Biological Nitrogen Fixation

Publication*:

Wiratni and Yang, R.Y.K., 2007, “Mathematical Modeling for Optimization of Biological Nitrogen Fixation in the Presence of Inorganic Nitrogen Fertilizer”, in Book 2, Rice Industry, Culture, and Environment, Indonesian Center for Rice Research (ICRR), Indonesian Center for Food Crops Research and Development (ICFORD), and Indonesia Agency for Agricultural Research and Development (IAARD), pp. 407-412

A mathematical model was developed by translating previous findings about cyanobacterial biological nitrogen fixation (BNF) into mathematical expressions. When the ammonium concentration is sufficiently low, some cells in the cyanobacteria population are differentiated to form heterocyst. Only these specialized cells are capable of nitrogen fixation. On the contrary, when the ammonium concentration is too high, the heterocyst formation is repressed so that the cyanobacteria population fails to accumulate ammonium in the medium. Based on those well accepted theory, the mathematical model presented in this paper predicts reasonably well the trend of the cell concentrations and the ammonium concentrations in the medium at different situations with respect to the external inorganic N concentrations. The parameters of the model were determined from the experimental data. For that purpose, Anabaena sp. (ATCC 29211)  was inoculated in flasks containing BG-11 medium with various additional inorganic ammonium concentrations. Samples were drawn at two-hour intervals to determine the cell concentrations and the ammonium concentration of the medium. The mathematical model may serve as a tool to estimate the optimum proportion of cyanobacteria inoculum to the inorganic N fertilizer concentration. The simulation using the mathematical model prior to field experiments can narrow the range of the variables to be studied. By doing so, field experiments can be more efficient in terms of time and research budget.

*First postdoctoral research under the supervision of Prof. Ray Y. K. Yang (Laboratory of Bioreaction Engineering, Chemical Engineering Department, West Virginia University, Morgantown WV, USA.

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