USE OP MANURE8 149 



food, and with this information and the knowleage of 

 what the crop in question requires, apply the proper 

 amounts of the fertilizers. The difficulty in the way 

 is, that while it is possible to determine with consider- 

 able accuracy how much nitrogen, phosphoric acid, 

 potash, lime, etc., a soil contains, there is no accurate 

 method for determining just how much of each of these 

 substances is in available form for plant food. We 

 may find by analysis that a soil contains .5 per cent 

 of potash, hut for all wo know from the- analysis, the 

 total amount may be unavailable for plants. On the 

 other hand, we do know from accurate analyses just 

 how much plant food is required to produce any single 

 crop, and can use the knowledge to advantage in apply- 

 ing fertilizers. 



But different plants vary greatly in their power of 

 procuring their food supplies from the soil; one, for 

 example, requiring large amounts of potash may be 

 able to obtain its supply of this constituent much more 

 easily and readily than another requiring a smaller 

 amount of it. In such cases analysis is not a safe guide. 



No fixed rules can be laid down for the use of 

 manures; different crops require very different treat- 

 ment, and even the same crop under varying conditions 

 of soil and climate takes up varying amounts of plant 

 food. The only reliable way of determining what dif- 

 t crops require in the way of plant food is by 

 experiment. Every farmer must determine for himself 

 the kind and amount of fertilizer his crops require, and 

 in doing this he may be greatly aided by a knowledge 

 of the composition and habits of growth of the crops. 



