Drip-irrigated Olive Orchards Research Articles

Performance of the METRIC model for mapping energy balance components and actual evapotranspiration over a superintensive drip-irrigated olive orchard

A field experiment was performed to evaluate the Mapping Evapotranspiration at High Resolution using Internalized Calibration (METRIC) model that was used for mapping surface energy balance (SEB) components (net radiation (Rni), soil heat flux (Gi), sensible heat flux (Hi), and latent heat flux (LEi)) at times of Landsat satellite overpasses in conjunction with the actual evapotranspiration (ETa) and crop coefficient (Kc) for a superintensive, drip-irrigated olive (Olea europeae L. cv Arbequina) orchard. The orchard is located in the Pencahue Valley, Maule Region, Chile (35 23' LS; 71 44' LW; 96 m above sea level), and the study was conducted on an experimental plot of 21.1 ha during the 2011/2012 and 2012/2013 growing seasons. Model performance was evaluated using measurements of LEi, ETa and Kc that were obtained from an eddy covariance (EC) system. Olive-specific functions for estimating aerodynamic roughness (zom), leaf area index (LAI), and Gi were employed in the METRIC algorithm. In addition, submodels of Rni and Gi were evaluated via ground-truth measurements from a Fritchen-type net radiometer and soil flux plates, respectively. The results indicated that the errors within the METRIC model for the SEB components were between 2% and 5% of the observed values, while those for ETa and Kc were between 4% and 6% of the EC values. In addition, both the root mean square error (RMSE) and mean absolute error (MAE) for the SEB components were less than 46 W∙m−2 at the times of satellite overpass. The RMSE and MAE values for the 24-h ETa were 0.42 and 0.31 mm·day−1, respectively, while the corresponding values for Kc were 0.09 and 0.02, respectively. The coefficients of variation (CVs) for the SEB components, ETa and Kc were less than 15%, and the largest intraorchard spatial variability occurred for LEi and, thus, ETa. The errors and uncertainties in the SEB and ETa estimates were small enough to warrant application of the METRIC model with olive-specific functions for zom, LAI and Gi to superintensive drip-irrigated olive orchards.

Spatial Distribution of Salinity and Sodicity in Arid Climate Following Long Term Brackish Water Drip Irrigated Olive Orchard

The availability of brackish groundwater in the Negev Desert, Israel has motivated the cultivation of various salinity tolerant crops, such as olives trees. The long term suitability of surface drip irrigation (DI) or subsurface drip irrigation (SDI) in arid regions is questionable, due to salinity concerns, in particular, when brackish irrigation water is employed. Nevertheless, DI and SDI have been adopted as the main irrigation methods in olive orchards, located in the Negev Desert. Reports on continued reduction in olive yields and, essentially, olive orchard uprooting are the motivation for this study. Specifically, the main objective is to quantify the spatial distribution of salinity and sodicity in the active root-zone of olive orchards, irrigated with brackish water (electrical conductivity; EC = 4.4 dS m−1) for two decades using DI and subsequently SDI. Sum 246 soil samples, representing 2 m2 area and depths of 60 cm, in line and perpendicular to the drip line, were analyzed for salinity and sodicity quantities. A relatively small leaching-zone was observed below the emitters depth (20 cm), with EC values similar to the irrigation water. However, high to extreme EC values were observed between nearby emitters, above and below the dripline. Specifically, in line with the dripline, EC values ranged from 10 to 40 dS m−1 and perpendicular to it, from 40 to 120 dS m−1. The spatial distribution of sodicity quantities, namely, the sodium adsorption ratio (SAR, (meq L−1)0.5) and exchangeable sodium percentage (ESP) resembled the one obtained for the EC. In line with the dripline, from 15 to 30 (meq L−1)0.5 and up to 27%, in perpendicular to the drip line from 30 to 60 (meq L−l)0.5 and up to 33%. This study demonstrates the importance of long terms sustainable irrigation regime in arid regions in particular under DI or SDI. Reclamation of these soils with gypsum, for example, is essential. Any alternative practices, such as replacing olive trees and the further introduction of even high salinity tolerant plants (e.g., jojoba) in this region will intensify the salt buildup without leaving any option for soil reclamation in the future.

Parameterization of a Clumped Model to Directly Simulate Actual Evapotranspiration over a Superintensive Drip-Irrigated Olive Orchard

