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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.
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    Optimizing water use in aerobic rice: Evaluating drip irrigation strategies and crop water stress index under Mediterranean conditions
    (Inst Investigaciones Agropecuarias - Inia, 2026) Colak, Yesim Bozkurt
    Increased limited water resources coupled with the increasing effect of climate change calls for more efficient use of water in plant production in the Mediterranean region. Therefore, assessment of threshold level of crop water stress index (CWSI) is of paramount importance for precision irrigation scheduling for rice in 2019 and 2020 under the Mediterranean environmental conditions. The experimental treatments consisted of two irrigation methods namely surface drip (DI) and subsurface drip systems (SDI), three irrigation levels designated as plant pan coefficients (I-1.00: Class A-pan (Ep) x 1.00; I-1.25: Class A-pan Ep x 1.25 and I-1.50: Class A-pan Ep x 1.50) and conventional flooding (CF) method as control plot. Canopy temperatures were measured throughout the growing season with an infrared thermometer and depending on the plant canopy temperature (Tc) and air temperature (Ta) difference (Tc-Ta) and air vapor pressure deficit (VPD), the equation of the lower baseline without water stress was determined as Tc-Ta =-2.2069VPD + 0.8263, and the upper baseline calculated under water stress conditions using values obtained from plants cut on different days was determined as 5.08 degrees C. Two years seasonal average CWSI values ranged from 0.09 in CF to 0.34 in SDI-I-1.00. According to the obtained results, it was determined that the infrared thermometer technique could be used in the irrigation programming of rice. It has been determined that if this technique is used in Mediterranean conditions, irrigation scheduling can be done in such a way that the average CWSI value is kept around 0.15 for drip irrigation, which provides water savings throughout the season.