Review
ABSTRACT
Regulated deficit irrigation (RDI) is considered among the best water-saving techniques for supplementing Regulated water to fully achieve the water needs of the plant while maximizing water productivity with little or no substantial decrease in final produce compared to the conventional forms of irrigating crops. The aim of this paper is to review existing RDI approaches used in citrus production as well as plant-water stress indicators. Most of the approaches employed in citrus RDI scheduling require weather data for evapotranspiration calculations which is very technical, laborious and time consuming. Nonetheless, the time domain reflectometer (TDR) offers a simple way of scheduling RDI based on the soil-water status at any given time. This approach will help address the challenges in setting up on-farm synoptic stations to measure weather data to compute evapotranspiration or from using data from weather stations which might be different from the farm conditions. The pros and cons of all the approaches have been discussed and recommended that the TDR can be adopted as an alternative to schedule irrigation in citrus orchards to ensure that plants are supplied with adequate volume of water for maximum water use efficiency.
Key words: Partial root-zone drying, plant-water requirement, plant-water stress, regulated deficit irrigation, remote sensing, subsurface irrigation.
INTRODUCTION
Agriculture, considered as one of the principal consumers of water resources uses more than 70% of the global freshwater (Dalin et al., 2019; Mekonnen and Gerbens-Leenes, 2020). Climate change, urbanization, industrialization, increasing population coupled with high demand for water for other uses bring about irrigation practices occurring under limited water conditions globally (Al-Ghobari and Dewidar, 2018; Kuscu et al., 2013). Irrigation management will focus on maximizing water productivity (yield produced from water used by crops) compared to productivity per unit area (Fereres and Soriano, 2006). To resolve problems of inadequate water supplies for agriculture, Deficit Irrigation (DI) as a management tool should be encouraged to realize the objective of reducing irrigation water use while maintaining or maximizing farmers profit without essentially varying the production area (Fereres et al., 2003; Rosa et al., 2020). Hence, adopting sustainable irrigation practices to ensure maximum efficient water usage efficiency is very important (García-Tejero et al., 2011a). Several studies suggest a shift in the assessment of effectiveness of irrigation schemes from yield per unit acreage to yield per unit water used up (Fereres and Soriano, 2007;Romero et al., 2006). Through effective irrigation, crop vegetative and reproductive development can be effectively managed. Irrigation operators are progressively exploring new ways to improve the WUE of crops through better irrigation management practices. Underpinning new irrigation techniques is an understanding of the associated physiological responses which predicts plant stimulus and support in exploring minimum water needs for economically viable returns (Bacon, 2004).
Deficit irrigation (DI) involves all farm activities aimed at supplying the plant with a volume of irrigation dose lower than the plant’s maximum water needs. In conditions where water availability is limited, DI has been extensively proven to be practicable by increasing water productivity while maintaining or improving plant yield (García-Tejero et al., 2011b; Zou et al., 2021).
In highly-dense orchard plants like apples, peaches, and avocados, where the ratio between asexual and sexual reproduction development is crucial, regulated deficit irrigation (RDI) has been used (Blanco et al., 2019; Vélez-Sánchez et al., 2021). The basic principle of RDI is to withhold irrigation water in the highly vegetative growing stages while fruit development or grain filling is minimum (Blanco et al., 2019; Lurbe, 2013). Normal irrigation regimes are restarted in the future when there is quick fruit development after the water restrictions. The main essence of water deficit is yield optimization per unit volume of irrigation water applied (Fernandes-Silva et al., 2018; Faghih et al., 2019; Blanco et al., 2020). Maximum profit may be achieved by reducing irrigation water used and costs through DI (Trout and Manning, 2019). This study aimed at reviewing existing RDI approaches used in citrus production. Most studies show that RDI schedules in citrus are mainly based on citrus evapotranspiration needs rather than considering the prevailing soil moisture content at any given time.
Nonetheless, water availability for plant optimum growth is determined by several factors including soil, weather, plant and other environmental conditions (de Jong van Lier, 2014). Hence, there is the need to seek alternative irrigation management techniques not solely dependent based on the plant’s full crop water requirements (ETc) replacement but rather the prevailing soil water conditions.
DEFICIT IRRIGATION
Definition and approaches to DI in citrus
DI is defined as any agronomic water management system or irrigation practice whereby plants are supplied with volumes of irrigation water below the full plant-water requirement or evapotranspiration needs provided by stored soil water, rainfall, and irrigation for optimum plant growth throughout the entire farming period (Chai et al., 2016). The principal idea underlying this method basically is by reducing the amount of irrigation water applied, positively enhance the crop’s stimulus towards an appreciable water stress level, increase the crop WUE and further reduce the volumes of water applied on the field (García-Tejero et al., 2011a; Tabatabaei et al., 2017). Even though there are no standardized water-stress levels assigned to plant-water relations, Chai et al. (2016)classified plant-water stress level using these following water content of the soil at field capacity as shown in Table 1.
Forms of RDI under citrus cultivation
Recently, water saving techniques like RDI has been adopted in most citrus growing orchards. RDI is mostly implemented on the field in the form of either growth stage-based DI or partial root-zone drying DI (Chai et al., 2016; Kadyampakeni et al., 2018). Table 2 shows the main approaches to RDI, their advantages, disadvantages and period of water application.
CITRUS IRRIGATION
Water scarcity in citrus production
Water availability is essential for crop production. Wright (2000)reported that mature citrus trees use about 64 and 511 L of water daily in winter and summer, respectively. Swain (2012)also indicated that matured citrus plant utilize more than 190 L of water in a day. These clearly show that citrus trees require much water for development and optimal production. Nonetheless, the increasing demand for water for domestic, industrial and other commercial purposes poses serious threat to the availability of water for agriculture. This predicts a great decrease regarding the availability of water resources needed for irrigating crops for increased food security globally and hence the necessity to improve on irrigation approaches which permit farmers to use less water with the minimum possible effect on yield. Insufficient water supply has several effects on citrus crop production such as peel cracking, reduced fruit size and quality, reduced titratable acids and lower economic returns for the farmer (Saitta et al., 2021).
