Extrapolating base-line trunk shrinkage reference equations across olive orchards

1" " Extrapolating base-line trunk shrinkage reference equations across olive orchards 1" . 2" 3" Corell, M.a,*, Girón, I.F.b, Moriana, A.a, Dell’Amico, J.c, Morales, D.c, Moreno, F.b 4" 5" aEscuela Técnica Superior de Ingeniería Agronómica. University of Seville, Carretera 6" de Utrera Km 1, 41013 Sevilla, Spain 7" bInstituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS-CSIC), P.O. Box 8" 1052, E-41080 Sevilla, Spain. 9" c Instituto Nacional de Ciencias Agrícolas, Cuba 10" 11" *Corresponding author: [email protected] Phone: (+34)954487298; Fax: (+34)954486436 12" 13" 14" 15" 16" 17" 18" 19" 20" 2" " Abstract 21" Maximum daily trunk shrinkage is a common measurement in irriation scheduling of 22" fruit trees. But the strong relationship between these measurements and the environment 23" severely limit field applications. Reference baselines are the solution for understanding 24" the influence of environmental conditions. Nevertheless, the extrapolation out of the 25" original conditions is not clear. The aim of this study was to compare several 26" approaches to estimate a reference baseline in an olive orchard where there were no 27" previous data from other seasons. Two orchards, separated 60 m, with different tree 28" density were used. Orchard 1 had greater tree density than orchard 2, though the age and 29" the cultivar were the same. Trunk diameters of both orchards were similar but the crown 30" volume of orchard 2 was slightly lower than orchard 1. The current reference baselines 31" of maximum daily trunk diameter in both orchards were not significantly different 32" between them (p<0.05). In orchard 1, the previous reference baseline was calculated in 33" a 5-year study (the so called multi-seasons approach). The multi-seasons approach was 34" not significantly different in slope but it was in the y-interception to the current 35" reference baselines in both orchards (p<0.05). This approach over-estimated the values 36" in both orchards. Two additional approaches were tested. These latter approaches used 37" data before massive pit hardening to estimate the current reference baseline. One of 38" them used the early data to estimate a complete reference baseline (the so-called early 39" approach). The other (the so-called y-early approach) used the same data only to 40" estimate the y-interception and assumed that the slope was the same as in the multi-41" seasons approach. The early approach under-estimated the value of maximum daily 42" trunk shrinkage. The early-y approach provided a satisfactory estimation of the 43" 3" " reference baseline and improved those obtained with the multi-seasons approach. The 44" limitations and uses in irrigation scheduling are also discussed. 45" 46" Keyword: Irrigation scheduling, plant water status measurements, trunk diameter 47" fluctuations, water relations. 48" 49" 50" 51" 52" 53" 54" 55" 56" 57" 58" 59" 60" 61" 62" 63" 64" 65" 66" 4" " 1. Introduction 67" The Olive (Olea europaea L.) is a traditional rain-fed fruit tree in the Mediterranean 68" basin. In the last 20 years, the intensification of olive cultivation has advanced greatly. 69" These new orchards are irrigated and have higher tree density than traditional ones. The 70" increase in cultivation has coincided with an increase in water demand for other uses 71" (Fereres and Evans, 2006) and this strongly limits the amount of water available for 72" irrigation purposes. 73" Regulated deficit irrigation (RDI) is a common irrigation scheduling technique 74" in fruit trees, which saves water with low or null variations in yield (Behboudian and 75" Mills, 1997; Naor, 2006). When RDI is applied, plant water status measurements are 76" needed to control the intensity of the plant water stress imposed (Fereres and González-77" Dugo, 2009). In deficit irrigation scheduling, techniques of continuous measurement of 78" plant water status allow adequate daily watering for control of water stress level (Ortuño 79" et al., 2010). Trunk diameter fluctuations have been suggested in several fruit trees as a 80" very efficient tool for RDI (i.e. almond, Goldhamer and Fereres, 2004; peaches, 81" Conejero et al., 2011), but not in others such as olive trees (Moriana et al., 2003; 82" Moriana et al., 2010). Trunk