Rice Yield Increases and Protein Content Decreases in FACE (Free Air CO2
Enrichment) Agricultural Fields
Abstract
The world’s first FACE (free-air CO2 enrichment) experiment in rice was conducted
at Shizukuishi, Iwate Prefecture over three cropping seasons in a farmer’s paddy field.
The elevated carbon dioxide (CO2) promoted rice growth, increased the number of
grains and resulted in a rice grain yield increase. If the applied nitrogen was less than
the normal level, the increase of rice grain yield under elevated CO2 was low. On the
contrary, if the amount was more than the normal nitrogen level, the increase of rice
grain yield was high. In addition, elevated CO2 reduced the protein content of rice.
Research Institute
(Kazuhiko Kobayashi, Hang-Yong Kim, Shu Miura, Tomio Terao, Masumi Okada, Mark
Lieffering, Mayumi Yoshimoto
National Institute for Agro-Environmental Sciences
Background and Purpose
Due to the continually rising of atmospheric CO2 concentration, it is feared that CO2
concentration will reach 550ppm (twice of the preindustrial era) during the latter half of
this century. From previous results, which were obtained under greenhouse and
chamber condition, because the photosynthetic rate and water use efficiency rise under
elevated CO2, the plant growth and the grain yield are expected to increase. However, in
these previous experiments because the environment inside the chamber is different
from actual agricultural fields, it is highly likely that the plant response to elevated CO2
is also different. This study aims to elucidate the effects of elevated CO2 on rice growth
and grain yield in a farmer’s paddy field by the world’s first FACE (Free-air CO2
Enrichment) experiment for rice .
Achievements and Features
1.
For three years from 1998 to 2000, we investigated the rice growth, grain yield, and
rice quality (Japonica cultivar Akitakomachi) in a farmer’s paddy field at
Shizukuishi,
Iwate
Prefecture
with
two
CO2
levels
(ambient,
ambient+200~250ppm), three levels of applied nitrogen (low, standard, and high
nitrogen) and four replications (Figure 1). The results showed that elevated CO2
promoted the dry weight growth of the rice with more than 11~13% increase at
harvest period. The grain yield increased by about 15% for high and normal
nitrogen levels and 7% for low nitrogen level with elevated CO2 (Figure 2). The
increase in the number of grains per area under elevated CO2 condition (Figure 2)
was due to the high absorption of nitrogen during panicle initiation stage. There
was no evidence that the fertility bearing percentage and one thousand kernel
weight were affected by elevated CO2. The harvest index (ear weight/total plant
weight) decreased by 2~3% with elevated CO2.
2.
With elevated CO2, the protein content in the white rice declined by 6~9 g kg-1
(7~12%) for any of the applied nitrogen (Figure 2). It is known that the low protein
will enhance the flavor. Based on our tasting tests, it may as well be admitted that
elevated CO2 indeed enhanced the flavor, but the difference is not that big.
3.
Compared with conventional field chamber experiments, grain yield in the FACE
experiment increased due to increasing CO2. If the applied nitrogen decreased, the
increase of the nitrogen content was enhanced, but the effect was gradually reduced
(Figure 3). The increase amount of grain yield from the field chamber experiment of
the University of Florida and International Rice Research Institute (IRRI) was
higher than that from the FACE. It is because that more nitrogen fertilizer was
applied. If the effect of nitrogen content was considered, the result from the FACE
experiment was similar with the conventional experiment. For rice quality, the
nitrogen concentration in brown rice produced in the chamber experiment was low.
This also was similar with the result of the FACE experiment. The fact that raising
CO2 concentration increases grain yield but reduces protein content in conventional
chamber experiments in a farmer’s paddy field, which was confirmed by the FACE
experiment.
Application and Notes
1.
If the results are used in testing rice growth models and their improvement, then it
will help increase the prediction accuracy of rice productivity in the future.
2.
Although an increase in CO2 concentration increases grain yield, if we understand
the mechanism, which depends on the applied nitrogen, it can lead to a better
cultivation method and a more suitable cultivar in a high CO2 environment in the
future.
Figure 1. FACE experiment in a farmer’s paddy field in Shizukuishi
The octagonal area is the elevated atmospheric CO2 area.
Figure 2. Due to elevated CO2, grain yield increased (top), the number of grains per
square meter increased (middle), and rice protein content of polished grains decreased
(bottom).
Above figure shows the average value of grain yield and number of grains over three
years, as well as white rice protein content in 1999. The numbers on the top of the
elevated CO2 bar are the relative ratio of change from a reference paddy field. High
nitrogen level is 120kg N ha-1 for 1998 and 150kg N ha-1 for 1999 and 2000, respectively.
Normal nitrogen level is 80kg N ha-1 for 1998 and 90kg N ha-1 for 1999 and 2000,
respectively. Low nitrogen is 40kg N ha-1 for 1998~2000.
Figure 3. Relationship between grain yield increase under elevated CO2 and applied
nitrogen
Because different CO2 concentrations were used in the experiments, the increase ratios
of grain yield shown above were converted results when CO2 concentration had a 200
ppm increment.