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Brackish water used for irrigation can restrict crop growth and lead to environmental problems. The alternate irrigation with saline water at different growth stages is still not well understood. Therefore, field trials were conducted during 2015–2018 in the NCP to investigate whether alternate irrigation is practicable for winter wheat production. The treatments comprised rain-fed cultivation (NI), fresh and saline water irrigation (FS), saline and fresh water irrigation (SF), saline water irrigation (SS) and fresh water irrigation (FF). The results showed that the grain yield was increased by 20% under SF and FS treatments compared to NI, while a minor decrease of 2% in grain yield was observed compared with FF treatment. The increased soil salinity and risk of long-term salt accumulation in the soil due to alternate irrigation during peak dry periods was insignificant due to leaching of salts from crop root zone during monsoon season. Although Na+ concentration in the leaves increased with saline irrigation, resulting in significantly lower K+:Na+ ratio in the leaves, the Na+ and K+ concentrations in the roots and grains were not affected. In conclusion, the alternate irrigation for winter wheat is a most promising option to harvest more yield and save fresh water resources.

Impact of soil water regimes on physiological responses and water use efficiency (WUE) for Vigna unguiculata L. Walp. (cowpea) inoculated with rhizobia still remains implicit. Therefore, the goal of the current study was to examine the leaf gas exchange, abscisic acid (ABA) and hydraulic signaling, WUE and carbon and oxygen isotopic compositions (δ13C and δ18O) of cowpea under different soil water levels. The treatments included soil water regimes at three levels (90%, 70%, and 50% of soil water holding capacity (SWHC)) and two inoculation forms (inoculated and non-inoculated with rhizobia). The results showed that across the inoculation treatments, reduced soil water regimes depressed both stomatal conductance (gs) and photosynthesis (An) of the leaves, nonetheless, the decrease of gs was more pronounced compared with the reduction in An. Consequently, the intrinsic water use efficiency (WUEi) was improved in the treatments under decreased soil water conditions. Plant WUE was also improved when soil water contents decreased as exemplified by the increased leaf δ13C and δ18O, indicating the enhanced plant WUE was mainly attributed to the decrease of gs. Significant interactions between soil water regimes and rhizobia treatments for root water potential (RWP), leaf water potential (LWP), and gs were found due to the different responses of rhizobia to varied soil water regimes. Inoculation could improve plant water status and gs under 70% and 90% SWHC compared to 50% SWHC with negative effect from rhizobia. A moderate soil water regime is suggested for cowpea production in terms of high WUE with a minor biomass reduction.

The effective water management in the North China Plain (NCP) needs a tool to predict winter wheat production due to water quality. A large quantity of brackish water is stored underground in this region, and whether this water can be used properly in agriculture is becoming a crucial issue that is about to be resolved. The SALTMED model is a generic modeling tool for efficient irrigation management strategies, especially for cyclic use of saline and fresh water as well as different water qualities, and it still needs further investigation for alternate irrigation using saline and fresh water at different growth stages of winter wheat. Therefore, the aim of this investigation was to evaluate the performance of SALTMED model and simulate the production of winter wheat grown under different irrigation strategies. Irrigation strategies comprised rain-fed cultivation (NI), fresh and saline water irrigation (FS), saline and fresh water irrigation (SF), saline water irrigation (SS), and fresh water irrigation (FF). Three-year observed data were used for the validations of SALTMED model. The values of evaluation indices of relative error, RMSE, NRMSE, index of agreement (D-index), and R 2 between simulated and observed grain yield were 6.8%, 0.8, 10.7, 0.9, and 0.9, respectively. The model results supported and matched the observed data and indicated similar differences among the irrigated and rain-fed treatments. It is concluded that the SALTMED model is able to predict grain yield of winter wheat and its productivity under the alternate irrigation using saline and fresh water and their interaction in the climate condition of the NCP.

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