diameter fluctuations are a daily cycle of shrinkage (from 83" the beginning of the day) and swelling (from mid-afternoon) which occurs in all plants 84" (Klepper et al., 1971). This daily cycle provides two parameters which are used in 85" irrigation scheduling: maximum daily trunk shrinkage and trunk growth rate. 86" Goldhamer and Fereres (2001) suggested the first approach for irrigation 87" scheduling with a trunk diameter fluctuations parameter. In a young orchard, these 88" authors suggested the comparison with maximum daily diameter to estimate trunk 89" growth. However, although this parameter is presented in several studies (i.e. 90" Goldhamer et al 1999) extrapolation to other locations is not easy. Moriana and Fereres 91" 5" " (2002), in olive trees, reported that maximum daily diameter would be difficult to 92" extrapolate to other conditions and suggested trunk growth rate (the slope of maximum 93" daily diameter) as easier to use in irrigation scheduling. However, only in young olive 94" trees, a good relationship between TGR and temperature has been reported (Pérez-95" López et al., 2008). No strong relationship between either of these parameters and a 96" meteorological variable has been found in mature orchards of any fruit species. This 97" lack of results is probably related to the strong relationship between fruit development 98" and both parameters (olive, Moriana et al., 2003; plum, Intrigliolo and Castel, 2007; 99" olive, Pérez-López et al., 2008). 100" Maximum daily trunk shrinkage is the indicator derived from trunk diameter 101" fluctuations most widely suggested in irrigation scheduling in several fruit trees (Ortuño 102" et al., 2010; Fernández and Cuevas 2010). The increase in maximum daily trunk 103" shrinkage has traditionally been associated with water stress conditions (Ortuño et al., 104" 2010), though it is also strongly related to evaporative demand (Herzog et al., 1995). A 105" reference is therefore needed in order to separate the effect of evaporative demand and 106" soil water deficit. Reference baseline is a simple regression equation that estimates 107" maximum daily trunk shrinkage in fully irrigated conditions from one meteorological 108" parameter. Parameters such as temperature or vapor pressure deficit would provide an 109" estimation of maximum daily trunk shrinkage in fully irrigated conditions and thus 110" irrigation could be scheduled according to the water stress level previously decided. 111" Goldhamer and Fereres (2001) suggested the maximum daily trunk diameter signal, 112" which is the ratio between the measured and the estimated values, as an indicator of 113" water stress level. 114" Previous studies conducted on olive trees have concluded that maximum daily 115" trunk shrinkage is not a reliable water status indicator in moderate water deficit 116" 6" " conditions (Moriana and Fereres, 2002; Moriana et al., 2010; Cuevas et al., 2012). 117" However, Moriana et al (2000) reported a maximum daily trunk shrinkage vs. stem 118" water potential relationship in olives that estimated a decrease in maximum daily trunk 119" shrinkage in severe water deficit conditions. Olive trees are a very drought resistant 120" species, in which severe water stress conditions during massive pit hardening (mid-121" summer) do not affect or only slightly reduce yield (Goldhamer, 1999). A reference 122" baseline would therefore be useful in order to impose such stress conditions during this 123" phenological period. 124" Several authors have reported reference baselines of maximum daily trunk 125" shrinkage in relation to different meteorological data. The most commonly reported are 126" vapour pressure deficit (VPD) and air temperature (amongst others, almond, Goldhamer 127" and Fereres, 2004; lemon, Ortuño et al., 2009; mandarin, Pagán et al., 2008; peach, 128" Conejero et al., 2011; plum, Intrigliolo and Castel, 2007). There are only three studies 129" of olives that estimated a reference baseline (Moriana and Fereres, 2004; Moreno et al., 130" 2006; Moriana et al., 2011). Moriana and Fereres (2004), with one season´s data, 131" suggested VPD as the meteorological variable but without comparison to other 132" meteorological data. Moreno et al (2006), with one season´s data, compared four 133" different meteorological measurements (VPD, temperature, radiation