Relationships between canopy structure and yield in rice plants. III. Direct sowing culture of lowland rice at five population density levels having two nitrogen levels on a well-drained paddy field.

Abstract

A study on the relationships between canopy architecture and yield of rice sown directly requires experimentation with population density of different magnitude and basal nitrogen levels. A lowland rice cultivar, Yamabiko, was sown directly in a square design at five population density levels (1600, 400, 100, 25 and 6.25 plant/m2 at seedling stage) having two nitrogen levels as basal dressing (0 kg-N/10a : 0-N plot and 10 kg-N/10a : 10-N plot) on a well-drained paddy field in 1972. Each plot was replicated three times. Plants were grown on available soil moisture for one month. Thereafter, field was flooded with irrigation water which was kept stagnant in the field till dowgh-ripe stage. The leaf stratified structure of each plot was evaluated on the basis of F1 and F2 scores obtained by the multivariate analysis method as described in part I14). The relationship between the leaf stratified structure and yield was analysed and the results were compared with those of a rice community of transplanting culture reported in two previous papers14, 15) in order to find the characteristics of the structure of this rice community sown directly. The results are as follows : 1. The relationship between F1 or F2 score and the leaf stratified structure and the seasonal trend of leaf stratified structure were virtually the same as those of two previous papers (Tables 1 and 2 ; Figs. 1, 2 and 3). 2. The yield (winnowed paddy) was maximum at 400 plant/m2 density level both in 0-N and 10-N plots and the yield of 10-N plot was about 19% higher than that of 0-N plot (Table 3). 3. The leaf stratified structure and top dry weight appeared to be independent of each other. 4. Positive correlation between yield and top dry weight at each growth stage was found in 0-N and 10-N plots. The correlation was higher at later stage of plant growth, and it was always higher in 0-N plot than in 10-N plot (Table 4). 5. The correlation between yield and F1 or F2 score was high and positive at the young panicle formation stage only in 0-N plot and at all stages except active-tillering in 10-N plot (Table 5). This trend was similar to that reported in part I, presumably due to the similarity of the weather between these experiments. 6. The relative strength of correlation between yield and F1 or F2 score compared with correlation between yield and top dry weight (see part II15)) was greater in the communities with larger leaf area index (LAI), which include 10-N plot or later stage of plant growth. By contrast, in the communities with smaller LAI, the relative strength was small. The smaller the LAI was, the higher was the change of this relative value (Figs. 4 and 5). 7. The comparison of the leaf stratified structure of a rice community sown directly with that of a transplanted community15) shows that the former structure had a tendency to have a high leaf weight percentage (see part I for the definition) in the lower stratum at the active-tillering stage and in the upper stratum after the young panicle formation stage (Fig. 6). The results of No. 1, 3, 5 and 6 are the same as those of two previous papers14, 15). It is therefore suggested that the relationship between the leaf stratified structure and yield of rice is little influenced by the differences in cultural methods as well as the yearly variations in the environmental conditions. It was observed that F1 and F2 factors maintained their individual characteristics in the three experiments. Thus, it is concluded that the statistical method used in the series of this study is very useful for analysing canopy architecture of rice community and for investigating the yielding ability of rice from the viewpoint of canopy architecture.