SOLAR RADIATION IN ESTIMATING THE MAXIMAL YIELDS OF SPRING CROPS

Abstract

The paper presents an approach to estimating the input of solar radiation to crop yields based on plant physiology, meteorology and energy balance with account of the photosynthetically active radiation (PAR) and its allocation to photosynthesis, water absorption, transpiration, heat exchange with the environment, regulatory and informational photobiological processes, and photomorphogenesis. The approach makes it possible to estimate the maximal possible productivity (MPP) and crop yield (MPY) of spring cereals under conditions optimal with regard to all other environmental factors. The role of critical illumination periods (CIP) in plant ontogenesis and the possibility to account of them in the novel approaches to agro-meteorological forecasting or crop yields. PAR inputs to wheat and barley crops over the time elapsing from coming-up to the end of flowering are calculated for Moscow, Kursk, Tambov, Voronezh, Samara, and Saratov regions. The resulting MPP and MPY may be 13 to 14 and 0.38 to 0.42 tons per hectare, respectively. Under optimal conditions, over 90% of PAR is allocated to transpiration (T). To reach MAP, about 180 mm of water per 1 m of soil must be used for T. Because in wheat and barley T occurs only under illumination and is proportional to gas exchange, a decrease in productive water store (PWS) is associated with a similar decrease in T and gas exchange. The calculated maximal actual yields (tons per hectare) are 0.38-0.40 in Moscow and Kursk regions, 31-33 in Tambov and Voronezh regions, and about 0.28 in Samara and Saratov regions. Noteworthy is that decreases in PAR and PWS are associated in decrements in gas exchange and mass gain, especially during critical periods of ontogenesis; therefore, accounting of PAR is important for assessing the conditions of crops and for forecasting possible crop yields.