4 - 



piration loss. Some of the plant growth effects observed with red 

 spider mite population have been indicated to be a result of injec- 

 tion or removal of growth promoting and inhibiting substances. In 

 mite-infected plum material, D.J. Avery and H.J. Lacey found greater 

 amounts of gi bberel 1 i n-1 i ke substances and smaller amounts of auxin- 

 like substances, except lAA. — Penn. State Horticultural Reviews, 

 October, 1969. 



*************** 



FACTORS AFFECTING NUTRIENT CONTENT OF APPLE FOLIAGE 



(Editors' Note. The following discussion of factors affecting nutri- 

 ent content of apple foliage was prepared by the late Dr. W.D. Weeks 

 and appeared in the May 10, 1964, issue of Fruit Notes . A review of 

 these factors appears essential from time to time because an increas- 

 ing number of growers are using leaf analyses as a guide for the 

 maintenance of optimum nutritional levels in apple orchards.) 



Crop size can have a considerable effect on the quantity of 

 several elements in apple foliage. Leaves from a tree with a large 

 crop will contain more nitrogen and less potassium than leaves from 

 a tree with a light crop. Leaves from a light crop tree may have a 

 leaf nitrogen which is 0.2 and 0.3 per cent lower than the same tree 

 when it has a full crop. Differences in leaf potassium as great as 

 0.4 per cent may occur between heavy and light crop years. Calcium 

 follows the same trend as nitrogen and exhibits about the same dif- 

 ference as nitrogen in leaf content between the light and heavy crop 

 year. Leaf magnesium is slightly higher in a heavy crop than in a 

 light crop year. Crop size has little, if any, effect on leaf phos- 

 phorus . 



The relative amount of one element in relation to another may 

 effect the mineral content of the leaf. For example, leaves which 

 are relatively high in nitrogen tend to have lower levels of potas- 

 sium and phosphorus and higher levels of magnesium and calcium than 

 leaves from trees which have a low to medium level of nitrogen. 

 High levels of potassium may depress leaf magnesium and calcium, par- 

 ticularly if the soil supply of magnesium and calcium are low. How- 

 ever, moderate levels of potassium do not seriously depress magnes- 

 ium where there is an adequate supply of magnesium. 



Another factor which may influence the leaf content of some 

 elements is soil moisture or rainfall. Leaf potassium is generally 

 lower in dry growing seasons than in years with adequate soil mois- 

 ture. Magnesium is generally lower in years which have above-normal 

 rainfall during the early part of the growing season. The magnitude 

 of the change in leaf content caused by seasonal rainfall will depend 

 upon the wetness or dryness of the season and the supply of nutrients 