Citrus crop critical periods
In citrus, the flowering stage is considered very critical and hence moderate water stress during this phenological period may reduce the number of fertilized ovules and an increase in fruit drop (June fruit drop) reduced number of fruits and subsequently compromising, yield (García-Tejero et al., 2010;Saitta et al., 2021). Other phases in fruit development are similarly regarded as extremely critical to deficit irrigation. Additional water stress on citrus trees in last stage of fruit development and ripening may lead to a decrease in produce resulting from the decreases in fruit sizes as well as peel creasing and cracking (González-Altozano and Castel, 1999; Pérez-Pérez et al., 2009; García-Tejero et al., 2010;Li and Chen, 2017; Saitta et al., 2021). The most suitable time to apply water stress in citrus is the time following “June fruit-drop”. This is because at the end of water deficit, fruits can grow faster when irrigation is brought back to the initial volume applied than those fruits under normal irrigation conditions (Mitchel and Chalmers, 1982; Chalmers, 1986;González-Altozano and Castel, 1999). Cohen and Goell (1988)and González-Altozano and Castel (2000)further indicated that deficit irrigation inhibited fruit development in terms of size though there was continuous accumulation of dry matter but after irrigation was restored, a counter-balance of fruit development ensued permitting fruits to grow quicker compared to fruits on the well-irrigated plants, and consequently attaining the same final size. Once RDI approaches are used during summer, there is the need to return irrigation volume to original volume (dose) satisfactorily prior to harvesting so as to permit a probable compensatory fruit growth. In July-August, when ‘Clementina de Nules’ in Valencia were subjected to moderate water-stress (that is irrigating up to only 50% of full ETc.), there was no substantial reduction in yield and fruit size. However, when citrus trees were severely water-stressed during summer there was reduced tree development and final fruit size but the total soluble solids increased (González-Altozano and Castel, 1999).
Effects of deficit irrigation on citrus yield
In fruit crops the main effect of DI is decreased vegetative growth (Lurbe, 2013; Blanco et al., 2020), affecting mostly the extension of sprouts and new branches (Hsiao, 1973, 1993; Lurbe, 2013). According to Hsiao et al. (1976)and Lisar et al. (2012), this decrease in foliage growth is an adaptive mechanism to plant-water stress because less plant foliage leads to low plant radiation interception and subsequently a decrease in water loss by transpiration. Wright (2000) also observed rolling-up of the outer canopy of citrus trees when subjected to moderately-to-severe water-stressed environments in order to minimize solar radiation interception. Reduced growth is observed in the main trunks and branches of deficit irrigated trees resulting to smaller canopy sized trees. Subjecting lemons however, to reasonable water restriction did not reduce branch or sprout development (Domingo, 1994;Lurbe, 2013). Some studies have recorded decreased root growth as an effect of DI on plant roots resulting from less available soil-water (Landsberg and Jones, 1981; Bevington and Castle, 1985; Lurbe, 2013). Kramer and Boyer (1995), however, argued that this growth reduction at the root zone is generally lower than what is observed in the aerial plant parts leading to an increase in the root-to-shoot ratio leading to an adequate water delivery to the leaves and fruits (Syvertsen, 1985; Lurbe, 2013). Crop sensitivity to a period of water restriction is a variable of the duration and intensity of the water deficit regimes (Fereres and Soriano, 2007). Managing water stress effectively is important for a successful RDI application: in the absence of accurate and reasonable water stress parameters, RDI might not be appropriate. This is because plant responsiveness to a certain water stress condition compared to the possible evapotranspiration may lead to varied degrees of crop water stress depending on the soil, environment and plant endogenic characteristics. Exceeding the maximum plant water stress value generally decreases the ultimate fruit size and farm financial returns. It is therefore prudent that when applying RDI strategies, one must regularly monitor the level of plant water in order not to exceed the acceptable documented values for various plant species (Lurbe, 2013).
CITRUS PLANT-WATER STRESS INDICATORS
García-Orellana et al. (2007)and González-Dugo et al. (2012)suggested the usage of plant-based parameters to monitor the crop water condition to know if plants have attained the required state of stress before the application of any successful RDI strategies. The most frequently used methods to study the water condition in fruit trees and other woody-plants are to measure the stem-water potential and stomatal conductance (Fernández, 2017). These approaches may be time-consuming, arduous, and requires manual operations (Romero-Trigueros et al., 2019). Lurbe (2013)emphasized that due to the challenges posed by these ‘classical’ approaches in detecting plant-water stress conditions, there is need to research into alternative ways which will do away with the challenges caused during the use of these ‘classical’ methods stated earlier.
Stem water potential (Ys)
The most widely used approach in studying the plant- water relations in fruit trees is to measure the stem-water potential (Ys) with the pressure chamber (Scholander et al., 1965; Levin, 2019). Ys is considered to be very responsive to high irrigation stress compared to leaf water potential owing to its accuracy in determining crop water stress in some types of fruit trees species owing to the rapid response to irrigation schedules (Garnier and Berger, 1985; Naor, 2000, 2004). Ys measures the potential energy which the vascular bundles use to retain water within the xylem tissues. Conventionally, plants grown in less humid soils tend to exhibit lower Ys compared to well-watered plants (González-Dugo et al., 2012). Environmental or endogenous factors, non-automation, laborious measurement coupled with low water availability are some of the disadvantages of using stem water potential in monitoring citrus water conditions (Lurbe, 2013; Romero-Trigueros et al., 2019). Figure 1 shows a picture of a Pressure chamber.
