Growth and competitive ability of new plant type, hybrid, and presently grown inbred rice (Oryza sativa L.) cultivars

The new plant type performed poorly and yielded lower than IR72 and the hybrid. It was also inferior in competitiveness. Plant height, dry matter production, panicle size, and harvest index of the new plant type were more sensitive to weed competition than those of IR72 and the hybrid. Increasing seeding rate increased leaf area index (LAI), crop growth rate (CGR), and dry matter accumulation of rice in the early growth stage, but did not increase grain yield under weed-free conditions. When rice was not weeded, increasing seeding rate reduced weed biomass and increased LAI and dry matter accumulation, regardless of cultivar. Increasing seeding rate also increased panicle number per unit area of rice, especially in the new plant type and decreased grain yield loss. The relationship between yield loss and Echinochloa crus-galli density and biomass at tillering were hyperbolic while the relationship between yield loss and E. crus-galli biomass at harvest was linear. E. crus-galli density decreased grains per panicle more than panicle density for the new plant type in both seasons. While it affected panicle density more than grains per panicle for IR72 and the hybrid in the dry season. The reverse was observed in the wet season. Effects of nitrogen input on the interaction between rice and weeds depended on the weed species. High-N input was beneficial for rice when weaker weed competitors were present while it was beneficial for weeds when the strong weed competitor E. crus-galli was present. Applying basal N did not affect grain yield or yield loss due to weed. There were no differences in total nitrogen uptake between the new plant type and IR72 under weed-free conditions and between weeded and unweeded plots at flowering in the field. In the greenhouse, nitrogen uptake per pot of the new plant type was less than that of IR72 and E. crus-galli at 8 weeks after sowing. Rice and E. crus-galli used the same resources. Initial biomass, CGR, LAI, and biomass at tillering were associated with weed biomass. However, only biomass at tillering directly affected weed biomass; initial biomass, CGR, and LAI indirectly affected weed biomass through the rice biomass