New York Agricultural Experiment Station. 91 



packages are required and three times as nuich freight must be paid, 

 all for the same amount of plant- food. 



4. What Amount of Each Fertilizing Constituent is Needed. 



Inseparably connected with the question of what elements of 

 plant-food are needed is the (juestion, " How much of each element 

 is needed 'i " Perhaps, the question more often asked than any 

 other relates to the quantities in which fertilizers should be applied. 

 Granting that we know fairly well whether we need to use nitrogen, 

 or phosphoric acid or potash compounds, or some combination of 

 these, how can we ascertain how much to put on an acre of land ? 

 This question is quite as complicated as the preceding one. A 

 variety of conditions must be considered. If we knew how much 

 available plant-food there were in an acre of soil, and how much the 

 gro\ving crop would require, the matter would be comparatively 

 simple, provided the mechanical condition of the soil was satisfac- 

 tory. The form of fertilizing material used would also need 

 consideration. 



There are two extremes which we must strive to avoid. On the 

 one hand, we can assume that the supply of food in the soil is fairly 

 abundant and make only small additions, thus running the risk of 

 using too small amounts for growing a good crop. On the other 

 hand, we may assume that the supply of food in the soil is decidedly 

 deficient and put on quantities of fertilizing material sufficient in 

 itself to grow a good crop. In this case, we run the risk of putting 

 on more than the present crop needs. If we can not hit upon the 

 desired medium, putting on amounts that will grow the best crop 

 most economically without leaving too much plant-food over, it is 

 better to make the mistake of putting on too much than too little. 

 "While only individual experimenting can determine in each case 

 how much nitrogen, potash, and phosphoric acid can be used to best 

 advantage, we can give some suggestions that may be helpful as a 

 guide. We will, therefore, consider some of the conditions which 

 determine the amount of fertilizer to be employed in raising crcips 

 most economically. 



How Can We Determine the Amount of Available Plant- 

 Food Present in the Soil ? — As pre\'iously pointed out, this can 

 not be satisfactorily determined by a chemical analysis of the soil. 

 It can really be done only in an indirect way and even then only 

 approximately ; and that is by comparing the behavior of crops 



