Adaptation of Grain Legumes to Terminal Drought after Rice Harvest in Timor-Leste

Abstract

In Timor-Leste, most paddy fields are abandoned after rice harvest due to limited water resources for another rice production cycle, particularly in lowland coastal areas. There is substantial scope for including legumes and other crops in the rice–fallow system in Timor-Leste. This study investigated the adaptation of grain legumes to terminal drought. The experiment was undertaken in 2018 and 2019 at field sites in Vemase and Laleia, respectively, on the northeast coast of Timor-Leste. The experiments used a split-plot design with two factors (water treatment and species) and three blocks (Vemase site) or four blocks (Laleia site). In 2018, the water treatments were well-watered control (W0), water withheld from flower initiation to maturity (W1), and water withheld after seedling establishment to maturity (W2). In 2019, the water treatments were well-watered control (W0) and water withheld from flower initiation to maturity (W1). Grain legumes were mungbean and soybean tested against grass pea (cv. Ceora), a well-known drought-adapted grain legume. The measured parameters included soil water content, crop phenology, plant growth and development, yield and yield components. The experiments revealed that mungbean is the most suitable grain legume crop after rice harvest under moderate drought conditions, while soybean is the preferred option under severe drought. Grass pea could be the best adaptive grain legume under severe drought in Timor-Leste when combined with the worsening conditions of climate change.

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

“…Early maturity reduced the impact of drought on the seed yield of kidney (common) bean [21], grass pea [6,9], and mungbean and soybean [8]. Mungbean and soybean are cultivated in lowland irrigated and rainfed areas in Timor-Leste and elsewhere in Asia [8,22,23]. However, kidney bean had vigorous growth and development in this study, with consistent seed yields in warm lowland climates.…”

“…The W1 treatment reduced the average number of filled pods per plant by 31.2% compared to controls. Soybean produced the most filled pods per plant (27.5), with the remaining species producing similar numbers (8)(9)(10)(11)(12)(13)(14)(15). At the Aileu site, soybean also produced the most filled pods per plant (20.5), with the remaining species producing similar numbers (5.9-10) (P < 0.001).…”

“…A study showed that adding soil inoculant and/or soil P enhanced root nodulation and growth of soybean [20]. Early maturity reduced the impact of drought on the seed yield of kidney (common) bean [21], grass pea [6,9], and mungbean and soybean [8]. Mungbean and soybean are cultivated in lowland irrigated and rainfed areas in Timor-Leste and elsewhere in Asia [8,22,23].…”

“…Water deficit decreases crop growth, development, yield, and yield components of grain legumes [5][6][7]. The extent of the yield reduction depends on the duration and intensity of the stress and varies between species and cultivars and climatic variations, as reported for mungbean, soybean, and grass pea [6][7][8][9][10]. Reduced soil water content to a moderate drought level (60% field capacity) reduced pod and seed numbers and seed yield per plant in mungbean (line 97001) [11].…”

“…Ceora), severe and moderate drought reduced seed yield by 87% and 24%, respectively [6,9]. Reduced seed yield is mainly due to limited photosynthesis and poor seed set and development [13], resulting in fewer pods per plant and seeds per pod [8]. Maximum root volume under water deficit avoids transient water deficit, as reported for faba bean accessions [14].…”