Vergara - 1976 - Physiological and morphological adaptability of ri

RICE PRODUCTIVITY IN CLIMATIC REGIONS or JAPAN 469
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DISCUSSION
Evans (Chairman): Muratas paper is particularly concerned with the early growth of the
crop. recognizing that this is a more limiting stage in the life cycle of rice crops in temperate
climates than in the tropics. At this stage, the dominant effects are those of temperature at the
growing point and the percentage of nitrogen in the leaves. whereas radiation has little or
very greatly reduced effect.
We emphasized Kudos condusion (1975) that accumulated dry weight at anthcsis may’ be a
major detenninant grain yield in temperate rice crops. along with radiation during the
grain-filling period.
hluratzfs paper is comprehensive exercise in the use of regression analyses to increase the
resolving power of the numerous growth-analysis experiments undertaken for the [BP program
in Japan. For example, net assimilation rate has proved difficult to relate in a meaningful way to
environmental factors because of the marked elTect of leaf area index on it and on canopy
structure Nlurata allows for this by relating NAR not to incident radiation but to an estimate
of mean light htensity in the canopy. Vfhile this results in a clear relation between NAR and
radiation over a range of environments. it does not satisfactorily‘ take into account such
phenomena as light saturation of individual leaves. llttWCliCI‘. Uchijimafs paper suggests that
because of their inclination most leaves in a rice crop are under relatively low irradiances.
The inclusion of thither terms for percentage of N in leaves, which has a major influence on
their photosynthetic capacity. or for time from transplanting. which governs the trend in
percentage of N in leaves. made the relation between radiation and NAR still closer. but this
alter all is what mierometeorological and phytotron experiments would lead us to expect.
However. it does allow Murata to compare photosynthetic rates in the field at many sites and
times.
‘YAtdANE: Table l shows the lowest yield in Akita. But Akita is famous as one of the highest
rice-yielding areas in Japan Farmers in Akita area have often won the first prize in the rice
yield competition sponsored by Etsahi newspaper company. Could you explain this point’?
Murcia: The high yrield of some farmers in Akita Prefecture was achieved by advanced techniques
of which we do not know the details. Anyway, the results of the lBP experiment are
more representative of the yields in this region than are those achieved by some farmers.
ltltWrElTH: The concepts of NAR and RGR were derived initially for spaced plants. When
plants are close enough to form a closed canopy. the growth rate of the stand becomes limited
by available light energy and not by the size of the photosynthetic synsteln. I suggest a lot oftime
and effort could be saved if we stopped calculating NAR and RGR for crop stands. CGR is
the quantity that matters, and nothing is gained by dividing it by either leaf-area index or plant
weight.