468 Mineral Nutrition of Plants • 



not maintained because of fertilizer deficiency, that would quickly be 

 picked up on the log and applications would be made. If weed control 

 gets out of hand, the moisture level also drops. 



If the moisture level is correctly maintained through the first eight 

 to ten months of growth along with a low total sugar level, the cane 

 growth is very heavy and is, of course, likely to be succulent. Lodging 

 of the cane in this condition will result in breakage and killing of 

 stalks, hence, we impose a hardening on such fields. Irrigations are 

 discontinued until the moisture index drops to about 77 per cent. 

 During this period, not only are the stalks hardened, but their sugar 

 content builds up. The stools and very likely also the roots become 

 loaded with sugar. That is, we not only consolidate tonnage gains made 

 to date, but we also prepare the roots for another spurt of growth. 



When the mid-crop hardening is completed, irrigation is resumed 

 on schedule. Usually the nitrogen index has dropped by this time and 

 the remaining fertilizer to be applied is now calculated and applied. 

 If the potassium index has fallen below the line, potash is also applied. 

 Thus, fortified with carbohydrate material and now with moisture and 

 needed fertilizers, the crop is off for its second season of growth. The 

 moisture level rises to between 80 and 83 per cent. Usually following 

 the lodging of stalks, if the second season fertilization and irrigations 

 are properly timed, a heavy flush of suckers is set off adding to the 

 stalk population in the field. 



After twelve months no further fertilization is practiced even though 

 deficiencies develop, but irrigations are kept on schedule. Up until the 

 crop is 17 to 18 months of age, our chief concern is the piling up of 

 tonnage. Except for the period of mid-crop hardening, we are not 

 concerned with quality. However, beginning with seven months before 

 harvest and continuing until harvest time, our concern is no longer one 

 of producing tonnage but becomes one of producing quality (8). Thus, 

 at seven months before harvest, every field is put on a weekly sampling 

 basis and the data are plotted on a ripening log. We know that for best 

 quality the tissue moisture level should drop gradually to a level of 

 72 to 73 per cent. We also have learned that this level must be ap- 

 proached gradually. If during the second season of growth the moisture 

 level has been higher— that is, 82 to 83 per cent— the irrigations are 



