Application of parametrization using the Richards function to nitrogen release from coated urea and growth of rice seeds

The Richards function can describe the cumulative frequency distribution accurately because the function has a high flexibility owing to the presence of the 4 functional parameters. Accordingly, the frequency distribution can be characterized by the 4 functional parameters. The parametrization was applied to the nitrogen release from coated urea and the growth of rice seeds with the passage of time. The Richards function accurately described these responses. For the analysis of nitrogen release, one of the 4 functional parameters reflected the nitrogen content of fertilizer, another one was calculated from the other parameters, and another one followed the Arrhenius equation. Accordingly, the nitrogen release from each type of coated urea at various temperatures could be characterized by 2 release parameters. Because the growth of rice seeds was too complex to be represented by the Arrhenius equation and the functional parameters were sensitive to a small deviation, the 4 functional parameters were transformed into 4 population parameters that were stable and comprehensive. Several factors affecting the growth could be analyzed using the population parameters although they may not affect the viability. Therefore, the analysis of nitrogen release and seed growth showed that the parametrization of the frequency distribution of responses using the Richards function could be applied.