Influence of Saline Water Irrigation on Root Distribution, Wheat Yield, and Soil Salinity

The development of irrigated agriculture in northwest China is restricted by shortages of fresh water and groundwater salinization. Saline water irrigation may cause salt accumulation in the soil, which results in salt stress to roots. The effects of water salinity and irrigation amount on wheat root distribution and yield, as well as soil salt distribution, were evaluated in field experiments conducted in 2014 and 2015 at the Shiyanghe Experimental Station of the China Agricultural University (102°52′E, 37°52′N), located in the Liangzhou District, in the city of Wuwei in northwest China. A total of 12 treatments including 4 levels of irrigation water salinity as indicated by electrical conductivity (0.65, 3.2, 5.2, and 7.1 dS m−1) and 3 levels of irrigation amount (205, 280, and 355 mm), were established using a randomized block design. Freshwater with an electrical conductivity of 0.65 dS m−1 and an irrigation amount of 355 mm was used as the control for salinity and irrigation level. The results showed that the influence of irrigation amount and water salinity on root distribution was mainly in the top 40-cm. Irrigation amount had no statistically significant (p>0.05) effects on the average root length density (RLD) in the 2-year experiment. A decrease in irrigation amount reduced root biomass (RB) at maturity when water salinity ranged from 0.65 to 5.2 dS m−1. Water salinity less than 3.2 dS m−1 stimulated root growth in the soil layers 10–40-cm at the heading stage without obvious yield reduction or salt accumulation. However, water salinities of 5.2 and 7.1 dS m−1 led to decreases in RLD in the 0–10-cm layer and RB at the maturity stage, and a significant decrease in yield (p<0.05) in both years. The interaction effects of irrigation amount and water salinity had no statistically significant (p>0.05) effects on root parameters and yield. In the absence of rainfall, a regime with irrigation amounts between 205 and 355 mm and water salinity between 0.65 and 5.2 dS m−1 can ensure a 70% yield.