Maximum Daily Trunk Shrinkage Research Articles

Assessing water stress in a high-density apple orchard using trunk circumference variation, sap flow index and stem water potential.

Automated plant-based measurements of water stress have the potential to advance precision irrigation in orchard crops. Previous studies have shown correlations between sap flow, line variable differential transform (LVDT) dendrometers and fruit tree drought response. Here we report season-long automated measurement of maximum daily change in trunk diameter using band dendrometers and heated needles to measure a simplified sap flow index (SFI). Measurements were made on two apple cultivars that were stressed at 7 to 12 day intervals by withholding irrigation until the average stem water potential (ΨStem) dropped below -1.5 MPa, after which irrigation was restored and the drought cycle repeated. Dendrometer measurements of maximum daily trunk shrinkage (MDS) were highly correlated (r² = 0.85) with pressure chamber measurements of stem water potential. The SFI measurements were less correlated with stem water potential but were highly correlated with evaporative demand (r² = 0.82) as determined by the Penman-Monteith equation (ETr). The high correlation of SFI to ETr suggests that high-density orchards resemble a continuous surface, unlike orchards with widely spaced trees. The correlations of MDS and SFI to ΨStem were higher during the early season than the late season growth. Band dendrometers are less labor intensive to install than LVDT dendrometers and are non-invasive so are well suited to commercialization.

In-situ and non-invasive measurement of stem water content of trees using an innovative interdigitated-electrodes dielectric sensor less susceptible to stem diameter variation

Stem water content (StWC) of plants is an important parameter for assessing plant response to drought stress in arid and semi-arid areas and for irrigation scheduling. The measurement accuracies of in-situ non-invasive approaches are degraded by plant growth and by diurnal changes in stem diameter associated with water content. Here we develop a frequency-domain (FD) dielectric sensor operating at 100 MHz with an innovative interdigitated-electrodes (IE) probe design for measuring StWC. We characterize the performance of the IE sensor and compare it with a previously described pair-strap-ring-electrodes (2RE) FD sensor. Simulations and experimental measurements were conducted to assess the electric field distribution and volume of sensitivity (VOS) of each probe, the sensitivity of each probe to stem diameter and the accuracy of each sensor for determining StWC of three apple trees in a greenhouse environment. The simulation analysis and the measurement showed that the IE probe has a smaller but denser VOS than the 2RE probe. The sensitivity test showed that the new IE probe (0.85 mV mm−1, R2 = 0.7108) was less susceptible to stem diameter variation in comparison with the 2RE probe (32.83 mV mm−1, R2 = 0.9977). The observations in the greenhouse showed that the three apple trees (AT-1, AT-2 and AT-3) experienced a daily dehydration-rehydration cycle and the averaged midnight-to-predawn StWC gradually decreased without irrigation. According to the reference values of the maximum daily trunk shrinkage (MDS) reported by a previous study, both AT-2 and AT-3 may experience water deficit before the irrigation. Besides, the stem diameter variation decreased the measurement accuracy of 2RE sensor to be ~0.0410 cm3 cm−3 mm−1. The stronger electric field intensity of the IE probe and its less susceptible to stem diameter variation make the new IE dielectric sensor an improved method for accurate in-situ measurement of diurnal stem water content.

Interaction of Maximum Daily Trunk Shrinkage and Fruit Quality in European Plum

Maximum daily trunk shrinkage (MDS) has been suggested as an appropriate indicator of plant water status because it is closely related to stem water potential. Interaction of MDS and fruit quality was studied in plum (Prunus domestica L. ‘Jojo’/Wavit and ‘Tophit plus’/Wavit) in temperate climate. According to the MDS data, trees were grouped as low MDS (LMDS) and high MDS (HMDS). Fruit quality was analysed during fruit development (95, 103, 117 DAFB for ‘Jojo’ and 99, 112, 121 DAFB for ‘Tophit plus’) before commercial harvest. Fruit picked at commercial harvest (137 DAFB and 140 DAFB for ‘Jojo’ and ‘Tophit plus’, respectively) were stored at 2 ± 0.5 °C (90 ± 2% RH) for 28 days, and 2 days shelf life at 20 °C providing 6 measuring dates postharvest. Results confirmed that MDS was positively correlated with water vapour pressure deficit also in the apparent temperate, semi-humid climate. Transpiration of fruit from high crop load and resulting HMDS trees, which can be assessed as physiologically drought, was low compared to that of fruit from LMDS trees. Furthermore, HMDS tree grown plums had enhanced soluble solids and dry matter contents with a tendency of reduced fruit size.

