Yoshida - 1981 - Fundamentals of Rice Crop Science

130 FUNDAMENTALS OF RICE CROP SCIENCE
Table 3.12. Nutrient removal by rice crops in the tropics and
Japan.
Yield
(t/ha)
Nutrient removal
(kg/t rough rice)
N P K
Tropics (IRRI)
IR8 a 8.70 18.9 5.2 35.5
Peta a 6.09 23.5 5.7 50.6
Av of 3 varieties
× 4 crops b 4.74 19.0 4.3 47.0
Mean 20.5 5.1 44.4
Japan c
Japan No. 1 contest 12.80 15.2 3.4 21.7
winner
(Mr. Kitahara, 1958)
Av of 14 agr.
exp. sta. 5.34 17.0 3.8 22.2
Mean 16.1 3.6 22.0
a From Table 3.11. b Tanaka et al (1964). c Calculated from
Yamazaki (1966) using a factor of 1.25 to convert brown-rice yield
to rough-rice yield.
son of the data obtained in the tropics and Japan indicates that lower amounts of
nutrients are absorbed in Japan to produce the same yield. The reason for such
difference is difficult to explain. One major reason for the difference in nitrogen
removal can be seen in the harvest index. A crop with a higher harvest index should
require less nitrogen because less nitrogen is retained by the straw. A luxurious
absorption of potassium by rice crops grown in the IRRI field may account for the
difference in potassium. Dividing 1 t rough rice by the nutrient removal values
gives the efficiencies of absorbed nutrients, i.e., kilogram rough rice per kilogram
nutrient absorbed. The nitrogen-removal value for the tropics is about 20 kg and,
hence, the efficiency of nitrogen use is about 50 kg rough rice/kgN. Similarly, the
efficiency of nitrogen use for Japan is about 62 kg rough rice/kg N. Thus, the
efficiency of nitrogen use appears to be 20% higher in Japan than in the tropics.
The foregoing discussion indicates that nutrient removal by a rice crop increases
almost proportionately as rice yield increases, and provides an empirical relationship
between yield and nutrient requirements.
3.5. MINERAL NUTRITION AND TILERING
Tillering is a characteristic of the rice plant, particularly that of transplanted rice.
Each node of a shoot — main culm and tillers — has a tiller primordium. Whether