140 



FUNDAMENTALS OF FRUIT PRODUCTION 



Amounts Used in Fruit Production. — In general the tree may be said 

 to require relatively large amounts of phosphorus for fruit production, 

 much larger than for mere vegetative growth. However, analyses would 

 indicate that the total amount required by the trees for the development 

 of their fruits and of their new vegetative tissue would not be more than 

 8 pounds per acre in a peach orchard yielding at the rate of 300 bushels; 

 the total phosphorus draft of most other deciduous fruits is not materially 

 greater. Considering the limited amounts of phosphorus used by decidu- 

 ous fruit trees, and the comparatively large amounts present in nearly 

 all soils as well as the supply in the subsoil available to deep-rooted trees, 

 it is evident that under average orchard conditions phosphorus is not 

 likely to be a limiting factor and that phosphorus fertilization is likely 

 to be of little direct use in assisting tree growth or in promoting fruit 

 production. On the other hand it may be of great value in promoting 

 the growth of grasses, legumes or other crops grown between the trees 

 for mulching or other purposes. This subject is discussed in some detail 

 under the heading of indirect methods of fertilization. 



Seasonal Distribution of Phosphorus. — There is a close similarity 

 between the seasonal distribution of phosphorus and nitrogen in many 

 parts of the fruit tree. 



0.5 



0.3 



Fig. 14. 



-Phosphorus content of plum leaves in percentages of dry weight. (Plotted 

 from data given by Richter.i^*) 



In Leaves. — Though leaf buds have a slightly higher percentage nitrogen 

 content than fruit buds, they have a sKghtly lower percentage of phosphorus. 

 The phosphorus content of the former has been found to be 0.576 per cent, of the 

 dry weight in the cherry and 0.594 per cent, in the plum; of the latter, 0.570 

 per cent, in the cherry and 0.592 per cent, in the plum.'^* 



The young leaf has about the same high percentage of phosphorus as the bud, 

 but this decreases rapidly with age as does the nitrogen, there being two periods 

 of rapid decUne, one in May, the other in September (see Table 25 and Figure 14). 

 The ratio of phosphorus to nitrogen in the young leaf is 1 : 6. Before leaf fall 

 it is 1 : 10 or 1 : 15. This indicates that the plant uses its phosphorus supply 