and reference 134" evapotranspiration) and reported that VPD and temperature presented the best 135" agreement with maximum daily trunk shrinkage data. Moriana et al (2011), in a five-136" year study, showed that maximum daily temperature was beteewn others (VPD and 137" temperatures at different time) the best fit with maximum daily shrinkage. These 138" authors also considered that maximum temperature was easier to obtain than VPD and 139" temperature measurements at different time of the day. 140" 7" " One of the main problems in the management of the reference baseline is 141" validation in other places or seasons. In order to eliminate the influence of inter-season 142" changes most studies use data from several seasons (i.e. Ortuño et al., 2009; Conejero et 143" al., 2011; Moriana et al., 2011). However, Goldhamer and Fereres (2004) reported a 144" reference baseline estimated only with the data of the beginning of the irrigation season. 145" The extrapolation of the reference baseline to other places (with different cultivars 146" or/and tree spaces) is more related to factors such as fruit load or tree dimensions and, 147" from our knowledge, there are no studies in the literature. Fruit load has been reported 148" as a significant factor that slightly varied the equations obtained (Intrigliolo and Castel 149" 2007; Conejero et al., 2010; Moriana et al., 2011). However, such differences are small 150" and, in a commercial orchard, fruit load could be not considered (Moriana et al., 2011). 151" The influences of tree age (Moriana and Fereres, 2004) or trunk diameter (Genard et al, 152" 2001; Intrigliolo and Castel, 2006) were also significant. Reference baseline would 153" therefore probably need a previous local calibration. 154" The aim of this study is to compare several approaches to estimating a reference 155" baseline in an orchard where there are no previous data. This reference baseline will be 156" used during the massive pit hardening period. Two approaches use current season data 157" before massive pit hardening. And a third approach uses a previous reference baseline 158" (Moriana et al., 2011), calculated on the same experimental farm, but in an olive 159" orchard with closer tree spacing. 160" 161" 2. Material and Methods 162" The experiment was performed in two orchards during the summer of 2011 at La 163" Hampa, the experimental farm of the Instituto de Recursos Naturales y Agrobiología de 164" Sevilla (IRNAS-CSIC). These orchards are located at Coria del Río near Seville (Spain) 165" 8" " (37º 17’’N, 6º 3’W, 30 m altitude). The sandy loam soil (about 2 m deep) of the 166" experimental site was characterized by a volumetric water content of 0.33 m3 m-3 at 167" saturation, 0.21 m3m-3 at field capacity and 0.1 m3m-3 at permanent wilting point, and 168" 1.30 (0-10 cm) and 1.50 (10-120 cm) g cm-3 bulk density. 169" The two olive orchards (Olea europaea L cv Manzanillo) were irrigated during 170" the previous season with no water limitation. Orchard 1 was 41 years old and the tree 171" spacing was 7 x 5 m. This orchard was the same where the reference baseline of 172" Moriana et al (2011) was calculated, but the trees used in the present study were 173" different. Orchard 2 was also 41 years old and tree spacing was 7 m x 7m. This orchard 174" was beside orchard 1 and separated by around 60 m. The crown volume and trunk 175" diameter of the experimental trees were not significantly different between orchards 176" (p<0.05, Table 1). However, the trees in orchard 2 had markedly lower values of crown 177" volume than orchard 1 (around 25% less) and lower ground cover (orchard 1 40%; 178" orchard 2 24%). The beginning of the massive pit hardening was estimated according to 179" Gijón et al (2010) at day of the year (DOY) 157 in the orchard 1 and 164 in the orchard 180" 2. 181" Pest control, pruning and fertilization practices were those commonly used by 182" growers and no weeds were allowed to develop in the orchard. Irrigation was carried out 183" during the night by drip using one lateral pipe per tree row and five emitters per plant, 184" delivering 8 L h-1 each. Micrometeorological 30 min data, namely air temperature, 185" solar radiation, relative humidity of air and wind speed at 2 m above the soil surface 186" were collected by an automatic weather station located some 40 m from the 187" experimental site. Daily reference evapotranspiration (ETo) was calculated using the 188" Penman-Monteith equation (Allen et al., 1998). 