Growth and yield of direct-seeded rice varieties and breeding line in flooded and non-flooded puddled clay soil conditions

Compared to other crops, rice grows best with abundant water supply. However, water is becoming scarce. In 2025, per capita available water resources are expected to decrease by 15-54%. Some areas will experience water shortage due to the El Nino phenomenon. Hence, future rice production will depend heavily on strategies that will use water efficiently. Water saving irrigation techniques such as reducing the amount of ponded water or floodwater, alternate wetting/drying or allowing the soil to dry out to certain extent before re-irrigating can be employed. However, water saving techniques may be risky and reduce yield because of water stress effects on the crop. Therefore, for a given variety or breeding line, there is a need to establish to what extent soil moisture content/tension can be reduced without a significant reduction in yield. Seeds of UPL Ri7 (an improved upland variety), PSB Rc9 (a new upland variety) and CT6510-24-1-2 (a breeding line from CIAT, Colombia) were pre-germinated and broadcast onto wet soil at a rate 80 kg/ha. There were three soil moisture treatments. For treatment 1 (flooded or 0 centibar or cb), about 3 cm of floodwater was maintained starting at 10 days after seeding (DAS) up to crop maturity. In treatment 2 (soil moisture tension or SMT = 15 cb), starting at 10 DAS, soil moisture content was allowed to decrease to 15 cb then flood-irrigated to 0 cb. In treatment 3 (SMT = 30 cb), starting at 10 AS, soil moisture content was allowed to decrease to 30 cb then flood-irrigated to 0 cb. Results of the study showed that water saving would be substantial with the use of direct-seeded culture and alternate wetting and drying to 15 cb and 30 cb SMT during the dry season for puddled clay soil. These were relatively mild soil moisture stresses considering that 30 cb SMT was at field capacity and water tables were relatively shallow (30 to 35 cm below the soil surface). These mild soil moisture stresses coupled with radiation load and evaporative demand in the dry season carried a penalty in terms of reduction in growth and yield. However, the yield advantage of UPL Ri7 and CT 6510-24-1-2 over PSB Rc9 under moisture stress suggests that the germplasm should be explored further for higher high advantage under our water saving schemes