STATE POMOLOGICAL SOCIETY. 57 



Other food elements may be present in excess. In general, the 

 law of the minimum holds that in order to grow at all, plants 

 require certain minimum amounts of certain factors. As the 

 amounts of these factors increase, so also the growth of the 

 plant progresses up to a more or less definite point known as 

 the optimum. Any further increase of the factors causes a 

 decrease in growth. All plants increase in growth until the 

 optimum of all necessary factors is reached. Thus we can see 

 that trouble in plant production may arise from too much of 

 any one factor as well as from a deficiency of a factor. For 

 example, there is an optimum amount of soil moisture needed 

 for the best development of plants, yet the plant may suffer 

 severely from either drought or an excess supply of water in 

 the soil. 



Plant food represents a certain set of factors that are neces- 

 sary in the proper development of apple orchards, yet plant 

 food is not the only requirement. We need a proper moisture 

 supply, proper pruning, and proper protection against the rav- 

 ages of insects and fungus diseases. Above all, we should 

 remember that the limiting factors in one orchard may be en- 

 tirely different from the limiting factors in another orchard. 

 In some sections of the county, a certain factor, say potash or 

 phosphoric acid, or even lime, may be deficient over a large 

 area. In my own section, the limiting factor in the soil for many 

 crops is phosphoric acid, yet phosphoric acid does not appear 

 to be the limiting factor in apple production in that section. One 

 orchard's food may be another orchard's poison. 



A large number of experiments in orchard fertilization have 

 been carried on in the United States, yet only a very few of 

 these experiments have been fundamental in principle or of 

 more than local value in their significance. Reports have been 

 made upon only five that have been carried on for a long period 

 of years. There are others that are under way that show 

 promise of ultimately throwing light upon the vexatious problem 

 of orchard fertilization. 



One of the most noted of these long time experiments is one 

 being carried on by the Woburn Experiment Station in Eng- 

 land. This experiment began in 1894 and is still in progress. In 

 general, this experiment shows but little if any benefit from the 

 application of either barnyard manure or commercial fertilizers. 



