Varietal variation in canopy development and radiation interception of sugarcane under two contrasting water regimes

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.