Role of salicylic acid in irrigation scheduling for rubber nurseries in the Intermediate zone of Sri Lanka

Salicylic acid (SA)is an important signaling molecule known to alleviate the negative effects of drought stress in plants. The present study was conducted in a protected house at Moneragala substation of Rubber Research Institute of Sri Lanka to examine the possibility of using salicylic acid to minimize the net irrigation water requirement (NIR) of rubber nurseries in the Intermediate Zone of Sri Lanka which has the sub-optimal environmental condition for rubber. A split-plot design with the treatment combination of different soil moisture depletion levels of irrigationnamely10%, 30%, 50%, 70%, and 90%) and salicylic acid (0.5 mM) application frequencies (once in two weeks, once a month, once in three months and no application (control)). The effect of treatment combination was assessed on morphological and physiological growth attributes of seedling rubber plants. NIR was estimated based on maximum allowable depletion level, crop evapotranspiration (ETc) and crop factor in irrigation scheduling. Results revealed that the growth of nursery plants with irrigation at a 10% moisture depletion level was greater those. Moderate to severe water stress conditions were developed with the moisture levels at 50 to 90% moisture depletions respectively. The plants treated with 0.5 mM SA at monthly intervals have shown a higher growth when compared with bi-weekly or once in three months SA applications. Therefore, plants treated with 0.5 mM SA as monthly application at 50 % moisture depletion level exhibited higher tolerance to water stress compared to non-treated plants. Estimated NIR has shown that SA applications have had significant effect on lowering ETc of rubber nursery plants and reduced the NIR of the rubber nursery by 25% of the total irrigation requirement.