Deficit Irrigation Treatments Research Articles

The Effect of deficit irrigation on Onion yield and water use efficiency: Concerning moisture stress areas of Arba Minch, Southern Ethiopia

To cope with scarce water supply, deficit irrigation is an important tool to achieve the goal of reducing irrigation water use and increasing water use efficiency (WUE) under scarce water resources. This experiment was conducted for the last three years (2018-2020)in Chano Mille Kebelle near Arba Minch to examine the level of deficit irrigation which allows the maximum yield of onion, WUE and economic return without significantly reducing the yield of onion. Randomized Complete Block Design was used to run the experiment with four Replications. The experiment comprised different levels of deficit irrigation treatment: 100% of ETc, 85% of ETc, 75% of ETc and 50% of ETc. Analysis of variance showed that there was a significant difference among treatments in terms of marketable yield,total yield, and WUE in three consecutive years. 100% of ETc gave the maximum marketable and total yield and WUE which was followed by 85% of ETc. Additionally, the combined analysis of the mean showed that the highest marketable yield 24.97ton ha-1 and a total yield of 28.63 ton ha-1 was observed from100% of ETc and followed by 22.13 ton ha-1of marketable yield and 26.86 ton ha-1of total yield from 85% of Etc without significant variation. The highestcombined WUE of 4.445kg m-3 resulted from 50% of ETc compared to the other levels of deficit irrigation (3.12 kg m-3 , 3.02 kg m-3, 4.27 kg m-3) from 100%, 85% and 70%, respectively. Given economic return, 100% of ETc yielded the highest net benefit of 208008 Birr/ha and followed by 198558 Birr/ha observed from 85% of ETc without significant economic return. The minimum (123858 Birr/ha gained from 50% of ETc. Based on these findings, 85% of ETc of deficit irrigation under moisture stress areas of Arba Minch should be applied to save water, and increase economic return and command area.

Sugarcane response to different soil water replenishment‐based deficit irrigation treatments during different growth stages in an Indian semi‐arid region*

AbstractThe objective of this study was to investigate the effect of a specified water deficit during a specified growth stage by replenishing root zone soil water. A field experiment was conducted with 27 treatments in randomized block design comprising groupings of different root zone soil water replenishment levels (100%, 70%, and 40%) during different growth stages (tillering, grand growth, and maturity) over three full‐year seasons of 2015–2017 in clay soils of semi‐arid western India. The full‐season 100% soil water replenishment produced higher yield (174 t ha−1), net monetary returns, and benefit‐cost (B:C) ratio that decreased linearly with linear decrease in water use. Full‐season 40% soil water replenishment caused a reduction in yield of about 40.7%, whereas a 70% replenishment caused a reduction in yield by 14%. The quality parameters of sugarcane improved non‐significantly in high‐water‐deficit conditions compared with full irrigation. The smaller range of water productivity in all seasons indicated a linear decrease when irrigation water increased and yields decreased under the different treatments. The net income and B:C ratio related to marketable cane yield was highest in 100% soil water replenishment (INR 274,000 ha−1 and 1.58, respectively) and then declined with the decrease in water use depth. The water deficit imposed during the long‐duration grand growth stage had adverse effects on cane yield, followed by tillering and maturity stages. Deficit irrigation scheduling at 100%, 70%, and 40% soil water replenishment at tillering, grand growth, and maturity stages, respectively, was appropriate. The water requirement of seasonal sugarcane under full irrigation and water deficit conditions was 1,320 and 1,150 mm, respectively.

The effects of deficit irrigation practices on evapotranspiration, yield and quality characteristics of two sesame varieties (Sesamum indicum L.) grown in lysimeters under the Mediterranean climate conditions

