Effect of combined water and salinity stress factors on evapotranspiration of Sedum kamtschaticum Fischer in relation to green roof irrigation

In dryland areas, secondarily treated municipal wastewater could be used in extensive green roof systems. In this study, the effects of water and salt stress on a crassulacean acid metabolism (CAM) plant, Sedum kamtschaticum Fischer, was evaluated under intermittent saline irrigation. The salinity of irrigation water varied from 6.0 to 18.0 dS m^?1. A reduction in soil water content and an increase in soil water electrical conductivity (EC) were observed during the irrigation interval (5–17 d) as a result of evapotranspiration (ET). The effect of soil water potential (SWP) on reduction of the ET ratio (ET_r) was successfully described with an equation that could be applicable to a wide range of soil salinities and water contents, to estimate ET. In this study, the stress factor was defined as the integration of solute potential, and matric potential less soil water content for optimum growth (less than ?0.1 MPa) with elapsed time. The stress factor rapidly reduced total ET in CAM plants but effectively increased water-use efficiency (WUE). Thus, by using CAM plants for green roofs under intermittent saline irrigation, the need for irrigation water is reduced without a considerable loss of plant biomass.     

Varying evapotranspiration and salinity level of irrigation water influence soil quality and performance of perennial ryegrass (Lolium perenne L.)

Increasing use of recycled water that is often high in salinity warrants further examination of irrigation practices for turfgrass health and salinity management. A study was conducted during 2011–2012 in Riverside, CA to evaluate the response of perennial ryegrass (Lolium perenne L.) ‘SR 4550’ turf to varying quality and quantity of irrigation water. A modified line-source sprinkler irrigation system provided a salinity gradient (EC_w ∼0.6–4.2 dS m⁻¹) in between lines. Irrigation was scheduled in four separate irrigation zones perpendicular to the irrigation lines according to 80, 100, 120, and 140% ET_o. Changes in turf quality (R² = 0.30***), were primarily driven by the number of days that the area had been irrigated with saline water. When data were separated by irrigation amount, both time and water quality accounted for 54% and 46% of the variability (P < 0.001) in quality and cover, respectively at 80% ET_o. A model was created to quantify decline in turf quality in relationship to %ET_o replacement and salinity accumulation in the rootzone (R² = 0.57). Our results suggest that perennial ryegrass requires irrigation scheduling at 140% ET_o, irrigation water quality below EC_w ∼1.7 dS m⁻¹, and EC_e below 3.8 dS m⁻¹ to maintain acceptable quality for 442 d in Riverside, CA.     

Energy partitioning and evapotranspiration of hot pepper grown in greenhouse with furrow and drip irrigation methods

Studying crop energy partitioning and evapotranspiration for different irrigation methods is important in optimizing efficient water-saving irrigation, developing suitable irrigation scheduling and improving crop water use efficiency. Two experiments were conducted to compare the energy partitioning and evapotranspiration of hot pepper (Capsicum annum L.) between furrow and drip irrigation methods under two adjacent solar greenhouses in northwest China. Results indicate that irrigation method affected the energy partitioning and evapotranspiration of hot pepper plants and these results were corroborated in a greenhouse study. Compared to drip irrigation, furrow irrigation increased daytime average net radiation (R_n), latent (λET) and sensible (H) heat fluxes by 12–29, 37–53 and 9–23%, respectively, but decreased soil heat flux (G) by 7–19%. Furrow irrigation also resulted in higher λET/R_n and lower H/R_n and G/R_n and increased total evapotranspiration by 55.5% and produced a higher crop coefficient. Total evapotranspiration was 562.3 and 361.6 mm over whole growth stage for furrow and drip irrigation methods, respectively. And drip irrigation increased the total yield and water use efficiency by 18.2 and 80.4%, respectively, before late fruit bearing and harvesting stage. In conclusion, drip irrigation is an effective and water-saving irrigation method in hot pepper production to be used in greenhouse.     

