Abstract:
The objective of this study was to evaluate canopy development, radiation interception
and radiation use efficiency (RUE) of commercial sugarcane varieties under different
growing conditions in Sri Lanka. A field experiment was conducted from April 2002 to
September 2003 at the Sugarcane Research Institute (SRI), Udawalawe (6021’N
latitude, 80°48’E longitude and 76 m altitude) where the annual average rainfall is
about 1450 mm with a distinctly bimodal distribution. Eight commercial sugarcane
(•Saccharum hybrid L.) varieties (i.e. SL7103, SL7130, SL8306, SL8613, SL88116,
SLI121, M438/59 and C o ll5) were grown under irrigated (soil water potential > -0.05
MPa) and rainfed conditions in split plot design. Vegetative growth, biomass
accumulation, canopy development, leaf angle and radiation intercepted by the canopy
of sugarcane were measured. Radiation intercepted per day, seasonal totals of
incoming radiation intercepted, fraction of incoming radiation intercepted, and light
extinction coefficient (k) and RUE were estimated. When average across varieties,
RUE reduced (58%) significantly (P=0.0001) under rainfed condition compared to the
irrigated condition due to the seasonal total radiation interception (Si) was greater in the
rainfed treatment. Si was greater because the rainfed crop took a longer time to mature.
RUE varied from 1.63 to 2.09 g M J'1 and from 0.71 to 1.03 g M J1 under irrigated and
rainfed conditions respectively. The importance of RUE in yield determination under
both water regimes varied for different varieties. The improved Sri Lankan variety,
SL8306 showed the highest RUE under both water regimes with higher canopy
development and lower k values consistent throughout the growing period. High levels
of cane yield, cane biomass and total biomass were positively correlated well with RUE
and varied for different varieties. It confirmed that, although the canopy with
horizontally oriented leaves could increase Si, a canopy with erect leaves important for
increasing biomass production and ultimately increasing RUE. As the erect orientation
of leaves is a genetically governed physiological trait, it could be used for the
hybridization programme of sugarcane to produce highly efficient solar energy utilizing
hybrids of sugarcane in Sri Lanka.
