In the present paper, we reported the potential utilization of winged bean (Psophocarpus tetragonolobus (L.) D.C.) as a cover crop to prevent erosion and to control weeds in abandoned fields. The yield of younger pods and mature seeds was estimated in the use as cover crop. Also the availability of winged bean residues as a green manure was tested after the younger pods were harvested as a vegetable crop. The rate of covering over soil by winged bean which was 0.6 m2 m-2 in the inter-row area 12 weeks after sowing due to the slow initial growth increased with almost completely covering being achieved 12 to 32 weeks after sowing. Therefore, winged bean is considered to prevent erosion and control weeds from the rainy season to the typhoon season in Okinawa. The total yield of the younger pods was 1.46 kg F. W. m-2 from 28 weeks to 34 weeks after sowing. In addition, the yield of the dried seeds was 0.18 kg D. W. m-2 in February after the younger pods had been harvested. Moreover uptakes of N, P and K in the aboveground parts of the winged bean at the end of the harvest of younger pods amounted of 20, 2.7 and 6.3 g m-2, respectively. It is concluded that a sufficient input could be achieved for use as green manure.
The effect of the day length on the development of bulbils in Chinese yam (D. opposita) and Water yam (D. alata) was investigated from March 2007 to January 2009. The initiation of bulbils in either species was not affected by the day length. However the time of bulbil initiation was different in Chinese yam and Water yam. Bulbil initiation in Chinese yam occurred earlier than in Water yam. Comparison of the time of tuber and bulbil development, showed that bulbil development occurred later than tuber enlargement in both species. When Long-day treatment (24 hrs) was applied after the solstice, the enlargement of the bulbils was inhibited in Water yam, but not effected in Chinese yam. The photoperiodic sensitivity of bulbil development in Chinese yam was lower than that in Water yam. Tuber development in both species was related to the photoperiodic sensitivity. The bigger bulbils as yam seed tubers developed in Water yam on Miyako island in Okinawa prefecture. Early planting (longer cultivation period) without stake cultivation may result in larger bulbils for seed tubers in Water yam on Miyako island in Okinawa prefecture.
The Kilombero valley is an inland flood plain located in the southern half of Tanzania. It covers an area of about 11,600 km2 (including marginal hills). People have used wetlands for rice cultivation and have converted this region into a major rice production area. Based on the physiographical and ecological structure, in the present study, the Kilombero valley was classified into four subdivisions: the flood plain zone, alluvial fan zone, flood savanna zone, and mountainous zone. In addition, the alluvial fan zone was further classified into six agroecological zones: alluvial fan extension, sheet flood area, spring water area, seasonal swamp, seasonal river bed, and surface water grassland. Under such diverse ecological conditions, farmers cultivate rice in various ways using indigenous technologies: in the flood plain zone, they cultivate deep-water rice; in the alluvial fan zone, the timing of seeding is determined carefully, as rice cultivation is highly dependent on flooding levels; in both the surface water grassland and flood savanna zones, paddy fields are surrounded by ridges for water harvesting, while in the mountainous zone, upland rice is cultivated. Such indigenous knowledge of ecosystems, in particular the hydrogeological peculiarities of each ecosystem, contribute to the stability of rice production in this area.
We investigated the use of cow dung as a mulching material which is commonly applied in Northeast Thailand. Air-dried cow dung (5.0 g) was added to 50 mL of water, mixed for 1 h, and the water-soluble nutrient contents of the samples were determined. A correlation was found between the water-soluble potassium concentration and EC. The amount of leached nutrients was determined by the filtration test performed with various amounts of water and at different intervals. The results showed that the leaching of PO4-P was related to the amount of water added. The amounts of leached NO3-N and K varied with the watering interval and the amount of water used. Plastic buckets (3.8 L; diameter, 0.16 m) were buried under the field, and other buckets filled with 2000 g of air-dried soil were set into the former buckets. The soil surface was mulched with cow dung in layers with varying thickness (0~40 mm), and 200 or 300 mL of water were added. The evaporation speed was determined by measuring the weight of the inner buckets. A correlation was found between mulch thickness (x cm) and the ratio of potential evaporation to actual evaporation (y) as follows: y = 0.20x-0.5 (R2 = 0.99). Typically, farmers use both hands to apply cow dung (approximately 400 mL) to the depression (diameter, 20 cm) and add water using a ladle (approximately 500 mL of water). Based on the results of our study, a larger quantity of water (approximately 1600 mL) should be supplied to avoid salt injury. The water supplied will be retained for approximately 1 month because of the effect of the mulch. The effect of the mulch is sufficient to retain moisture because transpiration of the young plants is limited. In terms of nutrient contents, K is expectable but N and P are not expectable.