The hot summers and rice in Japan

Abstract

The hot summersIn 2007, we had a very hot summer across Japan, and the maximum air temperature hit a new high of 40.9 in August. In 2010, we experienced another record hot summer, and the mean air temperature across the three months from June to August was the highest on record since 1898. In northern Japan in particular, the 3-months mean air temperature was by more than 2 higher than the normal. Similar anomaly was also observed in other part of the northern hemisphere (http://www.esrl.noaa.gov/psd/csi/events/2010/russianheatwave/prelim.html).No matter what the causes of the heat anomalies are, we should learn how the agriculture have responded to the heat, and be better prepared for the future when the current anomalies become the norm. This issue of Journal of Agricultural Meteorology focuses on the impacts of high temperature on rice production in Japan. Most of the articles are based on or prompted by the findings in the hot summers of 2007 and 2010. Rice in JapanRice plants are usually grown in flooded fields, which makes the micrometeorology of rice canopy unique. The free water surface serves as a major site of evaporation particularly before the canopy closure. The meristems of the rice plants are near the ground, and the young panicles are initiated submerged. The developed panicles are then pushed up by the elongating stems, and attain the flowering among the leaves at the canopy top. The temperature of the panicles is therefore determined by the energy budget of the water layer initially, and that of the top layer of the canopy later. The grain filling takes place at the canopy top while the water is being drained for the ease of heavy machineries to harvest grains. Increase in air temperature would affect the rice plants via the changes in the energy budget of the canopy (Fig. 1) and the panicles.Rice is also unique in the way how it is consumed: it is mostly purchased as grains and cooked at home. The appearance and the cooking quality of the grains are therefore quite important for the consumers and, hence, the market as well as the growers. Imperfectlyfilled grains with partial chalkiness would be priced much less than perfectly-looking grains. Some, if not all, of the appearance traits are indeed relevant to the cooking quality. The quality used to matter less when rice was the dominant source of food energy. In 1960, for example, 48 of total food energy supply came from rice, whereas in 2010 rice contributes to only 24 of the total energy supply. At the current satiety, people are concerned more with quality than quantity of rice.

Rice varietal differences in responses of stomatal gas exchange to supplemental nitrogen application

“…The mean annual temperature at this site was 16.1°C in 2010 and 15.6°C in 2011. The summer of 2010 was exceptionally warm in Japan (Kobayashi et al 2011); the high temperatures caused faster growth in 2010 than that in 2011. Thirteen rice varieties were tested (Table 1).…”

Yield and biomass under the different water levels on three Japonica rice cultivars

“…Rice plant has usually grown in flooded fields [1]. Many traditional farmers applied it, particularly in an area that has sufficient water.…”

Evapotranspiration in a rice paddy field over 13 crop years

“…The long-term measurements include data from years with unique characteristics, such as a nationwide cool summer in 2003 and warm summer in 2010, high rainfall in 2008, and particularly poor plant growth in 2012 because of low levels of fertilizer. Comparing patterns of rice ET in unusual years with relatively normal years provides useful information about how a natural rice ecosystem responds to unusual events Kobayashi et al, 2011 .…”