Stomatal conductance (gs)
Though laborious when used to determine plant water stress, gs measurement shows an advantage over Ys because of its non-destructive nature hence measurements can be done several times on the same leaves of one specific tree. Similar to Ys, gs is very responsive to less available soil water making less watered tress to generally possess less gs values compared to trees that are irrigated. Citrus trees are considered mesophytes with leaves exhibiting xeromorphic characteristics with most of the stomata found underside of the leaves whereas the upper surface is overlaid with thick waxlike cuticle that subdues cuticular transpiration (Spiegel-Roy and Goldschmidt, 1996;Carr, 2014). This makes citrus leaves to have lesser gs values compared with trees like almond, persimmon, or pistachio in similar soil-water environments. Measurement of gs depends on prevailing soil-moisture content, solar radiation, temperature, air vapor-pressure deficit (VPD), leave age, etc. (Jones, 1983). Oguntunde et al. (2007) and Villalobos et al. (2009)recounted that VPD plays an essential role in regulating transpiration in well-irrigated citrus plants hence citrus have reduced gs values in response to high VPD. Figure 2 shows the use of a potable Porometer to measure stomatal conductance in a leaf.
Sap flow
Measuring of sap flow is vital for studying plant-water relations in properly irrigated as well as highly stressed plants because it provides an exact approximation of water flow in plants (Smith and Allen, 1996). Several procedures are employed to measure sap flow in trees based on various approaches but the frequently used methods are by the use of heat pulse to trace sap flow (?ermák et al., 2004)and it has worked for several years (Lurbe, 2013). Some new methods formulated to quantify sap flow under varied experimental conditions include the Trunk-Sector Heat Balance (THB), Heat Dissipation (HD), Stem Heat Balance (SHB), Green’s Heat Pulse Velocity (HPV), Calibrated-Average-Gradient methods (CAG), among others (Testi and Villalobos, 2009; Fernández et al., (2008);Lurbe, 2013). Most citrus RDI trials performed have calculated water savings gained as the basis of water applied but not emphasizing the exact approximation of tree transpiration. Transpiration in plants is dependent on both available soil water as well as evaporation needs. Valancogne et al. (1997) andFernández et al. (2008) in the last few decades have described relative transpiration (that is, the fraction of sap flow in highly stressed and highly irrigated trees) as a water-stress parameter. Furthermore, additional indicators obtained during sap flow experiments might be used to identify water stress. In highly stressed olive trees, Fernández et al. (2001) and Nadezhdina et al. (2007)observed a slight transformation in the sap-velocity profile nearer to the cambium compared with highly irrigated trees. The authors proposed the likelihood of employing the sap flow ratio in the inner/outer xylem regions as a water stress parameter which could be used in automated irrigation-control systems. López-Bernal et al. (2010)found than in olive trees, there was a rise in the night-to-day sap flow ratio (N/D index) when the soil dried up signifying that the N/D index may be good water stress indicator. Figure 3 shows how the SFM1 Sap flow meter is used to measure transpiration or sap flow in plants.
Canopy temperature (Tc)
Plants in soil water-stressed conditions often have reduced stomatal conductance, thus minimizing the transpiration rate and hence an increase in leaf temperature. A very good plant-water stress parameter is obtained through estimating the ultraviolet radiations emanating from the tree cover (Jones, 1999; Merlot et al., 2002; Jones et al., 2002). Jones et al. (2009)observed that stomatal openings may be affected by several factors including highly water stressed soil, endogenous tree factors, biotic conditions (e.g. pests and diseases) as well as other environmental conditions like emerging radiation, air temperature, and wind. Additionally, tree morphology (that is canopy shape and leaf size) and other mechanisms regulating plant transpiration can directly affect canopy temperature (Scherrer et al., 2011).
Another technique for measuring the Tc is via thermal remote sensing. Thermal remote sensing could be applied to measure a wider crop coverage particularly through thermal imaging (Jones, 2004; Drechsler et al., 2019). Thermographic cameras mounted on airborne platforms or hand-operated cameras mounted on tripods platforms, or cranes may be used to acquire images (Möller et al., 2007; Berni et al., 2009; Romero-Trigueros et al., 2019)as seen in Figure 4. Several images can be acquired through automation to determine the mean Tc of (Fernández, 2017)and speeded with methods similar to what before the reference (Fernandez, 2017 ; Jiménez-Bello et al. (2011)established for subsequently analyzing the images acquired, allowing the images obtained from each tree to be analyzed in the absence of the operator, thereby reducing time wastage (about 16 min/image) compared to the manual method. Fuchs (1990)and González-Dugo et al. (2012)also suggested that the intra-crown standard deviation measurement can indicate the presence of water shortage in plants. González-Dugo et al. (2012)found in almonds an increasing variability of Tc in fully irrigated trees while Tc variability diminished when there was mild to severe water-stress. Intra-canopy variations in Tc, every single tree for analysis from a single operator however, did not affect water status in other woody plants like grapevines (Grant et al., 2007; Möller et al., 2007). Hence, further research should be conducted in different tree crops to assess the possibility of making intra- canopy Tc variations a good parameter to monitor plant-water conditions.
