Keywords: Sugar beet, internal quality, sugar extractability, nitrogen nutrition.

Quality of sugar beet is determined by sugar content and by impurities, chiefly α-amino N, K, Na, in the juice which reduce extraction. Root yield is normally negatively correlated with quality. Five empirical formulae used to derive a single figure expressing quality were compared in an experiment with increasing rates of N-fertilizer on four sites. Results were inconsistent, throwing doubt on their value.

The main factors affecting growth and beet quality are: season (weather), soil, site, cultivar and nutrition especially with N. The first three are outside the farmer's control. Plant breeding can contribute to quality improvement directly in sugar content and content of impurities and indirectly by improving stress tolerance.

The experiments showed that increasing N increases particularly α-amino N content and also K + Na, the latter also being much affected by site. α-amino N is favoured as a quality indicator in relation to N supply. Usually, the N rate giving maximum sugar yield also results in acceptable quality. Above this, α-amino N and K + Na both increase sharply.

M A Van der Beek and A W M Huijbregts, Institute for Sugar Beet research, The Netherlands.

20 Pages, 8 Tables, 4 Figures, 19 References.