Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RICE 141
3.12. Carbohydrate content of leaf sheath plus culm, nitrogen content of active leaf blade,
and active leaf blade ratio of IR8, 1967 dry season (Yoshida and Ahn 1968).
photosynthetic production increases relative to the absorption rate of ammonia, the
nitrogen content decreases and surplus photosynthates accumulate.
The close and inverse correlation between nitrogen nutrition and carbohydrate
accumulation suggests that the latter can be used as an indication of nitrogen
deficiency. A starch iodine test has been proposed to determine the need for
nitrogen topdressing at panicle initiation (Kiuchi 1968).
3.7.5. Partial productive efficiency
One of the central themes in plant nutrition is to find the particular growth stage
when supplying a nutrient produces the maximum yield per unit amount of nutrient
absorbed.
Partial productive efficiency of nitrogen for grain production is defined as:
(3.21)
where Y ( n ) = grain weight of the treatment
corresponding to period ( n ),
Y ( n – 1) = grain weight of the treatment
corresponding to period ( n – 1 ),
N ( n ) = total nitrogen uptake of the treatment
corresponding to period ( n ), and
N ( n – 1) = total nitrogen uptake of the treatment
corresponding to period ( n – 1).
In other words, partial productive efficiency is the amount of grain produced per
unit amount of nitrogen absorbed at a particular growth stage. Thus, the greater the
value of partial productive efficiency, the higher the efficiency of nitrogen
absorbed to produce grains. Partial productive efficiency of nitrogen for straw is
also defined in the same way as for grain.
The solution culture technique provides a convenient means to study partial
productive efficiency. In solution culture, the nutrient supply can be controlled