Remote sensing in water stress detection
Recently remote sensing is used to study crop drought, the dangers arising from forest and grassland fires, crop cultivation as well as changes in land-usage (Zhang et al., 2010). Through remote sensing, spatial and spectral imagery data can be obtained and characterized for drought, diseases in crops and insect invasion at diverse temporal resolutions (Lan et al., 2017). Vegetation water content estimated through remote sensing techniques can offer significant inferences on the vegetation’s physiological state (Peñuelas et al., 1994; Yi et al., 2013), decision in agricultural irrigation practices (Zhang et al., 2012; Yi et al., 2013, 2014), and assessment on plant-drought conditions (Cohen, 1991; Mirzaie et al., 2014). Moreover, remote sensing may be successfully used when characterizing vegetation water status, precisely reflecting the physiology of that vegetation experiencing high stress, quickly identifying water scarcity while instantly adopting good irrigation practices (Zhang et al., 2012; Yi et al., 2014; Cao et al., 2015). Sullivan et al. (2007)studied the response of cotton to water deficit and crop residue management by using a cheap unmanned aerial vehicle (UAV) fitted with a thermal infrared sensor which showed that thermal infrared emittance showed a positive responsiveness to canopy response in relation to measurements from ground tools and hence suggested that images acquired by thermal infrared at low-altitude UAV can be employed to control within-season canopy stress.
Remote sensing practices have successfully been used to study vegetation water conditions or crop water stress on a dynamic multi-scale and instantaneous observation; however, there are different views on the most appropriate technique among the water content indicators to employ to remotely study crop water stress levels. The main strengths and weaknesses of the procedures used to study plant-water status are presented in Table 3 below.
CITRUS WATER REQUIREMENTS
Calculating citrus water requirements
Doorenbos and Pruitt (1977) and Allen et al. (1998) estimated citrus water requirements (ETc.) as follows:
where ETo = reference evapotranspiration, Kc = the crop coefficient.
ETo is the rate at which “an extensive surface of green, well-watered grass of uniform height, actively growing and completely shading the ground evaporates water” (FAO-56 method). The values of ETo are depended on the prevailing climatic conditions of the study area and can be estimated by other approaches from available climatological data, with the FAO-Penman-Monteith method being the most commonly used (Allen et al., 1998).
Kc = the crop coefficient (the ratio between ETc and ETo) which differs with the definite crop features: type of plant, developmental period, plant size, and farm routines as well as loss of water from the soil).
Some experiments reported single annual Kc values for citrus trees (Grieve, 1989; Grismer, 2000), however, different experiments have proven that within a given growing season Kc values can vary. Castel et al. (1987)and Castel (1997)in Valencia showed varying Kc seasonal values when determining the monthly Kc values in both surface irrigated matured orange plantations as well as a drip-irrigated ‘Clementina de Nules’ tree planted in an accurate weighing lysimeter. Villalobos et al. (2009) explained that the differences in the results obtained by Castel and other related studies were as a result of the changes in soil evaporation situations and canopy ground cover ratio (GC) of crops, hence the necessity to measure transpiration and soil evaporation separately. Villalobos et al. (2009)subsequently proposed using transpiration models in calculating Kc values as a function of specific variables to minimize the repetition of experiments in diverse environments. Villalobos et al. (2009)then developed a direct connection for the citrus transpiration coefficient (Kp) and GC (from less than 0.01 to almost 0.80) that could also calculate citrus transpiration as:
However, Castel (2000) in his work, related Kc and GC, using a quadratic equation as:
Scheduling regulated deficit irrigation based on continuous monitoring of soil-water content within the soil profile
An alternative to applying RDI treatments is by the continuously the plant-water status using a soil moisture sensor (e.g., Time-Domain Reflectometer (TDR) and Frequency Domain Reflectometer (FDR)). The TDR/FDR readings measure the prevailing soil-water condition as a percentage volume of soil water content at field capacity. The TDR measures soil water indirectly by converting the travel time taken by electromagnetic waves (electronic pulse) in a waveguide (probe) sent into a porous medium (soil) for which the volumetric water content (θv) estimate is needed. The soil θv is then determined from the dielectric constant, k of the soil (Evett and Heng, 2008;Abdullah et al., 2018). The dielectric constant, k, has a minimum value of 1 in vacuum and 80 as in water which makes it highly possible for its use to measure θv. The velocity at which the electromagnetic wave moves along the conductors and through the soil is reduced as the dielectric constant, k, of the soil becomes high. Hence, increasing the water content increases the soil’s dielectric constant, k, and subsequently increases the travel time of the electromagnetic wave (Abdullah et al., 2018).
The automation, accuracy, ease of use and non-destructive nature of the TDR in measuring θv makes it a useful tool to monitor soil moisture content (Ihuoma, 2020). The TDR has been successfully used in potted experiments to monitor soil water content. Alordzinu et al. (2021)used the TDR (IMKO® Trime-Pico HD2 64) to successfully monitor and schedule irrigation in tomato grown in pots under greenhouse conditions. Additionally, Schumann and Waldo (2017)successfully used the TDR (Acclima®) to monitor the soil water content and schedule irrigation in hydroponically potted Tango citrus trees in Lake Wales, Florida as seen in Figure 5 below.
Measuring soil water content with the TDR/FDR shows a strong correlation with the values obtained when the gravimetric method of measuring the θv is used. This makes the use of these devices an option that can be used alone when measuring soil water content both in the laboratory and the field. Previous studies have shown strong correlation values (R2) above 0.85 for TDR/FDR soil-water measurements and gravimetric method shown in Table 4.
Notwithstanding the pros of using the TDR, the TDR has a few setbacks including high cost of purchasing, repairing and installing of sensors to cater for larger fields. Furthermore, TDR accuracy reduces in soils with high water content (Abdullah et al., 2018).
In scheduling irrigation with the TDR, first irrigate all the plants with equal volumes of water and allow them to stay within the soil for some time interval (depletion time). Monitor and estimate the reduction in field capacity (FC) and manageable allowable depletion (MAD) status of the soil using the TDR. The final soil moisture content at wilting point is determined using the TDR and compared with the initial field capacity determined, find a relationship between the initial estimated FC and TDR readings. The difference in water estimated in the laboratory using the gravimetric method. Based on the differences determined, find a relationship between the initial estimated FC and TDR readings. The difference in water amount obtained will be supplied to the soil to maintain its FC for optimum plant use. Hence, the plant is irrigated with the volume of water used up anytime the TDR readings show a reduction in the available volume of soil water at any particular time.