In this study, we investigated the effects of deficit drip irrigation practices on evapotranspiration, water-yield relations, and quality characteristics of two sesame varieties (Muganli-57 and Birkan) grown in the lysimeters under the Mediterranean climate conditions. Irrigation treatments were rainfed (non-irrigated) (I0), drip irrigation with 25% (DI25), 50% (DI50), 75% (DI75), and 100% (DI100) of cumulative evaporation (Epan) measured in Class A pan with three replications. The applied water was corrected by the percentage of vegetation cover until the full cover was attained. Evapotranspiration of Muganli-57 and Birkan ranged from 157.8 to 518.8 mm and 156.4 to 509.2 mm, on average, respectively. The yield values changed between 0.46 and 2.06 t ha−1 in Muganli-57 and between 0.35 and 1.95 t ha−1 in Birkan. Based on the 2-year results, water use efficiency (WUE) of Muganli-57 variety (3.5 kg ha−1 mm−1) was numerically higher than that of the Birkan variety (3.4 kg ha−1 mm−1). In both varieties, it was determined that deficit irrigation generally reduced the yield. However, WUE did not decrease monotonically with decreasing irrigation level. DI50 treatment maximized WUE for two varieties in both years while DI75 maximized WUE for Muganli-57 in 2014. Although irrigation-variety interaction affected relative water content, chlorophyll content index, and seed dry matter, their effect tended to be weak and inconsistent between the 2 years of the study. Deficit irrigation decreased the oil content of sesame and increased its protein content. Similarly, deficit irrigation treatments decreased the linoleic acid content and increased oleic acid content in 1 year but not the other. It was concluded that the Birkan variety is more suitable for irrigated conditions due to the growth characteristics and less saturated fatty acid content. On the contrary, Muganli-57 variety is suitable for non-irrigated conditions in terms of water economy and fatty acid composition.

Effects of pre-harvest deficit irrigation during the oil accumulation period on fruit characteristics, oil yield extraction, and oil quality in olive cv. Genovesa in an arid region of Argentina

The effect of pre-harvest deficit irrigation was studied as a tool to reduce fruit moisture and evaluate its influence on fruit characteristics, oil yield extraction, and oil quality. Two regulated deficit irrigation treatments (RDI) were evaluated over two seasons in a cv. Genovesa olive orchard. This study included a Control treatment, irrigated at 100% crop evapotranspiration over the season, and two RDI treatments, irrigated at 50% (RDI1) and 30% (RDI2) of Control. These treatments were applied from the end of pit hardening (mid-January) until harvest (early- April), when oil is accumulated in fruits. Fruit moisture decreased as the deficit irrigation period advanced, being significantly lower in RDI2 and RDI1 than in the Control treatment. Fruits harvested from the RDI2 treatment had lower moisture, dry mass and oil deposition, and higher maturation and pulp flavonoid compounds concentration than in RDI1 and Control. Pooled data across seasons showed that a 1% reduction in fruit moisture produced an increase of 0.16% in oil yield extraction. Phenolic compounds increased consistently with fruit moisture decreasing from 60% to 50%. However, when fruit moisture was as low as 35%, phenolic compounds were the lowest. Additional fruit samples from RDI2 were processed with water addition after malaxation. Water addition led to a general pattern of increases in oil yield extraction, reduction of phenolic compounds, and no influence on acidity, UV indexes, or fatty acids profile.

FAO56 crop and water stress coefficients for cotton using subsurface drip irrigation in an arid US climate

