Effects of soil moisture on the character of rice seedlings (Oryza sativa L.)

The characteristics of rice seedlings (Oryza sativa L.) before and just after transplanting are being studied from the morphological and physio-ecological view-points. In this paper, the differences in characteristics of rice seedlings grown under different soil moisture conditions were examined, as a first step in diagnosing the quality of the seedlings: 1. In all varieties, plant length, the number of living leaves, leaf area, stem thickness, top and root dry weights all increased with increasing soil moisture. The differences in these characteristics among the treatments expanded with the passage of time, and the seedlings in the paddy nursery plot showed spindly growth. On the other hand, the dry matter production of seedlings grown in the upland nursery plot was suppressed compared with the paddy nursery plot, but the upland nursery seedlings showed the features of so-called "pudgy seedlings" with upright leaves and relatively stout stems (Fig. 2). 2. Rooting ability, vertical standing ability, the amount of bleeding water and the degree of leaf die-off were hardly affected by soil moisture treatments. However, upland nursery seedlings were superior in all characteristics to paddy nursery seedlings with the growth advances. Also, upland nursery seedlings had greater starch accumulation and rooting ability, vertical standing ability or the area of leaves die-off. Furthermore, it is assumed that the upland nursery seedlings maintain higher root vitality during the late growing season since the amount of bleeding water is closely related to the root vitality (Fig. 3 and 4-A, -B, -C). 3. The amylase activity and starch accumulation measurements suggested that amylase activity tended to increae with increasing soil moisture and that a certain relationship exists between starch accumulation ability and amylase activity in rice seedlings (Fig. 4-D). The questions related to these points are left for future studies.