CONCLUSION
This review highlighted the feasibility of using the TDR as another alternative to schedule RDI in citrus by monitoring the prevailing moisture content of the soil rather than the evapotranspiration needs of citrus. Since availability of fresh water for agriculture is increasingly becoming scarce, it is prudent to adopt this approach of implementing RDI in order to ensure the sustainability of citrus production by optimizing water use efficiency.
CONFLICT OF INTERESTS
The authors have not declared any conflict of interests.
REFERENCES
Abdullah NHH, Kuan NW, Ibrahim A, Ismail BN, Majid MRA, Ramli R, Mansor NS (2018). Determination of soil water content using time domain reflectometer (TDR) for clayey soil, in: AIP Conference Proceedings 2020. pp. 1-7. |
|
Ahmadi SH, Andersen MN, Plauborg F, Poulsen RT, Jensen CR, Sepaskhah AR, Hansen S (2011). Effects of irrigation strategies and soils on field grown potatoes: Gas exchange and xylem [ABA]. Agricultural Water Management 97(10):1486-1494. |
|
Al-Ghobari HM, Dewidar AZ (2018). Integrating deficit irrigation into surface and subsurface drip irrigation as a strategy to save water in arid regions. Agricultural Water Management 209:55-61. |
|
Allen RG, Pereira LS, Raes D, Smith M (1998). Crop evapotranspiration: Guidelines for computing crop water requirements (No. 56), Irrigation and Drainage. Rome, Italy. |
|
Alordzinu KE, Li J, Appiah SA., AL-Aasmi A, Blege PK, Afful EA (2021). Water stress affects the physio-morphological development of tomato growth. African Journal of Agricultural Research 17(5):733-742. |
|
Bacon MA (2004). Water Use efficiency in Plant Biology. Journal of Biological Sciences 1:122-129. |
|
Berni JAJ, Zarco-Tejada PJ, Sepulcre-Cantó G, Fereres E, Villalobos F (2009). Mapping canopy conductance and CWSI in olive orchards using high resolution thermal remote sensing imagery. Remote Sensing of Environment 113(11):2380-2388. |
|
Bevington KB, Castle WS (1985). Annual root growth pattern of young citrus trees in relation to shoot growth, soil temperature, and soil water content. Journal of the American Society for Horticultural Science 110(6):840-845. |
|
Blanco V, Blaya-Ros PJ, Torres-Sánchez R, Domingo R (2020). Influence of Regulated Deficit Irrigation and Environmental Conditions on Reproductive Response of Sweet Cherry Trees. Plants 9:1-17. |
|
Blanco V, Torres-Sánchez R, Blaya-Ros PJ, Pérez-Pastor A, Domingo R (2019). Vegetative and reproductive response of 'Prime Giant' sweet cherry trees to regulated deficit irrigation. Scientia Horticulturae 249:478-489. |
|
Cao Z, Wang Q, Zheng C (2015). Best hyperspectral indices for tracing leaf water status as determined from leaf dehydration experiments. Ecological indicators 54:96-107. |
|
Carr MKV (2014). Fruit crops, in: Advances in Irrigation Agronomy. Cambridge University Press, New York, p. 78. |
|
Castel JR (1997). Evapotranspiration of a drip-irrigated clementine citrus tree in a weighing lysimeter. International Symposium on Irrigation of Horticultural Crops 449 (pp. 91-98). |
|
Castel JR, Bautista I, Ramos C, Cruz G (1987). Evapotranspiration and irrigation effeciency of mature orange orchards in Valencia (Spain). Irrigation and Drainage systems 1(3):205-217. |
|
?ermák J, Ku?era J, Nadezhdina N (2004). Sap flow measurements with some thermodynamic methods, flow integration within trees and scaling up from sample trees to entire forest stands. Trees 18(5):529-546. |
|
Chai Q, Gan Y, Zhao C, Xu HL, Waskom RM, Niu Y, Siddique KHM (2016) . Regulated deficit irrigation for crop production under drought stress. A review. Agronomy for Sustainable Development 36(1):3. |
|
Chalmers DJ (1986). Research and progress in cultural systems and management in temperate fruit orchards. Acta Horticulturae 106:215-226. |
|
Cohen A, Goell A (1988). Fruit Growth and Dry Matter Accumulation in Grapefruit During Periods of Water Withholding and After Reirrigation. Functional Plant Biology 15(5):633-639. |
|
Cohen WB (1991). Temporal versus spatial variation in leaf reflectance under changing water stress conditions. International Journal of Remote Sensing 12(9):1865-1876. |
|
Dalin C, Taniguchi M, Green T (2019). Unsustainable groundwater use for global food production and related international trade. Global Sustainability 2:1-11. |
|
de Jong van Lier Q (2014). Water Availability to Plants BT - Application of Soil Physics in Environmental Analyses: Measuring, Modelling and Data Integration, in: Teixeira, W.G., Ceddia, M.B., Ottoni, M.V., Donnagema, G.K. (Eds.), . Springer International Publishing, Cham, pp. 435-452. |
|
Domingo R (1994). Respuesta del limonero Fino al riego deficitario controlado. Aspectos fisiológicos. Tesis Doctoral. Universidad de Murcia. 237pp. Universidad de Murcia. |
|
Doorenbos J, Pruitt WO (1977). Guidelines for predicting crop water requirements (No. 2), FAO Irrigation and Drainage Paper, 24. Rome, Italy. |
|
Drechsler K, Kisekka I, Upadhyaya S (2019). A comprehensive stress indicator for evaluating plant water status in almond trees. Agricultural Water Management 216:214-223. |
|