Water shortages are a continuing reality for today’s irrigated agriculture especially in the arid US southwest where cotton (Gossypium hirsutum L.) is an important crop. Decreasing water availability in the region coupled with high cotton water requirements are inducing water conservation practices, including adoption of subsurface drip irrigation (SDI) and deficit irrigation management. A 3-year cotton study (2016, 2017, and 2018) was conducted on a sandy loam soil using SDI at Maricopa, Arizona, USA. The objectives were to determine the actual single (Kc act) and basal (Kcb act) crop coefficients, corresponding growth stage lengths, and water stress adjustment criterion for estimating crop evapotranspiration (ETc) by the widely used FAO56 crop coefficient procedures. Treatments evaluated were full irrigation (100%) and deficit irrigation (70%), both replicated three times and managed at an optimum N rate. Irrigation scheduling was based on a FAO56 Kcb curve locally developed in earlier studies at the Maricopa location using furrow irrigation. Actual ETc (ETc act) was determined by a soil water balance using 0–1.9-m soil profile water content measurements made every 6–14-days. The study also quantified the effects on ETc act and yield due to the deficit irrigation treatment. ETc act rates were high for the 100% treatment, often exceeding 12.0 mm d−1 during the mid-season stage in all years. Cumulative ETc act for the 100% treatment was 961, 1039, and 1008 mm; and lint yield was 1470, 1780, and 2200 kg ha−1 in 2016, 2017, and 2018, respectively. Treatment effects on both ETc act and cotton yield were significant in all years. Cumulative ETc act for the 70% treatment was 21–23% less than that for the 100% in each year. Lint yields for the 70% treatments were reduced 15–16% in two of the years, and by 36% in 2017 when soil water stress occurred earlier in the growing season. The 3-year average values of Kc act and Kcb act at mid-season were 1.31 and 1.26, respectively. Though higher than those previously reported for cotton at this location, these mid-season values are considered appropriate in this arid climate when using SDI and were consistent with the FAO56 mid-season standard cotton values after local climate adjustment. The observed average Kc act and Kcb act during the initial stage were ≈ 0.21 and they were 0.37 at the end of season, closely agreeing with the FAO56 tabulated cotton values for those stages. The average growth stage lengths determined for the SDI cotton are 33, 42, 51, and 28 for the initial, development, mid-season, and late season stages, respectively. The FAO56 water stress coefficient (Ks) was modeled for the 70% treatment using five different baseline values of depletion fraction for no stress (p) that varied from 0.60 to 0.70 in 0.025 increments. Best correlation coefficients (r) between the ETc act ratio of the 70% and 100% treatments with the modeled Ks of the 70% treatment were obtained with baseline p values of 0.60, 0.675, and 0.675 in 2016, 2017, and 2018, respectively. The three 3-year average baseline p value of 0.65, which is the same baseline p value for cotton in FAO56, is recommended for estimating ETc reduction due to water stress.

The mean value of gaussian distribution of excess green index: A new crop water stress indicator

The study proposed a new crop water stress indicator - the mean value of Gaussian distribution of excess green index for maize canopy (MGDEXG) within an RGB image. A series of RGB images were collected in a maize field under varying levels of deficit irrigation during 2013, 2015 and 2016 growth seasons in northern Colorado. To evaluate the sensitivity of MGDEXG to maize water status, canopy temperature, canopy-to-air temperature difference, crop water stress index (CWSI), leaf water potential, and sap flow were used as water status references. The results show that MGDEXG distinguished different levels of deficit irrigation treatments well and responded to the release and reimposition of deficit irrigation. The MGDEXG showed a significant correlation (p < 0.01) to different water stress references. Especially, the coefficient of determination (R2) with CWSI was 0.63 (n = 59) for 2013, 0.80 (n = 90) for 2015, and 0.80 (n = 50) for 2016. In addition, among the three Tc-based water stress indicators, the relationship between MGDEXG and CWSI was the most robust with the least annual changes of slope and intercept. The robust relationship between MGDEXG and CWSI could also show that MGDEXG was resistant to the micro-meteorological conditions within the field. Significant correlations (p < 0.01) were found between MGDEXG and leaf water potential with R2 of 0.85 and 0.87 for 2013 and 2015, and between MGDEXG and sap flow in 2015 (R2 = 0.62). MGDEXG relies only on the distribution of crop pixels within an RGB image and could be calculated easily, so it could be cheaper or easier to popularize than other crop water stress indicators in practice. Overall, our results show that MGDEXG could be successfully used as a maize water stress indicator. In the future, more field experiments are needed to further explore the changes of MGDEXG with different scale and spatial resolution of RGB images, and to evaluate MGDEXG for specific climate and crop varieties.

Evaluation of AquaCrop model in soybean cultivation under different planting dates and deficit irrigation treatments

Water stress has been identified as the major effective factor on soybean production growth in semi-arid regions. Planting date and irrigation management are the most important agronomic practices, which affect soybean growth and economic yield production. Today, to assess the impacts of destructive environmental stresses, calibrated models can be used to simulate and evaluate the growth of the crops under different scenarios. In this research, the AquaCrop model was evaluated for simulation of soybean yields and water productivity on varying irrigation levels and planting dates in northeast of Iran. For this purpose, root mean square error (RMSE), model efficiency (E), coefficient of determination (R2), and prediction error (p e) were applied to test the model performance. The calibrated AquaCrop model predicted soybean grain yield and biomass for all treatments with the prediction error statistics 0.27<RMSE-1, 5.1 e<5.6%, 0.91<R2-1 ha-1, R2 of 0.88, and p e of 7.6%. Subsequently, validation results were 0.93<E<0.96; 0.92<R2-1 for grain and biomass yield, respectively. The soybean yields and growth response to different irrigation water management and planting dates was adequately predicted by the AquaCrop model. Overall, the AquaCrop model is a suitable support tool for decision makers to simulate WP, grain yield (GY), and biomass (Bi) in soybean cultivation under various field managementin semi-arid environment.

