LIGHT INTERCEPTION AND YIELD AS INFLUENCED BY LEAF-AREA INDEX OF SUGAR-BEET

A field trial with plant population ranging from 20 000 to 240 000 plants/ha was conducted in 1993 to determine the light extinction coefficient of sugar beet canopies. The percentage of incident photosynthetically active radiation reaching the ground and leaf area index were measured several times during the growth period. The mean value for the extinction coefficient was 0.6093. A linear regression between the total of absorbed solar radiation and yield was calculated on this basis. Concerning the data of two additional field trials (1991 and 1992) the radiation use efficiency of total dry matter ranged from 0.74 to 1.88 g/MJ and from 0.30 to 0.75 g/MJ in the case of sugar yield. Optimal average leaf area index was derived from the relation between leaf area duration and yield. Beyond a leaf area index of about 4 m2/m2 the increase in total dry matter was negligible. The highest sugar yield was obtained as leaf area index ranged from 3.5 to 4.1 m2/m2. There were no certain relations between parameters of beet quality and leaf area duration.