Regulated Deficit Irrigation Treatments Research Articles

Effects of irrigation amounts and a deficit irrigation strategy on water status and yields of intensively cultivated jojoba (Simmondsia chinensis)

AbstractJojoba (Simmondsia chinensis) is cultivated for its seeds, which contain a high-value liquid wax. There is little known regarding irrigation requirements of intensively cultivated jojoba. The project’s objectives were to evaluate the effects of irrigation regime on water status, growth, yield, and water productivity (WP, wax yield per unit of water applied) of intensely cultivated jojoba. An experiment was conducted over six years in a 14-year-old commercial plantation in Israel’s Northern Negev Desert. Treatments included: Control irrigation according to best commercial practice of returning reference evapotranspiration multiplied by a crop coefficient (Kc) of 0.5; Low irrigation providing 75% (Kc = 0.375) of the control; High irrigation providing 125% (Kc = 0.625) of the control; Regulated deficit irrigation (RDI) according to the control treatment, terminated for one to two months, after the wax accumulation stage. Stem water potential (SWP) consistently indicated jojoba water status. Increasing water application from − 25% to the control and further to + 25% led to augmented vegetative growth and number of seeds, but yield was increased at rates lower than the differences in water application by the treatments, such that WP was negatively associated. Effects on yield were limited to higher yielding ‘On’ years. The RDI treatment resulted in yield not different from the control and 15% higher WP, but significantly inhibited seed removal during mechanical harvesting. The results suggest commercial potential for increasing profits through water savings. Further research is needed to determine RDI regimes without detrimental effects on harvesting efficiency.

Does Regulated Deficit Irrigation Affect Pear Fruit Texture by Modifying the Stone Cells?

Regulated deficit irrigation (RDI) strategies aim to improve water usage without reducing yield. Generally, irrigation strategy effectiveness is measured as fruit yield, with little consideration of fruit quality. As water deficit and increased plant cell sclerification are often associated, this study explored the effect of RDI on pear fruit stone cells, a crucial trait affecting flesh texture. The presence, distribution, and development of pear fruit stone cells under RDI and full irrigation were compared using Pyrus communis L. cv. Barlett trees, employing recently developed microscope image analysis technology. The control treatment was maintained under non-stress conditions, while the RDI treatment received an average of 15% of the control water during the latter part of Stage I fruit development. Observations at the end of Stage I and at harvest revealed no effect on stone cell presence under the RDI strategy tested. The relative area of stone cells within the flesh was greater at Stage I than at harvest, as stone cell expansion occurred early in development, while the (unsclerified) parenchyma cells, a dominant component of the fruit flesh, expanded until harvest. Stone cell cluster density was higher near the fruit core than in the cortex center and exterior. These initial results suggest that well-planned RDI strategies will generally not affect pear fruit stone cell content and, thus, textural quality. Microscope image analysis supported the results from previously used analytical techniques, mainly chemical, while providing a tool for better understanding the process and factors involved in the timing of stone cell differentiation.

Diversified cropping systems effect on the water status of mandarin trees under deficit irrigation

The diversified cropping systems has several environmental benefits, but there is no certainty about their effect on the water status of trees, especially in areas with permanent low availability of irrigation water. Therefore, our objective was to evaluate the effect of the establishment of diversified cropping systems in a traditional monoculture (MC) of adult mandarin trees on its water status and yield under sustained deficit irrigation (SDI) and regulated deficit irrigation (RDI). Six treatments were tested during three consecutive seasons: (i) a mandarin monoculture under SDI (MC-SDI), with permanent bare alleys and irrigated at ∼70 % ETc during the entire season (actual amount of irrigation water available in the area); (ii) a diversified mandarin crop (D1-SDI), irrigated as MC-SDI, with a rotation of fava bean and barley/vetch in the alleys; and (iii) a second diversified mandarin crop (D2-SDI), irrigated as MC-SDI, with a seasonal rotation of fava bean, purslane and cowpea. Additionally, three RDI treatments were evaluated, denoted as (iv) MC-RDI, (v) D1-RDI and (vi) D2-RDI, irrigated as MC-SDI, except during the stage II of fruit growth, when it was reduced by 50 % with an irrigation threshold of a solar midday stem water potential of ∼ –1.5 MPa. The mandarin yield was not affected by the effect of diversified cropping systems, but the RDI reduced it on average by 30.1 % with respect to SDI. The alley cropping of fava bean and barley/vetch during winter and spring under sustained deficit irrigation conditions reduced the water stress intensity of mandarin trees by 26.9 % over the entire season, while cultivation of purslane or cowpea during summer increased it by 60–144 %. Both diversifications required a greater amount of water than the monoculture, in these terms an additional reduction in the irrigation of mandarin trees, as in the RDI treatment, allowed to solve this additional water requirement, but promoted an increase in the water stress intensity of the trees, which may affect their productivity in the mid and long-term.

