LODGING REDUCES YIELD OF RICE BY SELF-SHADING AND REDUCTIONS IN CANOPY PHOTOSYNTHESIS

The adverse effects of lodging on light interception, canopy photosynt hesis and yield were evaluated during grain filling in modem irrigated rice and modern deepwater rice (DWR) cultivars. Lodging, i.e. the red uction in plant canopy height due to bending of the shoot from vertica l, occurred in canopies of modem irrigated and DWR growing in the fiel d under tropical conditions and ranged from 0 to 42% of canopies which were held erect using nets; this was associated with yield reductions of up to 2 t ha(-1). A 1% reduction in grain yield occurred for every 2% lodging when data from different seasons, cultivars, and lodging t reatments were plotted together. Lodging treatments which reduced cano py height by 75% (75% lodging) resulted in a suboptimal stratified lig ht interception of the canopy. In lodged and non-lodged canopies, more than 80% of light was intercepted within the top 5 cm and 80 cm of ca nopies respectively. Lodging reduced canopy photosynthesis by 60 to 80 % relative to erect canopies of DWR and irrigated rice respectively, a nd for DWR the reductions in canopy photosynthesis gave predicted redu ctions in yield which were equivalent to the measured yield. Data are used to support the hypothesis that the adverse effects of lodging dur ing grain filling are largely the result of self-shading by leaves and panicles.