Utilization of vetiver for saline and sandy soils improvement of northeast Thailand

For the salinity tolerance test, Prachuap ecotype (upland ecotype) could stand on the highest soil salinity level followed by Sri Lanka (lowand econtype), Songkhla 3 (lowland ecotype) and Kamphaeng Phet 1 (upland ecotype) respectively. Prachuap ecotype could stand up to 12 mS/cm on the first six weeks and up to 9 mS/cm at six months. Fruit trees that could be grown successfully in the highly saline and sandy areas were Sapota (Achras sapota L.), Tamarind (Tamarindus indica), Jujube (Ziziphus mauritiana L.), and Guava (Psidium guajava L.) respectively. They could stand upto 6.8, 6.0, 5.1 and 4.3 mS/cm respectively. Under saline field condition Tamarind performed best on growth. On low fertility Yasothon sandy soil (Oxic Paleustults), Prachuap and Sri Lanka responsed best for growth and yield followed by Songkhla 3 and Kamphaeng Phet 1 from the farm waste materials. The application of farm manure even at low rate helped vetiver roots much better in numbers and strength, while chemical fertilizer even at low rates helped on stand and more plant uniform. For field experiment on unfertilized Yasothon sandy soil, Prachuap gave the best growth and yield followed by Sri Lanka, Songkhla 3, Kamphaeng Phet 1, Nakhon Sawan and Roi Et respectively. Growing vetiver hedgerows at difference distances away from field crops plots revealed that if spacing was at 60 cm or narrower, yield of both field crop and vetiver would be reduced, but at 120 cm sweet corn yield would be increased. The first row of sweet corn planted at 90, 60 and 30 cm apart from vetiver rows were the causes of yield reduction when compared to 120 cm spacing. This first row's yield was also lowest significantly when compared to other rows of the same treatment. Experiment on the population of vetiver hedgerows on farm pond edges with 45 or 100 percent slope of saline and sandy Roi Et soil (Re-sa, Typic Natraqualfs) revealed that weight of sediment that could pass thru the 0, 1, 2 and 3 rows of vetiver were in the ratio at 4:3:2.2:1 respectively. Time of planting as well as planting technique could be important on this soil to control soil erosion hence improve pond water quality. Planting vetiver with local weeds on saline soil such as Panicu repens in the same or separate plots for the purpose of plant competition indicated that Panicum repens usually gave higher yield than vetiver but in some season yield could be closed when planted separately. For experiment on the effect of organic and chemical fertilizer on growth and yield of vetiver indicated that it soils were heavily affected by salt, vetiver were highly response on both kinds of fertilizer. But when soil was not so salty, plant would response more to chemical fertilizer. The lower growth and yield from less salinity plots might come from the local weed competitions.