The Effects of Alternate Saline and Fresh Water Irrigation on Soil Salinity and Physiological Traits of Summer Maize

【Background and objective】 The lack of freshwater is a main limiting factor in agricultural production in northern China. As a mitigation, brackish waters including saline groundwater and treated wastewater have been tipped as a supplementary source for irrigation. Since brackish waters are rich in dissolved salts, it is critical to assess the impact of long-term brackish water irrigation on soil quality and its consequence for crop growth. The purpose of this paper is to fill this knowledge gap by systematically studying the influence of alternate fresh and saline water irrigation on soil salinity and crop growth. 【Method】 The pot experiments were conducted under rain-proof conditions with summer maize used as the model plant. We compared four irrigation amounts: 60% (W1), 80% (W2), 100% (W3) and 120% (W4) of the potential evapotranspiration (ETc). Saline water with concentration of 3 g/L was irrigated at the cob development-pollination stage (B1), pollination stage-kernel development stage (B2), and pollination-harvest stage (B3), respectively. For each irrigation amount, freshwater irrigation in the whole growth season was taken as the control. In each treatment, we measured soil salt content, physiological traits and ultimate yield of the maize. 【Result】 ①For irrigation amount W4, alternate fresh and saline water irrigation desalinated the soil, especially B1 where the average salt content in 0~40 cm soil was 9.9% lower than that in W3. After harvest, B0 reduced initial salt content in 0~40 cm soil by 25.9%~42.6% depending on irrigation amounts, while B1, B2 and B3 resulted in salt accumulation with the salt content in the top 0~40 cm soil increased by 34.9%~58.5%, 73.7%~110.4% and 88.7%~128.7%, respectively, compared with the initial salt content. ②Irrigating with the saline water too early had a detrimental effect on leaves. It was found that B1 hindered photosynthesis with the net photosynthetic rate (Pn) and stomatal conductance (Gs) reduced by 40.5%~69.3% and 32.3%~68.0%, respectively, compared to that in B0. ③Irrigating with the saline water too early as in B1 hampered root development thereby reducing its water and nutrient uptake, which led to a yield reduction. In contrast, delaying the saline water irrigation as in B2 and B3 only marginally comprised the yield, with the yield reduction in B3 being 1.5%~2.0% compared with the control with freshwater irrigation. 【Conclusion】 Irrigating summer maize using saline water at concentration of 3 g/L does not considerably compromise its yield only when implementing at its late growth stage. An appropriate increase in irrigation amount can further reduce the risk of soil salinization and achieve high yield.