EXPERIMENT STATION BULLETINS. 581 



sufficient, it may affect growth and production in quite a similar man- 

 ner as when nitrogen is the limiting factor. The production of new 

 growth is inhibited, the leaves are light and yellow in color and the trees 

 as a whole appear devitalized. Under such conditions an application 

 of acid phosphate results in a vigorous vegetative growth of strong, 

 healthy shoots with large, dark-green leaves, showing that the un- 

 balanced condition of the soil for growth has been adjusted. From 5 

 to 10 pounds of acid phosphate per tree should be used in fertilizing 

 mature orchards under these conditions, the exact amount being esti- 

 mated by the apparent degree of deficiency of this element as well as 

 upon the size of the tree. Beneficial results may be expected on such 

 soils from subsequent applications every second year. 



Potash. While potash is another essential element for plant growtli 

 that is sometimes deficient in the soil, it is not so frequently a limiting 

 soil factor in Michigan as nitrogen or phosphorus. This element seems to 

 be most directly concerned in the development of strength and sturdiness 

 to the twigs, foliage and branches and in the maturing of the plant 

 tissues and fruit. Apparently, this element is not so essential during 

 the earlier season of growth and later in the season the average soil 

 of this State seems to contain enough available potash for the require- 

 ments of the tree. However, when an application of potash seems neces- 

 sar}-, from two to three pounds of muriate or sulphate of potash should 

 be applied per tree. 



While much information as to the probable deficiency of an orchard 

 soil may be obtained through studies of the soil, and by the growth and 

 production of the trees, the surest method of ascertaining a soil's de- 

 ficiency is by an actual orchard test. Such a test should precede any 

 extensive application of commercial fertilizer w^hen no very definite 

 indications of deficiencies are apparent, or when no such orchard tests 

 under similar conditions have been made in the locality. The simplest 

 orchard test for this purpose would consist of three plots using three 

 or more trees to a plot with a check or unfertilized row of trees be- 

 tween each. To one plot nitrate of soda might be applied; nitrate of 

 soda and acid phosphate to the second ; nitrate of soda, acid phosphate 

 and muriate of potash to the third. Such tests would indicate Avhether 

 any or all of these elements were needed. A general application based 

 upon these results could be quite safely made to the entire orchard 

 the following season. The amount to use from year to year will con- 

 tinue to be a matter of estimate based upon the results obtained from 

 the previous season. 



TRUNING. 



There are few mature apple orchards in this State that have not 

 suftered from the pruning saw. Injudicious pruning of apple trees has 

 been such a common fault that some growers are turning to the oppo- 

 site extreme in believing that trees are better unpruned. The degree 

 of jjruning required b}^ a tree and the results that may be expected are 

 so intimately dependent upon the condition of the tree and so closely 

 associated with the food and moisture supply of the soil that no simple 

 formula for pruning can be offered. 



Many fallacies exist in the minds of horticulturists regarding the 



