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Assessing the salt sensitivity of mature almond trees by replacing the resident saline irrigation with fresh water at different growth stages

Pitt, T., Stevens, R., Cox, J. W.
Acta horticulturae 2018 no.1219 pp. 251-258
almonds, developmental stages, electrical conductivity, freshwater, harvesting, irrigation, irrigation water, leaves, municipal wastewater, plant tissues, planting, recycled water, salinity, seeds, sodium, yield components
This South Australian study identified a salt affected almond orchard that had been irrigated with moderately saline recycled municipal wastewater since planting in 1998. The average electrical conductivity (EC) of the irrigation water was in excess of 1.8 dS m-1 (>1100 ppm). For three consecutive seasons, beginning in the 2013/2014 irrigation season, fresh water (EC<0.8 dS m-1) was substituted for the saline irrigation water at each of three phenologically different growth stages: pre-pit hardening, kernel growth and post-harvest. At other times, experimental plots were irrigated with the resident saline recycled water, as was the control throughout the season. On average, pre-harvest reductions in salt load affected the greatest reduction in end of season leaf concentrations of sodium and chloride. Non-saline irrigation applied prior to pit-hardening reduced sodium and chloride in the leaf by 19%, between pit-hardening and harvest by 48% and following harvest by 11%. Normalising plant tissue response, for inter-treatment differences in the seasonal salt load, isolated the effects of timing and confirmed that sodium and chloride uptake was most receptive to reduced salt load prior to harvest and that sodium uptake was particularly insensitive to post-harvest reductions in salt load. Yield components were less sensitive to the timing of reduced salt load and did not differentiate during the period of investigation, supporting the contention that salinity induced yield suppression persists long after the reduction or removal of the salinity pressure. Normalising response for inter-treatment differences in salt load suggested a 12% yield improvement per unit reduction in volume weighted salt load when applied post-harvest compared to less than 4% improvement when applied prior to harvest. Resolving the yield response remains a focus of this ongoing study, which will continue into the 2017/2018 irrigation season.