A study on different micro-irrigation techniques for mitigating water stress of immature rubber (<em>Hevea brasiliensis</em>) plants

Abstract

The Intermediate and Dry Zones of Sri Lanka have been targeted in expanding the rubber plantations with a view to expand the extent under planting to achieve national targets in natural rubber production. However, climatic conditions of these regions are suboptimal for growing of rubber. The mid-year dry period in these areas extends from June to September and as a result, plants experience a severe water stress especially in nursery and immature period. Therefore, this study was carried out in the Kilinochchi District, which belongs to the Agro-ecological Zone, DL3 in order to assess the performance of micro-irrigation techniques for immature or young rubber plants. Two micro-irrigation systems; viz. drip and spray jet were tested under three soil moisture depletion levels; 30, 50 and 70% of available soil moisture. Results showed that the growth of immature young rubber plants were highly responsive to moisture depletion levels and micro-irrigated systems. It was found that both drip and spray jet irrigation systems performed well in supplying water at 30% depletion level when compared to the depletion levels of 50 and 70%. Water stress is created by 70% depletion level with decreased chlorophyll content, stomata closure and increase in leaf temperature. Adequate irrigation at 30% depletion level in both systems resulted significant increment of chlorophyll content (p< 0.05). There was significant increment in chlorophyll content in plants which were irrigated with spray jet system when compared to drip system. Plants which were irrigated at 30% depletion level regulated higher stomatal conductance even under higher temperatures during mid-day period.