Maximum daily trunk shrinkage for estimating water needs and scheduling regulated deficit irrigation in peach trees

Water scarcity and increasing water use in many socioeconomic sectors lead to an urgent need to improve irrigation management, especially in arid and semiarid areas, such as southeast Spain. For this reason, we studied, during 3 years, the possibility of scheduling regulated deficit irrigation (RDI) using maximum daily shrinkage (MDS) measurements on peach trees [Prunus persica (L.) Batsch cv. “Catherine”] in Murcia (Spain). Three irrigation treatments were established: a control treatment (CET0), irrigated above the estimated crop water requirements, and two treatments based on measurements of maximum daily trunk shrinkage signal intensity (MDS SI), namely a precision treatment (CMDS) using a threshold value of MDS SI = 1 during all the period and a RDI treatment using MDS SI = 1 all the period except for stage II and post-harvest where MDS SI = 2. The low coefficients of variation for MDS SI indicated that this information was sufficient to adjust the irrigation schedule to maintain MDS SI close to the selected threshold values. Maintaining the MDS SI close to unity throughout the growing season allowed us to estimate peach water requirements (ETc). The RDI treatment significantly reduced pruning weight, but no differences were found in terms of reproductive growth and yield. Moreover, RDI increased water productivity and fruit quality, since soluble solids content and maturity index were higher in the RDI treatment compared to CET0 and CMDS. This study demonstrated that irrigation scheduling in peach trees based exclusively on MDS SI was feasible without detrimental effects on yield and fruit quality.

Maximum daily trunk shrinkage and stem water potential reference equations for irrigation scheduling in table grapes

A two-year experiment was conducted to investigate the suitability of reference lines for irrigation scheduling based on maximum daily trunk shrinkage (MDS) and midday stem water potential (Ψs) in a commercial orchard of table grape cv. Crimson Seedless grafted onto Paulsen 1103 (V. berlandieri R.×V. rupestres du Lot). Vines were irrigated (from April to October) above their full crop water requirements (110% of crop evapotranspiration, ETc) in order to obtain non-limiting soil water conditions. The reference equations obtained for MDS and Ψs with meteorological factors differed between the pre and post-veraison periods. Before veraison, MDS was the most reliable indicator for assessing the water status of vines, whereas Ψs correlated better with meteorological variables after veraison. The sensitivity of MDS to ascertain the plant water status decreased during post-veraison due to its dependence on growth and to daily fluctuation of stem diameter. Moreover, it can also be induced by changes in the transpiration and also on the accumulation of xylem abscisic acid ([ABA]xylem). Mean temperature (Tm) was the environmental variable that best correlated with MDS and Ψs at pre-veraison. However, post-veraison reference lines can be obtained for MDS and Ψs using reference evapotranspiration (ET0) and mean daily vapour pressure deficit (VPDm). The use of MDS signal intensity (SIMDS) around the unity and Ψs around −0.65MPa were the best criteria for irrigation scheduling in well-irrigated ‘Crimson Seedless’ table grapes growing in a semiarid climate of south-eastern Spain, during pre and post-veraison periods, respectively.

Reference values of maximum daily trunk shrinkage for irrigation scheduling in mid-late maturing peach trees

Precise irrigation is essential in arid and semi-arid areas where water is scarce, such as the South-East of Spain. Therefore, finding a precise and reliable plant water status indicator, which could be automatically monitored, is of paramount importance. Maximum daily trunk shrinkage (MDS) showed some potential for irrigation scheduling. However, MDS records may be difficult to interpret and reference baselines could be useful for this interpretation. In the current study, measurements of midday stem water potential (Ψs) and MDS were taken over a 3-year period in peach trees [Prunus persica (L.) Batsch cv. ‘Catherine’], in order to obtain reference baselines for irrigation scheduling. Plants were daily irrigated above their water requirements (∼120%) in order to obtain non-limiting soil water conditions. Climate parameters and MDS were recorded automatically, whereas midday stem water potential was assessed in the field every 3 days. The relationships between MDS and climate parameters such as ET0, daily maximum and midday air temperatures (Tmax and Tmid, respectively), maximum and midday air vapour pressure deficit (VPDmax and VPDmid, respectively) were determined. The results indicate that MDS records were better related to Tmid and Tmax than to other meteorological variables. The relationship between MDS and Ψs differed from year to year. However, these relationships varied greatly with the conditions of each year, tree phenological stage and crop load. Therefore, the growers must be aware of these factors when using MDS values for irrigation scheduling.

