No. 129.] 315 



only requires the plants to search for the food which they had 

 exhausted above, in order to obtain the quantity necessary to their 

 growth and development. 



Thus, in a deep alluvial soil, where the surface only has been 

 scratched for years, and may be for centuries, and where the su- 

 per soil is thoroughly exhausted of all the elements of crop-gro vis- 

 ing, while perhaps the sole of the plow has managed to make a 

 firm pan, a few inches below its surface, it is not necessary to 

 manure at all. Only break the pan and plough up the fresh soil, 

 and all turnip disease and clover sickness and root-swelling of 

 oats will be prevented. In fact, the soil below will contain a 

 pi*oportion of the food of plants suited to their wants, and hence 

 on such soils it will not be necessary always to carry back the 

 elements of which it is exhaused, because they are already pre- 

 sent, only locked up from the plant, and liberated and brought 

 within its sphere by the fad alone of deep cultivation. 



But on poorer and thinner soils this process would be unavail- 

 ing. The subsoil below is poorer than the soil above. To deepen 

 here were only to add to the previous poverty, and hence the 

 cultivator must hit upon some other mode of restoring fertility 

 than mere deep cultivation. Nay, we have seen the more deep 

 ploughing of ordinary land operate against immediate produc- 

 tiveness, and have for the time exactly the opposite tendency. 



But there are hundreds of means by which more or less of the 

 missing elements are restored by natural processes alone ; and 

 though it may be necessary to modify crops, so as to be assisted 

 by nature, still there are scarcely any of the known elements of 

 plants which are not provided for their use in a greater or less 

 degree in the wild field of nature. If we first take ammonia — the 

 symbol and vehicle of the nitrogen of plants — the staple of the 

 wheat plant, and perhaps the real test of the fertility of a soil, 

 other things being equal — of this Liebig is so certain that he not 

 only asserts its presence in the atmosphere, but declares that it 

 exi^sts in all soils in quantities more than sufficient to produce 

 any crop of corn, or graiu,or plants whatever. Mulder questions 

 this, it is true. Ee states that the atnaosphere contains an acci- 



