Soil Fertility and Rice Productivity in an Intermountain Basin of Northern Laos

抄録

Field researchers and agricultural extension workers often encounter field-to-field variations in soil properties and rice yields that make it difficult for them to transfer appropriate agricultural technology and suitable management practices to local farmers. To address this constraint, we examined grain yield and shoot biomass of rice (Oryza sativa L.) and the general fertility status of topsoils (0-10cm) collected from 80 paddy fields with different topographical positions in an intermountain basin in northern Laos. The soils of studied rice fields showed fewer nutrients such as exchangeable bases, CEC, and T-C and T-N contents than the soils of lowland rice fields in Thailand. While higher levels of exchangeable K and available P and Si were found in rice fields at the upper part of the basin and the floodplains located in river catchments, the rice fields located in the lower part of the basin had lower soil nutrients probably due to less flooding and inflow of soil nutrients from the surrounding hill slopes. The yield of high yielding varieties (HYVs) was strongly correlated to CEC, exchangeable Ca, Mg, and K, and available P and Si. On the other hand, indigenous varieties (IVs) did not show a proportional relationship with those elements. Higher yields of HYVs were found in rice fields where soil fertility was relatively high. However, the yields of HYVs were not significantly higher than the yields of IVs under low fertility conditions, indicating that it would be invaluable to supply chemical fertilizer to grow HYVs in such infertile rice fields. In contrast, planting IVs in such conditions could be a better choice for local residents to obtain stable rice production without costly agricultural materials.