Yoshida - 1981 - Fundamentals of Rice Crop Science

116 FUNDAMENTALS OF RICE CROP SCIENCE
3.3. Relationship between respiratory
rate and a -naphthylamine-oxidizing
power of rice roots (Yamada et al 1961).
through heading (Alberda 1954, Mitsui and Tensho 1953). At this time, rice plants
usually develop a fine, highly branched root mat in the soil surface or soil-water
interface (Alberda 1954, Fujii 1974, Kawata et al 1963). Since oxygen, either
carried by flowing water or generated by the photosynthesis of blue-green algae, is
abundant in these regions, it is postulated that the root mat serves as respiration
roots (Alberda 1954). As such, they absorb oxygen from the water and send it to
other root systems located in the anaerobic soil horizons. This role of the root mat,
however, has not yet been critically examined.
The formation of a root mat is closely related to water percolation and redox
potential. No root mat is formed when flooding and drainage are alternated every 2
days and the redox potential is kept high (Table 3.3). Plants grown in solution
Table 3.3. Effect of water environments on percentage of root
mat formation originated from each root unit. a
Root unit b (%)
Eh 7 of soil (mV)
Treatment 9th 10th 11th 3 cm 10 cm
deep deep
Flooded 16.7 14.3 4.5 –135 –155
(no percolation)
Percolated 4.7 8.2 9.0 –118 –128
(2.5 cm/day)
Midsummer drainage 4.4 3.0 4.5 –183 –123
Alternate flooding 0 0 0 +115 +120
and drainage
a Soezima and Kawata (1969). b lncludes roots from the lower region
of the nth node and those from the upper region of ( n – 1)th
node. Figures indicate percentages of root number originated
from each root unit in relation to the total root number.