Adaptation of Grain Legumes to Transient Water Deficit in Timor-Leste

Abstract

In Timor-Leste, it is possible to use residual soil water after rice harvest to produce grain legumes, despite the lack of supplementary irrigation. This study aimed to identify the growth of potential grain legumes adapted to transient water deficit after rice harvest. The experiment was undertaken in 2012 at the Hera Field Research of the National University of Timor Lorosa'e, representing lowland areas, and farmland in Aileu, representing highland areas. The experiment used a completely randomized design with two factors (water treatment and species) and three replications. Both sites had a well-watered control and drought treatment applied at flowering for 15 days before re-watering to maturity at the Hera site or five days when rain interrupted the treatment at the Aileu site. Grain legumes were peanut, soybean, kidney bean, white bean, speckled bean, cowpea (black), cowpea red, mungbean, and grass pea. The measured parameters included soil water content, pH and temperature, crop phenology, plant growth, yield, and yield components. The results showed that the Hera site had significantly lower soil water content than the control; no soil water measurement occurred at Aileu site due to rain interruption. On average, grain legumes at the Hera site germinated, flowered, set pods, and reached physiological maturity earlier than at the Aileu site. The fastest flowering species was soybean (48 DAS) at the Hera site and (winding) white bean at the Aileu site (61 DAS). The first species to set pods were mungbean, soybean, and kidney bean (55 DAS) at the Hera site and white and speckled beans (73 DAS) at the Aileu site. Mungbean matured first at both sites. Drought significantly reduced seed yield by 32.9% and 19.1% at the Hera and Aileu sites, respectively. At the Hera site, cowpea red and mungbean produced the highest seed yields (2.6 t/ha), followed by kidney bean (2.3 t/ha), and soybean (2.0 t/ha). At the Aileu site, cowpea black produced the highest seed yield (1.6 t/ha), with the remaining species between 1.2 t/ha (mungbean) and 0.02 t/ha (grass pea). The experiment identified mungbean, soybean, cowpea red, and kidney bean as the best grain legume options for lowland areas after rice harvest; further study is required for the upland areas. Kidney bean was the novel finding, tested for the first time in lowland areas, which had vigorous growth and high seed yield.