Effects of Different Shallow and Saline Groundwater Depths on Soil Salinity, Evapotranspiration, Grain Yield and Spike Traits of Winter Wheat

Abstract

The contribution of groundwater to evapotranspiration in crop irrigation scheduling is gaining importance worldwide. A two consecutive year wheat experiment was conducted in drainable lysimeters to evaluate the response of grain yield and quality, spike traits, water use efficiency, evapotranspiration and thousand kernel weight of wheat plants under twelve different shallow and saline groundwater conditions. The treatments included three groundwater depths (GWD) (D-1: 30 cm, D-2: 55 cm and D-3: 80 cm) and four groundwater salinities (GWS) (S-1: 0.38, S-2: 2, S-3: 4 and S-4: 8 dSm(-1)). The results show that the average decrease in grain yield for D-2 and D-1 compared to D-3 was 20.9% and 30.7%, respectively, while the decrease for S-2, S-3 and S-4 compared to S-1 was 11.8%, 18.0% and 25.1%. The highest evapotranspiration was found in the D3S1 treatment (630.1 and 550.1 mm in 2017-2018 and 2018-2019, respectively), which increased by 48.0% and 30.2% in the first and second seasons, respectively, compared to the D1S4 treatment. Thus, a GWD at 80 cm with 0.38 dSm(-1) GWS was able to meet 72% of the total water requirement of wheat under loam soil conditions. Water use efficiency values ranged from 1.49 to 1.65 kg m(-3) in the first season and from 1.18 to 1.73 kg m(-3) in the second season, with the highest water use efficiency values found at 80 cm GWD. Regression analysis showed that GWS had a greater effect on water use efficiency than GWD. On average, thousand kernel and hectolitre weights were highest under D3S1, reaching 49.6 g and 77.8 kg hl(-1), respectively. Soil salinity increased steadily with increasing GWS at all GWD conditions, and higher soil salinity values were observed at 30 cm GWD. In addition, controlling a groundwater depth at 80 cm with 8.0 dSm(-1) GWS did not significantly increase soil salinity, which did not result in high grain yield losses. Finally, it is recommended to control groundwater at a constant depth of 80 cm with 0.38 dSm(-1) GWS after the tillering period of winter wheat to save more irrigation water, control soil salinity and improve yield and grain quality in the region with shallow-saline groundwater.