Evett S, Heng LK (2008). Conventional Time Domain Reflectometry Systems, in: Evett, S. (Ed.), Field Estimation of Water Content (A Practical Guide to Methods, Instrumentation and Sensor Technology). International Atomic Energy Agency, Vienna-Austria. pp. 55-72. |
|
Faghih S, Zamani Z, Fatahi R (2019). Effects of deficit irrigation and kaolin application on vegetative growth and fruit traits of two early ripening apple cultivars. Biological Research 52:1-12. |
|
Fereres E, Goldhamer DA, Parsons LR (2003). Irrigation water management of horticultural crops, in: Hort Science. pp. 1036-1042. |
|
Fereres E, Soriano MA (2007). Deficit irrigation for reducing agricultural water use. Journal of experimental botany 58(2):147-159. |
|
Fernandes-Silva A, Oliveira M, Paço TA, Ferreira I (2018). Deficit Irrigation in Mediterranean Fruit Trees and Grapevines: Water Stress Indicators and Crop Responses., in: Ondrašek, G. (Ed.), Irrigation in Agroecosystems. IntechOpen, pp. 52-85. |
|
Fernández JE (2017). Plant-based methods for irrigation scheduling of woody crops. Horticulturae. |
|
Fernández JE, Green SR, Caspari HW, Diaz-Espejo A, Cuevas MV (2008). The use of sap flow measurements for scheduling irrigation in olive, apple and Asian pear trees and in grapevines. Plant Soil 305: 91-104. |
|
Fernández JE, Palomo MJ, Díaz-Espejo A, Clothier BE, Green SR, Girón IF, Moreno F (2001). Heat-pulse measurements of sap flow in olives for automating irrigation: Tests, root flow and diagnostics of water stress. Agricultural Water Management 51:99-123. |
|
Fuchs M (1990). Infrared measurement of canopy temperature and detection of plant water stress. Theoretical and Applied Climatology 42(4):253-261. |
|
García-Orellana Y, Ruiz-Sánchez MC, Alarcón JJ, Conejero W, Ortuño MF, Nicolás E, Torrecillas A (2007). Preliminary assessment of the feasibility of using maximum daily trunk shrinkage for irrigation scheduling in lemon trees. Agricultural Water Management 89(2):167-171. |
|
García-Tejero I, Durán ZVH, Muriel JL, Rodríguez PCR (2011). Water and sustainable agriculture., in: Springer Briefs in Agriculture. |
|
García-Tejero I, Durán-Zuazo VH, Muriel-Fernández JL, Martínez-García G, Jiménez-Bocanegra JA (2011). Benefits of low-frequency irrigation in citrus orchards. Agronomy for sustainable development 31(4):779-791. |
|
García-Tejero I, Romero-Vicente R, Jiménez-Bocanegra JA, Martínez-García G, Durán-Zuazo VH, Muriel-Fernández JL (2010). Response of citrus trees to deficit irrigation during different phenological periods in relation to yield, fruit quality, and water productivity. Agricultural Water Management 97(5):689-699. |
|
Garnier E, Berger A (1985). Testing water potential in peach trees as an indicator of water stress. Journal of Horticultural Science 60(1):47-56. |
|
González-Altozano P, Castel JR (2000). Effects of Regulated Deficit Irrigation on "Clementina de Nules" citrus trees growth, yield and fruit quality. The Journal of Horticultural Science and Biotechnology 75(4):388-392. |
|
González-Altozano P, Castel JR (1999). Regulated deficit irrigation in 'Clementina de Nules' citrus trees. I: Yield and fruit quality effects. The Journal of Horticultural Science and Biotechnology 74:706-713. |
|
González-Dugo V, Zarco-Tejada P, Berni JAJ, Suárez L, Goldhamer D, Fereres E (2012). Almond tree canopy temperature reveals intra-crown variability that is water stress-dependent. Agricultural and Forest Meteorology 154:156-165. |
|
Grant MO, Tronina L, Jones HG, Chaves M (2007). Exploring thermal imaging variables for the detection of stress responses in grapevine under different irrigation regimes. Journal of Experimental Botany 58(4):815-825. |
|
Grieve AM (1989). Water use efficiency, nutrient uptake and productivity of micro-irrigated citrus. Australian Journal of Experimental Agriculture 29(1):111-118. |
|
Grismer ME (2000). Long-term evapotranspiration from coastal avocado citrus orchard. Journal of Irrigation and Drainage Engineering 126(1):1-7. |
|
Hsiao TC (1993). Growth and productivity of crops in relation to water stress. Acta Horticulture 335:137-143. |
|
Hsiao TC (1973). Plant responses to water stress. Annual Review of plant Physiology 24(1):519-570. |
|
Hsiao TC, Acevedo E, Fereres E,Henderson DW (1976). Water stress, growth and osmotic adjustmen. Philosophical Transactions of theRoyal Society of London. B, Biological Sciences 273(927):479-500. Ihuoma SO (2020). The use of spectral reflectance data to assess plant stress and improve irrigation water management. McGill University, Montreal. |
|
Iqbal R, Raza M, Toleikiene M, Ayaz M, Hashemi F, Habib-ur-Rahman M, Zaheer M, Ahmad S, Riaz U, Ali M, Aslam M, Haider I (2020). |
|
Partial root-zone drying (PRD), its effects and agricultural significance: A review. 2020). Bulletin of the National Research Centre 44. |
|
Jiménez-Bello MA, Ballester C, Castel JR, Intrigliolo DS (2011). Development and validation of an automatic thermal imaging process for assessing plant water status. Agricultural Water Management 98(10):1497-1504 |
|
Jones HG (2004). Irrigation scheduling: Advantages and pitfalls of plant based methods. Journal of Experimental Botany 55(407):2427-2436. Jones HG (1999). Use of infrared thermometry for estimation of stomatal conductance as a possible aid to irrigation scheduling. Agricultural and Forest Meteorology 95(3):139-149. |