Influence of paclobutrazol and substrate on daily evapotranspiration of potted geranium

The application of plant growth regulators and the use of different culture media are common practices in potted ornamental crops. We report the results of a study to evaluate the effect of two substrates (peat moss or coconut fiber) and spraying 30 ppm paclobutrazol (PAC) on water resource management of zonal geranium (Pelargonium × hortorum L.H. Bailey) seedlings growing in a greenhouse during spring–summer. Growth, water consumption, leaching, evapotranspiration rate (ET), water use efficiency (WUE) and leaf water potential were determined. Plant growth was greater in peat moss (peat) than in coconut fiber (coconut), while the use of PAC decreased plant growth in both substrates, although more markedly in peat. Coconut produced a higher leaching fraction than peat in both PAC-treated plants and non-treated plants, although PAC application increased the leaching fraction in both substrates. Water consumption was lower in coconut than in peat and decreased in response to PAC. Peat was more effective at improving the water-use efficiency and increased the electrical conductivity in the leachate, while PAC decreased the latter in this same substrate. Daily ET showed a maximum of 200 mL/pot in peat and a minimum of 60 mL/pot in the coconut-PAC treatment. During the experimental period, accumulated ET values were higher in peat than in coconut, while the application of PAC reduced the value in peat but increased it in coconut. The evolution of ET per hour during the day showed that the highest rate (23 mL/h) was registered at midday in peat, while about 90% of ET occurred between 10 and 18 h in all treatments. When a cycle of water stress and recovery was applied, the peat induced the highest ET values of all treatments during the first days of drought, but the lowest ET after a week of drought. PAC modified this response, favoring a more balanced behavior of ET, although after the second cycle of drought this effect disappeared. Based on these results, the best strategy in normal irrigation conditions would be to use coconut fiber and not apply PAC, because this provides plants of excellent commercial quality with low water consumption. In plants at moderate water deficit PAC played a more important role than the substrate, improving the water status of plants with both substrates used. However, in the face of severe water stress the effect of PAC disappeared and peat acted as a better substrate than coconut fiber.     

Subsurface drip irrigation scheduling for cucumber (Cucumis sativus L.) grown in solar greenhouse based on 20 cm standard pan evaporation in Northeast China

The experiment was conducted in a solar greenhouse to determine the optimum irrigation frequency and quantity for cucumber under subsurface drip irrigation based on evaporation from a 20 cm diameter pan (E_p) placed above the crop canopy. Two irrigation intervals (I1: 4-day and I2: 8-day) and three plant-pan coefficients (K_cp1: 0.6; K_cp2: 0.8 and K_cp3: 1.0) were compared. Crop evapotranspiration (ET) and fruits yield increased with the increasing of irrigation water. The K_cp3 treatments had the highest yield, while K_cp2 had the highest irrigation water use efficiency (IWUE) and water use efficiency (WUE) values in both irrigation intervals. The yields of K_cp2 treatments decreased only 4.87% and 5.93% in both intervals though total irrigation water decreased 14.3% compared to K_cp3 treatment. Irrigation water amount significantly (P < 0.01) and positively affected the fruit number and fruit water content, whereas significantly and negatively affected the soluble sugar (SS), Vitamin C (Vc) and free amino acid (FAA) content in fruits. In conclusion, I2K_cp2 (0.8E_p with 8-day interval) was the optimum irrigation schedule for cumber plants grown in solar greenhouse under subsurface drip irrigation in arid and semi-arid areas that are in lack of water resources.     

Growth of Calamagrostis brachytricha Steud. and Festuca glauca Lam. and estimated water savings under evapotranspiration-based deficit irrigation

Summary

Calamagrostis brachytricha Steud. (feather reed grass) and Festuca glauca Lam. (blue fescue) were grown in mini-lysimeters under four irrigation regimes based on maximum crop evapotranspiration [ET_c; 100% ET_c (control)], 75% ET_c, 50% ET_c, or 25% ET_c in order to estimate potential water savings in landscape management. Plant responses showed that shoot width, the number of tillers, and shoot dry weights (DWs) in feather reed grass were affected by deficit irrigation, and that there were significant linear correlations between these measurements and irrigation regime. However, in 2006, none of these parameters showed any significant difference between 75% ET_c irrigation and the 100% ET_c control. In 2007, plant height and the number of tillers gave similar results. There were significant linear correlations between irrigation regime and shoot height, shoot width, and shoot DW in blue fescue plants in 2006 and in 2007, while plants irrigated at 75% ET_c showed no significant differences from control 100% ET_c plants in both years. To save water and ensure high aesthetic value, a 75% ET_c irrigation regime is recommended for both species. Crop coefficients (K_c) were calculated for both species in order to estimate the supplementary irrigation required under historical average conditions (between 1841-1993). Based on these K_c values, historical reference evapotranspiration, and average precipitation, the model indicated that both species required supplementary irrigation during May, June, September, and October. Annual supplementary irrigation was 349.1 mm for feather reed grass and 163.3 mm for blue fescue at 100% ET_c. Neither feather reed grass nor blue fescue required supplementary irrigation in July and August, which accounted for 62.4% of annual precipitation. Deficit irrigation at 75% ET_c would save 33.1% and 40.3% of annual water use for feather reed grass and blue fescue, respectively.     

