356 Report oF THE HorricULTURAL DEPARTMENT OF THE 
relative proportions of the different plant-food constituents. The 
averages were as follows: 
Nitrogen, 1 pound. 
Phosphoric acid, .27 pound 
Potash, 1.14 pounds 
Lime, 1.85 pounds 
Magnesia, 0.45 pound 
INTRODUCTION. 
The problem of feeding plants in the most effective and, at 
the same time, economical way is more complicated than any 
other we have to deal with in ordinary agricultural oper- 
ations. - Assuming that the physical properties of the soil are 
satisfactory, we ought to know, in order to solve the problem 
most satisfactorily, two important factors—first, the amount of 
plant food required by crops, and second, the amount of avail- 
able plant food which the soil can be relied upon to furnish 
during the growing season. It is less difficult to secure knowl- 
edge regarding the former question. Much study has been, and 
is being, given to the latter point, the determination of the 
amount of available plant food in soil, but a thoroughly reliable 
method cannot be said to have been found yet. 
The work presented in the first part of this bulletin was under- 
taken at the suggestion of the Director and its object was to 
study one of the factors indicated above, viz., to ascertain the 
amounts of certain plant-food constituents used in one growing 
season by fruit trees in bearing. For a strictly complete study,, 
we sught to know the amount of plant food used during the 
growing season by the fruit, leaves, new growth of wood, 
increase in size of trunk, branches and roots. So complete an 
investigation is impracticable, and we have to content ourselves 
with the results given by the fruit, leaves and new growth of 
branches. The plant food contained in these undoubtedly in- 
cludes much the larger part of the total used by the whole tree. 
The evidence furnished by chemical analysis of a given crop 
cannot be interpreted rigidly as showing how much plant food is 
actually required for that crop under any and all conditions. 
When there is an abundant supply of any form of plant food, a 
