EXPERIMENT STATION BULLETINS. 579 



advances, tlie soil temperature rises and the relative amount of these 

 elements in available forms increases, reaching a maximum about the 

 middle of the summer and then declining until in the fall there is again 

 practically no soluble plant food in the soil. In mid-summer when these 

 elements are most available in the soil, fruit spur growth should be 

 about completed. During the earlier part of the season is the period 

 when available nitrogen is most essential in promoting the development 

 of strong fruitful spurs and in favoring fruit setting. Phosphorus and 

 potash, while also essential, do not seem to be required quite so early 

 in the season. The problem of the grower, therefore, is to use such 

 cultural practices as are necessary to insure an adequate supply of these 

 essential elements as thej' are required for fruit growth. 



There are several practices that may help to insure this supply. An- 

 nual moderate pruning of the trees during the winter or early spring 

 indirectly helps to compensate for this deficiency since there will be 

 a smaller top growth to support. The early spring plowing of cover 

 crops that are still in a green, succulent condition and that will decom- 

 pose quickly and soon become available to the plants will tend to favor 

 growth. The early cultivation of orchard soils following plowing tends 

 to liberate plant food at this season. The application of fertilizer early 

 in the spring, either as decomposed stable manure or in such commer- 

 cial forms as will soon become available to the plants, may prove most 

 beneficial in encouraging an early, vigorous spur growth. 



The ideal of the Michigan fruit grower handling a bearing apple 

 orchard on the soil mulch system should be to furnish and maintain the 

 organic and nitrogenous content of the soil by the growing of cover 

 crops supplementing this practice by the addition of potash in the 

 commercial form and more frequently of phosphorus when such happen 

 to become limiting factors of production. In commercial practice, how- 

 ever, especially on light soils, it may frequently be found advantageous 

 to supplement the nitrogenous content of the soil by moderate applica- 

 tions of some quickly available form of nitrogen, applying it early in 

 the spring. As a matter of fact most growers are not maintaining either 

 the organic or nitrogenous content of their soils by cover cropping as 

 is evidenced by the present condition of their trees and the crops pro- 

 duced. As stable manure in sufficient quantities is rapidly becoming 

 a thing of the past, growers are bound to turn their attention more to 

 the commercial forms of fertilizers and unless used judiciously they are 

 quite apt to be disappointed with the results. 



COMMERCIAL FERTILIZERS. 



Commercial fertilizers can never be considered as full substitutes for 

 stable manure. They do not furnish the organic matter to the soils to 

 keep them mellow, friable and capable of holding moisture and it is only 

 when this physical condition of the soil is thus maintained that the 

 best results can be obtained with commercial fertilizers. Recent tests 

 have demonstrated that when commercial fertilizers are used the results 

 will also depend greatly upon the time of application and the availa- 

 bility of the forms used. 



Investigations on the causes of apple blossoms failing to set have 

 shown that this condition is closely associated with the question of plant 