Mycorrhizal colonization improves onion (Allium cepa L.) yield and water use efficiency under water deficit condition

Most plants benefit from mycorrhizal symbiosis through improvement of water status and nutrient uptake. A factorial experiment with complete randomized blocks design was carried out in greenhouse at Tabriz University, Iran in 2005–2006. Experimental treatments were (a) irrigation interval (7, 9 and 11 days), (b) soil condition (sterile and non-sterile) and (c) arbuscular mycorrhizal fungi (AMF) species (Glomus versiforme, Glomus intraradices, Glomus etunicatum) and non-mycorrhizal (NM) plants as control. Onion (Allium cepa L. cv. Azar-shahr) seeds were sown in sterile nursery and inoculated with fungi species. One nursery left uninoculated as control. Nine weeks old seedlings then were transplanted to the pots. Average pre-irrigation soil water contents reached to about 67, 61.6 and 57.5% of FC corresponding to 7, 9 and 11 days irrigation intervals, respectively. At onion bulb maturity stage (192 days after transplanting), yield, water use efficiency (WUE) and yield response factor (K_y) were determined. The results indicated that AMF colonization increased soil water depletion significantly. G. versiforme under both soil conditions (sterile and non-sterile) and G. etunicatum in sterile soil depleted soil water effectively (P < 0.05). Mycorrhizal fungi improved WUE significantly (P < 0.0001) in both soil conditions. It raised by G. versiforme about 2.4-fold (0.289 g mm⁻¹) in comparison with the control (0.117 g mm⁻¹). G. intraradices and G. etunicatum also had significantly higher WUE than control. Apparently water deficit in 11-day irrigation interval led to lower yield and WUE compared to 9-day interval; the later resulted highest WUE (0.254 g mm⁻¹). Mycorrhizal plants increased seasonal ET significantly due to enhancing in plant growth; G. versiforme in both sterile and non-sterile soil and G. etunicatum in sterile soil had the highest ET. Bulb yield was influenced by irrigation period and fungi species. G. versiforme produced higher yield than other treatments (135.27 g/pot). Mycorrhizal plants in 11-day irrigation interval in spite of suffering from water stress had more bulb yield than non-mycorrhizal plants in all irrigation intervals. Yield in general was higher in 9-day treatments than other irrigating internals significantly (P < 0.05). Onion yield response factor (K_y) was decreased by AMF colonization; implying that symbiosed plants become less responsive to water deficit (longer irrigation interval) compared to the control ones.     

Effects of water deficit on olive trees cv. Chemlali under field conditions in arid region in Tunisia

Water scarcity in the Mediterranean basin in addition to the extension of irrigated lands is one of the main factors limiting agricultural development. The need for supplementary irrigation of the Chemlali olive cultivar (Olea europaea L.) during summer and autumn periods was investigated. Leaf water content, gas exchange parameters, fruit development and yield in rain-fed and in irrigated plants have been monitored in 12-year-old olive trees grown under environmental conditions in semi arid regions characterized by high temperatures and high light intensity. Trees were subjected to three irrigation treatments, T0, T1 and T2 corresponding respectively to 0, 33 and 66% of crop evapotranspiration (ET_c) by a drip irrigation system. The water deficit during the summer (from June to August) led to the decrease of soil moisture, leaf water content and gas exchange parameters. Irrigated trees showed the same slow activity in the three summer months as the rain-fed trees. For all treatments, net CO₂ assimilation, stomatal conductance and transpiration rates were markedly decreased by environmental conditions (high air temperature and high light intensity) during the summer period. At the partial active growth phase of the Chemlali olive cultivar (September–November), a significant re-increase in all parameters was observed. However, net photosynthesis and stomatal conductance of control plants (T0) were, respectively, 57 and 40% lower than those of plants conducted under milder water contribution (T1). The decrease of physiological activity in irrigated plants during hot and dry (summer time) and cold (winter) seasons was a clear evidence that water supply during such periods will be without a great benefit for photosynthetic activity, and thus growth, if applied under critical conditions inducing the rest phase of the plant. The non-statistically significant slight differences as well in photosynthetic performances activities (Pn, Gs and E rates), as in olive production between the two irrigated treatments will not cover the expenses of water loss when applying irrigation at 66% of ET_c especially in arid region characterized by scant and irregular rainfall. On the light of these results, we can conclude that the irrigation of this species during the vegetative growth phase (in spring and autumn), and stopping it during the olive rest phase (in summer and winter) could be recommended at least under the experimental conditions of this study; and that the contribution of 600 mm of water per year (33% of ET_c) can respond to the needs of the Chemlali olive cultivar in a semi arid region without impairing photosynthetic activity and olive production.     

