Water use of alternately submerged and nonsubmerged irrigated lowland rice
2002
Belder, P. | Bouman, B.A.M. | Spiertz, J.H.J. | Lu, G. A. | Quilang, E.J.P.
The availability of freshwater for agriculture is declining in many parts of Asia, thus affecting lowland rice production. One water-saving management option in irrigated lowland rice systems is to reduce the amount of irrigation water per rice cropping season. Although farmers traditionally aim at having continuously flooded fields, water-saving techniques are receiving more and more attention. One water-saving technique is to keep the field alternately submerged and nonsubmerged (ASNS). Field experiments were conducted at sites in irrigated lowland areas in China (Hubei) and the Philippines (Nueva Ecija) to compare two water regimes: (1) continuously submerged (CS) and (2) alternately submerged and non submerged (ASNS). In ASNS regimes, fields were irrigated after at least 3 days without ponded water (up to 12 days just before panicle initiation). Nitrogen treatments were 180 kg ha-1 applied in various splits and no N fertilizer (control). Savings in irrigation water in the ASNS treatments were 53-87 mm (13-16%) compared with the CS regime. Rice grain yields ranged from 7.2 to 8.7 t ha-1 and were not significantly affected by the water regimes. Water productivity was 0.91 - 1.48 kg grain m-3 water applied. In two out of three experiments, water productivity was significantly higher in the ASNS regime than in the CS regime. The depth of the (perched) groundwater level was 0-30 cm below the soil surface in all experiments, thus minimizing the effect of aboveground water status on water availability for the rice plant. The soil moisture potential at PhilRice was never below -20kPa. The experiments were conducted in extremely poorly drained, heavy-textured soils with a low seepage and perolation rate (max. 3.9 mm d-1 in the CS regime). The evaluation of ASNS regimes was based on soil texture, the formation of cracks that can cause bypass flow, and groundwater depth. These criteria were identified as the most relevant for recommendations on water management of water-saving regimes for lowland rice production.
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