466 Mineral Nutrition of Plants 



The nitrogen index which is the total organic nitrogen content of the 

 green tissue of the leaf blades expressed in the dry-weight basis is plotted 

 in the third section. Also along this curve are indicated the various appli- 

 cations of fertilizers made to the crop. At the top of this section is a 

 record of the accumulating age of the crop. 



At the bottom are the actual dates on which sample collections were 

 made. 



Below this is the section dealing with the moisture index. The actual 

 tissue moisture levels are graphed. At the top, the downward pointing 

 arrows indicate dates of irrigation rounds. At the bottom, the vertical 

 bars indicate the rainfall received. 



The Primary Index, or the total sugar level of the leaf sheaths is 

 plotted next as percentage of the dry weight. 



The potassium and phosphorus indices are shown next with the 

 normal line dotted across the space at 2.25 and 0.080, respectively. The 

 values are potassium and phosphorus contents expressed on the basis 

 of the sugar-free dry weight. 



At the bottom of the log are certain miscellaneous data which make 

 the record for the crop complete. The log once completed becomes a 

 permanent record for that crop. It has several uses: it is an excellent 

 source of research material; it, along with others on the same field, 

 serves to point up long-time trends; it is useful in comparing one field 

 with another and often points up needs for differential preparation or 

 cultivation. But its most important use is in guiding the current crop 

 in its growth and culture to maturity. 



To show its application I shall very briefly describe its use in handling 

 a ratoon crop. 



As soon as a field of cane is harvested and the cane lines are reshaped, 

 the first irrigation water is applied. Fertilizer applications are then 

 made. Nitrogen is always applied, and in high production areas 75 

 pounds of the element are put on. Potash is also applied at once if the 

 previous crop log showed need for potash. If it did not, no potash is 

 applied unless and until the potassium index drops below the normal 

 line. Phosphates usually are not applied to ratoons but only to plant 

 crops. During this early period of a ratoon, irrigations are based on a 

 schedule. The tensiometer (9) is being used to excellent advantage 