Effect of Regulated Deficit Irrigation on the Growth, Yield, and Irrigation Water Productivity of Processing Tomatoes under Drip Irrigation and Mulching

The application of regulated deficit irrigation (RDI) strategies with high water-saving effects for processing tomatoes is an important current research trend. In this study, we aimed to reveal the patterns of growth, yield, and irrigation water productivity (WPI) in response to the water deficit in processing tomatoes under drip irrigation and plastic mulching in Xinjiang. To determine a more precise irrigation regime, various degrees of RDI treatments were applied to processing tomatoes in 2022 and 2023. A total of five water gradients were set up: RI (Regular Irrigation; 4500 m3/ha), W1 (4185 m3/ha), W2 (3870 m3/ha), W3 (3555 m3/ha), and W4 (3240 m3/ha). The results revealed that under RI, the yield and irrigation water productivity were 142 t/ha and 31.49 kg/m3, respectively. Compared with RI, W1 exhibited an increase in yield and irrigation water productivity of 12.13% and 22.39%, respectively; however, other treatments exhibited a decrease. The main reasons for the increase in yield under the W1 treatment were: the W1 treatment, improved photosynthetic performance, increased dry matter accumulation, and improved soil moisture conditions, thus promoting plant growth and development. In addition, in terms of water regulation at various fertility stages, moderate water deficiency at the seedling stage (S), flowering stage (F), and maturity stage (M) and rewatering at the fruit expansion stage (E) were more conducive to optimizing the yield structure. In conclusion, considering plant growth status, dry matter accumulation, yield, and WPI, we suggested that the W1 treatment is the optimal RDI mode most suitable for drip irrigation under mulching for processing tomatoes in Xinjiang. This study provided a theoretical and technical basis for the promotion of “water-saving and efficiency-enhancing” production of processing tomatoes.

Adapting Almond Production to Climate Change through Deficit Irrigation and Foliar Kaolin Application in a Mediterranean Climate

Irrigation is the best strategy to reduce the adverse effects of water stress on almond trees [Prunus dulcis (Mill) D.A. Web] and improve their productivity. However, in the current context of climatic change, in which the amount of water available for irrigation is increasingly limited, deficit irrigation (DI) strategies have become essential in the almond orchards of southern Europe. Other practices, such as the foliar application of reflective compounds, are being implemented. A three-year experiment (2019–2021) was set in a factorial design in which the effect of regulated deficit irrigation and foliar kaolin spray was evaluated on physiological (predawn leaf water potential, relative water content, leaf area, leaf gas exchange, and chlorophyll fluorescence) and agronomic parameters (yield, yield components, and water use efficiency (WUE)). The treatments include full irrigation (FI), which received 100% of ETc (crop evapotranspiration) during all irrigation seasons; regulated deficit irrigation (RDI), which received 100% of ETc until the kernel-filling stage, reducing the application to 35% ETc during the kernel-filling stage until harvest; and both irrigation regimes combined with kaolin application and two cultivars, Constantí and Vairo. More negative water potential values were observed in the RDI treatments compared to the FI treatments. There were no significant differences in the stomatal conductance, photosynthetic rate, or transpiration rate between treatments with RDI and FI, demonstrating the almond tree’s good adaptation to irrigation reduction in the kernel-filling stage. The two cultivars had different responses in cumulative yield throughout the three years of the trial. The cv. Constantí did not present significant differences between the FI and RDI treatments, translating into improved WUE. In contrast, the cv. Vairo suffered a reduction in accumulated performance in the RDI treatments with respect to the FI. The foliar application of kaolin did not present differences in yield and very few in the physiological activity of the almond trees. With the results obtained, we can suggest that under the conditions of our experiment, the combination of RDI and the kaolin foliar application can help save irrigation water and produce almonds more sustainably.

