SURPLUSES AND DEFICIENCIES 201 



uses. This surplus is merely tolerated and usually no harmful influence 

 results. Among these elements may be mentioned potassium, calcium 

 and magnesium. As with the preceding list, their application in fertilizers 

 may indirectly benefit the plant through improving physical and chemical 

 conditions within the soil, or restoring a proper ratio between them in the 

 case of the last two. 



It would seem that sufficient evidence to support these statements has been 

 presented in the discussion of the individual elements that has preceded. It is 

 realized, however, that they run counter to the opinions that have been expressed 

 in a great number of published statements dealing with this question, to many 

 recommendations that have been made for the fertilization of fruit trees, to 

 what has in some instances become more or less well established practice and to 

 the apparent results of certain plot experiments. This is true particularly in the 

 cases of potassium and calcium. It seems desirable, therefore, to bring together 

 the results of some of the orchard fertilizer experiments with potash and lime 

 and examine them somewhat critically. Table 66 presents such data gathered 

 from many sources. It does not include all the records that might be assembled, 

 but it represents the results of American plot trials. 



In some cases the application of potassium- or of calcium-carrying fertilizers 

 has resulted in increased yields; in others in decreased yields. The increases 

 outweigh the decreases in both number and amount; but in the Pennsylvania 

 experiments alone, of those included in the table, are the increases striking or 

 to be regarded as of considerable significance. These particular Pennsylvania 

 records are extremes purposely chosen from a large number, the great majority 

 of which show no such marked response from potash applications. Furthermore, 

 the different check plots in these two orchards show such variation as to justify 

 some hesitancy in drawing conclusions when comparing the results of one fer- 

 tilizer treatment with those of another on a plot some distance removed from 

 the first. For instance, it may be questioned if the plots treated with lime alone 

 and with nitrogen alone were as good at the outset as those receiving nitrate of 

 soda and muriate of potash. In nearly every case in which comparison is possible 

 between potash or lime treated plots and those treated with nitrogen alone or in 

 combination, nitrogen stands out as the element most needed, the one from the 

 application of which the greatest response is obtained. The fact that in most 

 cases the application of nitrogen alone resulted in yields exceeding those afforded 

 by potash or lime is further evidence that there was an ample supply of these 

 two elements in the soil for larger crop production, that they were present in an 

 available form and that they were not the real hmiting factors. Theoretically 

 potassium and calcium are to be considered as possible limiting factors just as 

 nitrogen or iron or phosphorus or sulfur. Here and there is to be found evidence 

 that occasionally they actually are not present in an available form and in 

 quantities sufficient for the trees' requirements, but in the great majority of 

 cases there is no occasion to supplement the supply already present in the soil. 



3. Certain elements, such as copper, arsenic and lead, are occasionally 

 found in plant tissues and when present in considerable amounts they 

 have toxic effects. However, their presence is the result of spray applica- 