Establishing of Optimum Nutrient Ranges for Canola Leaves Affected by Compost and Zinc by DRIS Analysis

DRIS method is one of the important methods that reflect the status of the nutrients within the plant tissue. Field experiment were carried out at the Research and Production Station of the National Research Centre, Nubaria region, Beheira Governorate, Egypt during 2019/2020 to evaluate leaf nutrient optimum ranges of canola affected by compost addition (0, 2, 4 and 6 ton fed-1) to the soil and foliar application of zinc (0, 50 and 100 ppm) under water regimes at 75 and 40% water holding capacity. A remarkable increase the macronutrient contents due to the addition of compost and had a positive effect, especially with the rates 4 and 6 ton fed-1 + zinc sulfate foliar spraying at a rate of 100 ppm under sufficient and deficit irrigation treatments. Under water stress, in the control treatment as compared to the treatment combination (4 ton/fed compost + 100 ppm Zn), the N index was decreased from (-143.2) to (-76.1) in this time the nitrogen a negative DRIS index indicates that the nutrient level is below the optimum. Phosphorus index was recorded (-98) reduced to (-39.4) and a negative DRIS index indicates that the phosphorus level is below optimum in these treatment combinations. Also, the DRIS index for potassium was recorded (241.2) decrease up to (115.5) and the potassium has a positive DRIS index indicates that the nutrient level is above or near to the optimum. DRIS norms could be used to test the nutritional balance of nutrients in plant and diagnose nutrient requirements through calculating DRIS indices or direct application of physiological diagnosis (PD) chart. &#x0D; Objective: The objectives this study to evaluation of canola leaf nutrient optimum ranges affected by organic compost addition to the soil and micronutrient such as of zinc foliar application.

Long-term almond yield response to deficit irrigation

A substantial area of the new almond plantations in Spain is under irrigation but because of water scarcity, deficit irrigation (DI) strategies have to be adopted. This study assesses the long-term sustainability of different DI strategies over 6 years (2014–2019) on a mature almond [Prunus dulcis (Mill) D.A. Web] orchard in southern Spain. Four irrigation treatments were imposed: full irrigation (FI); two moderate DI, (SDIM) and (RDIM), where applied irrigation was 65% of FI but differed in the seasonal water distribution; and a severe DI, where applied irrigation was 35% of FI. The results emphasise the key role of soil water storage and the importance to consider crop evapotranspiration (ETC) as the principal driving variable of productivity instead of irrigation in many situations. Soil water partially buffered the irrigation reductions imposed, leading to no significant differences in yield performance between the two different moderate DI treatments. The water production functions (yield versus applied irrigation and yield versus ETC) did not show statistical differences when comparing the first (2014–2016) against that of the second triennia (2017–2019), suggesting the non-existence of exhaustion or adaptation phenomena that could jeopardize the longer term sustainability of DI strategies. Average annual ETC ranged from 580 mm in the RDIS treatment to a maximum value of 1300 mm, yielding between 1370 and 2750 kg ha−1 of nuts, and showed that water deficits caused yield losses ranging from 0.05 to 0.35 kg m−3 of irrigation water depending on the irrigation level.

Spring deficit irrigation promotes significant reduction on vegetative growth, flowering, fruit growth and production in hedgerow olive orchards (cv. Arbequina)

