Bilinear thermal time models for predicting flowering time of rice

Abstract

Temperature is a dominant factor in rice development. Various thermal time methods are a possible way to model the development, and are able to predict phenological stages such as flowering. In our studies three different bilinear models were studied concerning the predicting of duration from emergence to flowering of rice based on phenological data collected from rice experiments carried out in the Irrigation Research Institute between 1991 and 1999 with the rice variety Ringola. The advance from linear model, which is preferred in agriculture involves an upper threshold temperature as a second parameter, and describes the development rate with a constant (Method 1) and two different steepness functions of linear decrease (Method 2 and 3) above this threshold. The duration of the phenological phase showed only slight variations (coefficient of variation, CV=6.43), thus the average number of days offered an acceptable prediction. The linear method did not show a significant improvement (CV=3.96) on the le...