Intercropping to Mitigate Salinity Stress on Watermelon: Halophyte Performance in a Greenhouse Pot Study

Increased continuous irrigation due to drought conditions and above average temperatures, and resulting salt buildup in soils, can lead to a decline in yields in salt-sensitive species such as watermelon. This greenhouse investigation is phase one of a two-phase study aimed at assessing the potential benefits of utilizing halophytic species as companion crops to watermelon in salt-affected soils. From this initial screening, two species will be selected for intercropping with watermelon in a field setting. Based on a set of criteria, the six species chosen for this screening were four-wing saltbush (Atriplex halimus), barley (Hordeum vulgare), garden orache (Atriplex hortensis), purslane (Portulaca oleracea), saltwort (Suaeda salsa), and wheat (Triticum aestivum). Treatments of 0, 3, and 6 dS/m irrigation water were applied to plants over a 5-week period and plant species were replicated 5 times within each treatment level in a randomized complete-block design. Preliminary results from soil bulk electrical conductivity averaged over the entire 5-week period indicate that barley had the lowest soil EC in the 3dS/m treatment level at 0.30 dS/m followed by garden orache, wheat, and four-wing saltbush (0.41, 0.43, and 0.47 dS/m, respectively). In the 6 dS/m treatment level, garden orache had the lowest soil EC at 0.55 dS/m followed by wheat, four-wing saltbush, and barley (0.61, 0.67, and 0.69 dS/m, respectively). Purslane and saltwort consistently had the highest soil bulk EC at both salt treatment levels (0.71and 0.65 dS/m at 3dS/m, and 0.90 and 0.83 dS/m at 6 dS/m, respectively) and, therefore, may not be taking up and accumulating as much salt as the other species. Plant growth data indicate garden orache was unaffected by salt treatments. It had the highest average absolute growth rate of all 6 species and was the only species to exhibit significantly higher absolute growth when treated with salt when compared to no salt treatment. These preliminary results suggest wheat, barley, four-wing saltbush, and garden orache, in particular, may be well-suited as companion plants to watermelon. Due to its slow growth rate, however, four-wing saltbush may not be practical for use in a field production setting. Plant tissue analysis of Na⁺ and Cl^- accumulation as well as total root and shoot biomass will further help us determine which species we will select for phase two of our study.