Suitability of slightly saline irrigation for alleviating drought stress in taro and yam in Tonga: Implications for climate‐resilient Pacific cropping systems

Societal Impact Statement There is an increasing risk of drought and salinisation of soil and groundwater globally, including in Pacific Island countries such as Tonga. Irrigating crops with slightly saline water, such as that produced by emerging desalination technologies, could help to alleviate droughts. We conducted field trials in Tonga to test the salt tolerance of two important food security crops in the Pacific: taro and yam. Both crops maintained good yields under saline irrigation, demonstrating their salt tolerance and the potential for slightly saline irrigation to enhance the resilience of future agricultural systems to the effects of climate change. Summary To study the salt tolerance of taro and yam to identify how they withstand soil and water salinisation and determine the cultivars that can be irrigated with slightly saline water (≤10 dS m −1 ) to reduce yield losses during droughts. Two field experiments were conducted in Vaini, Tonga. For Experiment 1, we grew one taro cultivar ( Colocasia esculenta cv. huli mama'o) under four irrigation treatments: rainfall only, groundwater (<1 dS m −1 ), low salt (3–4 dS m −1 ) and high salt (6–7 dS m −1 ). For Experiment 2, we grew two yam cultivars ( Dioscorea cayenensis ssp. rotundata cv. lose and Dioscorea alata cv. kahokaho) underneath rain shelters under two treatments: groundwater and high salt. Fresh and dry weights, dry matter content, leaf number and size, chlorophyll concentration, stomatal conductance, macronutrients and micronutrients and soil salinity were measured. The high salt treatment reduced taro corm dry weight by 25% compared with the groundwater control ( p < .05), but it did not significantly affect tuber dry weight in either yam cultivar. Soil salinity was not increased by high salt irrigation in Experiment 1, but it was in Experiment 2 (under shelters). Both taro and yam appear to be tolerant to irrigation with slightly saline water during short droughts in Tonga and other Pacific Island countries. Yam was better able to tolerate the high salt treatment than taro. Rainfall during our study was effective at leaching modest salt additions from the soil in the absence of shelters.