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    Eco-physiological response of grain amaranth to regulated deficit and conventional deficit irrigation applied with surface and subsurface drip irrigation systems
    (Cambridge Univ Press, 2024) Gonen, Engin; Colak, Yesim Bozkurt; Ozfidaner, Mete; Yazar, Attila; Tanriverdi, Cagatay
    Understanding the water use of drought-tolerant crops of the drought-prone Mediterranean regions is important for sustainable agriculture. The aim of this study was to evaluate the yield and yield responses of amaranth (Amaranthus hybridus L.) to different irrigation strategies conducted in 2019 and 2020 under Mediterranean climatic conditions using surface drip (SD) and subsurface drip (SSD) systems. Strategies investigated were: regulated deficit irrigation (RDI), conventional deficit irrigation (DI25, DI50, DI75), full irrigation (FI) and rainfed treatment. The highest grain yield was observed in FI treatments; RDI treatments produced 5% lower grain yield than the FI treatments, although the RDI treatments resulted in water savings of 23 and 21% for SD and SSD systems, respectively. DI treatments resulted in lower leaf water potential (LWP) and higher crop water-stress index (CWSI) compared to FI in both systems values. The results showed that optimum irrigation conditions to obtain the highest amaranth grain yields were associated with an LWP of -1.0 MPa and an average CWSI of about 0.25. The FI treatments under SSD systems had the highest grain production, followed by FI under SD and RDI under both the drip systems. Under SD and SSD systems, RDI saved 23 and 21% water, respectively, and produced a yield statistically comparable to that of FI. The SSD methods generated higher net income than SD. From these results it can be concluded that both RDI and DI75 could be a good alternative to FI under the conditions of water scarcity in the Mediterranean region.
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    Evaluating soybean yield responses to future climate change and irrigation regimes: a DSSAT multi-model assessment
    (Frontiers Media Sa, 2026) Baydar, Alper; Colak, Yesim Bozkurt; Ozfidaner, Mete; Gurkan, Hudaverdi; Gonen, Engin
    Introduction Climate change is expected to intensify temperature and precipitation variability in Mediterranean regions, creating uncertainty for soybean production.Methods In this study, the DSSAT-CROPGRO-Soybean model was run with three global climate models under two emission pathways (RCP 4.5 and RCP 8.5) across three future time periods: near-future (2016-2040), mid-century (2041-2070), and late-century (2071-2098). Bias correction significantly enhanced the reliability of climate inputs by reducing systematic temperature deviations and improving agreement with observed meteorological conditions. The model was calibrated and validated using observed phenology, leaf area index (LAI), biomass, and yield across three irrigation treatments (I100, I70, and I50).Results The model showed good correspondence between observed and simulated values. Taylor diagram analysis revealed correlation coefficients generally exceeding 0.95, coefficients of determination (R & sup2;) ranging from 0.74 to 0.99, and acceptable RMSD values across treatments. Future projections indicated that yield responses varied across future periods and irrigation conditions. Under late-century conditions, RCP 8.5 produced higher yields than RCP 4.5 by approximately 4-17% under irrigated conditions and 6-20% under rainfed conditions across the considered GCMs.Discussion Elevated CO2 partly mitigated the effects of warming; however, seasonal soil water availability remained the primary constraint on yield. The results demonstrated that the calibrated DSSAT-CROPGRO-Soybean model provides a reliable basis for predicting the adverse effects of future climatic conditions on soybean production, while multi-GCM climate projections indicated that the magnitude of these effects may vary substantially depending on emission scenario, projection period, and water availability.