積算気温に基づく水稲の葉重と地上部重の簡易モデル

Abstract

This study was conducted to develop a simple model of leaf dry weight and top dry weight of rice (Oryza sativa L.) plants. Rice variety “Nipponbare” was sown five times at one-month interval from April through August, 1992, and was transplanted in a paddy field at National Institute of Agro-Environmental Sciences (NIAES), Tsukuba, Japan about three weeks after the sowing. Plants samples were taken every two weeks to measure biomass and leaf area. Photon flux densities upon and below the rice canopies were measured to calculate light interception by the rice plants. Incident shortwave radiation and air temperature were recorded at the NIAES weather monitoring station. The data on biomass, light interception and the weather variables were used to develop the model. In the model, total leaf dry weight was described by a combination of exponential and linear functions of accumulated air temperature, and the dead leaf dry weight was expressed as a linear function of accumulated air temperature. Leaf dry weight was defined as the difference between the total and dead leaf dry weight, and was used to calculate light interception. Top dry weight was estimated as the product of the intercepted shortwave radiation and the radiation-use-efficiency (RUE). The model fitted rather well to the observation of the leaf dry weight, but it overestimated top dry weight with a constant RUE throughout the growing season. To correct the overestimation, the total leaf dry weight was further divided into active leaf dry weight and the senescent leaf dry weight, among which only the active leaf dry weight was used to calculate the light interception. The leaf senescence was assumed to be a function of accumulated air temperature. The revised model gave a good fit with regard to the top dry weight, and may be useful to represent crop production.