水稲の葉層構造と収量の解析 : 第2報 稈長の異なる2品種を作期, 栽植密度を異にして単植および混植した場合

抄録

Two lowland rice cultivars, Yamabiko and Tokai No. 31, were grown either in single or mixed cropping at three levels of planting density (40, 20 and 10 hill/m²) in three cropping seasons (early, normal and late planting) in 1969. Each plot was replicated two times. The community grown in mixed cropping was expected to have higher yield than single cropping due to its deeper canopy. Single plant per hill was grown in a square plantation. The leaf stratified structure of each plot was evaluated on the basis of F₁ and F₂ scores obtained by the method as described in the previous paper. The relationship between the leaf stratified structure and yield was analysed mainly for mixed cropping. 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 in the previous paper: F₁ score increased with the increase of the leaf weight percentage (see the previous paper for definition) in the upper stratum, followed by the simultaneous decrease of the percentage in the lower stratum, while F₂ score increased with the decrease of the percentage in the middle stratum. The leaf weight percentage in the upper stratum increased as the crop grew (Table 1 and 2; Fig. 1, 2 and 3). 2. The leaf stratified structure and top dry weight appeared to be independent of each other as was found in the previous paper. 3. High and positive correlation between yield (hulled rice) and top dry weight at each growth stage was found in many plots as was found in the previous paper. This trend was found more clearly in Tokai No.31 than in Yamabiko and at late cropping season than early cropping season (Table 4). 4. In the plots showing the higher correlation between yield and F₁ or F₂ score, the yield increased when the leaf weight percentage was larger in upper stratum at tillering stage, while the higher yield was resulted from the higher leaf weight percentage in lower stratum during panicle formation and heading stages (Table 5). These were in contrast with results of the previous experiment conducted in 1968, and this difference between yeas was thought to be due to the difference of weather. 5. The correlation between yield and F₁ or F₂ score was found to be relatively high when top dry weight and leaf dry weight were greater. On the other hand, the yield was more correlated to the top dry weight in a crop of smaller leaf canopy (Fig. 4, Table 6). 6. The relative yield difference (R_y) between single and mixed cropping was calculated as, R_y = (γ_m - γ_s) ÷ γ_s × 100(%), where γ_m is the total yield of Yamabiko and Tokai No.31 grown in mixed cropping and γ_s is the mean yield of two cultivars grown in single with same treatment. Then, the F₁ and F₂ scores of the average leaf stratified structure of the two cultivars grown singly in each plot at four growth stage were calculated in the order: (1) The leaf dry weights of two cultivars were summed up regardless of their height. (2) Furthermore, leaf dry weight was evenly divided into five vertical strata whose height was regarded as same as Yamabiko. (3) The percentages of leaf dry weights in five strata to the total leaf dry weight were calculated. (4) They were standardised to constitute the standardised vector of leaf weights of five strata. (5) The vector was multiplied by the eigenvector to calculate the average F₁ and F₂ scores of single cropping, which makes it possible to compare these scores with others found in mixed cropping. Then, each score of single cropping was subtracted from the score of the corresponding plot of mixed cropping. [the rest omitted]