Damon Boynton 291 



measurements. If shoot length, leaf numbers, leaf size, and leaf color 

 are all abnormally low or abnormally high, it is likely that both the 

 food reserve and the current nitrogen supply were abnormally low or 

 high. If growth, leaf numbers, and leaf size are low and leaf color is 

 high, it is likely that food reserve was low but that the current nitrogen 

 supply has been increased. If growth, leaf numbers, and leaf size are 

 high and leaf color is low, then it is likely that the food reserve was 

 considerable but the current nitrogen supply is not great enough to 

 maintain color. Determination of leaf color at intervals throughout the 

 growing season may give additional diagnostic evidence of the course 

 of current nitrogen supply. Figure 3 shows the chlorophyll trends and 

 total nitrogen trends in leaves from a Mcintosh apple orchard under 

 six nitrogen treatments, involving different levels, times, and methods 

 of application. In all cases the midseason peaks of the curves are de- 

 termined by the total rate of nitrogen application: the higher the rate, 

 the higher the peak. The peak for treatment C was reached later than 

 for the other treatments; this was associated with the fact that three of 

 the six urea sprays were applied after the middle of June. All of the 

 chlorophyll curves tended to flatten at the end of the growing season 

 more than they do in many years. This may be due to the fact that the 

 orchard was harrowed several times in July in order to eliminate deep 

 ruts created by the heavy spray machinery, a practice which may have 

 released nitrate in midsummer and checked the normal sod cover at 

 the end of summer. Yields were low in this orchard due to poor 

 pollination and there were no significant differences among them, but 

 fruit color was inversely related to nitrogen in all cases. It would seem, 

 from this and other studies, that the seasonal chlorophyll curve as- 

 sociated with highest yield potential and best fruit color would be 

 rather high in early summer and rather low at harvest time. The leaf 

 color range of 1.8 to 2.0 mg. per 65 sq. cm. surface, in July, reflects a 

 compromise between these two opposing objectives. Of course, interpre- 

 tation of such measurements must be based on experimental nitrogen 

 response studies over a period of years in the climatic zone where the 

 diagnosis is needed. This is because the nitrogen responses of an apple 

 variety differ in different zones as well as from year to year. Whereas 

 the range of group 3 in Table VI seems to be correlated with satis- 



