In this study, yield and water productivity response of rice to various irrigation levels applied with subsurface and surface drip systems in 2019 and 2020 in the Mediterranean Region of Turkey was evaluated in comparison with conventional flooding (CF). The 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: Evaporation from Class A pan (Ep) × 1.00; I_1.25: Ep × 1.25 and I_1.50: Ep × 1.50) and CF as control. The effects of drip systems and coefficients on yield and yield components were statistically significant (P < 0.01). DI produced higher yield than SDI. CF produced significantly greater yield than both DI and SDI systems. With two drip systems, average water savings of 60.5% in I_1.00, 54.5% in I_1.25 and 49% in I_1.50 were achieved as compared to CF. However, yield reductions of 15% in I_1.50, 20% in I_1.25, 29% in I_1.00 were observed for DI; corresponding values for SDI were 20, 28 and 44%, respectively. Drip irrigation in aerobic rice production system had almost twice the water productivity based on total irrigation water applied (WP_I) or total water input (irrigation + rainfall) (WP_I+P) compared with CF. During the study years, the highest WP_I and WP_I+P values were found in DI-I_1.00 (0.81–0.73 kg/m³) and (0.85 and 0.74 kg/m³), respectively. In conclusion, DI-I_1.50 treatment is recommended for sustainable aerobic rice production since DI-I_1.50 resulted in water saving of 49% but yield decrease of 15% as compared to CF.

This study addresses the assessment of crop water stress index (CWSI) of bell pepper (Capsicum annuum L.) and net income generated under regulated deficit irrigation (RDI), conventional deficit irrigation and partial root-zone drying (PRD) and full irrigation (I₁₀₀) using surface- and subsurface-drip systems (DI and SDI) during 2016 and 2017 in the Mediterranean region. The experimental design was split-plots with four replications. RDI was supplied with 50% of I₁₀₀ during vegetative stage until flowering, then received 100% of crop water requirement. PRD₅₀ received 50% of I₁₀₀, but from alternative laterals each watering. The results revealed that CWSI was correlated significantly (P < 0.01) and negatively with yield, yield per plant, total soluble solid, ETa, fruit weight and plant height indicating that yield of bell pepper declined with increasing CWSI values (P < 0.01). Bell pepper should be irrigated at mean CWSI value of 0.20 without any yield reduction. CWSI in the RDI and I₇₅ treatments were slightly greater than 0.20. Irrigation treatments had significant effect on yield and quality traits. The highest total soluble solutes were found in PRD₅₀ and I₅₀. The DI I₁₀₀ treatment generated the highest net income followed by the SDI I₁₀₀ and RDI. In conclusion, RDI and I₇₅ appear to be good alternatives to I₁₀₀ for sustainable bell pepper production in the Mediterranean region.

Increased water scarcity necessitates the implementation of water-conserving irrigation management practices to sustain crop production, especially in water-limited areas. Field experiments were conducted to evaluate midday leaf water potential (LWP) of bell pepper (Capsicum annuum L. var. annuum) irrigated differentially using surface drip (DI) and subsurface drip irrigation (SDI) systems during 2016 and 2017 growing seasons in the eastern Mediterranean environmental conditions. The treatments considered were deficit irrigations (I₅₀, I₇₅), regulated deficit irrigation (RDI), partial root-zone drying (PRD₅₀) and full irrigation (I₁₀₀) under DI and SDI systems. The experimental design was completely randomized in a split-plot system with four replicates per treatment. Deficit irrigation treatments of I₇₅ and I₅₀ received 75% and 50% I₁₀₀, respectively; RDI was supplied with 50% I₁₀₀ during vegetative growth stage until flowering, then received 100% of crop water requirement; PRD₅₀ plots received 50% I₁₀₀. Bell pepper plant water status was estimated by LWP. Higher LWP values were determined in I₁₀₀ for two drip systems than the I₇₅, I₅₀, and PRD₅₀; LWP correlated significantly (P < 0.01) and negatively with fresh pepper yield, DM yield, leaf area index (LAI), and mean soil water content and all these relations are best described with the curvilinear equations. In conclusion, bell pepper should be irrigated at mean LWP values between -0.89 and -0.95 MPa without any yield reduction. It is also concluded that RDI and I₇₅ treatments appear to be good alternatives to I₁₀₀ for sustainable bell pepper production under the Mediterranean environmental conditions.

This study evaluated the yield and water productiivty response of quinoa to regulated deficit irrigation (RDI), partial root-zone drying (PRD) and conventional deficit irrigation (DI) and full irrigation (FI) using surface (SD) and subsurface drip (SSD) systems in 2016 and 2017 in the eastern Mediterranean region of Turkey. The treatments consisted of RDI, PRD50, DI50, DI75 and FI. A rainfed treatment (RF) was also included in the study. The experimental design was split plots with four replications. DI75 and DI50 received 75 and 50% of FI, respectively. PRD50 received 50% of FI, but from alternative laterals. RDI received 50% of FI during vegetative stage until flowering, and then received 100% of water requirement. The results showed that quinoa under SD used slightly more water than SSD due to reduced surface evaporation. RDI resulted in water saving of 23 and 21% for SD and SSD, respectively, compared to FI; and RDI produced statistically similar grain yields to FI. DI75 treatment resulted in water savings of 16% for both drip methods in the first year and 10 and 25% for SD and SSD systems, respectively, in the second year. PRD50 produced greater yield than DI50 eventhough they received the same amount of irrigation water. RF and PRD50 treatments resulted in significantly greater water productivity (WP) values than other treatments. There was no significant difference between SD and SSD regarding the grain and dry matter yields and WP values. Thus, RDI and DI75 appear to be good alternatives to FI for sustainable quinoa production in the Mediterranean region.

A field experiment was carried out to evaluate the effect of different conventional and supplemental irrigation strategies on leaf stomatal conductance (g_s) and chlorophyll content (SPAD) yield and irrigation water productivity (IWP) of wheat using sprinkler line source in 2014 and 2015 in the Mediterranean region. The irrigation strategies were, supplemental irrigation (SI) during flowering and grain filling (SIFG), SI during grain filling (SIG), SI during flowering (SIF) and conventional irrigation (CI). These strategies were conducted under four irrigation levels 25, 50, 75, 100% and a rain-fed as control. The results indicated that CI₁₀₀ and CI₇₅ produced the greater grain yield and IWP, respectively. CI₁₀₀ resulted in the increased chlorophyll content by 8.8% over rain-fed. The results confirmed that the SPAD and stomatal conductance values were not equally sensitive to water stress during growth stages. The wheat crop suffered a greater SPAD and g_s reductions when the water stress occurred during the grain filling stage (SIF strategy) compared to other strategies, which means that the grain filling stage is more sensitive and effective to decrease the yield of winter wheat. The higher grain yields were achieved when the seasonal mean g_s reached 207.4 mmol/m²s in CI and 169.2 mmol/m²s in SI, and the stomatal closure responded well to low, moderate and severe drought treatments. The leaf stomatal conductance (g_s) was correlated linearly with grain yield. These relations could be used as a physiological indicator to evaluate water stress effect on the growth and productivity of wheat.

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.