59 



With iron the case is very similar. This element is almost uni- 

 versally present in agricultural soils and the total amount required 

 is so small that its addition can scarcely be expected to produce 

 any important effect. This also is borne out by such experimental 

 results as are now available. 



From the large amount of potash carried by the fruit, one might 

 suppose that its addition to the soil would be very important in im- 

 proving yields, and this idea has been widely proclaimed, especially 

 by those considering only the chemical composition of the fruit. 

 As indicated later, however, it seems that most orchard soils are al- 

 ready sufficiently supplied with potash in available forms and that 

 the chief shortages occur in the nitrogen and phoshates. This is 

 the case notw^ithstanding the fact that the latter materials are actu- 

 ally required in considerably smaller amounts. 



From these facts it is evident that there is comparatively little 

 relation between response and requirements in the case of plant 

 food and that something more than a knowledge of the chemical 

 composition of the fruit and wood is needed before one can prop- 

 erly fertilize an orchard. Even with the additional knowledge of 

 the composition of the soil, the problem is not much simplified 

 because it is impossible as yet to duplicate sufficiently the conditions 

 existing in any soil. 



A chemist may determine the total amount of plant food pres- 

 ent, but he can not yet determine their actual availability to the trees 

 with sufficient accuracy to be of much value. The practical and 

 proper fertilization of an orchard, therefore, becomes an experi- 

 mental problem, and its solution is dependent primarily upon the 

 pomologist or horticulturist. In other words, the question is not 

 so much what amounts of plant food are annually taken up, nor 

 what amounts are present, but rather it is what responses are made 

 when certain kinds and quantities of plant food are actually added 

 to an orchard soil. 



It is to get light on the latter question in connection with ten 

 different types of soil that we have been working at the Pennsyl- 

 vania Station since 1907. Altogether in the case of apples we have 

 ten experiments on bearing trees, and two on young trees involving 

 a total of more than 2,800 trees, located in different parts of the 

 State, all of which bear more or less directly upon the present ques- 

 tion. For the present, however, we shall call special attention to but 

 three of these experiments, since they bring out most clearly the 

 principal points involved. 



Effects of Plant-Food Additions to Orchards. 



Some of the effects of adding plant-food to orchards are shown 

 in Table 11. This table gives the yields obtained during the past 

 five years in a lo-plot experiment with Baldwins, now 24 years of 

 age, located on a Volusia silt loam in Lawrence County, north of 

 Pittsburgh. In estimating the influence of the treatments, the 



