Improved yield-salinity relationship considering salt and root distribution dynamics

Abstract

Alternate drip irrigation of brackish and freshwater (ADI) is an effective strategy to relieve salt stress in crops and increase crop yield compared to irrigation using only brackish water (B). However, the correlation between the soil salinity as well as maize root distribution dynamics and crop yields under ADI treatment remains unknown. A three-year field experiment under ADI treatment was carried out from 2019 to 2021 to evaluate the effects of irrigation using only freshwater (F), B, or both brackish and freshwater (1B1F, 2B1F, 3B1F; after irrigating with brackish water once, twice, and thrice including alternate irrigation with freshwater) on root growth and crop yield. This study aimed to capture the dynamics of the electric conductivity of a saturated paste extract (ECe) and root length density (RLD) at different soil depths during different crop growth periods under different ADI treatments. Moreover, to unravel the two-dimensional distribution of soil salt and root growth in the soil profile, ECe and RLD in the area under plastic film mulching (the mulched area) and the no mulching area (bare area) were measured. This study also evaluated the yield-salinity relationship using salt and root distribution dynamics (Y-SI) and the response of maize crops on ECe and RLD. The result of this study demonstrated that the estimation accuracy of the Y-SI was higher than the yield-salinity relationship by the Food and Agriculture Organization of the United Nations. MRE decreased by 4.9% for the Y-SI using ECe and RLD with eight positions (Y-SI 8) compared to only one position (Y-SI 1). The salt stress level decreased with increasing soil layer, specifically in the 0–40 cm soil layer in mulched area. The higher irrigation frequency of brackish water was associated with a higher ECe, longer salt stress duration, lower RLD during the last two growth stages, and a lower maize yield. Compared with F treatment, average ECe in the 0–40 cm soil layer under 1B1F, 2B1F, 3B1F, and B treatments increased by 22.7%, 30.6%, 35.1%, and 46.5%, average proportion of high salt stress (>3.8 dS m−1 for ECe) duration increased by 8.9%, 16.9%, 21.0%, and 26.4%, average RLD decreased by 6.6%, 16.9%, 21.7%, and 26.9%, and average relative maize yield decreased by 1.9%, 4.9%, 12.2%, and 16.1%, respectively. In general, the 2B1F treatment could be recommended as the optimal irrigation strategy with a reduction of 1800 t ha–1 for freshwater irrigation compared to the B treatment, but only a 4.9% decrease for maize yield compared to the F treatment.