Effect of deficit irrigation and mulching on the agronomic and physiological response of mandarin trees as strategies to cope with water scarcity in a semi-arid climate

In order to increase the crop water productivity (WPc) of the agricultural systems, and to support farmers in minimizing uncertainty of water availability, we conducted a three-years experiment in a commercial adult mandarin orchard to quantify the effect of sustained and severe deficit irrigation in combination with the use of geotextile mulch on the agronomic and physiological response of the crop. For this purpose, five treatments were tested: (i) a control (CTL) irrigated at 100% of the crop evapotranspiration (ETc) during the entire season; ii) sustained deficit irrigation (SDI), irrigated at ∼70% of CTL; (iii) regulated deficit irrigation (RDI), irrigated as SDI, except during the initial period of the second fruit growth stage, when trees were irrigated at 35% of the CTL, maintaining a moderate water stress level of around –1.5 MPa of stem water potential (Ψs), until fruits reached 70% of their final size. In addition, two geotextile mulch treatments were established, using the same irrigation criteria as the SDI and RDI treatments. The available irrigation water supplied about 66% of the crop evapotranspiration, but if it is managed under a SDI regime with the incorporation of mulching it is possible to increase the crop sustainability and reduce the pressure over the water resources. Since SDI did not reduce the yield with respect to the CTL treatment, it increased WPc by 35% and the incorporation of mulch significantly increased the water status of the soil and the crop, thus reducing the intensity of water stress by 18% on average, which was expressed in a higher leaf gas exchange rate and was also a factor that significantly increased crop production variables and WPc.

The effect of alternate partial root-zone drying and deficit irrigation on the yield, quality, and physiochemical parameters of milled rice

While paddy fields produce a high yield, they also require a large amount of water and produce a significant amount of methane. Therefore, the adoption of water-saving irrigation techniques for rice cultivation is critical. Furrowed rice farming may be a viable alternative to paddy rice cultivation. The objective of the present study was to evaluate the impact of alternate partial root-zone drying irrigation on rice yield, milled rice quality, and cooking quality under furrow rice cultivation. A two-year field trial was conducted on a local rice cultivar, Tarom Hashemi, in 2015 and 2016. Seven water regimes, including three levels of regulated deficit irrigation (RDI), three levels of alternate partial root-zone drying irrigation (APRDI), and conventional flooding irrigation (CFI), were used in this study. In RDI and APRDI treatments, plots were irrigated when soil matric potential had reached −0.1 (RDI1 and APRDI1), −0.3 (RDI3 and APRDI3), and −0.6 bar (RDI6 and APRDI6). RDI1 and APRDI1 treatments produced milled rice yield similar to the CFI, while irrigation water productivity (IWP) was significantly higher by 22.9% and 45.7%, respectively. Regardless of the soil water potential, the IWP in APRDI treatments was 16% higher than that of RDI treatments. Severe water stress (RDI6 and APRDI6) caused a marked increase in amylose content and alkali spreading value of milled rice resulting in improved cooking quality. Nitrogen uptake in APRDI treatments was 2% higher than that of RDI treatments. On average, methane emission per milled grain yield declined by 77.9% and 78.7% in RDI and APRDI treatments, respectively. Our data indicate that the expensive and laborious practice of puddling can be avoided to increase water productivity and improve rice quality without sacrificing yield. The results also show that furrow rice cultivation could significantly reduce the methane emission contribution of rice production.

