Radiation interception and growth of sugar beet at different sowing dates in Canterbury

Abstract

Measurements of photosynthetically active radiation above and below the canopy, and leaf area index were used to determine a radiation extinction coefficient for sugar beet from 4 sowing dates. This coefficient (0.613) were not affected by sowing date. It was used to determine the relationship of total crop dry weight, root dry weight, and root sugar yield to intercepted radiation for these 4 sowing dates and for similar sowing dates the previous season. The slopes of the regression lines were linear throughout the growing season, except for that of the total crop dry matter, which had a 2-stage linear regression in the second season. The efficiency of conversion of intercepted photosynthetically active radiation averaged 2.6 (total dry weight), 1.7 (root dry weight), and 1.3 g/MJ (sugar yield). There appeared to be little effect of sowing date in the first season. In the second season, the conversion efficiencies for root and sugar yields for the different sowing dates were related to the intensity of virus yellows infection. Maximum radiation interception was not achieved until January or February, irrespective of sowing date. Leaf area expansion in spring was restricted by low temperatures. It was concluded that increased sugar beet yields were most likely under managements which promote earlier leaf area expansion.