An irrigation experiment was conducted during 5 years in two hedgerow olive orchards (C and L) cv. Arbequina in Central Spain. The control treatments (C1 and L1) were irrigated to maintain the “wetted bulb” near field capacity throughout the season. Three deficit-irrigation treatments were applied from shoot growth (April-May) until pit hardening (beginning of July) with water applications relative to control, C2, C3, C4 (50, 25, 0%) and L2, L3, L4 (40, 17, 0%), respectively. Treatments reverted to full irrigation after pit hardening. During the treatment period a series of phenological events occurs: bud break, shoot growth, flower differentiation, flowering, fruit set, fruit drop and pit hardening. Responses of vegetative growth, flowering, fruiting, fruit characteristics and production were evaluated through their relationships with midday stem water potential (Ψstem). Flowering was shown to be the most sensitive period to deficit irrigation and the major determinant of final production through reductions on fruit number and oil content. With high water during flowering (mean Ψstem before irrigation >−1.0 MPa) trees developed more nodes, leaves, fertile inflorescences and fruits per inflorescence with consequent high production (1278 kg oil ha−1). Oil production was significantly reduced (64% of maximum) when Ψstem was allowed to fall below −1.5 MPa at flowering and was halved at −1.7 MPa, reducing water productivity from 0.26 to 0.21 kg oil m−3. In contrast, Ψstem could be reduced to −1.8 MPa after flowering until pit hardening without effects on fruit drop, fruit size or oil content. Fruit drop increased when Ψstem from flowering until pit hardening was below −2.71 MPa. Fruit oil content at harvest was strongly related with fruit dry weight at pit hardening. Vegetative growth occurred continuously during spring, although mainly during flowering, and could not be reduced by deficit irrigation without reducing production. The results are advantageous to irrigation management in this and similar climatic regions where Spring is a critical period for olive production due to variable temperature, rainfall and crop water demand. They establish the high thresholds of Ψstem required to guide irrigation management during Spring without yield loss, and the substantial resulting loss when this threshold is exceeded. They also reveal that deficit irrigation strategies cannot be used in Spring to control canopy size in hedgerow orchard without serious impact on yield.

Yield and Fruit Quality of Strawberry Cultivars under Different Irrigation Regimes

Strawberry (Fragaria×ananassa Duch.) production requires the input of large amounts of water provided by irrigation during the entire production cycle. However, water availability is shrinking in many important strawberry cropping areas, such as Huelva (in Europe), compromising the environmental sustainability and economic viability of strawberry production. Besides technical approaches, water-saving strategies are necessary for improving strawberry water productivity such as the use of low water-consumptive cultivars with high productivity or cultivars allowing deficit irrigation (DI) strategies. A two-year field experiment was conducted to compare the physiological and agronomical response of six commercial strawberry cultivars (‘Sabrina’, ‘Fortuna’, ‘Splendor’, ‘Primoris’, ‘Rabida’ and ‘Rociera’) to six different water treatments ranging from 65% to 140% of estimated ‘Sabrina’ evapotranspiration (ETcSab; ~224–510 mm year−1). Cultivars differed substantially in yield and water consumption linked to their biomass partitioning into reproductive/ vegetative organs, determining different yield efficiency (YE). Their water needs (IN) conditioned their response to different water supplies, involving significant yield losses in DI treatments (&lt;20% IN) but not decreasing fruit quality. The highly-consumptive and productive ‘Rabida’ and ‘Rociera’, reduced yields by DI (&lt;40%) but were still profitable; the low-water-consumptive but still productive ‘Fortuna’, ‘Splendor’ and ‘Primoris’ represent significant water-savings (&lt;20%) in strawberry cultivation.

Effect of regulated deficit irrigation on alfalfa performance under two irrigation systems in the inland arid area of midwestern China

Irrigation plays a fundamental role in sustanining the productivity of agricultural systems in the inland arid area of midwestern China. Deficit irrigation can help to balance yield outcome and water input. Few studies have investigated the impact of deficit irrigation on alfalfa performance, which shows great differences from grain crops in water requirement and management strategy. The study aimed to evaluate the effect of regulated deficit irrigation on forage yield and quality of alfalfa (Medicago sativa). A three year trial was carried out with two irrigation systems (flood irrigation, FI and subsurface drip irrigation, SDI) and seven contrasting regulated irrigation treatments, and alfalfa growth, productivity and water use were measured. Under both irrigation systems, alfalfa forage yield decreased with decreasing irrigation amount under whole stage irrigation, while forage quality improved. However, the performance of alfalfa was different when deficit irrigation was applied at various growth stages. Compared with other deficit irrigation treatments, regulated deficit irrigation at single growth stage usually led to a higher yield. There was an exponential relationship between plant height and forage yield (R2 = 0.62 for FI and R2 = 0.57 for SDI) and a linear relationship between leaf area index and forage yield (R2 = 0.56 for FI and R2 = 0.64 for SDI). There was a negative correlation between forage yield and quality, which was closer to some quadratic relationships. Therefore, regulated deficit irrigation can help to achieve an ideal yield (up to 34.9 t/ha) and quality in this area. In the inland arid area of midwestern China, subsurface drip irrigation showed a higher irrigation water use efficiency (13.8–84.4 kg/(ha mm)) than flood irrigation (10.8–66.6 kg/(ha mm)) for alfalfa production. With limited water supply, deficit irrigation at single growth stage usually maintained a higher forage yield compared to slightly stressed irrigation during the whole growth. Deficit irrigation at the branching stage led to more negative effect on forage yield compared to other single stages.