Application of water-saving irrigation and biostimulants on the agronomic performance of maize (Zea mays)

Water deficit can limit maize yield; therefore, appropriate choices of irrigation schemes or water-saving irrigation strategies to maximize WUE are needed for sustainable agriculture in response to environmental challenges and climate change. The objectives of our study were to evaluate and compare the effects of regulated deficit irrigation (RDI) and partial root-zone drying irrigation (PRDI) schemes with various field capacity (FC) conditions on yield components, water use efficiency (WUE), photosynthesis capacity, and chlorophyll fluorescence parameters of the maize plant in a pot experiment. Moreover, we also investigated foliar application of glycine betaine (B, 50 mM) and soil-treated chitin (C, 2 g/kg) to plants against water supply limitations and highlighted their potential for the sustainable production of maize. Significantly higher plant height, cob fresh and dry weights, and total dry weight of maize were observed in RDI with the 75 % FC condition compared to the control (full irrigation with 100 % FC). PRDI treatment resulted in significantly higher economic yield, WUEyield, and WUEbiomass compared to RDI treatment. Total water used in PRDI at 50 % FC saved 72 % of water resources compared to the control. Furthermore, values for effective quantum yield (ФPSII), photochemical quenching (qP), and electron transfer rate (ETR) of maize subjected to 75 % FC were higher than under 50 % FC and the control, while maximal quantum efficiency (Fv/Fm) levels of maize were higher under 50 % FC than under 75 % FC. All agronomic traits, chlorophyll content (as SPAD value), transpiration rate, net photosynthesis value, WUEyield, and WUEbiomass of plants subjected to PRD-50 %FC with spraying B alone showed higher values compared to other chemical applications and no chemical treatment. Applying C alone to maize plants under PRDI-50 % FC increased qP and Fv/Fm compared to other chemical treatments. Evaluating water deficits with non-destructive measurements are applicable to large-scale water management of maize plants, thereby enabling scarce water resources to be conserved.

Assessment of crop water stress index and net benefit for surface- and subsurface-drip irrigated bell pepper to various deficit irrigation strategies

AbstractThis 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.

Regulated Deficit Irrigation during Vegetative Growth Enhances Crop Water Productivity in Chickpea (Cicer arietinum L.)

To optimize irrigation, agronomists need to modulate crop water productivity (CWP) throughout phenology. We compared regulated deficit irrigation (RDI) and sustained deficit irrigation (SDI) in chickpea (Cicer arietinum L. var. Blanoro), expecting RDI during vegetative growth (VG) to enhance CWP, as opposed to flowering (F) and pod-filling (PF) stages. The effects of RDI and SDI on grain yield, plant height, weight, grain caliber, pods and grains per plant, harvest index, and CWP, were tested through a complete randomized block experiment during the years 2020 and 2021, comparing full irrigation (FI, ETc = 100%), SDI (SDI75, ETc = 75% during all stages), and six RDI treatments varying in ETc% across phenology: VG50, VG75, F50, F75, PF50, and PF75. VG75 had higher CWP while minimizing impacts on productivity. During 2020, the plants were taller (0.44 ± 4.4 m), and increased in harvest index (0.47 ± 0.06), and CWP (0.90 ± 0.2 kg m−3) (p < 0.05), while in 2021, plants were heavier (11.4 ± 2.8 g) and increased in caliber (46.1 ± 3.0 grains); grain yield did not differ between the years (p ˃ 0.05), reaching 861.8 (2020) and 944.7 kg ha−1 (2021). Our results highlight the relevance of maintaining 100% ETc during flowering, and the maintenance of RDI at 75% ETc during vegetative growth.

