Evaluation of maize productivity considering solar energy use limitation by environmental factors

Evaluation of maize productivity under different climatic conditions was ma de by determination of the amount of the incident solar radiation energy in the PAR range, which can be potentially used by plants for photosynthesis. An irradiance, which can be stored in primary photosynthesis, designated a s photosynthetic energy, W-ph, was estimated taking into account the action spectra of photosynthesis. Limitation of the W-ph usage, owing to unfavora ble environmental factors was considered. Quantitative evaluation of limita tions by two such factors, air temperature and soil water potential, was ma de by means of the coefficients F(i), which were defined as the ratio betwe en the photosynthetic rate at a given value of a particular environmental f actor and that at the optimal value for this factor. The coefficients F(i), were determined from the dependencies of the photosynthesis rate on air te mperature and soil water potential as obtained in chamber and field experim ents. In general terms, the fraction of W-ph, which can be utilized under a given climatic condition, was named bioclimatic potential, W-pc. In our mo del, the effect of monodominancy, when strong action of one factor suppress es the influence of any other factor, was considered. In this case, the bio climatic potential, designated W' (pc), was calculated by multiplying W-ph times the coefficient F, for the factor which was most limiting during the period of measurement. There was close correlation between values of biocli matic potential for the period of vegetation, W'(pc,v), and total dry matte r. W'(pc,v) use efficiency in the maize crop was also evaluated for five va riants of mineral nutrition.