582 STATE BOARD OF AGRICULTURE. 



effect of pruning upon growth and fruit production, but much light has 

 been shed upon this subject by recent investigations. 



The pruning of trees while dormant has been commonly regarded as 

 a practice that results in increased vigor of the plant. Since severe 

 dormant pruning usually causes a stimulated vegetative growth of the 

 remaining branches, it might appear that such was the case, especially 

 if judgment is based on the length of twig growth of the remaining 

 parts the following season. Annual twig growth alone, however, is 

 not a correct index of a tree's vigor. Studies have shown that the 

 total amount of w^ood laid down over the entire plant is a more accu- 

 rate index of a tree's vigor. When a tree is severely pruned during the 

 dormant season, the equilibrium that naturally exists between the top 

 and root systems, as determined by the environment and food supply, 

 is broken. While this results in a more rapid vegetative growth of the 

 remaining parts after pruning, this growth is not sufficient to compens- 

 ate for the loss of branches caused by pruning and for the new growth 

 that otherwise would have been produced. So far as the effect on growth 

 is concerned, the less a tree is pruned the larger and heavier it becomes. 

 Therefore, pruning is at the expense of total growth rather than result- 

 ing in a gain in total growth. 



It is also sometimes considered that a heavy pruning of the top in- 

 duces a renewed and strengthened root development. A study of plant 

 physiology reveals the dependence of root growth upon the food supply 

 assimilated in the leaves. Any severe reduction of foliage naturally 

 limits the food supply to the root system, which in turn proves a limit- 

 ing factor of root growth. Severe top pruning, therefore, tends to re- 

 tard root growth and development rather than to stimulate or invigor- 

 ate it. 



W^hile pruning results in a more rapid vegetative growth of the re- 

 maining branches, its effect upon fruit production is less definite; the 

 results depend largely upon the vigor of the tree, the degree of prun- 

 ing practiced, and the character of the pruning. The heavy pruning 

 of trees already in a vigorous condition of growth encourages further 

 vegetative development at the expense of fruit production. Heavy 

 pruning of trees just coming into fruiting further retards the time of 

 bearing. W^hen the lack of fruitfuluess, however, is due to what is 

 called a "general devitalized condition" of the tree as characterized by 

 little, new spur or twig growth and small light-colored foliage, dormant 

 pruning results in a stimulated growth of the remaining spurs and 

 twigs which in turn may or may not result in increased fruit produc- 

 tion. This so-called "devitalized condition" of the tree Krauss has 

 found is caused by an accumulation of the carbohydrates to such a 

 degree in excess of the available soil nutrients that their efficient util- 

 ization is prevented. When a tree has reached the period of full bear- 

 ing, its roots have penetrated all the available soil area so that in soils 

 of but moderate fertility the proportion of soil nutrients absorbed to 

 that of the leaf area, which in turn measures the carbohydrate supply, 

 is apt to become less each year. The nitrogen and other soil nutrients 

 then become the limiting factors of fruitfuluess and growth. While 

 pruning will not increase the supply of nitrogen and other food ele- 

 ments in the soil, it reduces the supply of carbohy^lrates and in that 

 way tends to readjust this balance. Even under these conditions if the 



