Effects of Population Ratios between Rice and Weedy Rice on Competitive Ability for Growth and Yield of Pathum Thani 1 Rice Variety

Abstract

      The objective of this study was to evaluate the effect of population ratios of Pathum Thani 1(PTT1) and weedy rice on plant growth and yield competitive ability. Two pot experiments were laid out in completely randomized design (CRD) with 5 ratios of PTT1:weedy rice (4:0, 3:1, 2:2, 1:3 and 0:4 plants per pot) and 4 replications. Experiment 1 explored the effect of population ratios of PTT1 and weedy rice on seedling growth. Ten-day-old seedlings were transplanted to pots containing 10 L of full-strength nutrient solution. After 14 days the shoot and root growth of PTT1 in treatments 4:0, 3:1, 2:2 and 1:3 were not statistically different. Likewise, the shoot and root growth of weedy rice were not affected by treatment. However, the mean shoot height, leaf number per plant, root length and root number per plant of PTT1 were 35.1, 29.3, 30.0 and 36.3% higher, respectively, than in weedy rice. Experiment 2 explored the effect of population ratios of PTT1 and weedy rice on plant growth and yield. Seven-day-old seedlings were transplanted to pots containing 10 L of paddy soil in the same population ratios as in experiment 1. At harvest (100 days after transplanting), competition from weedy rice decreased the number of tillers and the percentage of filled grain (16.7 and 16.1%, respectively); increased the percentage of unfilled grain (45.8%); and reduced grain yield (15.2%) in PTT1 in the 1:3 treatment. However, growth and yield of PTT1 at treatment of 3:1 and 2:2 were not affected by competition from weedy rice. The results indicate that 1) competition between commercial rice and weedy rice has a greater effect on later vegetative and reproductive growth than on young seedlings,and 2) competition from weedy rice can have a large negative impact on rice yield when the density of weedy rice is higher than the commercial rice.