マラヤにおける水稲の生育相と施肥の効果に関する研究 : 第5報 主要品種の耐肥性と収量構成要素の解析

抄録

Experiments were carried out form 1967 to 1969 in a double cropping area of West Malaysia using five varieties, i. e., Ria (IR 8), Mahsuri, Bahagia (sister line of IR 5) and two local long term varjeties under three fertilizer levels. The results obtained are summarized as follows : 1. Short term varieties showed shorter plant height and culm length and smaller straw weight but greater number of panicles than those of long term varieties(fig.1). The peak of LAI in Ria was observed at the heading stage rather than the stage of young panicle formation. The adverse tendency was found in the other varieties, particularly two long term varieties.The culm length, LAI and N percentage in the straw tended to increase when the fertilizer increased, though the number of panicles showed less increase in the long term varieties than short term varieties. The correlations between LAI, and rumber of palicles and spikelets per sq. meter, and also correlations between grain yield, and number of panicles and LAI were found respectievly (fig. 3). 2. In the double fertilized plots, Ria and Bahagia were short in the culm length but higher in the grain/straw ratio and ratio of yield increase over non-fertilized plot among five varieties (table 1). It was found that LAI at the heading stage was correlated to the dry matter increase after heading, and the dry matter increase per unit leaf area was also correlated to the ratio of yield increase. This could be attributed to the better balance between photosynthesis and respiration and also higher contents of nitrogen in the the steaw in Ria and Bahagia (table 1). The grain/straw ratio was regarded as an index of fertilizer response. It also showed a definite relation to the culm length, i. e., the shorter the culm length the higher is the grain/straw rstio. 3. In a double cropping pilot project area, Ria gave grain yield 22 % more than Mahsuri, due to the high percentage of ripened grains and heavy weight of 1, 000 gains (table 2). The average yield of Bahagia in 19 farmers' fields was 10% higher than Ria, due to the high percentage of ripened grains (higher than Ria by 19%); though the number of panicles and spikelets per sq. meter were less with Ria. 4. It can reasonably be considered that the number of panicles per unit area contributed greatly to the yield, and the number of spikelets per unit area also contributed to the yield through the increase of panicle number by the denser planting (fig. 4). The weight of straw was also highly correlated to the number of spikelets and yield particularly in Ria. The percentage of ripened grains was also regarded as an important factor to increase yields (fig.4). It is very likely that Ria expresses the highest yielding ability under heavy fertilized conditions rather than with dense planting, although it has a defect of low percentage of ripened grains under adverse field conditions. Bahagia expresses a high ripening ability in the farmers' fields, although it has a limitation in increasing yield due to lodging. 5. It can be said that Ria and Bahagia are the most desirable varieties as far as yield and fertilizer response are concerned (fig. 2). The two long term varieties show the luxurious growth, resulting in the poor fertilizer response and low yield.