Does wet seeding combined with Sub1 varieties increase yield in submergence prone lowlands of West Africa?

Early season flash flooding and submergence greatly impair rice production in the rainfed lowlands of West Africa. Here, rice establishment is by transplanting into puddled soil. Crops established during the early part of the rainy season are adversely affected by submergence, while delaying transplanting until the flood waters have receded results in the use of old seedlings and terminal drought stress. While the use of submergence tolerant (Sub1) rice varieties can greatly reduce the yield loss caused by 1-2 weeks of early season submergence, changing to wet seeding at the start of the rainy season may confer additional advantages. Elsewhere, wet seeding has been shown to enable more timely (earlier) crop establishment and more rapid early growth, and thus the potential to provide greater resilience to submergence. Therefore, the objective of this study was to assess the performance of two Sub1 varieties developed for West Africa (FARO 66, FARO 67) under transplanted and wet seeded conditions, in comparison with the predominant local variety (WITA 9). On-station experiments were carried-out over three seasons (dry 2018, wet 2019, dry 2019) at Mbe Research Station of the Africa Rice Center, Bouake, Cote d'Ivoire. The fields were submerged for 1-2 weeks at 5-7 weeks after seeding, and the wet season crop was sown at the beginning of the rainy season. Yield of the Sub1 varieties was 1.1-4.5 t ha(-1) higher than that of WITA 9, depending on season and establishment method. Wet seeding resulted in much higher yields of WITA 9 than transplanting in the wet season, but yield of the Sub1 varieties was not affected by establishment method in any season. However, tiller survival and biomass production of the wet seeded Sub1 crops were less affected by submergence than the transplanted crops. Wet seeding also reduced labour requirement and cost, and increased profitability. Furthermore, establishment of the wet season crop at the beginning of the rainy season would facilitate intensification to two crops per year. Therefore, the adoption of Sub1 varieties, could enable significant progress towards the goal of self-sufficiency in rice production in West Africa. Combining Sub1 with wet seeding would provide further benefits in terms of increased profitability and resilience to flash flooding.

Automated summary

Early season flooding and submergence greatly affect rice production in West Africa. This study evaluated the performance of submergence tolerant rice varieties (Sub1) under different establishment methods. The results showed that wet seeding combined with Sub1 varieties can reduce yield losses, labor requirements, and increase profitability and resilience to flash flooding.