イネ科牧草の群落構造と乾物生産特性

抄録

In order to know the differences of canopy structure and its relationships with dry matter production, productive structure, growth parameters (CGR, LAI, NAR), extinction coefficient (K) and efficiency of solar energy utilization (Eu) were investigated in the primary swards of fourteen varieties of seven grasses (shown in Table 1). The results obtained are summarized as follows: 1. There were little differences in the productive structure of non-photosynthetic system, but the productive structure of photosynthetic system differed considerably among grasses. The grasses could be grouped into 4 different types according to their mode of the vertical distribution of leaf dry weight and leaf area within the canopy. Tall fescue had the greater leaf distribution towards the base of canopy (triangular type); Reed canarygrass and smooth bromegrass had the leaf distribution which was most abundant in the middle layers and became smaller towards the base and the top of canopy (oval type): Orchardgrass and meadow fescue had the relatively uniform leaf distribution over all layers (rectangular type). In timothy and perennial ryegrass the varietal difference was found, namely, one was the table type which had a greater leaf distribution towards the top of canopy, and the other was the oval type. 2. CGR indicated highly significant correlation with NAR, but not correlated with LAI. CGR also correlated significantly with K and Eu. 3. The rectangular type canopy, which was found in orchardgrass and meadow fescue could utilize light energy in a better way than other types. 4. Among grasses, there were definite differences in the LAI absorbing 95% of the incoming light within canopy. This LAI, corresponding to the critical LAI, was also in agreement with the LAI above the layer indicating the highest leaf area density within canopy. 5. The critical LAI correlated with CGR (r=0.746), Eu (r=0.842) and K (r=-0.747). On the other hand, NAR indicated negative significant correlaiton with the ratio of non-productive system to productive system, when the leaf dry weight below 50% light condition was added to non-productive part. Thus, it was concluded that the critical LAI, not mean LAI, played the most significant role in dry matter production under over-luxuriant canopy.