Response of Spring Wheat (Triticum aestivum) to Deficit Irrigation Management under the Semi-Arid Environment of Egypt: Field and Modeling Study

In many areas of the world, water shortages prevail and threaten food production. Deficit irrigation was commonly investigated in dry areas as a precious and sustainable production approach. Using the CropSyst model to simulate the effects of different deficit irrigation treatments could help draw conclusions and save time, effort, and money. Therefore, the aims of this research were (i) to calibrate and validate the CropSyst model for wheat under different sustained and phenological stage-based deficit irrigation treatments, (ii) to simulate the impacts of the latter treatments on limiting wheat yield reduction. Two field experiments were conducted in Nubaria (Egypt), representing an arid environment. They included seven irrigation treatments: (1) 100%, (2) 75%, or (3) 50% of crop evapotranspiration (ETc) during the whole crop cycle; (4) 50% ETc at tillering only, or (5) at booting only, or (6) at grain filling only, or (7) at both tillering and grain filling, with the replenishment of 100% ETc to the treatments (4) to (7) in the remaining phenological stages. The results revealed that phenological stage-based deficit irrigation of wheat resulted in lower yield reduction compared to sustained deficit irrigation treatments, with a 6% yield reduction when 50% ETc was applied at the booting stage. Wheat yield loss was reduced to 4 or 6% when 95 or 90% of ETc were applied, respectively. The CropSyst model accurately simulated wheat grain and total dry matter under deficit irrigation with low RMSE value. In conclusion, the CropSyst model can be reliably used for evaluating the strategy of planned deficit irrigation management in terms of wheat production under the arid environment.

Adaptation of citrus orchards to deficit irrigation strategies

In this study, the adaptation characteristics of orange trees, related to the application over a decade of deficit irrigation (DI) strategies, have been explored. To this purpose, the analysis of a minimal dataset composed of physiological information (stem water potential - Ψstem and sap flow - SF measurements), yield (fruits number and weight) and qualitative parameters (titratable acidity, TA; and total soluble solids, TSS) was performed with reference to the last irrigation seasons (i.e. 2018–19). The applied irrigation treatments were the following: sustained deficit irrigation (SDI); regulated deficit irrigation (RDI); partial root-zone drying (PRD), each distributing a water deficit of about 19%, 29% and 52%, respectively, compared to the control treatment (FI) supplying the full irrigation level (100% ETc). In general, higher water use efficiencies (WUE) have been obtained in DI treatments, which guarantee greater water savings (up to 50%), without affecting yield and quality characteristics. In particular, the most stressed treatment (PRD), while reaching the lowest Ψstem values (−1.8 to −2.0MPa), as also shown by SF versus Ψstem clusters, resulted in WUE values for yield (WUEY), TA (WUETA) and TSS (WUETSS) parameters of approximately 2.6, 2.9, and 3.1 times greater than FI, respectively. Overall, this study allowed identifying the cumulative adaptation characteristics of the orange trees under study to the application of long-term DI strategies and showing that trees were able to achieve yields and qualitative features similar to those obtained with FI, even after 10 years of application of deficient irrigation regimes.

