Soil water potential and recoverable water stress in drought tolerant and susceptible rice varieties

• Soil water potential may be an effective drought recovery parameter.
• Water flow model may be used to extend the operational range of tensiometer beyond −100 kPa.
• Controlled water stress during the vegetative stage may increase rice yield.

We conducted a two-year field experiment to determine if water stress could be exploited to recover yield in one drought resistant (Vandana) and three susceptible (IR36, IR72 and Swarna) rice varieties. Stress was induced in active tillering, flowering and grain filling stages by suspending irrigation until the soil became sufficiently dry and plants began to show stress symptoms when irrigation was resumed, such that plants could recover from stress. We observed that terminal soil water potential (SWP) as low as −110 kPa in the active tillering stage was less detrimental to relative water content, proline content, and electrolyte leakage. A 27% rise in the level of stress led to ∼8%, 44% and 21% increase in yield in IR36, Vandana and Swarna. The possible causes are 23%, 39% and 10% increase in the corresponding root biomass of the varieties, resulting in higher water uptake in the vegetative stage treatment plots. This was further supported by high correlations between yield and terminal SWP in this treatment. Critical limits of SWP may be identified to exploit the potential of rice varieties to sustain or improve yield under water stress. Results also suggest an opportunity to design a water saving strategy in lowland rice production.