Analysis of Effects of Environmental Factors and Cultivation Practices on Variation in Rice Yield in Rain-fed Paddy Fields of the Central Plain of Laos

摘要

Yield and yield components of rice were analyzed in a total of 113 paddy fields in a typical rice-growing village in the central plain of Laos in order to determine how rain-fed lowland rice production could be improved. Average grain weight decreasedsignificantly from 242.3 g m~(-2) in 2005 to 154.1 g m~(-2) in 2006 due to low rainfall in June, August and September. High-yield plots were located near the settlement or drainage channels in both years, and received water from the settlement or drainage channels. All the yield component values, as well as straw weight, decreased significantly in 2006 except for 1000-grain weight. The variations in yields and yield components were extremely large, especially in 2006. Plots with small numbers of spikelets per m~2 and a low percentage of ripened grains were observed in 2006. These plots tended to be transplanted later, mainly in August, and were located far from the settlement. The variation in grain weight was closely related to the straw weight, number of spikelets per m~2 and number of spikelets per panicle in both years. Correlation coefficient analysis suggested that the higher volumetric water content of surface soil and the planting of improved cultivars were more effective for increasing grainweight than fertilizer application, soil properties, transplanting period, growth duration or plot altitude.