Changes of health-promoting bioactive compounds and related enzymes of ‘Hutai No.8’ grape (Vitis vinifera L.) in response to deficit irrigation

ABSTRACT The objective of this study was to investigate the changes of health-promoting bioactive compounds and related enzymes of ‘Hutai No.8’ grape (Vitis vinifera L.) in response to deficit irrigation. The experiment had five irrigation treatments: FI (75%–90% of FC [field water holding capacity] from budburst to full maturation), DI (same as FI except 50%–60% of FC from peasize to full maturation), DI1 (same as FI except 50%–60% of FC from peasize to véraison), DI2 (same as FI except 50%–60% of FC from véraison to mid-ripening) and DI3 (same as FI except 50%–60% of FC from mid-ripening to full maturation). Results showed that contents of different bioactive compounds and activity of related enzymes in grape leaves and berries tissue increased over control due to the application of deficit irrigation, and these changes were dependent on the fruit developmental period. Correlation analysis revealed the most significant positive relationship was observed between bioactive compounds and related enzymes activities in the grape seeds (r = 0.804). However, the most significant negative relationship was observed between bioactive compounds and polyphenol oxidase activity in the grape leaves (r = −0.769). Deficit irrigation treatment after véraison is an efficient approach for inducing the accumulation of bioactive compounds.

Irrigation Management Effects on Crop Water Productivity for Maize Production in the Texas High Plains

Corn (Zea mays L.) was grown under full and deficit irrigation in two research field locations near Bushland, TX, in 2018 to compare seasonal water use of two irrigation management approaches. Full irrigation was achieved in both fields by allowing no more than 55% depletion of plant available soil water. However, irrigation depth and frequency were different in each field. The USDA-ARS Conservation and Production Research Laboratory (CPRL) weighing lysimeter fields were generally irrigated twice weekly using irrigation depths ranging from 19 to 32 mm. The Texas A&M AgriLife Research Emeny field was irrigated only once per week, having greater application depths ranging from 35 to 42 mm. Deficit irrigation treatments of 75% of full irrigation were also performed in both research fields. Yield and crop water productivity values for the 100 and 75% lysimeter field irrigation treatments were greater than corresponding values for the Emeny field. Emeny field yields may have been slightly reduced by heat stress incurred between irrigations during early grain fill whereas more frequent irrigations on the lysimeter fields may have reduced heat stress during that period. Results from this study suggest that evaporative losses associated with the more frequent, smaller application depth irrigations on the lysimeter fields did not contribute to appreciably lower CWP values, as losses were likely mitigated by the rapid development of the corn canopy. These findings suggest that corn yield is principally dependent upon seasonal water inputs and losses from frequent, smaller depth irrigations are minimal outside of incomplete canopy conditions.

Influence of kaolin application on most important fruit and leaf characteristics of two apple cultivars under sustained deficit irrigation

BackgroundApple is one of the oldest and most valuable fruits. Water restriction is one of the major problems in the production of this fruit in some planting areas.MethodsEffects of kaolin spray treatments were studied on two early apple cultivars of Golab and Shafi-Abadi under sustained deficit irrigation (SDI) in Alborz province, Iran during 2017 and 2018. Irrigation treatments were 100%, 85%, and 70% ETc and kaolin application were concentrations of 0, 3 and 6% in 2017 and 0, 1.5 and 3% in 2018.ResultsResults showed that 85% ETc treatment compared to other irrigation treatments improved apple tree crown volume in 2017. Deficit irrigation treatments significantly reduced fruit weight in both years. Application with 6% kaolin resulted in 33.3% increase in apple fruit weight compared to non-kaolin treatment at 100% ETc irrigation in the first year. Severe deficit irrigation (70% ETc) significantly reduced apple fruit length in both years, but 6% kaolin increased fruit length in both apple cultivars in 2017. Severe deficit irrigation treatment increased the firmness of apple fruit compared to control and mild deficit irrigation (85% ETc) in the first year of experiment. There was no significant difference between irrigation treatments for apple fruit firmness in the second year of experiment. Kaolin treatments of 1.5% and 3% at full irrigation increased the soluble solids content of apple fruit by 36.6% and 44.1% in 2018, respectively. Deficit irrigation treatments significantly increased leaf proline content compared to control in both years. In the first year, kaolin treatments increased leaf proline but in the second year, leaf proline was not significant. Deficit irrigation treatment of 70% ETc and 6% kaolin had the highest amount of glycine betaine content, malondialdehyde and hydrogen peroxide in apple leaf in the first year of experiment.ConclusionsSevere deficit irrigation stress (70% ETc) increased the activity of nonenzymatic defense systems of apple trees. Kaolin as a drought stress reducing agent can be recommended in apple orchards of Golab and Shafi-Abadi cultivars as an effective and inexpensive method to improve tolerance to drought stress conditions.