Quantification of Leaf Water Potential,Stomatal Conductance and Photosynthetically Active Radiation in Rainfed Hazelnut

Hazelnut (Corylus avellana L.) is mostly grown in rainfed condition in Turkey as well as other some countries in the world without more yield reduction. However, there is not enough information about how to give yield without more reduction in rainfed hazelnut orchard. In an endeavor to search this question, quantifications of leaf water potential (LWP), stomatal conductance (g_s) and photosynthetically active radiation (PAR) of hazelnut tree were investigated in rainfed hazelnut orchard in the summer of 2013 and 2014. Additionally, possible effects of those quantifications on rainfed hazelnut trees vs. soil water content (SWC) was investigated. Results of this study exhibited that yearly ET (evapotranspiration) of rainfed hazelnut trees was higher in 2014 than 2013 even though seasonal ET of rainfed hazelnut trees was higher in 2013 than 2014. Hence, yield, LWP and g_s were higher in 2014 than 2013 but PAR and SWC (even all the study season) were mostly higher in 2013 than 2014. Moreover, relationships of LWP, g_s and PAR and responses of LWP, g_s and PAR to SWC were non stronger. These differences could be attributed differences of climate variability such as precipitation and temperature during the observed period throughout the season in the studied years. However, rainfed hazelnut trees may be required supplement irrigation in dry summer, such as year of 2013, to avoid summer water stress. Finally, it can be concluded that hazelnut trees can be grown well and give normal yield for the areas which have about 950 mm precipitation.     

Effectiveness of water pillow irrigation method on yield and water use efficiency on hot pepper (Capsicum annuum L.)

A study was conducted to elucidate the effect of water pillow (WP) irrigation method, a new alternative method to furrow irrigation, on the yield and water use efficiency (WUE) of hot pepper in a semi-arid climatic condition. In this research, treatments used were: (i) WP method and its 7-day irrigation interval (WP₇), (ii) WP method and its 9-day irrigation interval (WP₉), (iii) WP method and its 11-day irrigation interval (WP₁₁) and (iv) furrow irrigation (FI) method and its 5-day irrigation interval (control) were employed. Although the plants were grown under different irrigation methods and interval conditions, there were no statistical differences in yield and biomass of hot pepper plants between FI and WP treatments (P < 0.05). Water use efficiency (WUE) and irrigation water use efficiency (IWUE) values significantly increased with the application of WP irrigation method (P < 0.05). The highest WUE and IWUE values obtained from WP₁₁ treatment in both years. As a result, we conclude that WP method is a way to save water and increase the yield in semi-arid areas where climatic conditions require repeated irrigation in the hot pepper production area.     

An integrated method for irrigation scheduling of potted plants

Hourly meteorological and soil water potential data collected during the summer season on a container crop of 2-year-old plants of Hypericum hidcote were used to develop a methodology that integrates climate-based (AET = ETo × K_c) and soil-based methods (soil water potential measurements by tensiometers) for the automatic control of the irrigation of plants growing in pots. Hourly ETo values were calculated by the CIMIS equation, derived from the Penman formula. Tensiometric data, by a soil-specific tensiometric curve, were transformed into pot water weight and used to estimate actual hourly evapotranspiration (AETt).     

