464 Mineral Nutrition of Plants 



yields. In still others, such as Puuokumau, weed control has not been 

 very successful. 



I have said very little so far about the fertilizer requirements of the 

 sugar cane crop. It should be very apparent to you that the amounts of 

 mineral nutrients required by a crop are determined very largely by 

 the climate in which the crop is growing. It seems only common sense 

 that a crop growing in an area capable of producing 125 tons of cane 

 per acre will require more plant food than one growing in an area 

 capable of producing 50 tons per acre. The actual fertilizer applied 

 will be the difference between that required by the plant in a given 

 energy level and that available to the crop from the soil and irrigation 

 water. It follows as a corollary that since climate is dominant in 

 determining the quantity of growth obtained in the various areas of 

 the islands, successive yields on a given field will also vary according 

 to the weather actually experienced by each crop in the succession, and 

 that, therefore, the fertilization of a given crop can reasonably be 

 expected to vary from the previous crop. Furthermore, another variety 

 of sugar cane can have a different requirement not only because its 

 needs are different but also because its ability to extract the needed 

 materials from the soil is different. With such a variety of circum- 

 stances affecting the welfare of a crop, it seems obvious to me that the 

 well-being of a crop has to be followed while it grows, and that empiri- 

 cal practices at best can be successful only occasionally. 



summary: the crop log 



To bring into focus, then, the requirements of a crop as it grows so 

 that it can be fed, and otherwise nurtured and guided to a successful 

 harvest, the crop log (/, 6, 2, 3) was developed and is now in practical 

 and successful use on over fifty thousand acres of sugar cane. Such a 

 crop log is shown in Figure 1. It is a record of the crop's progress from 

 its start until harvest and is made up of certain physical and chemical 

 measurements and observations which serve as a guide to its handling. 



In the top section is a record of the maximum and minimum tem- 

 peratures and sunlight experienced by the crop as it grows. Below this 

 is the Growth Index section. If elongation measurements are kept, they 

 are recorded here. Accumulated growth is indicated on the top line. 

 The green weight of the sheath sample per stalk is also recorded. 



