Genotypic, physiological and morphological variation for rice grown under a raised beds system

Abstract

Lowland rice (Oryza sativa L.) uses more irrigation water than most other crops. This raises issues on how to reduce the water use (WU) in rice while maintaining and increasing production to meet growing world demand. The saturated soil culture/raised beds system is a potentially useful system that can save water and maintain high grain yield and hence increase water use efficiency (WUE). However, there is limited information about this system, particularly about the physiological responses and variety differences in response to this system. The objectives of this study were to investigate WU and WUE of different water management systems for growing rice, and to measure the response of different varieties in terms of key physiological and morphological characters to the various water conditions.There were 3 to 10 varieties in each of the four glasshouse experiments. The varieties used were from different origins such as Australia, USA, China, Indonesia, Japan and Africa. There were three water systems designed to simulate the field practices of conventional flooded system (FL), saturated soil culture (SSC) and aerobic condition where the soil water was re-watered to field capacity daily (FC). Field experiments were conducted in southern NSW to compare six varieties under FL and SSC.The experiments in the glasshouse also included variations in the level of the water table from the soil surface, and in the method of adding water to the soil in the SSC treatments. These aimed at simulating raised bed and aerobic rice systems practiced in the field. These different SSC treatments included water level at 10 cm below the soil surface and added either from the top (10T) or the bottom (10B) of the pot, and at 15 (15B) and 20 cm (20B) with water added from the bottom. There were two water level treatments in SSC in experiments 1, 2 and 4, and one in experiment 3.In all treatments the water was supplied to the designated level on a daily schedule. In the FC treatment the minimum available water content ranged from 23 to 84%. In all other treatments the plants most likely had access to free water for the whole daily period.The results of the glasshouse experiments indicated that the available soil water in the pot system used to simulate FC was not sufficient to maintain maximum growth in rice. While the available soil water in the pot fell to 23% in experiment 3, it was at 84% of the total available water range (field capacity-wilting point) in experiment 4 and still there was a significant effect on many parameters. The mean reduction from FL across four experiments in leaf elongation rate (LER), stomatal conductance (SC), leaf water potential (LWP) and total dry matter (TDM) was 22, 27, 12 and 31%, respectively. There was no change in the WUE of the FC system compared to the FL.n n n n n n n n n n n