Combined effects of deficit irrigation and crop level on early nectarine trees

A three-year long experiment was implemented in an early nectarine (Prunus persica L. Batsch cv. Flanoba) commercial orchard to evaluate the effects of deficit irrigation and different crop levels on vegetative growth, plant water status, and fruit yield and quality. Three irrigation treatments were assessed: (i) control, full irrigation (TCTL); (ii) normal practice of the farmer (TFRM); and (iii) regulated deficit irrigation (TRDI), which involved irrigating the crop at the same level as the control (TCTL) during the critical periods of the first year and at 60% TCTL during postharvest. In the last two growing seasons the irrigation was scheduled to maintain the signal intensity (SI) of maximum daily trunk shrinkage (SIMDS=MDSTRDI/MDSTCTL) at different water stress levels depending on the phenological stage: SI=1.0 (non-water stress) and SI=1.4 (moderate water stress). Besides, during the last two seasons, the interactions between TCTL and TRDI were studied at five different crop levels, which were obtained by controlling the distance between fruits left on the branches: from very low (16cm between fruits) to very high (8cm between fruits). Crop water use efficiency (WUE) of TRDI was higher than in TCTL and TFRM, increasing by around 25% in 2010 and 2011, and around 74% the final year. Interestingly, TFRM increased the WUE from the first year by more than 30%. The yield/annual increase in trunk-cross-sectional area (ΔTCSA) ratio increased in TRDI with respect to the other treatments as the experiment progressed, reaching differences of 53%. Vegetative growth was clearly sensitive to deficit irrigation with a strong correlation between the increase in the water stress integral obtained by midday stem water potential (Ψstem) and the reduction in TSCA. In contrast, fruit production and quality were not affected by water deficit. As regards the interaction between crop level and water deficit, fruit firmness was the only fruit quality parameter studied that presented significant differences, the highest values corresponding to the fruits from TRDI trees and the lowest crop level. In early nectarine trees, the postharvest period can be considered as a non-critical period for applying RDI strategies but only when the water stress integral applied is of low intensity in May and June (much lower than 9MPa day), in order to limit the decrease in vegetative growth and so not affect the following harvests.

Subsurface drip irrigation affects trunk diameter fluctuations in lemon trees, in comparison with surface drip irrigation

The aim of this work was to assess the suitability of using trunk diameter fluctuations for irrigation scheduling in a subsurface drip irrigation system in adult lemon trees. The experiment was carried out over two consecutive years in an experimental orchard located in Torre Pacheco (Murcia, Spain) in 18-year-old ‘Fino 49’ lemon trees (Citrus limon (L.) Burm. fil.) grafted on Citrus macrophylla Wester. Well-watered trees were maintained with surface (SUR) and subsurface (SUB) drip irrigation systems by applying irrigation water independently, maintaining in both systems the soil water content of the root zone at ≈80% of the amount of water available and the midday stem water potential (Ψstem)>−1.3MPa. Following these criterias for irrigation scheduling, the use of the SUB system increased the water use efficiency in lemon trees, due to an irrigation water saving of 19% without the yield being affected. However, the SUB system induced different trunk growth dynamics, which produced different reference equations for the maximum daily trunk shrinkage (MDS) and Ψstem. In spite of this, the prediction power of MDS was similar for both systems. In both cases, the environmental variable that best correlated with Ψstem and MDS was the daily mean air temperature. Thus, based on these results, MDS measurements can be suitable for adjusting the irrigation scheduling of lemon trees, but differences found between irrigation systems in the MDS reference baselines highlight the necessity of determining the baselines for each irrigation system.

Deficit irrigation strategies combined with controlled atmosphere preserve quality in early peaches.