|
Jones HG (1983). Estimation of an effective soil water potential at the root surface of transpiring plants. Plant, Cell and Environment 6(8):671-674. |
|
Jones HG, Serraj R, Loveys BR, Xiong L, Wheaton A, Price AH (2009). Thermal infrared imaging of crop canopies for the remote diagnosis and quantification of plant responses to water stress in the field. Functional Plant Biology 36(11):978-989. |
|
Jones HG, Stoll M, Santos T, de Sousa C, Chaves MM, Grant OM (2002). Use of infrared thermography for monitoring stomatal closure in the field: application to grapevine. Journal of Experimental Botany 53(378):2249-2260. |
|
Kadyampakeni DM, Strauss S, Schumann A (2018). Citrus Water Use and Root Density Patterns as Influenced by Citrus Greening and Regulated Deficit Irrigation under Greenhouse Conditions, in: 131st Annual Meeting of the Florida State Horticultural Society,. Florida State Horticultural Society, Fort Lauderdale, Florida, USA, pp. 70-76. |
|
Kramer PJ, Boyer JS (1995). Water relations of plants and soils. Academic Press, New York. |
|
Kuscu H, Karasu A, Oz M, Demir OA, Turgut I (2013). Effect of irrigation amounts applied with drip irrigation on maize evaporation, yield, water use efficiency and net return in a sub-humid climate. Turkish Journal of Field Crops 18(1):13-19. |
|
Lan YB, Chen SD, Fritz BK (2017). Current status and future trends of precision agricultural aviation technologies. International Journal of Agricultural and Biological Engineering 10(3):1-17. |
|
Landsberg JJ, Jones HG (1981). Apple orchards. Water deficits and plant growth, 6th ed. Academic Press, London. |
|
Levin AD (2019). Re-evaluating pressure chamber methods of water status determination in field-grown grapevine (Vitis spp.). Agricultural Water Management 221:422-429. |
|
Li J, Chen J (2017). Citrus Fruit-Cracking: Causes and Occurrence. Horticultural Plant Journal 3(6):255-260. |
|
Lisar S, Motafakkerazad R, Hossain M, Ismail MMR (2012). Water Stress in Plants: Causes, Effects and Responses, in: Ismail, M.M.R., Hasegawa, H. (Eds.), Water Stress. InTech, Rijeka, Croatia, pp. 1-14. |
|
López-Bernal A, Alcántara E, Testi L, Villalobos FJ (2010). Spatial sap flow and xylem anatomical characteristics in olive trees under different irrigation regimes. Tree Physiology 30(12):1536-1544. |
|
Lurbe BC (2013). 'Regulated deficit irrigation in citrus: agronomic response and water stress indicators.' Universidad Politécnica de Valencia, Spain. |
|
Martínez-Gimeno MA, Jiménez-Bello MA, Lidón A, Manzano J, Badal E, Pérez-Pérez JG, Bonet L, Intrigliolo DS, Esteban A (2020). Mandarin irrigation scheduling by means of frequency domain reflectometry soil moisture monitoring. Agricultural Water Management 235 106151. |
|
Mekonnen MM, Gerbens-Leenes W (2020). The Water Footprint of Global Food Production (Review). Water 12:1-12. |
|
Merlot S, Mustilli AC, Genty B, North H, Lefebvre V, Sotta B, Vavasseur A, Giraudat J (2002). Use of infrared thermal imaging to isolate Arabidopsis mutants defective in stomatal regulation. The Plant Journal 30(5):601-609. |
|
Mirzaie M, Darvishzadeh R, Shakiba A, Matkan AA, Atzberger C, Skidmore A (2014). Comparative analysis of diferent uni- and multi-variate methods for estimation of vegetation water content using hyper-spectral measurements. International journal of applied Earth Observation and Geoinformation 26:1-11. |
|
Mitchel PD, Chalmers DJ (1982). The effect of reduced water supply on peach tree growth and yields. Journal of the American Society for Horticultural Science 107:853-856. |
|
Möller M, Alchanatis V, Cohen Y, Meron M, Tsipris J, Ostrovsky V (2007). Use of thermal and visible imagery for estimating crop water status of irrigated grapevine. Journal of Experimental Botany 58(4):827-838. |
|
Nadezhdina N, Nadezhdin V, Ferreira MI, Pitacco A (2007). Variability with xylem depth in sap flow in trunks and branches of mature olive trees. Tree Physiology 27(1):105-113. |
|
Naor A (2004). The interactions of soil-and stem-water potentials with crop level, fruit size and stomatal conductance of field-grown 'Black Amber' Japanese plum. The Journal of Horticultural Science and Biotechnology 79(2):273-280. |
|
Naor A (2000). Midday stem water potential as a plant water stress indicator for irrigation scheduling in fruit trees. Acta Horticulturae 537: 447-454. |
|
Oguntunde PG, Van de Giesen N, Savenige HHG (2007). Measurement and modelling of transpiration of a rain-fed citrus orchard under sub humid tropical conditions. Agricultural Water Management 87(2):200-208. |
|
Peñuelas J, Gamon JA, Fredeen AL, Merino J, Field CB (1994). Reflectance indices associated with physiological changes in nitrogen- and water-limited sunflower leaves. Remote sensing of Environment 48(2):135-146. |
|
Pérez-Pérez JG, Robles JM, Botía P (2009). Influence of deficit irrigation in phase III of fruit growth on fruit quality in 'Lane Late' sweet orange. Agricultural Water Management 96(6):969-974. |
|