Continuous Third Phase Fruit Monitoring in Olive with Regulated Deficit Irrigation to Set a Quantitative Index of Water Stress

The transversal fruit diameter (FD) was monitored continuously by automatic extensimeters (fruit gauges) in order to monitor fruit growth dynamics under deficit irrigation treatments. The daily diameter fluctuation (ΔD, mm), the daily growth (ΔG, mm), the cumulative fruit growth (CFG, mm), and the fruit relative growth rate (RGR, mm mm−1 h−1) of four olive cultivars (Ascolana dura, Piantone di Falerone, Arbequina, and Lea) were studied during the third phase of fruit growth. Two regulated deficit irrigation treatments DI-20 (20% of ETc) and DI-10 (10% of ETc) were applied. The daily hysteretic pattern of FD versus the environmental variable of vapor pressure deficit (VPD) was evaluated using the data of a local weather station. The assessment of fruit growth parameters showed cultivar-specific response to water stress. For instance, after performing deficit irrigation, minimum RGR in different cultivars downsized with various slopes which suggested a very different response of the cultivars to dehydration. On the other hand, the daily hysteretic pattern of FD versus VPD was detected in all the studied cultivars, and a quantitative index (height of hysteresis curves) used for explanation of hysteresis magnitude’s changed according to the deficit irrigation treatments. The results showed a significant reduction of height of hysteresis curves by irrigation treatments which were not cultivar-specific. The quantitative index for hysteresis curve magnitude’s change in the four olive cultivars of Ascolana dura, Piantone di Falerone, Arbequina and Lea can efficiently estimate the plant water response to irrigation treatment in olive orchards. However, further investigation needs to be done to implement precise irrigation systems.

Exploring the Ability of Solar-Induced Chlorophyll Fluorescence for Drought Monitoring Based on an Intelligent Irrigation Control System

Drought is one of the most devastating disasters and a serious constraint on agricultural development. The reflectance-based vegetation indices (VIs), such as Normalized Difference Vegetation Index (NDVI), have been widely used for drought monitoring, but there is a lag in the response of VIs to the changes of photosynthesis induced by drought. Solar-induced chlorophyll fluorescence (SIF) is closely related to photosynthesis of vegetation and can capture changes induced by drought timely. This study investigated the capability of SIF for drought monitoring. An intelligent irrigation control system (IICS) utilizing the Internet of Things was designed and constructed. The soil moisture of the experiment plots was controlled at 60–80% (well-watered, T1), 50–60% (mild water stress, T2), 40–50% (moderate water stress, T3) and 30–40% (severe water stress, T4) of the field water capacity using the IICS based on data collected by soil moisture sensors. Meanwhile, SIF, NDVI, Normalized Difference Red Edge (NDRE) and Optimized Soil Adjusted Vegetation Index (OSAVI) were collected for a long time series using an automated spectral monitoring system. The differences in the responses of SIF, NDVI, NDRE and OSAVI to different drought intensities were fully analyzed. This study illustrates that the IICS can realize precise irrigation management strategies and the construction of regulated deficit irrigation treatments. SIF significantly decreased under mild stress, while NDVI, NDRE and OSAVI only significantly decreased under moderate and severe stress, indicating that SIF is more sensitive to drought. This study demonstrates the excellent ability of SIF for drought monitoring and lays the foundation for the future application of SIF in agricultural drought monitoring.

The water status of pear (Pyrus communis L.) under application of regulated deficit irrigation in high tropical latitudinal conditions

Irrigation management in fruit crops affects the water status of the plant, which directly affects production and quality in various growing cycles. The objective was to evaluate the impact of regulated deficit irrigation (RDI) on the water status of the pear tree cv. 'Triunfo de Viena', under high tropical latitudinal conditions. The applied irrigation treatments corresponded to water regimens with one control (T1), irrigated at 100% of ETC; 74% and 48% crop evapotranspiration (ETc) in the T2 treatment and 60% and 27% ETc in the T3 treatment during the period of rapid fruit growth, in 2014 and 2015, respectively. During the rest of the season, all treatments were watered equally to 100% of the ETc. This implied water savings in the deficit treatments T2 and T3 of 26.4% and 39.6% during 2014 and 51.7% and 72.8% in 2015, respectively. The leaf water potential at predawn (Ψpdl), mid-day stem water potential (Ψstem), the water potential of the fruit at predawn (Ψpdf), and water potential of the fruit at mid-day (Ψf) were clear indicators of the water status of the plant, however, between treatments were generally not different. Ψstem remained between −0.25 and −1.03, showing that RDI treatments evaluated did not cause water stress. The parameters obtained from the pressure-volume curve were similar between treatments because irrigation levels did not generate water stress, mainly due to rains and water reserves in the soil during the experiment. Therefore, osmotic adjustment was not made in any of the treatments. Maximum daily trunk shrinkage was a good indicator of hydric status and responded quickly to environmental conditions allowing its use in irrigation management and, adjusting to a crop under specific conditions. The results contributed to an understanding of the mechanisms of the water status of pears under RDI in high tropical latitudinal conditions.