189" 9" " Irrigation requirements were determined as the difference between crop 190" evapotranspiration (ETc) and rainfall. Soil moisture was not considered in the water 191" balance in order to obtain no water stress conditions. ETc was determined according to 192" daily reference evapotranspiration (ETo) and a crop factor based on the time of the year 193" and the percentage of ground area shaded by the tree canopy (Fereres and Goldhamer, 194" 1990). The crop coefficient values (Kc) considered were 0.76 in May, 0.70 in June, 0.63 195" in July and August, 0.72 in September and 0.77 in October (Fernández et al., 2006). The 196" values of the coefficient in relation to the percentage of ground covered by the crop (Kr) 197" were 0.8 in orchard 1 and 0.48 in orchard 2. The values of crop evapotranspiration (ETc) 198" and total amount of applied water (rainfall not included) during the experimental period 199" (from the end of April until the middle September) are shown in Table 2. 200" Trunk diameter fluctuations (TDF) are a daily cycle of shrinkage and swelling. 201" TDF were measured throughout the experimental periods, using a set of linear variable 202" displacement transducers (LVDT) (model DF±2.5 mm, accuracy ±10 µm, Solartron 203" Metrology, Bognor Regis, UK) attached to the main trunk, with a special bracket made 204" of Invar, an alloy of Ni and Fe with a thermal expansion coefficient close to zero 205" (Katerji et al., 1994). Measurements in 6 trees in orchard 1 and 5 trees in orchard 2 were 206" taken every 10 s and the datalogger (model CR10X with AM 416 multiplexer, 207" Campbell Sci. Ltd., Logan, USA) was programmed to report 15 min means. Maximum 208" daily trunk shrinkage (MDS) was calculated as the difference between the maximum 209" daily diameter, which occurs at the beginning of the day, and the minimum daily 210" diameter, which occurs at mid-afternoon (Goldhamer et al., 1999). 211" The determination of the reference baseline supposed fully irrigated conditions. 212" Several parameters were measured in order to establish the water status of the tree (soil 213" moisture, maximum trunk diameter, stem water potential). Soil moisture was measured 214" 16" " rest of seasons (with medium and high yield). Therefore, the multi-season approach 364" could be useful in conditions of significant yield. 365" Although significant yield would be expected an estimation of the reference 366" baseline with current season data and with the local conditions would be a better 367" approach than the multi-season approach. The approach suggested by Goldhamer and 368" Fereres (2004) in almonds (the so-called early approach) was used in this way. 369" However, the early approach was the worst in both orchards (Figs. 3 and 4). These 370" disagreements with the results in almonds of Goldhamer and Fereres (2004) are 371" probably related to the differences between the water relations of both fruit species. The 372" daily cycle of stomatal leaf conductance in full irrigated conditions is not limited by 373" evaporative demand in almond (Marsal and Girona, 1997) while in olive trees there is a 374" reduction at midday (Angelopoulos et al., 1996). Such differences in the daily pattern 375" stomata could suggest different respond to high transpiration conditions. According to 376" the present study, maximum daily trunk shrinkage greater than 400 µm was under-377" estimated with the early approach (Fig. 4). Therefore, the greatest conditions of 378" transpiration likely changed the amount of water that the trunk transferred to the 379" transpiration stream. In olive, the tree could increases the amount of water from the 380" trunk more than in almond and then maximum daily shrinkage was higher than 381" expected, Such increase could be related to the greater capacity of dehydration in olive 382" trees (Fereres, 1984). 