The model is not variety-specific, so it makes no
allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the
implication must be that some of the changes in agronomy have tended to decrease the yields significantly.
The changes in agronomic practice most likely to be responsible are the extension of the
crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irrigated
area.
INTRODUCTION
Sugar yields have risen by 0.11 t/ha per year in recent
years in the UK (Bruhns et al. 2005). Similar increases
over the last 30 years are being reported in France
(0.17 t/ha per year; ITB 2003) and in trials in
Germany (0.14 t/ha per year; Ma¨ rla¨ nder et al. 2003).
It is usually assumed that these increases result from a
combination of the use of improved varieties and
improved agronomic practice (ITB 2003; Ma¨ rla¨ nder
et al. 2003). These assumptions are justified only if
changes in the weather, over a period of a few years,
have had no impact on yield. However, our climate
has been changing over recent decades probably in
response to increasing atmospheric concentrations of
CO2 and other ‘greenhouse’ gases (Long et al. 2004).
Much attention has been given to the likely impacts
of the large climate changes that are expected during
the rest of