen in the 

 soil, is due to the action of a minute plant, and goes on quite 

 independent of the growth of our crops. We get, however, in 

 the fact an explanation of the extremely different results ob- 

 tained by the use of different manures. One farmer applies lime, 

 or even ground limestone to a soil, and obtains an increase in 

 his crops ; probably he has supplied the very substance which 

 has enabled the nitrification of the organic nitrogen to increase; 

 another applies potash, a third phosphates ; if either of these 

 are absent, the crops cannot make use of the nitric acid, how- 

 ever great may be the amount diffused through the soil. 



It may possibly be said that the use of mineral manures tends 

 to exhaust the soil of its nitrogen ; this may, or may not, be 

 true ; but even if the minerals enable the crop to take up a 

 larger amount of the nitric acid found in the soil year by year, 

 this docs not increase the exhaustion, as the minerals only tend 

 to arrest that which otherwise might be washed away. 



We must look upon the organic nitrogen in the soil, as the 

 main source of the nitrogen which grows our crops. Whatever 

 may be the amount derived from the atmosphere, whether in 

 rain, or dew ; or from condensation by the soil, or plants, it is 

 probable that, where the land is in arable cultivation, the ni- 

 trogen so obtained, is less than the amount washed out of the 

 soil in nitric acid. Upon land which is never stirred by the 

 plow, there is much less waste and much less activity. 



The large increaie in the area of land laid down to perma- 

 nent pasture in England, is not due alone to the fall in the price 

 of grain. The reduction of fertility in many of the soils, which 

 have been long under the plow, is beginning to be apparent. 

 Under these circumstances a less exhausting course of treat- 

 ment becomes necessary, and pasture, with the production of 

 meat, milk, and butter, takes the place of grain fbkb. 