383" Maximum daily trunk shrinkage is affected by several factors which would 384" change the pattern of its relationship with temperature in the long term, water status 385" conditions (Genard et al., 2001) and wood composition (Drew and Dones, 2009) are 386" probably the most important. Such changes would probably vary the reference baseline 387" even though fully-irrigated conditions were performed during the current or previous 388" 17" " season. The present study confirmed that these changes occurred, but only in the y-389" interception, while the slope of the equation was not affected (Fig. 4). The early-y 390" approach made it possible to obtain the reference baseline before massive pit hardening 391" with only the estimation of the y-interception. The extrapolation to other Manzanillo 392" orchards is probably possible, but further work is needed to study the influence of the 393" cultivar. Moriana and Fereres (2004) reported reference baseline using vapor pressure 394" deficit (VPD) with different cultivars and age orchards, but similar environmental 395" conditions. When VPD is considered for the same fruit load an almost equal slope was 396" found between mature cv Manzanillo (Moriana et al. 2011) and mature cv Picual 397" (Moriana and Fereres, 2004). The influence of tree age is probably different, young cv 398" Arbequino showed a different slope and y-interception than mature cv Picual (Moriana 399" and Fereres, 2004) and mature cv Manzanillo (Moriana et al., 2011). Goldhamer and 400" Fereres (2001) suggested that the maximum daily trunk shrinkage would be smaller in 401" young trees than in mature because of the greater growth in the former. In almonds, the 402" reference baseline reported in several studies for young orchards was similar with 403" different cultivars (Fereres and Goldhamer, 2003; Goldhamer and Fereres, 2004). Egea 404" et al. (2009) with three season´s data in a young almond orchard suggested that the 405" reference baseline could be estimated every 1-2 years with the data of the beginning of 406" the season, though slight differences due to phenological stage were reported. 407" 408" 5. Conclusions 409" The extrapolation of reference baseline of maximum daily trunk shrinkage to other 410" orchards was possible in mature cultivar Manzanillo. The reference baselines were 411" similar between orchards, though spacing and ground cover were different. Slight 412" variations in the y-interception were found in both reference equations. The multi-413" 18" " season approach, a general equation previously calculated, over-estimated both 414" reference baselines. Such results were probably related to the extremely low fruit load in 415" both orchards in comparison with the ones obtained when the multi-season approach 416" was calculated. A multi-season approach would be useful in conditions of significant 417" yield. An early approach that estimated the complete (slope and y-interception) 418" reference baseline was not possible because significant variations in the slope were 419" found with the increase in maximum daily trunk shrinkage. This result is not consistent 420" with the ones reported in almond. The differences in the stomata leaf conductance 421" pattern between both species were probably related to the lack of results. The reference 422" baseline in all the estimations was similar in slope but different in y-interception. The 423" early-y approach that only estimated this latter component of the reference baseline 424" presented a good fit between observed and measured data during the period of pit 425" hardening. According to the present results and literature the early-y approach would be 426" useful in the estimation of reference baseline in mature orchards even when different 427" cultivars were considered. 428" 429" Acknowledgements 430" This research was supported by the Spanish Ministerio de Economia y Competitividad 431" (MINECO), (AGL2010-19201-CO4-03 project). The stay of D. Morales and J. 432" Dell’Amico was supported by the AECID project D/030431/10. Thanks are due to A. 433" Montero and J. Rodriguez for help with field measurements and to professors M. Cera 434" and C. Cortés for help in the statistical analysis. 435" 436" 437" 19" " Reference 438" Allen, R.G., Pereira, L.S., Raes, D., Smith, M. 1998. Crop evaportranspiration. 439" Guideline for computing crop water requirements. FAO irrigation and drainage 440" paper nº 56. Roma.FAO. 441" Angelopoulos, K., Dichio, B., Xiloyannis, C. 1996. Inhibition of photosynthesis in olive 442" trees (Olea europaea L.) during water stress and rewatering. J Exp Bot 47, 1093-443" 110. 