Effect of Regulated Deficit Irrigation on the Quality of ‘Arbequina’ Extra Virgin Olive Oil Produced on a Super-High-Intensive Orchard

The expansion of the super-high-intensive cultivation of olive groves requires irrigation techniques that are compatible with the increasing scarcity of water due to climate change and olive oil demand. For this, the effect of two regulated deficit irrigation treatments (RDI) and a sustained deficit irrigation (SDI) treatment was studied. The treatments consisted of: (i) control treatment, which supplied 100% of the water lost by evapotranspiration (ET0); (ii) the “optimal RDI” treatment, which only reduced irrigation water (~37–54% reduction) during the pit hardening stage; (iii) the “confederation RDI” which limited water restriction to the donation of the Guadalquivir hydrographic confederation (~72% reduction); and, (iv) the “confederation SDI”, similar water restriction (~72%) but dying the whole tree cycle. In general, the reduction in the irrigation water caused no negative effects on the studied parameters. However, the total phenolic content (TPC) was increased when the deficit irrigation was applied. Fatty acid profile showed changes with respect to the control, increasing oleic acid and the total content of monounsaturated fatty acids (MUFA). For the volatile compound profile, reducing water intake caused changes in mayor volatile compound (trans-2-hexenal), related with green flavors. The application of deficit irrigation treatments increased the value obtained in the fruity parameter with respect to the control. On the other hand, irrigation deficit treatments did not generate changes in the olive oil yield.

Improving the Phenolic Content of Tempranillo Grapes by Sustainable Strategies in the Vineyard.

Wine phenolics are of considerable interest due to their implication in the organoleptic appreciation of wines and due to their bioactive functions as antioxidants. In this work, the effects of sustainable strategies in the vineyard, regulated deficit irrigation treatments (RDI) and crop load level (CL) on Tempranillo grape phenolics over two seasons was studied. Rainfed (T), early (EDI) and late (LDI) regulated deficit irrigation was applied. Cluster thinning (TH) and control (C) without cluster removal were also applied under each irrigation treatment. The effect of CL remained independent of RDI for all compounds, except for phenolic acids. The RDI influence on the grape skin phenolic profile was higher than CL in the dry season (2009); however, in 2010, the effect of CL was greater. In 2009, a tendency to increase anthocyanin and hydroxycinnamic acid content in grape skins was registered in EDI with respect to T. However, significant decreases in hydroxycinnamic and flavanol compounds were found in LDI. In 2010, the wettest year, CL increased all phenolic families’ content. Thus, it can be concluded that the effects of RDI and cluster thinning treatments depend on the family of compounds considered and the meteorological conditions of the year.

Effect of arbuscular mycorrhizal fungi inoculation on growth and physiology performance of olive trees under regulated deficit irrigation and partial rootzone drying

