A Year-Round Opening-Air Experiment System for Global Warming to Predict Future Paddy Field Ecosystem Abstract The paddy field is the representative agricultural land ecosystem of Japan. In order to understand the impact of global warming on the paddy field ecosystem in Japan, i.e. growth and yield of rice, balance of carbon and nitrogen, we designed a year-round opening-air experimental system for global warming to monitor annual paddy field ecosystem. National Institute for Agro-Environmental Sciences Background and Purposes Global warming can affect paddy field ecosystem. However, how it influences the rice growth and rice yield, and emission of carbon dioxide and methane from paddy field ecosystem during the summer season is still unclear. In addition, temperature rise during the winter fallow season could change the annual balance of carbon and nitrogen through soil water and soil microbe activity and dynamically impact on the rice growth environment and greenhouse gas emission in summer on a long term. To investigate their relationships, we developed a world first year-round opening-air experimental system to monitor paddy field ecosystem during the summer rice growth period and the winter fallow period and to study the effect of global warming on this ecosystem. Achievements and Features Four replicated global warming paddy plots and a control plot were established in an experimental field located in National Institute for Argo-Environmental Sciences (each 4 5m). To simulate the summer rice growth period, the floor heating cables were installed in the underwater furrows. With a temperature controller, the water temperature in warming plot was adjusted 2 higher than in control plot (Figure 1: PROSPECT) to warm the ground temperature of the paddy-rice rhizosphere. Because controlling the ground temperature during the winter fallow period by heating cables is difficult, we developed another device to raise nighttime ground temperature by using infrared radiation reflection sheet to control the radiation cooling in the evening (Figure 2: PROPHET). The stretching and winding sheet was automatically operated by a motor, which was controlled by data logger. With this method, the night ground temperature in warming area can be maintained at 1~4
higher than in control area. In particular, the thermal effect at 10cm depth ground by coating sheet can remain to next day. So the soil is steadily kept warm. Through investigation of paddy-rice heading day in the developed year-round opening-air experimental plot, the variation of the heading day among cultivars with respect to global warming is displayed in Table 1, and interesting results about global warming on paddy-rice growth are also obtained. From the collected data, we can find the influence of global warming on productivity and substance circulation in paddy field ecosystem. Notes PROSPECT: Paddy Rice On-season Powered Elevation of Cultivation Temperature. PROPHET: Paddy Rice Overnight Passive Heating Experiment in Tsukuba. ) This research was supported by Administrative Cost Subsidy and the project on Evaluation, Adaptation and Mitigation of Global Warming in Agricultural, Forestry and Fisheries: Research and Development of Ministry of Environment Government of Japan.
Figure 1. Global warming paddy field experiment (PROSPECT) While monitoring water temperature, the temperature controller is used to automatically adjust the output of the floor heating cables. The temperature in warming plot is set up 2 higher than in control plot. The data of system state and the temperature of water and ground are recorded in data logger.
Figure 2. Global warming experiment during the non-cropping winter fallow period (PROPHET) During non-rainfall evening, the reflect sheet of infrared radiation is extend to prevent the radiation cool. The winder is controlled by a motor to automatically stretch and wind the sheet. With no much electricity needed by this system, the soil can be steadily kept warm on long-term.
Table 1. The paddy-rice heading day in the opening-air experimental plot The variation of heading day among cultivars with respect to global warming is different. Some cultivars head earlier; and other cultivars do not change. Because there is no closed system like weather control room, the real cultivation environment is very similar with the opening-air experimental system. Cultivars Warming area Present area Akitakomati Hatsuboshi Koshihekari Takanari Hinohikari Wuxianjing No. 14 8/11 8/13 8/16 8/23 8/28 9/4 8/13 8/15 8/16 8/25 8/29 9/4 Average 8/21 8/22