Improved water-use efficiency by deficit-irrigation programmes: Implications for saving water in citrus orchards

Water efficiency is a key concept to solve water-shortage problems in semiarid areas. Deficit irrigation (DI) in many crops has frequently proved to be an efficient tool to optimise water-use efficiency. Three different DI strategies were studied for commercial orchards of mature sweet orange (Citrus sinensis L. Osbeck, cv. Salustiana and cv. Navelina) from 2006 to 2008: sustained deficit irrigation (SDI), regulated deficit irrigation (RDI), and low-frequency deficit irrigation (LFDI) all defined physiologically with stem-water potential thresholds. The experimental research plots were located in the Guadalquivir river basin, SW Spain. The effects of DI treatments on the fruit yield and on the crop-water status, by the integrated stem-water potential (Ψ_int) were analysed. Also, the benefits of DI in terms of agricultural water-use efficiency (WUE_agr) and financial water-use efficiency (WUE_f) were estimated for each irrigation strategy. Different relationships were estimated between these parameters and irrigation and total water applied, in order to establish the best irrigation strategy for different irrigation regimes. Yield and Ψ_int showed significant differences consistent with the water amounts applied, although the crop response was influenced by other parameters such as crop variety and irrigation strategy. In this sense, treatments with similar irrigation rates and Ψ_int resulted in different yield values, evidencing the importance of these factors. Regarding the crop variety, the results showed that cv. Salustiana responded better than cv. Navelina to DI, from the physiological and agricultural perspectives. In terms of water savings, the RDI and LFDI reduced water use by between 1000 and 1250 m³ ha⁻¹, respectively, with similar yields in comparison to the fully irrigated treatment, significantly improving the WUE. Consequently, the WUE_f, and WUE_agr were more strongly affected by deficit-irrigation strategy rather than the total water supplied. Thus, the amount of irrigation water would have a relative importance but other variables such as the irrigation strategy, would decidedly influence prudent water management in semiarid areas.     

中观尺度果园蒸散研究进展

提高水资源利用效率是农业可持续发展的关键。中观尺度的果园水分耗散及其规律研究对于指导果园科学灌溉管理、提高水资源利用效率更具有实践生产意义。着重概述中观尺度植被蒸散的测算方法,及其在果园生态系统蒸散研究的应用。目前,应用于中观尺度果园蒸散测定技术主要有涡度相关技术、波文比-能量平衡技术和闪烁通量仪;广泛应用于果园蒸散估算模型主要有Penman-Monteith模式和Priestley-Taylor模式和作物系数法。最后,展望中观尺度果园蒸散研究的热点问题。     

荔枝不同栽培措施与微喷灌对土壤水分的影响

大棚避雨栽培通过喷灌可控制土壤湿度,地膜覆盖可保持土壤湿度,生草栽培土壤湿度随气候（降水）而变化;对果园进行微喷灌,可节水增效,用水量10 kg·m^-2,喷2～3 h可达45 cm深土壤,各地根据实际情况,一般需喷灌2～4 h,1 m^2树冠灌水用量10～20 kg就能满足荔枝丰产稳产优质高效对水分的需求。     

Water use and fruit yield of mango (Mangifera indica L.) grown in a subtropical Mediterranean climate

Mango (Mangifera indica L.) is one of the most important fruit crops in tropical and subtropical regions worldwide. On the coast of Granada and Malaga (SE Spain), irrigated subtropical fruit species have been introduced and cultivated on terraces with a considerable economic importance as the only European production region. The subtropical fruit production in this zone is possible with intensive irrigation on terraces, which are economically more profitable than traditional rainfed crops (almond and olive), which have been replaced or abandoned. A 2-year monitoring period was conducted using drainage lysimeters to determine the crop coefficients (Kc) and fruit yield in mango (Mangifera indica L. cv. Osteen) orchards. Also, some quality parameters such as titratable acidity, total soluble solids, and vitamin C were evaluated under these conditions. The averaged Kc values of mango trees varied within production cycle of 0.43, 0.67, and 0.63 at flowering, fruit set, and fruit growth, respectively. In this study, the fruit yield under full water requirements (100% ET_C) averaged 24.1 kg tree^?1, amounting to 21.2 kg ha^?1 mm^?1 in terms of water-use efficiency. The quality parameters of the mango fruits harvested in the study area were satisfactory. Thus, this study highlights the need to optimize the irrigation-water use according to actual mango requirements, thereby achieving more sustainable Mediterranean subtropical farming in orchard terraces.     

