Deutscher Tropentag, October 9 - 11, 2002 in Kassel-Witzenhausen "Challenges to Organic Farming and Sustainable Land Use in the Tropics and Subtropics"

Effect of Depth of Water and Duration of Inundation on Rice-Weed Competition and Grain Yield of Rice in the Central Plains of Thailand

Asian Institute of Technology, Thailand

Abstract

Rice is the main source of energy and income of the people in the Asian countries. It is also the dominant crop in small-holder agriculture. Rice yields are often reduced by weed competition. Weeding has a high labour requirement and hence, this has led to a widespread use of herbicides. Herbicides are known to cause a number of problems, of which the development of herbicide-resistant weed ecotypes and weed resurgence are two most crucial situations that are likely to demand the development of more toxic and long effective herbicides. Therefore, the use of non-herbicide weed control measures has been favoured by many agriculturists. This study was conducted to determine the effect of depth of water and duration of inundation on rice-weed competition and grain yield of rice in comparison to the traditional system of manual weeding and herbicide-based weed control.

The experimental treatments composed of five depths of water (viz. 0, 2, 4, 6 and 8 cm) maintained from the time of seeding and two levels of weeding (viz. weeded at panicle initiation and maintained non-weeded throughout the growing period) were compared with the traditional system and also with a plot weeded with commonly used herbicides in a split plot design with three replicates.

The population and growth of weeds were highest in plots where the water depth was maintained at 0 cm, while increasing the water depth from 2 to 8 cm significantly reduced both parameters. There was a significant reduction in the weed population in the plots treated with herbicides during the initial growing period compared to low water depths maintained and the traditional system. Weeds that emerged later in herbicide treated plots caused significant yield reductions.

Rice plants at 0 cm water depth had lower number of effective tillers and panicles per plant, which significantly increased with water depths up to 6 cm, and decreased at 8 cm water level. Removal of weeds at the panicle-initiation (PI) stage enhanced grain yields compared to the herbicide treated plots. Productive grain number per panicle remained almost unchanged at water depths from 2 to 8 cm once the weeding was adopted at PI stage. However, when weeding was not adopted at PI stage, increasing water depth showed a significant increase in the productive grain number per plant. The final grain yield showed no significant changes over water depths from 0 cm (4.1 t/ha) to 8 cm (4.4 t/ha) when weeding was practiced. Without weeding, the grain yields varied from almost zero t/ha to 4.4 t/ha with increasing water depth from 0 cm to 8 cm. This study reveals the possibility for reducing or even replacing herbicide with water management for weed control. This option is a promising alternative for areas such as the Central Plains of Thailand.

Keywords: Rice-weed competition, transplanted rice, water depth, water management, weed management

Contact Address: Senaratne Ranamukhaarachchi, Asian Institute of Technology, Agricultural Systems and Engineering, P.O. Box 4, Klong Luang, 12120 Pathumthani, Thailand, e-mail: ranamukaait.ac.th