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

Evaluation of maize productivity under different climatic conditions was made 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 as photosynthetic energy, W (ph), was estimated taking into account the action spectra of photosynthesis. Limitation of the W (ph) usage, owing to unfavorable environmental factors was considered. Quantitative evaluation of limitations by two such factors, air temperature and soil water potential, was made by means of the coefficients F(i), which were defined as the ratio between the photosynthetic rate at a given value of a particular environmental factor and that at the optimal value for this factor. The coefficients F(i), were determined from the dependencies of the photosynthesis rate on air temperature and soil water potential as obtained in chamber and field experiments. 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 model, the effect of monodominancy, when strong action of one factor suppresses the influence of any other factor, was considered. In this case, the bioclimatic 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 bioclimatic potential for the period of vegetation, W'(pc,v), and total dry matter. W'(pc,v) use efficiency in the maize crop was also evaluated for five variants of mineral nutrition.