Romero-Trigueros C, Gambín JMB, Tortosa PAN, Cabañero JJA, Nicolás EN (2019). Determination of Crop Water Stress Index by Infrared Thermometry in Grapefruit Trees Irrigated with Saline Reclaimed Water Combined with Deficit Irrigation. Remote Sensing 11:3-20. |
|
Romero P, Navarro J, Pérez-Pérez J, García-Sánchez F, Gómez-Gómez A, Porras I, Martínez V, Botía P (2006). Deficit irrigation and rootstock: their effects on water relations, vegetative development, yield, fruit quality and mineral nutrition of Clemenules mandarin. Tree Physiology 26(12):1537-1548. |
|
Rosa L, Chiarelli DD, Rulli MC, Dell'Angelo J, D'Odorico P (2020). Global agricultural economic water scarcity. Science Advances 6(18): 1-10. |
|
Saitta D, Consoli S, Ferlito F, Torrisi B, Allegra M, Longo-Minnolo G, Ramírez-Cuesta JM, Vanella D (2021). Adaptation of citrus orchards to deficit irrigation strategies. Agricultural Water Management 247: 1-13. |
|
Scherrer D, Bader MK, Körner C (2011). Drought-sensitivity ranking of deciduous tree species based on thermal imaging of forest canopies. Agricultural and Forest Meteorology 151(12):1632-1640. |
|
Scholander PF, Hammel HT, Bradstreet ED, Hemmingsen EA (1965). Sap pressure in vascular plants. Science 148(3668):339-346. |
|
Schumann A, Waldo L (2017). Understanding Soil-Moisture Sensor Data. Citrus Industry Magazine 8:1-15. |
|
Shukla A, Pancha H, Mishra M, Patel PR, Srivastava HS, Patel P, Shukla AK (2014). Soil Moisture Estimation using Gravimetric Technique and FDR Probe Technique: A Comparative Analysis. International Journal of Applied and Natural Sciences Applied and Natural Science 8:89-92. |
|
Smith DM, Allen SJ (1996). Measurements of sap flow in plant stems. Journal of Experimental Botany 47(12):1833-1844. |
|
Spiegel-Roy P, Goldschmidt EE (1996). Biology of Citrus. Cambridge University Press. |
|
Sullivan DG, Fulton JP, Shaw JN, Bland G (2007). Evaluating the sensitivity of an unmanned thermal infrared aerial system to detect water stress in a cotton canopy. Transactions of the ASABE 50(6):1963-1969. |
|
Swain S (2012). Growing Citrus in the North Bay. Carlifornia. |
|
Syvertsen JP (1985). Integration of water stress in fruit trees. Hort Science 20:1039-1043. |
|
Tabatabaei SH, Fatahi Nafchi R, Najafi P, Karizan MM, Nazem Z (2017). Comparison of traditional and modern deficit irrigation techniques in corn cultivation using treated municipal wastewater. International Journal of Recycling of Organic Waste in Agriculture 6(1):47-55. |
|
Tanriverdi C, Degirmenci H, Gonen E, Boyaci S (2016). A comparison of the gravimetric and TDR methods in terms of determining the soil water content of the corn plant. Agronomy 59:153-158. |
|
Testi L, Villalobos FJ (2009). New approach for measuring low sap velocities in trees. Agricultural and Forest Meteorology 149(4):730-734. |
|
Thompson RB, Gallardo M, Valdez LC, Fernández MD (2007). Using plant water status to define threshold values for irrigation management of vegetable crops using soil moisture sensors. Agricultural Water Management 88(3):147-158. |
|
Trout TJ, Manning DT (2019). An Economic and Biophysical Model of Deficit Irrigation. Agronomy 111:3182-3193. |
|
Valancogne C, Dayau S, Ferreira Gama MI, Ameglio T, Archer P, Daudet FA, Cohen M (1997). Relations between relative transpiration and predawn leaf water potential in different fruit tree species. International Symposium on Irrigation of Horticultural Crops 449, 423-430. |
|
Vélez-Sánchez JE, Balaguera-López HE, Alvarez-Herrera GJ (2021). Effect of regulated deficit irrigation (RDI) on the production and quality of pear Triunfo de Viena variety under tropical conditions. Scientia Horticulturae (Amsterdam). 278:1-7. |
|
Villalobos FJ, Testi L, Moreno-Perez MF (2009). Evaporation and canopy conductance of citrus orchards. Agricultural Water Management 96(4):565-573. |
|
Wright GC (2000). Irrigating Citrus Trees [WWW Document]. Publ. AZ 1151. Univ. Arizona Coop. Ext. |
|
Wu Y, Zhao Z, Liu S, Huang X, Wang W (2020). Does partial root-zone drying have advantages over regulated deficit irrigation in pear orchard under desert climates? Scientia Horticulturae. 262:1-8. |
|
Yi Q, Wang F, Bao A, Jiapaer G (2014). Leaf and canopy water content estimation in cotton using hyperspectral indices and radiative transfer models. International Journal of Applied Earth Observation and Geoinformation 33:67-75. |
|
Yi Q, xiang, Bao, A. ming, Wang, Q., Zhao, J (2013). Estimation of leaf water content in cotton by means of hyperspectral indices. Computers and Electronics in Agriculture 90:144-151 |
|
Zhang J, Xu Y, Yao F, Wang P, Guo W, Li L, Yang L (2010). Advances in estimation methods of vegetation water content based on optical remote sensing techniques. Science China Technological Sciences 53(5):1159-1167. |
|
Zhang L, Zhou Z, Zhang G, Meng Y, Chen B, Wang Y (2012). Monitoring the leaf water content and specific leaf weight of cotton (Gossypium hirsutum L.) in saline soil using leaf spectral reflectance. European Journal of Agronomy 41:103-117. |
|
Zou Y, Saddique Q, Ali A, Xu J, Khan MI, Qing M, Azmat M, Cai H, Siddique KHM (2021). Deficit irrigation improves maize yield and water use efficiency in a semi-arid environment. Agricultural Water Management 243:1-6. |
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