Due to the water scarcity in the Mediterranean countries, irrigation must be optimized while keeping fruit quality. The effect of deficit irrigation strategies on changes in quality parameters of the early "Flordastar" peaches was studied. The deficit irrigation was programmed according to signal intensity of the maximum daily trunk shrinkage; deficit irrigation plants were irrigated to maintain maximum daily trunk shrinkage signal intensity values close to 1.4 or 1.3 in the case of DI1 or DI2 plants, respectively. Results were compared to a control watered at 150% crop evapotranspiration. Fruits were stored up to 14 days at 0 ℃ and 95% Relative Humidity (RH) in air or in controlled atmosphere (controlled atmosphere; 3-4 kPa O2 and 12-14 kPa CO2), followed by a retail sale period of 4 days at 15 ℃ and 90-95% Relative Humidity in air. Weight losses were lower in controlled atmosphere stored peaches from deficit irrigation. Air-stored fruits developed a more intense red color due to a faster ripening, which was not affected by the type of watering. At harvest, deficit irrigation peaches showed higher soluble solids content, which provided a better sensory evaluation. The soluble phenolic content was initially higher (55.26 ± 0.18 mg gallic acid equivalents/100 g fresh weight) and more stable throughout postharvest life in DI1 fruits than in those from the other irrigation treatments. Concerning vitamin C, control fruits at harvest showed higher ascorbic acid than dehydroascorbic acid content (5.43 versus 2.43 mg/100 g fresh weight, respectively), while water stressed peaches showed the opposite results. The combination of DI2 and controlled atmosphere storage allowed saving a significant amount of water and provided peaches with good overall quality, maintaining the bioactive compounds analyzed.

Usefulness of stem dendrometers as continuous indicator of loquat trees water status

Postharvest regulated deficit irrigation (RDI) is an effective strategy to hasten flowering and harvest in loquat (Eriobotrya japonica Lindl.) trees, which in the Mediterranean countries has been related to an increase in the economic return. The success of an RDI strategy, however, depends on the duration and severity of the water stress reached by the trees. When RDI is applied, then, it is important to regularly monitor the plant water status. The measurement of the trunk diameter variations by means of stem dendrometers, which can be automated to remotely determine the plant water status, is a proven method for many fruit trees. In loquat, however, its use has not been yet assessed. In this experiment performed in a loquat orchard planted with the cv. ‘Cardona’ during the summer of 2009, the suitability of using stem dendrometers to detect plant water stress was assessed by taking measurements in fully irrigated and trees subjected to a drought cycle of 47 days. Results showed that at the beginning of the drought cycle period there was an increase in the maximum daily trunk shrinkage (MDS) in non-irrigated trees even before that clear differences in stem water potential (Ψs) could be detected between treatments. However, when plant water stress became more severe (Ψs lower than −1.4MPa), MDS did not increase further. The maximum trunk diameter (MXTD) evolution in control trees showed a steadily increase in trunk growth during the whole experimental period. In non-irrigated trees, however, MXTD remained stable until the end of the treatment when irrigation was resumed. The Ψs was the most sensitive indicator to water stress due to its very low tree-to-tree variability in comparison with the other indicators. Overall results show that trunk diameter variations have some limitations to monitor plant water status in loquat RDI orchards and therefore new alternatives should be explored.

A new approach to ascertain the sensitivity to water stress of different plant water indicators in extra-early nectarine trees

The sensitivity to water stress of different plant water indicators was evaluated during the late postharvest period of extra-early nectarine trees growing in a commercial orchard and submitted to two irrigation treatments: (i) a control (TC), irrigated at 120% of crop evapotranspiration to avoid any soil water limitations, and (ii) a water deficit treatment (TD), irrigated at 50% of TC. The plant indicators studied were: the maximum daily trunk shrinkage (MDS); trunk growth rate (TGR); midday stem water potential (Ψstem); leaf conductance (Gs); and net photosynthesis (Pn). Although the highest signal intensity (SI) values – the ratio of deficit irrigation treatment values to control values – were reached by TGR, Gs and Pn (2.6, 3 and 2.9, respectively), the sensitivity (S) values – calculated as the ratio of SI to coefficient of variation (SI CV−1) – were higher in Ψstem and MDS (14 and 11.4, respectively), since their CV values were the lowest (11 and 14%, respectively). A new approach (S*) is proposed to calculate the sensitivity of the plant water indicators, since the standard method can result in high sensitivity values without identifying differences between irrigation treatments. While S is more influenced by the CV values, S* would be influenced by both the SI and CV values.

