Growth of Rice Plants (Oryza sativa L.) Under Non-Flooded Water-Saving Paddy Fields

摘要

The effects of water saving non-flooded irrigation management on growth and yield components of a lowland japonica rice cultivar Nipponbare was examined in a well-drained paddy field with low ground water table for 4 years from 2001 to 2004 in Nishitokyo, Japan. The significant reduction in tiller number and aboveground biomass after about 1 month of non-flooded water management (e.g., 7 August in 2003) was the primary cause for yield reduction. Infertile tiller was fewer but spikelet development was reduced to a small extent under non-flooded conditions, with greater numbers of spikelet abortion. All these subsequently reduced both sink (e.g., panicle number and grain number per area) and source (e.g., LAI) capacities. Non-flooded water management, intended to maintain near saturated soil conditions, recorded slightly lower soil volumetric water content and soil water potentialand also lower leaf and plant water content and tendency of delayed recovery of leaf water potential during evening. Both root length density (at maturity) and bleeding sap rate (at heading) were reduced under non-flooded conditions, which may be due to the reduced shoot growth and hence assimilate supply to rootsand increased soil strength. Transpiration was reduced and leaf temperature increased in non-flooded conditions. Plant nitrogen content was lower in non-flooded conditions. The 1000-grain weight to a small extent also reduced under non-flooded conditions (except for 2001 when ripened grain percentage was extremely low), which was associated with its earlier leaf senescence after flowering. Ripened grain percentage was not reduced in 3 years except for 2001, because sink size was not very large and there was no severe water deficit after heading in non-flooded conditions. Our study indicated that water supply from transplanting to panicle initiation should not be extremely omitted in well-drained paddies to achieve sufficient vegetative growth for minimizing yield reduction under water-saving non-flooded conditions.