Agriculture water resources are limited in several Mediterranean regions. In this context, the current study was conducted to examine the response of mychorrizal olive plants to two water-saving irrigation techniques, namely partial-root zone drying (PRD) and regulated deficit irrigation (RDI). Young olive (Olea europaea L., cv Picholine marocaine) trees were grown with (+AMF) or without (-AMF) Rhizophagus irregularis using a split-root experiment, which consists in dividing the root system of the plant in two parts placed in separate pots. The pots were exposed simultaneously to three different water regimes: Control, with both root compartments well irrigated; RDI, with both compartments irrigated (50% of the control); and PRD, with one compartment irrigated (50% of the control), while the other compartment was kept dry switching every 10 days. Stomatal conductance (gs), leaf relative water content (RWC), vegetative growth (shoot length, total leaf area and leaf number), proline and sugar contents and leaf carbon isotope discrimination (δ13C) were measured in order to evaluate the influence of arbuscular mycorrhizal (AM) symbiosis on the tolerance of the olive tree to water stress induced by RDI and PRD. The low soil moisture under this two water treatments have a negative effect on all studied parameters. However, the olive plants inoculated with the AM fungi (AMF) generally have significant great growth indices in comparison with the non-inoculated ones. Furthermore, at physiological (gs and RWC) and biochemical (proline, sugar and δ13C) level, +AMF olive plants exhibit better performance under drought than -AMF ones. These responses were mostly, earlier under PRD treatment. AM olive plants can tolerate better the water deficit stress of RDI and PRD treatments saving up to 50% of the irrigation water.

Partial root zone drying increases peppermint essential oil yield and water productivity

The effects of varying irrigation volume and placement (regulated deficit irrigation that irrigated the entire root zone versus partial root zone drying that irrigated only half of the root zone at a time), on drip-irrigated peppermint (Mentha piperita L.) were studied. Treatments included full irrigation (FI) and regulated deficit irrigation receiving 85%, 70%, 55% and 40% of the irrigation volume of the full irrigation treatment (RDI85, RDI70, RDI55 and RDI40 respectively), and partial root zone drying receiving 70%, 55% and 40% of the irrigation volume of the full irrigation treatment(PRD70, PRD55 and PRD40 respectively). Plants were harvested at mid-flowering stage over two consecutive seasons. The steam distillation method used to extract essential oil. At the first harvest, biological yield (dried leaf and stem weight) generally did not significantly differ between the full irrigation, partial root zone drying, and regulated deficit irrigation treatments, but yield of RDI40 decreased by 33% compared to FI plants. However, deficit irrigation strategies significantly increased essential oil yield and ratio (Percentage of essential oil in 80 g of leaves), with the highest biological yield in FI and highest essential oil yield in PRD70, at rates of 1942 kg/ha and 23.7 kg/ha, respectively. Irrigation water productivity based on oil yield was significantly higher in partial root zone drying treatments than full irrigation and regulated deficit irrigation treatments, with the highest value achieved in PRD55 at a rate of 0.0191 kg/m3. At the second harvest, plant biological yield components were not affected by the irrigation treatments, but again the partial root zone drying treatments produced higher essential oil ratio and yield. Since the major goal of peppermint production is to extract its oil, it is recommended to apply a moderate water deficit with the PRD70 and PRD55 techniques, to allow significant (30–45%) water-saving and also reasonable yield.

Advancing knowledge about restricted irrigation strategies on commercial peach plantation under Mediterranean condition

This study was conducted to investigate the effects of different restricted irrigation strategies on peach trees. Sustainable and regulated deficit irrigation treatments were applied during the 2018/2019 production season in a commercial plot of “Bénédicte” variety located at the Atlas Mountain’s region of Morocco. Five different treatments were tested: T1, T2 and T3 with an application of respectively 125% (over-irrigation), 100% (control) and 75% (deficit-irrigation) of Crop Water Requirement (CWR) throughout the whole crop cycle; These treatments were classified under Sustainable Deficit Irrigation treatments (SDI). Regulated Deficit Irrigation treatments (RDI) comprising of treatments T4, and T5 which correspond respectively to applications of 75% ETc and 50% ETc during the pit hardening stage (PH), and 100% ETc during the rest of the cycle. The results showed that deficient irrigation treatments had no effect on vegetative growth parameters.A downward trend in average fruit weight and size at harvest was observed in the T3 treatment. A significant increase in sugar content was observed in T3 and T5 compared to the control T2. With regard to biochemical parameters, the deficient treatment (T5) recorded the highest proline content in response to water stress, followed by T3 and T4. Therewas no significant difference between the crop yields under SDI and RDI treatments, but T4 produced arelatively higher yield of 47 T/Haamong the treatments.Thisled to the water use efficiency (WUE) performance ranking: T3 with 10.63 kg/m3, T4 (75% PH) was in second place with a WUE of 9.6 kg/m3, finally T5 with an efficiency of 9.35 kg/m3.