Assessment of discretely measured indicators and maximum daily trunk shrinkage for detecting water stress in pomegranate trees

Measurements obtained by the continuous monitoring of trunk diameter fluctuations were compared with discrete measurements of midday stem water potential (Ψstem) and midday leaf conductance (gl) in adult pomegranate trees (Punica granatum L. cv. Mollar de Elche). Control plants (T0) were irrigated daily above their crop water requirements in order to attain non-limiting soil water conditions in 2009 and 2010, while T1 plants were subjected to water stress by depriving them of irrigation water for 34 days in 2010, after which time irrigation was restored and plant recovery was studied for 7 days. T1 plants showed a substantial degree of water stress, which developed slowly. Maximum daily trunk shrinkage (MDS) was identified to be the most suitable plant-based indicator for irrigation scheduling in adult pomegranate trees, because its signal:noise ((T1/T0):coefficient of variation) ratio was higher than that for Ψstem ((T1/T0):coefficient of variation) and gl ((T0/T1):coefficient of variation). MDS increased in response to water stress, but when the Ψstem fell below −1.67MPa, the MDS values decreased. For non-limiting water conditions, MDS could be predicted from mean daily air temperature (Tm) through exponential equations fitted to pooled data across several seasons. First-order equations were also obtained by pooling data across several seasons to predict MDS from crop reference evapotranspiration (ETo), mean daily air vapour pressure deficit (VPDm), Tm and solar radiation (Rs), but these should be used only within a certain range of values (ETo, 2.1–7.4mm; VPDm, 0.64–2.96kPa; Tm, 12.1–28.3°C; Rs, 119.4–331.3Wm−2). Hence, automated MDS measurements have the potential to be used in irrigation scheduling of pomegranate, and these values can be normalized to non-limiting water conditions by locally derived empirical relationships with meteorological variables.

Feasibility of using trunk diameter fluctuation and stem water potential reference lines for irrigation scheduling of early nectarine trees

A three-year experiment on early nectarine (Prunus persica L. Batsch cv. Flanoba) trees was carried out with the aim of studying the impact of environmental variables on the trunk diameter fluctuation parameters and the usefulness of the reference-lines derived from the relationship between different meteorological variables and plant water status indicators for sustainable irrigation scheduling. Plants were drip-irrigated and submitted to non-limiting soil water conditions. Measurements of stem water potential at midday (Ψstem), trunk daily growth rate (TGR) and maximum daily trunk shrinkage (MDS) were related with meteorological variables. MDS presented the best fitting line-regressions with both the average air temperature and vapour pressure deficit during the period 11.00–15.00h solar time, since the most important fraction of trunk shrinkage occurred during that period of time, reaching 74% of MDS (on average over the three years studied), and sometimes 90%. The cause of the poor correlation of MDS with ET0 is discussed. Despite the continuous trunk growth of the trees during the experimental period and slight difference in crop load, inter-annual differences were not observed for the three reference lines obtained in any given year (fruit growth, early and late postharvest period).

Remote management of deficit irrigation in almond trees based on maximum daily trunk shrinkage. Water relations and yield

This study assesses the usefulness of the remote scheduling of regulated deficit irrigation (RDI) in almond based on the maximum daily trunk shrinkage signal intensity (SIMDS). The 2-year experiment was carried out in SE Spain on 12-year-old almond trees (Prunus dulcis (Mill.) D.A. Webb cv. Guara). Four irrigation treatments were established to evaluate soil–plant water status, yield and water productivity: (i) control treatment (CTL), irrigated to satisfy the maximum crop water requirements (ETc), (ii) RDI1 and (iii) RDI2, both established to maintain different target thresholds of SIMDS according to the phenological stage and (iv) farmer treatment (FRM), irrigated by the grower according to his own experience. In 2009 and 2010 strategies 1.3-2.2-1.6 (SIMDS target threshold for each tree development stages II–III, IV and V, respectively) and 1.6-2.8-1.6 were applied in RDI1, respectively, and strategies 1.0-2.8-1.3 and 1.0-3.2-1.0 in RDI2. A supervisory control and data acquisition platform (SCADA) was created to monitor and remotely manage the irrigation scheduling. The obtained results indicate that SIMDS is a suitable parameter for irrigation scheduling throughout the growing season. The greater or lesser accuracy of fit of the measured SIMDS values to the thresholds depended on the phenological stage and the target stress intensity. SIMDS threshold values higher than 2.8, which involve midday stem water potential (Ψstem) values lower than −1.9MPa, were not suitable for almond irrigation management under our growing conditions. SIMDS-based RDI strategies were able to generate moderate to severe water stress in almond trees, which resulted in seasonal water savings around 50%. RDI strategies proved to be more cost-effective than full irrigation and farmer deficit irrigation treatment given the high price of irrigation water.