444" Behboudian, M.H., Mills, T.M., 1997. Deficit irrigation in deciduous orchards. Hort. 445" Rev. 21, 105-131. 446" Brough, D.W., Jones, H.G., Grace, J. 1986. Diurnal changes in water content of the 447" stems of apple trees, as influenced by irrigation. Plant Cell Environ. 9, 1-7. 448" Conejero, W., Mellisho, C.D., Ortuño, M.F., Galindo, A., Pérez-Sarmiento, F., 449" Torrecillas, A. 2010. Establishing máximum daily trunk shrinkage and midday 450" stem wáter potential reference equations for irrigation scheduling of early 451" maturing peach trees. Irrig. Sci. 29, 299-309. 452" Conejero, W., Mellisho, C. D., Ortuno, M. F., Moriana, A., Moreno, F., Torrecillas, A. 453" 2011. Using trunk diameter sensors for regulated deficit irrigation scheduling in 454" early maturing peach trees. Environ. Exp. Bot. 71, 409-415. 455" Cuevas MV, Martín-Palomo MJ, Díaz-Espejo A, Torres-Ruíz JM, Rodríguez-456" Dominguez CM, Pérez-Martín A, Pino-Mejías R, Fernández JE (2012). 457" Assessing water stress in a hedgerow olive orchard from sap flor and trunk 458" diameter measurements. Irrig. Sci. doi 10.1007/s00271-0.12-0357-x. 459" Drew, D.M., Downes, G.M. 2009. The use of precision dendrometers in reaserch on 460" daily stem size and wood property variation: A review. Dendrochronologia 27, 461" 159-172. 462" 20" " Fereres, E. 1984. Variability in adaptive mechanisms to water deficits in annual and 463" perennial crop plants. Bull. Soc. Bot. France. 131, 17-32. 464" Fereres, E., Evans, R.G. 2006. Irrigation of fruit trees and vines: an introduction. Irrig. 465" Sci. 24, 55-57. 466" Fereres, E., Goldhamer, D. 1990. Deciduous fruit and nut trees. In: Stewart, B.A., 467" Nielsen D.R. (Eds), Irrigation of Agricultural Crops. Agronomy Monograph No. 468" 30. American Society of Agronomy, Madison, pp. 987-1017. 469" Fereres, E., Goldhamer, D. 2003. Suitability of stem diameter variations and water 470" potential as indicators for irrigation scheduling of almond trees. J. Hort. Sci. 471" Biotech. 78,139-144. 472" Fereres, E., González-Dugo, V. 2009. Improving productivity to face water scarcity in 473" irrigated agriculture. In: Crop Physiology: applications for genetic improvements 474" and agronomy. Sadras, V. and Calderini, D. (eds). Pp 122-143. Amsterdam, 475" Academic Press. 476" Fernández, J. E.; Cuevas, M. V. 2010. Irrigation scheduling from stem diameter 477" variations: A review. Agr. Forest Meteorol., 150, 135-151. 478" Genard, M., Fishman, S., Vercambre, G., Huguet, J.G., Bussi, C., Besset, J., Habib, R. 479" 2001. A biophysical analysis of stem and root diameter variations in woody 480" plants. Plant Physiol. 126, 188-202. 481" Gijón, M.C., Pérez-López, D., Guerrero, J., Couceiro, J.F., Moriana, A. 2010. Riego 482" deficitario controlado en olivo y pistachero. Agricultura 930, 458-462 483" Goldhamer, D.A. 1999. Regulated deficit irrigation for California canning olives. Acta 484" Hortic. 474, 369-372. 485" 21" " Goldhamer D.A.; Fereres E. 2001. Irrigation scheduling protocols using continuously 486" recorded trunk diameter measurements. Irrig. Sci. 20, 115-125 487" Goldhamer, DA; Fereres, E 2004. Irrigation scheduling of almond trees with trunk 488" diameter sensors. Irrigation Sci. , 23: 11-19. 489" Goldhamer, D., Fereres, E., Mata, M., Girona, J., Cohen, M. 1999. Sensitivity of 490" continuous and discrete plant and soil wáter status monitoring in peach trees 491" subjected to deficit irrigation. J. Am. Soc. Hortic. Sci. 124, 437-444. 492" Herzog K.M., Hüsler R., Thum R. 1995. Diurnal changes in the radius of a subalpine 493" Norway spruce stem: their relation to the sap flow and their use to estimate 494" transpiration. Trees 10, 94-101. 495" Intrigliolo, D.S., Castel, J.R. 2006. Usefulness of diurnal trunk shrinkage as a water 496" stress indicator in plum trees. Tree Physiol., 26 303–311 497" Intrigliolo, D.S., Castel, J.R. 2007. Crop load affects maximum daily trunk shrinkage of 498" plum trees. Tree Physiol., 27: 89-96. 499" Katerji,N., Tardieu,F.,Bethenod,O., Quetin, P. 1994. Behavior of Maize stem diameter 500" during drying cycles:comparison of two methods for detecting water stress. Crop 501" Sci. 34, 165-169. 502" Klepper, B., Browing, V.D., Taylor, H.M. 1971. Stem diameter in relation to plant water 503" status. Plant Physiol. 48, 683-685. 504" Marsal, J., Girona, J. 1997. Leaf water relations parameters in almond compared to 505" hazelnut trees during a deficit irrigation period. J. Amer. Soc. Hort. Sci. 122, 506" 582-587. 