Physiological responses of orange trees subject to regulated deficit irrigation and partial root drying

Variations in climate, crop, and field conditions have caused different results in applying regulated deficit irrigation (DI) and partial root drying irrigation (PRD) for citrus. In this study field grown, Washington Navel orange trees were exposed to RDI and PRD practices at two reduced irrigation levels: 80% and 50% of full water requirement under a semi-arid climate. Applying DI-80 and PRD-80 resulted in a moderate water stress condition for the experimented trees and saved ~ 15% of the seasonal irrigation without significant yield reduction (~ 3 to 5%). Applying DI-50 and PRD-50 saved up to 40% of the seasonal irrigation, but the trees experienced a severe water stress condition with ~ 28% yield reduction in DI-50 and 19% in PRD-50 trees. The fruit weight was not significantly affected by the irrigation techniques, and the yield reduction in DI treatments was attributed to the fruitlet abscission and the lower number of fruits per tree. A higher leaf water potential, more controlled vegetative growth and greater yield resulted from the trees irrigated at 80% irrigation level. Internal fruit composition was equally enhanced in DI and PRD fruits and was more notable at the 50% irrigation level. A more effective drought management mechanism was found in the PRD-treated trees and was more notable and beneficial in the severe water stress level. In high water stress conditions, the soil water content (SWC) had a more remarkable impact on controlling the stomatal response compared to vapor pressure deficit (VPD), while in low water stress conditions, the effect of VPD was more evident.

Influence of irrigation and fertilization on the sterol and triterpene dialcohol compositions of virgin olive oil

The objective of this work was to evaluate the influence of irrigation and fertilization with nitrogen and potassium on the sterol and triterpene dialcohol contents in two trials of cv. Arbequina in super-intensive orchards in Madrid and Lleida (Spain), using a completely randomized block design. No significant differences in total sterols between deficit and full irrigation treatments were observed. Under very dry conditions, the sterol levels from fully irrigated trees were higher than from rain-fed treatments and the triterpene dialcohol erythrodiol+ uvaol content was lower in the irrigated treatments in Lleida. In the fertilizer trial with full irrigation, total sterols were higher in the two N treatments compared to the unfertilized one; while erythrodiol + uvaol decreased. The application of K fertilizer had no effect on total sterol or triterpene dialcohol contents. A proper fertilization and irrigation are vital to obtain high quality EVOOs that meet the regulatory range in sterol and erythrodiol + uvaol contents.

Understanding the relationship between biomass production and water use of Populus tomentosa trees throughout an entire short-rotation

Understanding the relationship between tree production and water use, as well as the main environmental and plant-related drivers of water use, is crucial for the development of production prediction models and reliable water management strategies under different climatic conditions. However, the relation between tree water use and biomass production has never been assessed throughout the entire rotation for poplar trees. Meanwhile, it remains poorly understood how the transpiration driving factors of poplars will change with stand age. Therefore, we investigated the relationship between transpiration (E) and aboveground biomass (ABM), as well as the main drivers of E for 2- to 5-year-old (2016–2019) Populus tomentosa trees under three water treatments. The annual increase in ABM depended on annually accumulated E and their relationship could be fitted with a logistic curve in each growing season (R2 > 0.89). Throughout the whole rotation period, compared with the non-irrigated trees, full irrigation trees produced 59% more biomass with only 12% more E, while deficit irrigation trees attained 46% more biomass with 32% more E. The daily E had a strong exponential relationship with vapor pressure deficit (D) during years 3–5 of the rotation, and the asymptote of this relationship increased with tree age (1.6 kPa (2017), 2 kPa (2018), 2.5 kPa (2019)). The E was also strongly linearly correlated to solar radiation (Rs) for each year although with slightly weaker relationships than for D. Similar to other poplar species, P. tomentosa showed effective stomatal control on E. However, soil water content had almost no effect on E for all treatments, no matter which soil layer was considered. D and Rs were the major drivers of P. tomentosa transpiration during the growing season, even during drought periods, in the study region. Our findings will not only help to deepen the understanding of poplar water use characteristics and the underlying mechanisms, but also help to develop models for predicting the biomass production.