Evaluation of nonlinear regression models to quantify barley germination rate response to temperature and water potential

Temperature and moisture are the main effect on seed germination, which are determine the rate of germination of non-dormant seeds. In order to quantifying the germination-rate of barley (Hordeum vulgare L.) in response to temperature and water potential, germination of this crop was investigated as affected by temperature (5, 10, 15, 20, 25, 30 and 35 ˚C) and water potential (0, -2, -4, -6 and -8 bar) at the Seed Technology Laboratory, Gorgan University of Agricultural Science and Natural Resources. Results showed that the temperatures, the water potentials and their interactions were significantly influenced germination rate and percentage of barley. In this work it has been compared four non-linear regression models (original beta, 3-piece segmented, 2-piece segmented and modified beta) to describe the cardinal temperatures for the germination of barley. The original beta model was selected as the best model to predict germination rate. Based on the model outputs, the base, the optimum, and the maximum temperatures for germination of barley were estimated as -0.9, 27.5 C and 35.7 ˚C, respectively. The biological hours for germination at zero water potential was 23.4 h. Cardinal temperatures were not influenced by water potentials. However, the numbers of biological hours for germination increased 2.6 h/bar by decrease each bar of water potential.