507" Martín-Vertedor, A.I., Pérez-Rodríguez, J.M., Prieto-Losada, H., Fereres, E. 2011. 508" Interactive responses to water deficits and crop load in olive (Olea europaea L., 509" cv. Morisca) I. - Growth and water relations. Agr. Water Manage. 98, 941-949. 510" 22" " Moreno, F., Conejero, W., Martin-Palomo, M. J., Giron, I. F., Torrecillas, A., 2006. 511" Maximum daily trunk shrinkage reference values for irrigation scheduling in 512" olive trees. Agr. Water Manage. 84, 290-294. 513" Moriana, A., Fereres, E. 2002. Plant indicators for scheduling irrigation of young olive 514" trees. Irrig. Sci. 21, 83-90. 515" Moriana, A., Fereres, E. 2004. Establishing references values of trunk diameter 516" fluctuations and stem water potential for irrigation scheduling of olive trees. 517" Acta Hortic. 664, 407-412. 518" Moriana, A., Fereres, E., Orgaz, F., Castro, J., Humanes, M.D., Pastor, M. 2000. The 519" relations between trunk diameter fluctuations and tree water status in olive tree 520" (Oleaeuropea L). Acta Hortic. 537, 293-297. 521" Moriana, A., Orgaz, F., Fereres, E., Pastor, M. 2003. Yield responses of a mature olive 522" orchard to water deficits. J. Am. Soc. Hortic. Sci..128, 425-431. 523" Moriana, A., Giron, I.F., Martin-Palomo, M.J., Conejero, W., Ortuno, M.F., Torrecillas, 524" A., Moreno, F. 2010. New approach for olive trees irrigation scheduling using 525" trunk diameter sensors. Agric. Water Manage. 97, 1822-1828. 526" Moriana, A., Moreno, F., Giron, I.F., Conejero, W. Ortuño, M.F., Morales, D., Corell, 527" M., Torrecillas, A. 2011. Seasonal changes of maximum daily shrinkage 528" reference equations for irrigation scheduling in olive trees: Influence of fruit 529" load. Agric. Water Manage. 99, 121-127. 530" Naor, A. 2006. Irrigation scheduling and evaluation of tree water status in deciduous 531" orchard. Hort. Rev. 32, 111-165. 532" Naor, A., Gal. Y., Peres, M. 2006. The inherent variability of water stress indicators in 533" apple, nectarine and pear orchards and the validity of a leaf selection procedure 534" for water potential measurements. Irrig. Sci. 24,129-135. 535" 23" " Ortuño, M. F., Garcia-Orellana, Y., Conejero, W. 2009. Assessment of maximum daily 536" trunk shrinkage signal intensity threshold values for deficit irrigation in lemon 537" trees. Agric. Water Manage. 96, 80-86. 538" Ortuño, M.F., Conejero, W., Moreno, F., Moriana, A., Intrigliolo, D.S., Biel, C., 539" Mellisho, C.D., Pérez-Pastor, A., Domingo, R., Ruiz-Sánchez, M.C., Casadesus, 540" J., Bonany, J., Torrecillas, A. 2010. Could trunk diameter sensors be used in 541" woody crops for irrigation scheduling? A review of current knowledge and 542" future perspectives. Agric. Water Manage. 97, 1–11. 543" Pagán, E., Pérez-Pastor, A., Domingo, R., Conesa, M.R., Robles, J.M., Botía, P., 544" García-Oller, I., Caro, M. 2008. Feasibility study of the maximum daily trunk 545" shrinkage for scheduling mandarin trees irrigation. Ital. J. Agron. 3, 691-692. 546" Pérez-López, D., Moriana, A., Rapoport, H., Olmedilla, N., Ribas, F. 2008. New 547" approach for using trunk growth rate and endocarp development in the irrigation 548" scheduling of young olive orchard. Sci. Hort. 115, 244-251. 549" Scholander, P.F., Hammel, H.T., Bradstreest, E.A., Hemmingsen, E.A. 1965. Sap 550" pressure in vascular plant. Sci. 148, 339-346. 551" Simonneau, T., Habib, R., Goutouly, J.P., Huguet, J.G. 1993. Diurnal changes in stem 552" diameter depend upon variations in water content: direct evidence in peach trees. 553" J. Exp. Bot. 44, 615-621. 554" 555" 556" 557" 558" 559" 24" " 560" Table 1. Dimensions and distance in the orchard of the experiment. There were no 561" significant differences between orchard 1 and orchard 2 in crown volume or trunk 562" diameter. 563" 564" 565" 566" 567" 568" 569" 570" 571" 572" 573" 574" 575" 576" Distance (mxm) Ground cover Crown Volume (m3 tree-1) Trunk Diameter (m) Orchard 1 7x5 40% 31.3±4 0.24±0.01 Orchard 2 7x7 24% 23.6±2 0.23±0.01 25" " 577" Table 2. Crop evapotranspiration, irrigation applied and yield components: yield (Yield (kg tree-1) and harvest (t ha-1). ETc (mm) Irrigation applied (mm) Yield (kg tree-1) Yield (t ha-1) Orchard 1 299.7 285.4 8.9 ± 6.0 2.5 ± 1.7 Orchard 2 214.0 196.7 2.9 ± 1.4 0.6 ± 0.3 578" 579"