Effect of vegetation on the convection of ponded water in a paddy field

Abstract

To investigate the effect of vegetation on the convection of ponded water in a paddy field, the temperature profile of ponded water and the amount and spectral energy distribution of solar radiation were measured using lysimeters located in plots with and without dense paddy rice vegetation. In the vegetated plot, the water-surface temperature was higher than that of the soil surface in the daytime, and the temperature difference reached a maximum of 1.7°C at approximately 12:00 hours, indicating no convection of ponded water. However, when the amount of solar radiation in the unvegetated plot was experimentally reduced to vegetated-plot levels using shade cloth, the temperature difference between the water and soil surfaces was approximately 0°C in the daytime, indicating that convection had occurred. In the shaded unvegetated plot, the amount of visible radiation 10 cm above the water surface was greater than that of near-infrared radiation. However, in the vegetated plot, the amount of visible radiation was lower than that of near-infrared radiation. Visible radiation passes through ponded water and increases the soil-surface temperature. In contrast, near-infrared radiation is absorbed at the water surface and increases the water-surface temperature. The reduction of visible radiation by vegetation affects the temperature profile in ponded water. Thus, vegetation altered the spectral energy distribution of solar radiation, reducing the convection of ponded water during the day. © 2006 Japanese Society of Soil Science and Plant Nutrition.