Revaluation of the high yielding rice variety from the nitrogen and water use efficiency

(1)在土壤氮素矿化水平不同的3个试验点(四川中国、京都和奈良)，研究了土壤氮素肥力对小穗生产力的影响。中国的土壤矿化氮素水平高于京都和奈良。中国对土壤氮素的吸收及其对颖花生产力的影响高于京都和奈良。(2)1998-2000年在奈良樱井县进行了轮作稻田和连作稻田的水稻生长特性研究。在不施氮肥的情况下，旱作水稻的生物量、产量和氮素吸收普遍高于常规旱作。这似乎是由于秸秆还田土壤氮素释放量较大所致。然而，在本研究中没有观察到土壤干燥对氮素矿化的影响，而且土壤矿化氮的总量(SMN)在CPF中更大。结果表明，与常规旱作相比，旱作旱作对氮素吸收的贡献更大，氮素利用率更高。(3)水稻品种对大气湿度的响应存在差异。在低湿度条件下，水稻品种的气孔密度较高，气孔较长，气孔开度较大，叶片水势较低，水分利用效率较低。在高湿条件下，水稻品种的蒸腾速率、气孔开度和水分利用效率基本一致。这些在低湿度条件下的形态生理特性上的差异可能是造成水稻植株生长和干物质生产差异的原因之一。

(1) In 3 experimental sites (Sichuan Province China, Kyoto and Nara) of which the mineralization soil nitrogen level differed, the effect of the soil nitrogen fertility on the spikelet productivity was investigated. Mineralized soil nitrogen level in China was higher than Kyoto and Nara. The nitrogen uptake from soil and its' effect on the spikelet productivity was high in China than Kyoto and Nara.(2)The growth characteristics of paddy rice were evaluated in rotational paddy field (RPF) and continuous paddy field (CPF) at Sakurai, Nara, in 1998-2000. Without N fertilizer application, biomass production, yield and N uptake of rice were generally higher in RPF than in CPF. It seemed that greater nitrogen release from soil in RPF caused this increase. However, soil drying effect for N mineralization, often expected in RPF, was not observed in this study, and the total amount of mineralized N from soil (SMN) was greater in CPF. We concluded that higher N uptake observed in RPF could be explained by 1) greater N contribution from subsoil, 2) higher recovery rate of N, compared with CPF.(3)The varietal differences in the response to atmospheric humidity were examined using japonica and indica variety. Under low humidity, as compared to the indica varieties, the japonica varieties had a higher stomatal density, longer stomatal and longer stomatal aperture, resulting in a lower water potential in leaf blades and lower water-use efficiency. Under high humidity, the japonica and indica varieties showed a similar transpiration rate, stomatal aperture and water-use efficiency. These differences between the japonica and indica varieties in morphophysiological characters under low humidity might cause the varietal differences in the plant growth and dry matter production in rice.