The effects of the introduction of direct seeding, supplementary irrigation, and chemical fertilizers on rice grain yield were investigated in farmers’ paddy fields in a rain-fed rice-growing village in Northeast Thailand during the years 2002, 2003 and 2004. Since transplanting was carried out only under adequate water conditions, the unavailability of irrigation and small amount of rainfall during planting time limited the area transplanted, which accounted for less than 30% of the whole paddy field area. Nitrogen fertilizer was applied to paddy fields both with and without supplementary irrigation at approximately the same level per unit area. The yield survey in selected paddy plots showed that yields in direct-seeded paddy fields without supplementary irrigation were lower than those in other paddy fields with different planting methods and water regimes in 2002, when planted rice experienced a rain shortage from late June to late August. Similar results were obtained in 2003 and 2004 though there was no significant difference among yields statistically. Based on the crop performance evaluation for whole paddy field, direct-seeding method for rice was often inferior to the transplanting one, especially in paddy fields without supplementary irrigation. The recent prevalence of supplementary irrigation and application of chemical fertilizers was considered to contribute to the improvement of rice grain yield in unproductive paddy fields under rain-fed conditions. Direct-seeding method should be further improved in fields without supplementary irrigation.
The effect of plant aging on the root development of sago palm was investigated in both Tebing Tinggi Island, Riau (deep peat soil area) and in Kendari, Southeast Sulawesi (mineral soil area), Indonesia. The results were as follows: 1) Value of root dry weight was higher at the central position (0 m from a main stem or trunk) than that at positions 1 and 2 m from the main stem or trunk, and was higher at soil depths of 0 to 30 cm than 30 to 60 cm and 60 to 90 cm in both regions. 2) Sago palm roots in both regions started to increase horizontally before the trunk formation stage, while after trunk formation, the roots increased vertically as aging progressed, and expanded downwards. 3) Root dry weight value in Kendari was significantly higher than in Tebing Tinggi. However, a higher percentage of dead roots and a lower percentage of small roots were found in Kendari than in Tebing Tinggi, especially in deep soil layers in younger palms. In Kendari, the roots were more concentrated in the upper soil layers than in Tebing Tinggi after the trunk formation. This last result may be associated with the soil hardness due to high bulk density and low nutrient levels in deep soil layers of mineral soils.
Internodes of floating rice begin to elongate during vegetative growth and then elongate rapidly in response to flooding. After floodwaters recede, the upper parts of the elongated shoots stay erect due to gravitropic bending of the leaf-sheath pulvini of shoots and continue to grow upwards. We have characterized the gravitropic response of leaf-sheath pulvini of floating rice using isolated stem segments with pulvini. When stem segments with five upper pulvini excised from plants during vegetative growth were gravistimulated, the stem segments with the uppermost to the fourth pulvini displayed a gravitropic curvature, and a maximum curvature response occurred in the segments with the second highest pulvinus. In response to gravistimulation, the segments started to bend upwards after a lag time of 37 min, showed a maximum bending rate of 2.4 degrees per hour at 6-7 h after gravistimulation, and ceased bending after almost 48 h. The bending of the stem segments occurred in response to the orientation of the segments at angle values of as low as 1°or 2°in relation to the gravitational force. The stem segments excised from vegetatively growing plants showed a slightly stronger graviresponse than those excised from reproductively growing plants. The strong response of the pulvini of vegetatively growing shoots to gravistimulation is considered to be one of the characteristics of kneeing in floating rice.
Stem segments excised from vegetatively growing shoots of floating rice displayed a gravitropic curvature in response to gravistimulation. Using stem segments, we investigated the involvement of plant hormones in the gravitropic bending response of pulvini and the effect of submergence on the response. The application of the auxin transport inhibitor N-1-naphthylphthalamic acid to gravistimulated stem segments resulted in a 75% reduction in the bending of the pulvini, which was completely removed by unilateral application of indole-3-acetic acid to the underside of the pulvini. Although the exclusive application of gibberellic acid (GA3) did not affect the bending response of gravistimulated pulvini, the gibberellin biosynthesis inhibitor ancymidol reduced the bending of gravistimulated pulvini by 30%, and the reduction was removed by the application of GA3. In addition, the application of ethylene alone did not affect the bending response of gravistimulated pulvini, although gravistimulation promoted the production of ethylene in stem segments. The ethylene biosynthesis inhibitor aminooxyacetic acid suppressed the bending response of gravistimulated pulvini by 28%, and the suppression was removed by the application of ethylene. These results suggest that the asymmetric distribution of auxin in gravistimulated tissues of floating rice pulvini plays an important role in the bending response, in which gibberellins and ethylene might also be, at least, partly involved. The gravitropic bending of floating rice stem segments occurred under submergence under both light and dark conditions, whereas the gravitropic bending of submerged stem segments of wheat and oat was still observed under light but not under dark conditions.