Seeded Rice Cultivation Research Articles

Effects of the Combined Application of Ethephon and Gibberellin on Growth of Rice (Oryza sativa L.) Seedlings

Improvement of early seedling growth, such as seedling emergence and vigor is one of the most important agronomic traits in direct seeding rice cultivation. The effects of two plant growth regulators (PGRs), gibberellic acid (GA3) and ethephon (ET), on seedling growth under flooded soil conditions at different temperatures and water depths were investigated. The PGRs were applied during the seed soaking process. A single treatment with GA3 or ET increased seedling growth. However, combined application of GA3 and ET was more effective than that of GA3 or ET alone in many cases at both growing temperatures (15 and 20ºC). The growth of different organs in the rice seedlings, such as the coleoptiles, first leaves, and second leaves was also increased by PGR treatment. The nitrogen concentration of the shoot and the ratio of shoot dry weight to shoot length did not differ significantly among the treatments. The results of our study show that rice seedling growth in direct seeding cultivation may be improved by treatment with GA3 and ET in combination.

Improvement of Lodging Resistance in Submerged Direct Seeding Rice (Oryza sativa L.) Cultivation Using a Newly Developed 'Shooting hill-seeder'. Effect of seedling density on the lodging resistance of hill-seeded rice as compared with that of broadcast-seeded rice.

打込み式代かき同時土中点播機を用いた安定的湛水直播栽培法の確立のため, 異なる苗立ち密度(40, 80および160本m-2)における耐倒伏性を散播水稲と比較して点播水稲の耐倒伏性に関する特性解明を行った. その結果, 点播水稲は散播水稲に比較して稈が長くなるために稈基部にかかる力が大きくなるが, 有効茎歩合が高いために耐倒伏性に関連した稈の形質が優れること, 押し倒し抵抗値が顕著に大きいことにより稲株の耐倒伏性が強化され, 倒伏を生じにくいことが明らかとなった. また, このような播種様式間差は苗立ち密度の高い条件で顕著となった. 押し倒し抵抗値の変動要因を検討した結果, 散播水稲において1株穂数が10本以下の株は押し倒し抵抗値の変動が大きく, 1株穂数の減少により抵抗値が顕著に低下するのに対し, 1株穂数が10本以上の株は押し倒し抵抗が安定して高かった. このことから, 散播水稲では苗立ち密度40本m-2以上の条件では1株穂数が10本以下となるために, 苗立ち密度の変動により1株穂数が変動するのに対し, 点播水稲は標準的な播種条件(条間30cm, 株間20cm)では苗立ち密度が40～160本m-2(1株苗本数が2～10本)の間で変動しても1株穂数が20～26本と安定して多いことにより, 苗立ち密度が変動しても点播水稲の耐倒伏性が安定して高いものと推察された. 湛水直播栽培では苗立ち密度の変動が避けられないため, このような特性を有する点播栽培は湛水直播栽培の安定化に有効であると考えられる.

Improvement of Lodging Resistance in Submerged Direct Seeding Rice (Oryza sativa L.) Cultivation Using a Newly Developed 'Shooting hill-seeder'. Method of hill-seeding for the improvement and stabilization of lodging resistance.

By using a newly developed 'Shooting hill-seeder', it is easy to adjust the hill space within a row or the seeding depth, and change the hill-seeding form in the submerged direct seeding rice cultivation. In this study, the effects of these seeding conditions on the lodging resistance of hill-seeded rice were examined. It was suggested that the increased hill space within a row resulted in lower lodging resistance because of the elongation of culm and decrease in pushing resistance of the hill. These results show the importance to adopt a variety with high lodging resistance, or to control the nitrogen uptake by improvement of fertilizer application or water management, when a large hill space is necessary. On the other hand, the hill-seeding form did not seem to affect the lodging resistance. Furthermore, in hill-seeded rice, the chance of shallow seeding is rare, and the degree of lodging due to shallow seeding is extremely small as compared with broadcast-seeded rice. These characteristics are very important for the stabilization of the submerged direct seeding cultivation, in which unification of the seeding depth is difficult, and the stabilization of seedling emergence is important.

Present Condition and Problems of Direct Seeding Rice Cultivation

Present Condition and Problems of Direct Seeding Rice Cultivation