Extrapolating base-line trunk shrinkage reference equations across olive orchards

Maximum daily trunk shrinkage is a common measurement in irrigation scheduling of fruit trees. But the strong relationship between these measurements and the environment severely limit field applications. Reference baselines are the solution for understanding the influence of environmental conditions. Nevertheless, the extrapolation out of the original conditions is not clear. The aim of this study was to compare several approaches to estimate a reference baseline in an olive orchard where there were no previous data from other seasons. Two orchards, separated 60m, with different tree density were used. Orchard 1 had greater tree density than orchard 2, though the age and the cultivar were the same. Trunk diameters of both orchards were similar but the crown volume of orchard 2 was slightly lower than orchard 1. The current reference baselines of maximum daily trunk diameter in both orchards were not significantly different between them (p<0.05). In orchard 1, the previous reference baseline was calculated in a 5-year study (the so called multi-seasons approach). The multi-seasons approach was not significantly different in slope but it was in the y-interception to the current reference baselines in both orchards (p<0.05). This approach over-estimated the values in both orchards. Two additional approaches were tested. These latter approaches used data before massive pit hardening to estimate the current reference baseline. One of them used the early data to estimate a complete reference baseline (the so-called early approach). The other (the so-called y-early approach) used the same data only to estimate the y-interception and assumed that the slope was the same as in the multi-seasons approach. The early approach under-estimated the value of maximum daily trunk shrinkage. The early-y approach provided a satisfactory estimation of the reference baseline and improved those obtained with the multi-seasons approach. The limitations and uses in irrigation scheduling are also discussed.

Diurnal variations in water relations of deficit irrigated lemon trees during fruit growth period

Field-grown lemon trees (Citrus limon (L.) Burm. fil. cv. Fino) were subjected to different drip irrigation treatments: a control treatment, irrigated daily above crop water requirements in order to obtain non-limiting soil water conditions and two deficit irrigation treatments, reducing the water applied according to the maximum daily trunk shrinkage (MDS) signal intensity (actual MDS/control treatment MDS) threshold values of 1.25 (T1 treatment) and 1.35 (T2 treatment), which induced two different drought stress levels. Daily variations in leaf (Yleaf) and stem (Ystem) water potentials, leaf conductance, net photosynthesis, sap flow (SF) and trunk diameter fluctuations were studied on four occasions during the lemon fruit growth period. Ystem and Yleaf revealed a diurnal pattern in response to changes in evaporative demand of the atmosphere. Both water potentials decreased in response to water deficits, which were more pronounced in the T2 treatment. Ystem was seen to be a better plant water status indicator than Yleaf. The difference between the two values of Y (Ystem - Yleaf = DY) was closely correlated with sap flow, making it a suitable measure of leaf transpiration. Using the slope of this relationship, the canopy hydraulic conductance (KC) was estimated. When other continuously recorded plant-based indicators are not accessible, the concurrent measurement of leaf and stem water potentials at midday, which are relatively inexpensive to measure and user-friendly, act as sufficiently good indicators of the plant water status in field grown Fino lemon trees.

Suitability of trunk diameter reference lines for irrigation scheduling with saline water in late mandarin trees with different crop load

A two year experiment on Fortune mandarin trees (Clementina×mandarina Dancy (Citrus clementina Hort. Ex. Tanaka×Citrus reticulata Blanco)) grafted onto Cleopatra mandarin (Citrus reshni Hort. ex. Tanaka) rootstock was carried out with the aim of studying the suitability of midday stem water potential (ψstem) and trunk diameter reference baselines for irrigation scheduling. Plants were drip-irrigated with saline water during the second year (EC25°C≈4dSm−1). Measurements of ψstem, trunk daily growth rate (TGR) and maximum daily trunk shrinkage (MDS) were related with meteorological variables. Among them, MDS presented the best behavior. The mean temperature during the period 10.00–15.00h solar time (Tmd) was the environmental variable that best correlated with MDS, although there were no differences with other T-related variables (daily mean and daily maximum values). MDS data from stage III did not correlate with meteorological variables and fit-linear regressions became better with data from stages I and II (March–October), this being the period which covers 80% of total crop water requirements. Despite the different conditions that the trees were submitted to during the experimental period, i.e. irrigation water with different salinity and crop load, inter-annual differences were not observed in the reference baselines obtained.

