Overhead-irrigation with saline and alkaline water: Deleterious effects on foliage of Rhodes grass and leucaena

Saline and alkaline water represents a potentially valuable resource provided its irrigation does not decrease plant growth. Although the adverse effects of salts within the rooting environment are well-studied, comparatively little is known regarding the direct effects of overhead-irrigation of saline and alkaline water on plant foliage. The present study examined the potential deleterious effects of saline (electrical conductivity, EC, ≤15dSm−1) and alkaline (≤2000mgL−1, CaCO3 equivalent) water on foliage of Rhodes grass (Chloris gayana cv. Reclaimer) and leucaena (Leucaena leucocephala ssp. glabrata cv. Tarramba) under a range of growing-conditions. Foliage of leucaena was sensitive, with necrosis and chlorosis evident for saline water at an EC ≥3dSm−1 and alkaline water containing ≥500mgL−1 (CaCO3 equivalent). For leucaena, this damage to the foliage reduced relative shoot fresh mass and chlorophyll fluorescence for saline-treatments, but alkalinity did not reduce relative shoot fresh mass or chlorophyll fluorescence in any treatment. In contrast to leucaena, relative shoot fresh mass of Rhodes grass was not reduced by foliar-applied salinity in any treatment (nor did alkalinity reduce growth of Rhodes grass). It was noted that growing conditions influenced the magnitude of the deleterious effects, with salinization of the soil slightly increasing tolerance to foliar-applied saline water for leucaena. This study has demonstrated that whilst saline and alkaline water can potentially be used for overhead irrigation, differences in observed tolerance exist between plant species, and are influenced by growing conditions.