Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RICE 135
on the techniques used for measuring the photosynthetic rate, range of experimental
conditions, physiological status of the plant, and degree of fitness.
The photosynthesis of single leaves can be described by the fundamental
equation:
(3.17)
where C a = the concentration of carbon dioxide in the air and C c = the concentration
of carbon dioxide at the carboxylating surface.
The resistance in equation 3.17 is composed of boundary layer ( r a ), stomatal
( r s ), mesophyll ( r m ), and carboxylating ( r c ) resistance. When they are connected in
series, the total resistance is given by:
Resistance = r a + r s + r m + r c (3.18)
The boundary-layer resistance is related to leaf size and shape and wind velocity.
Nitrogen nutrition may affect any other resistance or all other resistances at the
same time.
When rice plants are subjected to a nitrogen deficiency, the stomatal resistance
of leaves, particularly that of the lower leaves, increases sharply, indicating that
the stomates are closed to a considerable degree. This increased stomatal resistance
is associated with a decrease in photosynthetic rate. Thus, the leaf photosynthetic
rate is highly correlated with leaf conductance, a reciprocal of stomatal
resistance (Fig. 3.10). Since stomatal resistance is the first critical step in carbon
dioxide diffusion in leaf photosynthesis, the linear relationship between the leaf
photosynthetic rate and leaf conductance may be interpreted as evidence of the
effects of nitrogen nutrition on leaf photosynthesis via stomatal control.
3.7 NITROGEN
3.7.1 Occurrence of deficiency
Nitrogen is the most important nutrient for rice, and its deficiency occurs almost
everywhere unless nitrogen is applied as a fertilizer.
Fertilizer-requirement trials conducted throughout Japan indicate clearly that
lowland rice responds better to nitrogen applications than to applications of
phosphorus and potassium (Table 3.15). Yet, lowland rice depends more on soil
fertility than on fertilizers. When neither compost nor nitrogen fertilizer is applied,
the yield index of lowland rice is 78, whereas the indices of upland rice, barley,
and wheat are less than 40. The dependence of lowland rice on soil fertility is best
illustrated by a Japanese saying: “Grow paddy with soil fertility, grow barley with
fertilizers.”
3.7.2. Forms of nitrogen
In solution culture, rice can absorb and use ammonia-N, nitrate-N, urea-N, and
amino acid-N. Ammonia is the major and stable form of nitrogen in submerged