MANURK3. 171 



to supply nitrogen to plants ; but it has other offices 

 which are of consequence. It assists in some of tho 

 chemical changes necessary to prepare the matters 

 in the soil for assimilation, and gives to the water in 

 which it is dissolved an increased power to dissolve 

 mineral plant food. 



Although, in the course of nature, the atmospheric 

 fertilizers are largely supplied to the soil, without 

 the immediate attention of the farmer, it is not l>e- 

 yond his power to cause their absorption in still 

 greater quantity. The means for doing this have 

 been repeatedly given in the preceding pages, but it 

 may be well to name them again in this chapter. 



The condition of the soil is the main point to be 

 considered. It must be such as to absorb and retain 

 ammonia to allow water to pass through it, and be 

 discharged below the depth to which the roots of 

 crops are searching for food and to admit of a free 

 circulation of air. 



The power of absorbing and retaining ammonia is 

 not possessed by sand, but it is a prominent property 

 of clay, charcoal, and some other matters named as 

 absorbents. Hence, if the soil consist of pure sand, 

 it will not make use of the ammonia brought to it 

 from the atmosphere, but will allow it to evaporate 

 immediately after a shower, or to be washed through 

 it by rains. Soils in this condition require additions 

 of absorbent matters, to enable them to use the am- 

 monia received from the atmosphere. Soils already 

 containing a sufficient amount of clay or charcoal, aro 

 thus far prepared to receive benefit from this source. 



