17:15 〜 18:30
[AGE27-P09] Water and Mass Transfer in Soils and Optimal Farmland Management in the Rice Terraces of the Philippine Cordillera
キーワード：フィリピン・コルディリェーラの棚田群、世界遺産、棚田、湛水管理、亀裂
In the Rice Terraces of the Philippine Cordilleras, the World Heritage Site, soil-related problems such as the collapse of rice terraces and low productivity are becoming more serious. The rice terraces in the study area are characterized by the fact that the entire mountain slope is terraced, that there are villages within the terraced rice paddy basin, and that farming has been conducted using indigenous knowledge such as constant flooding and application of rice straw as a fertilizer. Therefore, in this study, we evaluated how these farming and environmental factors affect the soil environment, and discussed farmland management methods to improve the soil environment.
Field surveys and sampling were conducted in Bangaan and Batad in Ifugao Province to determine the amount of organic matter, total nitrogen, and minerals such as exchangeable cations, available phosphorus, and available trace elements in the soil. In addition, the drainage of paddy fields may cause cracks in the dry rice field surface and the collapse of terraced rice field. Therefore, we examined the effect of soil drying on permeability; samples were prepared using 100 cc samplers, dried, and saturated permeability experiments were conducted. The degree of drying (water content ratio) and dry density were used as parameters.
The field survey revealed that there is no unified knowledge about soil in the region, and the agricultural extension system is not functioning, so there are no opportunities to acquire agricultural knowledge. Soil analysis showed that the soil was generally deficient in nutrients, but on the other hand, the plots located directly under the village had excessive amounts of organic matter, which was thought to be mainly due to domestic wastewater from the village. On the other hand, in the field directly under the village, the amount of organic matter was excessive. In addition, the application of raw rice straw with high C/N ratio may have caused nitrogen starvation. The plots with excess organic matter were reported to have stunted rice growth and poor workability, and it was also confirmed that the plots were abandoned.
The results of the hydraulic conductivity tests showed that even when the samples were dried to quite low water content at 0.07, at dry densities of 1.0 and 1.2 g/cm3, the hydraulic conductivity when the samples were re-saturated was similar to that when the samples were flooded without drying. Regardless of the drying density, the lowest permeability was observed in the range of 0.25-0.40 at water content. In the experiment with different dry densities, permeability decreased due to clogging at dry densities below 0.9 g/cm3 . These results suggest that hydraulic conductivity can be stably maintained at dry densities of 1.0 g/cm3 or higher.
From all results, drainage in the field was desirable to mitigate soil reduction and decompose organic matter, and permeability of terraced fields could be stably maintained if the dry density was 1.0 g/cm3 or higher. Drying up to a water content ratio of 0.25-0.40 was considered to stabilize the functioning of the tillers because the shrinkage reduced the permeability.
Field surveys and sampling were conducted in Bangaan and Batad in Ifugao Province to determine the amount of organic matter, total nitrogen, and minerals such as exchangeable cations, available phosphorus, and available trace elements in the soil. In addition, the drainage of paddy fields may cause cracks in the dry rice field surface and the collapse of terraced rice field. Therefore, we examined the effect of soil drying on permeability; samples were prepared using 100 cc samplers, dried, and saturated permeability experiments were conducted. The degree of drying (water content ratio) and dry density were used as parameters.
The field survey revealed that there is no unified knowledge about soil in the region, and the agricultural extension system is not functioning, so there are no opportunities to acquire agricultural knowledge. Soil analysis showed that the soil was generally deficient in nutrients, but on the other hand, the plots located directly under the village had excessive amounts of organic matter, which was thought to be mainly due to domestic wastewater from the village. On the other hand, in the field directly under the village, the amount of organic matter was excessive. In addition, the application of raw rice straw with high C/N ratio may have caused nitrogen starvation. The plots with excess organic matter were reported to have stunted rice growth and poor workability, and it was also confirmed that the plots were abandoned.
The results of the hydraulic conductivity tests showed that even when the samples were dried to quite low water content at 0.07, at dry densities of 1.0 and 1.2 g/cm3, the hydraulic conductivity when the samples were re-saturated was similar to that when the samples were flooded without drying. Regardless of the drying density, the lowest permeability was observed in the range of 0.25-0.40 at water content. In the experiment with different dry densities, permeability decreased due to clogging at dry densities below 0.9 g/cm3 . These results suggest that hydraulic conductivity can be stably maintained at dry densities of 1.0 g/cm3 or higher.
From all results, drainage in the field was desirable to mitigate soil reduction and decompose organic matter, and permeability of terraced fields could be stably maintained if the dry density was 1.0 g/cm3 or higher. Drying up to a water content ratio of 0.25-0.40 was considered to stabilize the functioning of the tillers because the shrinkage reduced the permeability.