Abstract
We examined the effects of remaining soil moisture and irrigation on dry season cropping in uncultivated lowland rice fields in a mountainous area of Vientiane Province in Lao PDR. In the un-irrigated soybean cropping experiment, the soil moisture decreased to pF3.0 (depletion of moisture content for optimum growth) within 3 weeks of sowing, and the remaining soil moisture was not enough for cropping. In the irrigated experiment based on the trial calculation of the water requirement and irrigation interval calculated from the results of soil moisture monitoring, the soybean yield was one-sixth of the national average. Although the calculated water requirement corresponded with the estimated total evapotranspiration during the planting period, it was less than the evapotranspiration at the middle stage of soybean growth. Following irrigation, while the soil moisture level did not return to the field capacity, the groundwater level increased in some cases. Cracks were present on the clay soil surface. The results suggest that high-intensity irrigation caused preferential flow through the cracks, which increased infiltration losses and decreased the effectiveness of the irrigation.
