一、二期稻作土壤環境、根部活力與產量之分析比較

Abstract

為探討本省第二期稻作單位面積產量較第一期稻作為低有關之根部原因，方浴水稻各生育期調查土壤環境、根部活力與葉部營養要素含量之差異，進而研討與產量之關係。謹將結果摘要於後。 大部份之稻根分布於地表下15公分以內之耕土層。該土層之地溫在水稻孕穗期以前，一直以二期作較一期作者為高。又該層土壤之氧化還原電位（Eh值）在糊熟期以前，均是二期作者較低。該等差異在水稻生育之愈早期愈為明顯。 二期作水稻之根部長期生長於還原狀態較為明顯，亦即較為不利之土壤環境中，而整個生育時期其氧化力卻常低於一期作稻根，故容易遭受還原性物質之侵害。再者，生育初期遇高溫之二期作稻根雖然伸長快速，分枝根較多，但其根徑較細，生育後期則腐敗根之比率較一期稻作者為多。又由稻葉及稻田土壤中磷、鉀含量分析之結果推論得知，二期作稻根對營養要素吸收之能力較差。以上可能是二期稻作之稔實率與千粒重較低，以至產量較低之主要原因。 Two crops of rice can be cultivated in a year in most part of Taiwan. The first crop is grown in the former half of a year, and the second crop is in the later half. However, the yield per unit area of the second crop is always about 20% lower than that of the first in the past years. The research was designed to elucidate the causes of low yield of the second rice crop especially concerning the roots and their growth environments. Results were summerized as follows. Most of the root system distributed in the plowed soil, i. e., in a layer about 15 cm below the surface of the soil. It was found that before booting stage the temperature of this layer of the second crop was always higher than that of the first crop. And until dough stage, the Eh value of this layer of the second crop was always lower than that of the first crop. Moreover, in the earlier stage, the tendency was more clear. The roots of the second rice crop always grew in more reduced and unfavorable environment of the paddy soil. Furthermore, their oxidizing abilites were always lower than those of the first crop. Therefore, their roots could more easily be damaged by reduced substances in the soil. It was also noticed that the elongation rate of the roots of the second crop was faster but the roots became thinner when they grew in a higher temperature during the early growth stage. The outer morphological appearance also showed that the ratio of rotten roots of the second crop was higher at later growth stage. The analyses of phophorus and potassium in rice leaves and paddy soil revealed that the absorption ability of the second crop was lower than that of the first crop. The above facts may be the main cause of lower percentage of fertile grain as well as lower grain weight, and consequently influence the yield in the second rice crop.