Damon Boynton 287 



remove soluble nitrogen from the soil solution during the latter part 

 of the growing season. This means that fertilizer practices in apple 

 orchards should be designed to encourage grass growth. In New York 

 apple orchards, grass responds most often to nitrogen and liming. 

 Usually sparse grass growth in the areas between the trees is due to 

 lack of nitrogen. Failure of cover growth from lack of calcium and 

 magnesium occurs under the trees where acidification by sulfur sprays 

 has been most rapid. While there is no experimental substantiation of 

 this idea, it is probably worth while from the standpoint of nitrogen 

 control alone to fertilize for healthy grass growth in Mcintosh apple 

 orchards. 



The use of supplementary mulching materials spread under apple 

 trees is a common practice in many New York apple orchards. When 

 these mulches are composed of materials high in carbon, like straw 

 or nonleguminous hay, their initial effect is to depress the available 

 nitrogen supply in the soil. This effect may be apparent for a year or 

 more in apple trees mulched with high carbon materials. If the mulch 

 blanket is maintained over a period of years, ultimately nitrates will 

 build up under it and will remain high throughout the entire year. 

 Thus, heavy mulching even with nonleguminous materials causes a 

 loss of control of nitrogen effects. There has been no critical study of 

 moderate mulching in relation to nitrogen fertilization, but it is prob- 

 able that if annual mulch additions are light enough so that grass 

 grows through the blanket freely, satisfactory nitrogen control may 

 be maintained. 



Pruning and spraying practice 



Pruning and spraying practices may have important indirect in- 

 fluences on the nitrogen requirements and responses of apple trees. 

 Heavy pruning has been repeatedly demonstrated to act in the same 

 way as nitrogen fertilization, and in orchards where pruning is severe, 

 the nitrogen fertilizer program may be somewhat curtailed in order 

 to improve fruit color without loss of productivity. 



Nitrogen fertilization, to a considerable extent, has been used as a 

 means of overcoming the detrimental effects of fungicides on vegeta- 

 tion of apple trees. It was a common experience for apple growers 



