• 作者： 林安秋; 蘇新
• 作者服務機構： 國立臺灣大學農藝系
• 中文摘要： 本試驗研究乃以光合作用觀點探討第二期稻作低產之原因供改善第二期稻作之參考為目的。
  試驗以同一品種在同一地區而分別在第一、二期作栽培，並在相同肥培管理條件下進行為原則。
  光合作用之測定乃仿?戶等 之方法測定自然狀態下之群落光合作用。試驗結果摘要如下：
  1.水稻一、二期作群落光合作用之日變化，在成熟初期以前，完全受日照所支配；日照增
  強，光合作用隨而增高，多雲或陰天降低，雨天降為更低，一日之變化成為變動型(fluctuated
  type)，成熟後期為平坦型(flat type)。第二期稻作之光合作用能力較第一期作為低，光合作用升
  高之時間第二期作後半期較一期作為遲，降為最低之時間第二期作亦較一期作為早。
  2.第一期作之光飽和點，成熟初期以前為0.5～0.6 cal/cm /min.（以下略寫1y∕min.），成
  熟後期之光合作用能力降低，飽和光度亦降為0.4 ly/min.，第二期稻作之光飽和點較第一期作為
  低，為0.4～0.5 ly/min.，成熟後期更低(0.3 ly/min.) 群落狀態下之光飽和點，因品種、期作
  別、生育期而異。達光飽和點之光合作用能力及光合作用效率(photosynthetic efficiency)，第
  二期稻作均較第一期作為低。
  3.葉中之葉綠素含量，第二期稻作均較一期稻作同生長期者為低，且二期稻作在最大分蘗
  期後急速下降，臺中在來一號一期作亦然。葉面積指數（LAI）之最大時期，第一期稻作在抽穗
  期以後，適逢後期之強日照及長日，光合作用能力大，有利於第一期稻作之收量，而第二期稻作
  之LAI最大時期是在抽穗期前，抽穗期以後急速降低，又逢二期稻作收量生產期之短日與低日
  照強度，光合作用能力低，不利於穀粒之收量。
  4.第二期稻作抽穗期前之高溫，加速光合成系之衰敗，而收量生產期之低日照及短日，限
  制光合作用，乃是第二期稻作低產之最主與原因。
  5.配合光合作用之能量(solar energy)利用，以估算理論最高產量結果得知，一、二期作
  增產之僭力甚大，尤以本省南部地區為最。但二期稻作仍較一期作為遜色。欲提高二期稻作之產
  量，以直播，流水灌溉以增加單位面積之有效分蘗數；增施適量素肥料以提高葉面積、葉綠素含
  量及含N量，或防止光合成系之早期衰敗等栽培技術之改良，均可達成，但是其效果有限。如欲
  將第二期稻作產量提高與第一期作相等，北部地區，僅靠栽培技術之改良方法，實難達成。必須
  配合育種或引種方可。適於第二期作之水稻品種，必須植株矮，葉厚而濃綠，葉直立之早熟（一
  百天左右）及對溫度、日照鈍感之品種。在二期稻作適用之品種未選得前，絕不可為二期稻作之
  增產而忽略增產條件優厚之一期稻作，以免因小失大。
  型
• 英文摘要： The purpose of this study was to elucidatethe causes of low yield of the second crop ofrice according to the photosynthesis. The authormodified the method of Togari (1956) to constructan apparatus (Fig. 1）for measuring the photo-synthesis in the field under natural conditions. The results obtained were as follows: 1. The daily changes of the photosynthetic capacity of the 1st and 2nd crop before early maturing stage was fluctuated propor- tionally to light intensity. The photosyn- thesis began at sunrise, reaching a maximum at about 10:00 AM., and decreased to the lowest at sunset. The diurnal course of photosynthetic capacity seemed to be a fluctuating curve, but it became flat type at late maturing stage. 2. The saturation point was at 0.5-0.6 1y∕min. before early maturing stage, but it decreased to 0.4 ly/min. at late maturing in the Ist crop. It was comparatively low at the 2nd crop, 0.4-0.5 ly/min. before early maturing stage, decreased to 0.3 ly/min. at late maturing. The photosynthetic capacity and photo- synthetic efficiency at the saturating point was lower at 2nd crop than the 1st crop. The results indicated that the plant under field condition had different demand for light intensity for the maximum photo- synthetic activity at different growth stage and crop seasons. 3. The chlorophyll content of the leaf was lower in 2nd crop, and it decreased quickly after the maximum number of tillers stage. The maximum leaf area index (LAI) of the Ist crop appeared exactly after heading, it just met the need of the benefit of photo- synthesis, so the grain yeild increased, while the maximum leaf area index of 2nd crop appeared before heading, after that, it de- creased immediately. Then, the disadvantage of sunshine, caused the low yield of 2nd crop. 4. According to the experiment results, high temperature affected tillering and deteriorated photosynthetic system before heading, then, the unfavourable solar light limited the photosynthesis after heading, and caused the low yielding of the 2nd crop in Taiwan. The theoretic maximum production of the1st and 2nd crop utilizing solar energy by photo-synthesis was estimated. It was found that thetheoretic maximum yield of the "ideal rice plant"was four times more than the real rice produc-tion. The yield of the 2nd crop is lower thanthe 1st crop for about 15 to 30 percent. There-fore, it is possible to raise the production of"double croping" if we are able to utilize thesolar energy effectively. Also we could be ableto raise the grain yield of the 2nd crop to acertain extent by way of agronomic performance,such as by direct sowing method to increasethe number of tillers per unit area or applicationof chemical fertilizer to increase LAI and chlo-rophyll contents, etc. But the only way to raisethe yield of the 2nd crop to as high as the 1stcrop is through breeding. Therefore, the adap-tible, early maturing and non photosensitivevarieties which are short, thick, dark green anderect leaf should be obtain through breeding.
• 中文關鍵字： --
• 英文關鍵字： --