Sensitivity of Trunk Diameter Fluctuations inVitis viniferaL. Tempranillo and Cabernet Sauvignon Cultivars

The effects of different applied water amounts on the behavior of parameters derived from trunk diameter fluctuations were studied during three consecutive seasons (2004 to 2006) in a mature vineyard planted with Vitis vinifera cv. Tempranillo and cv. Cabernet Sauvignon in Albacete (Castilla-La Mancha, Spain). Maximum daily trunk shrinkage (MDS) was calculated from trunk diameter fluctuations. The response of MDS to different irrigation treatments varied in the amplitude of the signal between the two cultivars. Tempranillo MDS was significantly higher than that of Cabernet Sauvignon in the period before veraison for the three years. MDS decreased in magnitude after veraison regardless of irrigation treatment and tended to be similar in the two varieties, except for one year where there were cultivar differences in yield caused by differential effects of a frost. Irrigation treatment differences in MDS were significant in 2004 and 2005 at pre- and postveraison, while in 2006 they were nonsignificant, possibly due to the very low yield caused by a late frost which differentially affected the cultivars, suggesting that yield level may be another factor to consider when attempting to use MDS for irrigation management. It appears that the use of trunk diameter sensors for irrigation scheduling in winegrapes would require a specific calibration for the different cultivars.

Using trunk diameter sensors for regulated deficit irrigation scheduling in early maturing peach trees

The aim of this paper was to test the possibility of scheduling regulated deficit irrigation (RDI) using exclusively maximum daily trunk shrinkage (MDS) measurements, and that RDI strategies can be applied in early maturing peach trees reducing significantly the seasonal water use. During three growing seasons, 6-year-old peach trees ( Prunus persica (L.) Batsch cv. Flordastar) grafted on P. persica × P. amygdalus GF-677 peach rootstock were submitted to different drip irrigation treatments. Control (T0) plants were irrigated above the estimated crop evapotranspiration level (≈130% ET C) and T1 plants were submitted to RDI, which were irrigated in order to maintain MDS signal intensity (SI) values close to unity (no irrigation-related stress) from the fruit thinning stage to 2 weeks after harvest, at MDS SI values close to 1.3 during the early postharvest period, and at MDS SI values of 1.6 during the late postharvest period. The RDI strategy assayed reduced the seasonal water applied by 35–42% with respect to estimated ET C without affecting yield efficiency components or the distribution of different peach fruit categories, while improving water productivity. The only vegetative growth component affected by RDI was pruning weight, indicating that vigor regulation as a result of RDI may decrease the competition for assimilates between vegetative apexes and reserve tissues. Also, the absence of any significant effect of RDI on the ratio between yield and the increase in trunk cross sectional area suggested similar carbon partitioning schemes during fruit growth. To improve the precision of MDS SI-driven schedule in RDI strategies changes in the irrigation protocol should be considered so that the scheduled water deficit levels are attained more rapidly. For this, when it is necessary to change from a MDS SI threshold value to a higher one, the daily irrigation rate should be decreased by more than 3%.

Establishing maximum daily trunk shrinkage and midday stem water potential reference equations for irrigation scheduling of early maturing peach trees

Measurements of midday stem water potential (Ψstem) and maximum daily trunk shrinkage (MDS) were taken over a 4-year period in early maturing peach trees (Prunus persica (L.) Batsch cv. Flordastar) grafted on GF-677 rootstock. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that seasonal reference equations can be obtained for MDS and Ψstem using crop reference evapotranspiration (ETo), daily mean vapour pressure deficit (VPDm) and mean daily air temperature (Tm) in the case of MDS, and ETo and VPDm in the case of Ψstem. In this way, VPDm was seen to be the best predictor of MDS and Ψstem, without both were influenced significantly by yield or crop load variations between years. When the postharvest regression between MDS or Ψstem and the meteorological parameters mentioned were broken down into early and late postharvest periods, the correlation coefficients improved and were closely related to the presence or absence of sugar-demanding sinks, such as active root growth. A negative linear relationship between MDS and Ψstem was found, pointing to unchanging radial hydraulic conductivity in the bark tissues and suggesting that MDS depends to a great extent of the water potential.