Seasonal variations in leaf gas exchange of plantain cv. Hartón (Musa AAB) under different soil water conditions in a humid tropical region

The seasonal effect of soil water availability on leaf gas exchange of plantain plants cv. Hartón growing on two different texture soils (loamy and clayey) were evaluated. Soil water deficits corresponded to 48, 24 and 4 days without precipitation. Daily measurements of leaf gas exchange and microclimatic conditions were carried out at 2 h intervals in a humid tropical environment south of Maracaibo Lake, Venezuela. The results show that cv. Hartón is sensitive to conditions of low water deficit on loamy and to a much greater degree on clayey soils. A marked reduction in leaf conductance (g_s) was observed under severe as well as moderate deficit (below 50 mmol m⁻² s⁻¹) on clayey soils. Under low deficit g_s increases to values between 60 and 100 mmol m⁻² s⁻¹. The same trend was observed in plants on loamy soils but higher g_s for all conditions were obtained compared with plants on clayey soil. Stomatal closure produced a reduction of 85 and 55% of total assimilation (A_tot) for severe and moderate deficit in plants on clayey soils, respectively. While plants on loamy soil exhibited a 65 and 35% reduction, respectively. Water use efficiency (WUE) consistently decreased as available soil water decreased on both soil types. Independently of soil water conditions, higher WUE were always obtained for loamy soils. This suggests that cv. Hartón does not have the ability to adjust the CO₂ assimilation to transpiration ratio in order to optimize gas exchange. This evidences the importance of maintaining high conditions of available soil water in order to avoid lower assimilation rates that probably influence negatively on yield and fruit quality.     

Effects of different mulches and irrigation methods on root growth,nutrient uptake,water-use efficiency and yield of strawberry

Field studies were conducted for two consecutive years under sub-temperate climatic conditions at Nauni in district Solan of Himachal Pradesh (30°52′N, 77°11′E 1175 asl) on loamy sand Inceptisols to investigate the effect of different mulches (hay: HM, black polyethylene: BP) on root growth, nutrient uptake, water-use efficiency (WUE) and yield of strawberry cv. Chandler under drip (DI) and surface irrigation (SI) systems. Unmulch (UM) and rainfed treatments were kept as control. Higher soil moisture content was registered under both the mulch materials during entire crop growth period. However, it was greater under BP mulch as compare to HM. The moisture conservation increased by 2.80–12.80% under BP mulch as compared to UM. HM treatment, irrespective of irrigation method increased the minimum soil temperature (2.8–5.2 °C) and reduced the maximum soil temperature (2.7–5.8 °C) as compared to UM. BP mulch increased the minimum soil temperature from 0.4 to 2.5 °C. Application of irrigation moderated the soil (minimum 2.6 and maximum 1.4 °C) temperature. Both the mulch materials were effective in enhancing root growth, nutrient uptake, WUE and yield. Application of mulch enhanced the root growth (63%), nutrient uptake (179.20%), WUE (84.40%) and yield (343%) under DI. However, respective increase under SI was 23.60, 83.80, 109.40 and 219.20%. Under DI, 51% of irrigation water was saved and about 19% higher fruit yield was obtained as compared with SI treatment. Linear regression model could significantly describe the variations in nutrient uptake (N, P and K) and WUE of strawberry under sub-temperate climatic conditions, root mass density was better indicator for estimating nutrient uptake of strawberry.     

Capability of the ‘Ball-Berry’ model for predicting stomatal conductance and water use efficiency of potato leaves under different irrigation regimes

The capability of the ‘Ball-Berry’ model (BB-model) in predicting stomatal conductance (g_s) and water use efficiency (WUE) of potato (Solanum tuberosum L.) leaves under different irrigation regimes was tested using data from two independent pot experiments in 2004 and 2007. Data obtained from 2004 was used for model parameterization, where measurements of midday leaf gas exchange of potted potatoes were done during progressive soil drying for 2 weeks at tuber initiation and earlier bulking stages. The measured photosynthetic rate (A_n) was used as an input for the model. To account for the effects of soil water deficits on g_s, a simple equation modifying the slope (m) based on the mean soil water potential (Ψ_s) in the soil columns was incorporated into the original BB-model. Compared with the original BB-model, the modified BB-model showed better predictability for both g_s and WUE of potato leaves on the parameterization data set. The models were then tested using the data from 2007 where plants were subjected to four irrigation regimes: non-irrigation (NI), full irrigation (FI), partial root-zone drying (PRD), and deficit irrigation (DI) for 3 weeks during tuber initiation and earlier bulking stages. The simulation results showed that the modified BB-model better simulated g_s for the NI and DI treatments than the original BB-model, whilst the two models performed equally well for predicting g_s of the FI and PRD treatments. Although both models had poor predictability for WUE (0.47 < r² < 0.71) of potato leaves, the modified BB-model was able to distinguish the effects of the irrigation regimes on WUE being that the WUE was generally greater for PRD than for FI and DI plants. Conclusively, the modified BB-model is capable of predicting g_s and of accounting for the differential effects of irrigation regimes on WUE of potato leaves. This information is valuable for further simulating potato water use thereby optimizing WUE under field conditions.     

