Comparison of dry matter production and associated characteristics between direct-sown and transplanted rice plants in a submerged paddy field and relationships to planting patterns

In a previous study, we demonstrated that rice plants, broadcast in a submerged paddy field, had a high grain yield that was due to the production of a greater weight of dry matter, as compared with conventionally transplanted plants, when lodging did not occur. In the present study, we examined possible causes of the greater production of dry matter by plants broadcast in a submerged paddy field by comparing the characteristics of plants subjected to different methods of cultivation [the direct-sown plants (DSP) and transplanted plants (TP)] and with different planting patterns (51.3 hills m(-2) and one plant per hill, namely, planting pattern I; and 17.5 hills m(-2) and three plants per hill, namely, planting pattern III). The dry weight of aboveground parts at harvest and the grain yield were larger for DSP than for TP when we compared plants with the same planting pattern, and they were larger for plants in planting pattern I than for those in pattern III when we compared plants with the same cultivation method. Differences in grain yield reflected differences in dry matter production. The factors responsible for the differences in dry matter production among plants depended on the growth stage. At the tillering stage, the number of tillers and, therefore, the leaf area index (LAI) increased rapidly and the interception of solar radiation by the canopy was larger in the DSP than in the TP, irrespective of the planting pattern. These factors were related to the higher crop growth rate (CGR) in the DSP than the TP. After the panicle formation stage, when the canopy closed completely and the interception of solar radiation exceeded 90%, the canopy consisted of more erect leaves and the extinction coefficient of the canopy was smaller for plants in planting pattern I than for those in pattern III, irrespective of the cultivation method. These features were responsible for the larger CGR of plants in planting pattern I than in pattern III. The plants in planting pattern I produced a larger number of crown roots than those in pattern III. During the ripening stage, the decrease in exudation rate was smaller, the amount of nitrogen accumulated was larger, and levels of chlorophyll and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) remained higher in the former plants than in the latter, irrespective of the cultivation method. These characteristics might also contribute to the elevated production of dry matter by the plants in planting pattern I. (C) 2003 Elsevier B.V. All rights reserved.