小規模稲作農家に資する移植システムに関する研究

概要

The objective of this research is to develop a transplanting system beneficial to small- scale rice farmers. In general, this research combines two correlated techniques that are rice transplanting machine and rice mat seedlings. A simple mechanism termed free- pivoting suspension is developed and used as a simplification of the structure of a one- wheel two-row rice transplanter. Additionally, mat seedlings named arrayed mat seedlings are conceived with an intension of reducing the number of seeds used per nursery tray while covering the same area of planting as broadcast seedlings so that seeds can be saved and seedlings plant last longer. In the end, the arrayed mat seedlings are tried on the free-pivoting suspension rice transplanter as a combination of the two techniques.

　In CHAPTER 1, the background of this study is described and the advantages of a simplified structure on a rice transplanter and of saving seeds on rice seedlings are raised up as the main purposes of this study. Mechanization of the operation of transplanting which represents 25% of the total labor requirement in rice farming is generally used to face the unbalanced demand and supply in rice. Mechanical transplanting saves labor while improving the quantity and quality of rice production; it combines both machine and seedlings. First, a walk-behind rice transplanter was developed with a simplified suspension mechanism that eliminates the use of a hydraulic cylinder while maintaining enough control of the position of the wheel relative to the body of the machine during transplanting. With the simplified mechanism, the structure of the transplanter would become simple and easy to fabricate in addition to the weight and the cost that would be reduced. Second, a new arrangement of seedlings was developed to reduce the quantity of seeds required per nursery tray for the same area of planting. With this method, seeds can be saved and, subsequently, the low density would allow more nutrients, light and aeration to the plants to live longer.

　In CHAPTER 2, a mechanism termed free-pivoting suspension is developed as a simplification of the suspension mechanism of a walk-behind rice transplanter. The free- pivoting suspension of the wheel was mounted on a modified rice transplanter with a clamping device installed for switching between the free-pivoting and the fixed suspensions. The fixed suspension was first tested in various settings of the depth of the wheel and the hardpan in order to elucidate the necessity of adjusting the depth of the wheel over that of the hardpan. As an improvement, the free-pivoting suspension was compared with the fixed suspension. Thereafter, ameliorations were made on the weight distribution of the rice transplanter to further improve its mobility performance before finally testing it in transplanting seedlings on a varying soil pan of field. With the fixed suspension, it was found that adjusting the wheel to the same depth as the hardpan is necessary for maintaining a horizontal position of the body while generating low and stable slippage at the wheel. With the free-pivoting suspension, in the field of varying soil pan, the pitch angle of the transplanter was maintained stably at an average of 1.8º on the soil surface, compared to 4.7º that tended to change with the sinkage of the wheel with the fixed suspension. With the free-pivoting suspension, an addition of 98 N of weight on the wheel reduced the slippage by half on uniform surfaces of the soil pan. The prototype of rice transplanter achieved an average slippage of 10.3% and a lodging angle of the planted seedlings of 17° when planting seedlings in the field of varying soil pan.

　In CHAPTER 3, a seedling arrangement in array was developed to reduce the amount of seed per nursery tray, and so, to extend the lifespan of the seedling plants. The arrayed seedlings were made by sowing 82 g of germinated seeds in a 30-row arrayed of furrow scratched on a coco-peat mat with a grinder. They were grown with broadcast seedlings (138 g of germinated seeds) used as the control. The 30-row arrayed and the control seedlings were transplanted with a 30-lateral feed rice transplanter set at 7 mm vertical feed and a 26-lateral feed transplanter set at 13 mm vertical feed, respectively. The 30- row arrayed seedlings allowed a 40% saving of seeds over the control and the remaining seedlings survived until headings. The combination of the 7 mm vertical feed and the 30 lateral feeds setting of the transplanter reduced the number of trays per unit of area to 46%. However, the percentage of hill mortality investigated upon harvest in the arrayed seedlings was significantly high (19%), which was partly attributed to the narrow and sharp tines of the planting mechanism for high-density seedlings that damaged the grown- up singular plants of the seedlings although they were spared at transplanting.

　In CHAPTER 4, based on the result from the 30-row arrayed seedlings (CHAPTER 3), another experiment was carried out as a follow-up. The objective was to save seeds while covering the same area of planting as that of broadcast seedlings by focussing on settings to reduce hill mortality. The arrayed mat seedlings were prepared by sowing seeds in 26-furrow arrays on coco-peat mats made with a plastic mold. They were transplanted with the use of a conventional 8-row transplanter, set at 26 lateral feeds and three vertical feeds (7, 10, and 13 mm), and grown along with the broadcast (control) seedlings. The arrayed seedlings were prepared with 40% fewer seeds than were the control and their foliar ages were 3 to 4 on the day of transplanting. Neither of the seedlings were suitable for the 7 mm vertical feed in terms of missing hills at transplanting. The arrayed seedlings at transplanting missed 11.3% and 6.3% of hills in the 10 and 13 mm-vertical feed, respectively, but they were still larger than those in the control (9.0% and 3.3%). With the arrayed seedlings, the hill mortality during the growth period was low (< 5%) and the grain yield was 500 g/m2, which were not different from the control. In CHAPTER 5, the 26-row arrayed seedlings were tested on the prototype of the free- pivoting suspension rice transplanter with an objective of combining the two techniques (i.e. the seedlings and the transplanter) so that they would simultaneously profit small- scale farmers. The test was carried out in a varying soil pan of the field. The rice transplanter was loaded with 98 N weight as was suggested in CHAPTER 2 and set at 16 mm- vertical feed. Three types of seedlings were prepared: 26-row arrayed seedlings on a scratched and a pressed coco-peat mat (sown at 90 g of germinated seeds per tray) and broadcast seedlings on soil only (sown at 150 g of germinated seeds per tray) as the control. The mobility performance of the rice transplanter, such as forward speed and slippage, were measured and hills investigation including measurements of plant depth and lodging angle were carried out right after the transplanting operation whereas hill mortality was investigated 12 days later. During the experiment, the forward speed of the rice transplanter was between 0.5 m/s and 0.6 m/s with a slippage average of 10.7% which tended to increase with the depth of the hardpan. The plant numbers per hill were one to three with a missing hill of 8.9% on the average, which was not significantly different among the seedling types. At 12 days after transplanting, the hill mortality was low <2% and not different among types of seedlings. They tended to decrease with an increase in the number of the singular plants per hill. The depth of planting was between 2 and 4 cm whereas the lodging angle was slightly large (31°) but was recovered 12 days after transplanting.

　In CHAPTER 6, the general conclusion of each section of this study is elaborated and the prospect of the study is described. On one hand, the prototype of rice transplanter indirectly preserves small rice fields from abandoning and helps traditional farmers to easily adopt mechanical transplanting. However, the performance of the rice transplanter can further be improved by changing the weight distribution on the machine without compromising the engine power and by using a wider size of the wheel lugs. On the other hand, the use of the coco-peat mat in the arrayed seedlings helps to preserve the environment as it alleviates soil displacement from mountains to the paddy field. Nonetheless, the arrayed seedlings should be improved by adjusting the orientations of the seeds in the mat in the same direction, by adding guides near the position the tines pick up seedlings, and by designing tines with a similar width as the pitch of the arrays to minimize the percentage of the missing hill at transplanting and the hill mortality.

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