Deficit Water Irrigation in an Almond Orchard Can Reduce Pest Damage

Irrigated almond orchards in Spain are increasing in acreage, and it is pertinent to study the effect of deficit irrigation on the presence of pests, plant damage, and other arthropod communities. In an orchard examined from 2017 to 2020, arthropods and diseases were studied by visual sampling under two irrigation treatments (T1, control and T2, regulated deficit irrigation (RDI)). Univariate analysis showed no influence of irrigation on the aphid Hyalopterus amygdali (Blanchard) (Hemiptera: Aphididae) population and damage, but Tetranychus urticae Koch (Trombidiformes: Tetranychidae) damage on leaves was significantly less (50–60% reduction in damaged leaf area) in the T2 RDI treatment compared to the full irrigation T1 control in 2019 and 2020. Typhlocybinae (principal species Asymmetrasca decedens (Paoli) (Hemiptera: Cicadellidae)) population was also significantly lower under T2 RDI treatment. Chrysopidae and Phytoseiidae, important groups in the biological control of pests, were not affected by irrigation treatment. The most important diseases observed in the orchard were not, in general, affected by irrigation treatment. The multivariate principal response curves show significant differences between irrigation strategies in 2019 and 2020. In conclusion, irrigation schemes with restricted water use (such as T2 RDI) can help reduce the foliar damage of important pests and the abundance of other secondary pests in almond orchards.

Evapotranspiration characteristics and soil water balance of alfalfa grasslands under regulated deficit irrigation in the inland arid area of Midwestern China

Drought has been a major limiting factor affecting agricultural production in the world. Accurately quantitative analysis of the dynamic changes of evapotranspiration and soil water balance is very important for effectively managing water resources and improving water use efficiency under water scarcity. Soil water balance for perennial forage is more complex than the annuals due to stronger roots and periodic evapotranspiration. The objective was to explore the evapotranspiration characteristics and soil water balance of alfalfa (Medicago sativa L.) grasslands under border irrigation at different stand ages and irrigation treatments. A 3-yr field experiment with a full irrigation and 6 regulated deficit irrigation treatments was conducted, and growth-related indicators, soil evaporation and soil water dynamics were observed regularly. Daily evapotranspiration and soil water balance were computed using a modified dual-Kc model which is able to simulate evaporation and transpiration separately. The results showed that soil water simulated by the model and the measured value were in good agreement, and regression coefficients were higher than 0.6 and close to 1.0 in most cuts. The change trend of root zone water under deficit irrigation at single growth stages was similar to that under full irrigation. Under irrigation, the transpiration was the main water loss of alfalfa grasslands. The daily actual evapotranspiration of alfalfa in the 1st cut was higher than 8.0 mm d−1 and even over 15.0 mm d−1 at the middle and later growth stages. In contrast, in the 2nd and 3rd cut, it was always less than 10.0 mm d−1. The daily actual evapotranspiration decreased significantly and immediately after cutting, and daily actual transpiration was reduced to less than 1.0 mmd−1. The change trend of daily actual evapotranspiration under deficit irrigation at single growth stages was also similar to that under full irrigation. The seasonal evapotranspiration could reach 800 mm and was reduced by deficit irrigation. The average proportion of soil evaporation to total evapotranspiration was 18%. With the decrease of irrigation amount, the evapotranspiration, transpiration and irrigation water compensation decreased, while evaporation remained relatively stable and the ratio of evaporation to evapotranspiration increased. A lower relative evapotranspiration deficit (0.041) was obtained under moderate deficit irrigation at the budding stage than those in other deficit cases (0.086 or over). In conclusion, in the arid and semi-arid areas, deficit irrigation could be applied to alfalfa grassland at the budding stage in alfalfa production.