EFFECTS OF WATER PONDING ON DECREASING LEAF AND PANICLE TEMPERATURE IN RICE PADDY FIELDS

Several studies have suggested the spikelet fertility would be significantly damaged if the air temperature ( T a ) was high at heading and flowering stage. In this study, we evaluated the effect of water ponding in two paddy fields to decrease leaf temperature ( T l ) and panicle temperature ( T p ) during the 2014 growing season. Within the first conventionally water managed paddy field (cultivar Akitakomachi), we set 1 m × 1 m experiment plot (Plot A 1 ) from July 8 th to August 24 th , and water was put in 15 cm depth in the morning at 8:30. For expecting larger difference of leaf and panicle temperature between in and outside the plot, the plot was expended to 2 m × 2 m (Plot A 2 ) from August 25 th to September 8 th , 2014, and water was put in 15 cm depth at noon. This method was also used in the plot B (2 m ×2 m) which was installed in another conventionally water managed field (cultivar Nikomaru) from September 9 th to 30 th , 2014. T l and T p were measured every two or three hours during daytime in every 10 cm canopy layer in and outside plots. In the first experimental paddy field, at largest, T l and T p in the plot were 4.3 ℃, 5.5 ℃ lower than T l and T p outside the plot, respectively. T p was 6.6 ℃ lower than T a under low relative humidity condition. In the second experimental paddy field, T l and T p in the plot were 3.6 ℃, 3.4 ℃ lower than T l and T p outside the plot, respectively. It revealed water ponding was a useful method to decrease leaf and panicle temperature under larger solar radiation, higher air temperature and lower relative humidity conditions at heading and flowering stage.