Seasonal variation of radiation interception and radiation use efficiency in sugar beet (Beta vulgaris L.)

Abstract

A high correlation existes between crop growth and the rate of radiation intercepted. The efficiency of radiation interception and absorption is dependent on leaf area index, light extinction coefficient and radiation use efficiency. In order to study mentioned coefficients a randomized complete block design with four replications was conducted during 2005 for different sugar beet cultivars (7233, 7112, 436, 276 and Rasoul) at Ferdowsi University of Mashhad experimental farm station. The cultivars were cultivated in eight rows with 50 centimeters distance in plots with 12 meter length and optimum condition of nutrients and irrigation. In addition to measuring the radiation above and under the canopy, the plots were sampled 9 times during growing season and leaf area index, total dry matter and finally light extinction coefficient and radiation use efficiency were measured. Mean maximum leaf area index was 3.51. The final yield of total dry matter for different genotypes varied from 15670 to 25920 kilogram per hectare. There were no significant differences among genotypes in light extinction coefficient and radiation use efficiency and their mean values were about 0.56 and 1.23 g.Mj-1 , respectively. Seasonal variation of radiation use efficiency was similar to leaf area index changes during the crop growth cycle and maximum radiation use efficiency was located before the reaching of maximum green leaf area index. Sugar content was increased proportional with total and root dry matter in most of crop growth cycle. Considering the importance of light extinction coefficient and radiation use efficiency in crop growth models and also their spatio-temporal variability under different management, it is necessary to perform more experiments in different years and locations with various treatments, to obtain a range of these coefficients for modeling studies.