A comparative study of young ‘Thompson Seedless’ grapevines (Vitis vinifera L.) under drip and furrow irrigation. II. Growth, water use efficiency and nitrogen partitioning

The response of 3-year-old grapevines (Vitis vinifera L. cultivar ‘Thompson Seedless’) to furrow and drip irrigation was quantified in terms of water status, growth, and water use efficiency (WUE). Drip irrigation was applied daily according to best estimates of vineyard evapotranspiration while furrow irrigations were applied when 50% of the plant available soilwater content had been depleted. Drip and furrow irrigated vines showed similar water status (midday leaf water potential, Ψ₁) and shoot growth patterns throughout the season. Dry weight partitioning was not significantly different between treatments but root mass was somewhat larger for the furrow than drip irrigated vines. Nitrogen concentrations of the fruit and roots were significantly (P < 0.05) less for the drip irrigated vines when compared with the furrow treatment. Similar WUE (kg water kg⁻¹ fresh fruit wt.) were obtained for both treatments indicating that furrow irrigation was as efficient as drip irrigation under the conditions of this study. The data indicate that drip irrigation may increase the potential for control of vine growth by making vines more dependent on irrigation and N fertilization than furrow irrigation.     

Regulated deficit irrigation in `Clementina de Nules' citrus trees. I. Yield and fruit quality effects

Summary

An experiment on Regulated Deficit Irrigation (RDI) was performed during 1995 and 1996 in a ten year old, drip-irrigated `Clementina de Nules' mandarin orchard in Moncada, Spain. Treatments consisted of a control, where irrigation was applied without restriction during the whole year at 125% ET_lys and RDI treatments where irrigation was reduced to 25% or to 50% of crop evapotranspiration measured by a weighing lysimeter (ET_lys) during one of the following periods: I) flowering and fruit set (spring, 20 March to 3 July in 1995, and 1 April to 1 July in 1996); II) initial fruit enlargement phase (summer, 4 July to 7 August in 1995, and 2 to 28 July in 1996), and III) final fruit growth and maturation phases (end of summer–autumn, 8 August in 1995, and 29 July in 1996 to harvest). An additional treatment, denominated 50%–Year, was irrigated at 50% ET_lys during the whole year. The effects of the treatments on yield and fruit quality in relation to tree water status (pre-dawn (c^a) and midday (c^md) leaf water potential, and their time integral) show large differences in sensitivity to water stress according to phenological stage. The critical periods were the flowering and fruit set phases. The main treatment effects during each period were: In spring, a decline in c^a and c^md with respect to the control of only 0.1 to 0.2 MPa reduced yield by 62% and 28%, respectively for the 25% and 50% levels, due to an increased ``June drop'' and consequent fewer fruit harvested per tree. Final fruit size and quality were similar to those of the control. In summer, RDI treatments allowed water savings between 7 and 14% without affecting yield or fruit quality, providing that a threshold value of c^a–1.3 MPa is not surpassed. In autumn, for the 25% and 50% levels there was a 25 to 11% reduction of fruit size, respectively, with some external peel disorders (creasing) which reduced fruit quality, even at the lower water stress levels reached in the 50% treatment during this period (c^a 20.64 MPa and 20.83 MPa in 1995 and 1996, respectively). In treatment 50%–Year, where water application was 44% of that in the control, minimum c^a values were around 20.6 MPa and 20.8 MPa in 1995 and 1996, respectively. Tree growth was reduced in both seasons and average yield decreased by 17%. Yield loss was due to smaller, not fewer fruit. This treatment increased TSS and acids in the juice, without affecting the maturity index or creasing. However, in the current market situation, this irrigation strategy could be recommended only as a long-term one in cases of very high water prices.