Abstract The aim of this research was to evaluate the clumped model for estimating latent heat flux (LE) and actual evapotranspiration (ETa) over a non-water-stressed olive orchard. Additionally, submodels to compute the net radiation Rn, soil heat flux G, and canopy resistance were also included. For this objective, a database was used from an experimental unit inside a commercial superintensive drip-irrigated olive orchard located in the Pencahue Valley, Maule Region, Chile (35°23′S, 71°44′W; 96 m above sea level) during the 2009/10 and 2010/11 growing seasons. The evaluation was carried out using measurements of LE obtained from an eddy covariance (EC) system. In addition, estimated values of Rn, G, and were compared with ground-truth measurements from a four-way net radiometer, soil heat flux plates with soil thermocouples, and a portable porometer, respectively. Results indicated that the clumped model underestimated LE and ETa with errors of 11.0% and 3.0%, respectively. Values of the root-mean-square error (RMSE), mean bias error (MBE), and index of agreement dr for LE were 35 W m−2, −1.0 W m−2, and 0.96, while those for ETa were 0.48 mm day−1, 0.04 mm day−1, and 0.64, respectively. The submodels computed Rn and G with errors less than 6% and RMSE values less than 65 W m−2, while the Jarvis-type model predicted with RMSE = 41 s m−1 and MBE = 7.0 s m−1. Finally, a sensitivity analysis indicated that the ETa estimated by the clumped model was significantly affected by variations of ±30% in the values of the LAI and the minimum stomatal resistance rstmin.

Assessment of olive transpiration derived from a remote sensing energy balance model compared with sap flow measurements

A remote sensing energy balance (R(SEB)) algorithm was used to estimate transpiration (TRSEB) from a high density and drip-irrigated olive (Olea europaea L. 'Arbequina') orchard, located in Pencahue Valley, Maule Region of Chile (35°23'S; 71°44'W). Meteorological variables over the orchard such as solar radiation, air temperature, relative humidity, wind speed and canopy temperature from zenith were recorded during the southern hemisphere summer, from January through February 2015. The RSEB model was evaluated using sap flow measurements obtained from compensation heat-pulse sensors. In 30-min intervals, the results showed that RSEB model estimated the olive transpiration with errors of 16%, presenting a root mean square error (RMSE) of 0.2 L h-1 and a mean absolute error (MAE) of 0.1 L h-1. On a daily basis, the RSEB model was able to predict the olive transpiration with RMSE and MAE values of 0.68 and 0.57 mm day-1, respectively. The overall analysis suggested that the model underestimates transpiration with errors of 10% on a daily basis.

Implementation of a Two-Source Model for Estimating the Spatial Variability of Olive Evapotranspiration Using Satellite Images and Ground-Based Climate Data

A study was carried out to evaluate the potential use of the two-source Shuttleworth and Wallace (SW) model to compute the intra-orchard spatial variability of actual evapotranspiration (ET) of olive trees using satellite images and ground-based climate data. The study was conducted in a drip-irrigated olive orchard using satellite images (Landsat 7 ETM+), which were acquired on clear sky days during the main phenological stages (2009/10 growing season). The performance of the SW model was evaluated using instantaneous latent heat flux (LE) measurements that were obtained from an eddy correlation system. At the time of satellite overpass, the estimated values of net radiation ( Rn i ) and soil heat flux ( G i ) were compared with ground measurements from a four-way net radiometer and soil heat flux plates, respectively. The results indicated that the SW model subestimated instantaneous LE (W m−2) and daily ET (mm d−1), with errors of 12% and 10% of observed values, respectively. The root mean square error (RMSE) and mean absolute error (MAE) values for instantaneous LE were 26 and 20 W m−2, while those for daily values of ET were 0.31 and 0.28 mm d−1, respectively. Finally, the submodels computed Rn i and G i with errors of between 4.0% and 8.0% of measured values and with RMSE and MAE between 25 and 39 W m−2.

Microbial-based soil quality indicators in irrigated and rainfed soil portions of Mediterranean olive and peach orchards under sustainable management

The main objective of this study was to apply microbial indicators of soil quality in drip-irrigated olive and peach orchards managed with sustainable agricultural practices. Soil characterization was carried out in different areas of the orchards along the row, under the drippers (Rdr), and along the inter-row, rainfed (IRrf), to evaluate the effects of irrigation. Two parameters were followed during one year: a) a biochemical soil indicator (Nc/Nk ratio) based on soil N/C turnover and soil enzyme activities, and b) the abundance of three important N-cycling genes (nifH, amoA and nosZ). Localized irrigation caused higher values of water content in the Rdr areas, compared to IRrf. The Nc/Nk ratio exhibited all the attributes of a reliable soil fertility indicator, being generally higher in irrigated Rdr areas. The abundance of nifH and amoA in the soil showed a trend similar to Nc/Nk, being affected by higher soil water content, while nosZ abundance was generally insensitive to irrigation. Both Nc/Nk and gene abundances, much more than the measured chemical, biochemical and molecular soil parameters considered alone, can give a precise idea on N and C soil dynamics, that in turn, affect soil quality and fertility.

Estimation of Energy Balance Components over a Drip-Irrigated Olive Orchard Using Thermal and Multispectral Cameras Placed on a Helicopter-Based Unmanned Aerial Vehicle (UAV)

A field experiment was carried out to implement a remote sensing energy balance (RSEB) algorithm for estimating the incoming solar radiation (Rsi), net radiation (Rn), sensible heat flux (H), soil heat flux (G) and latent heat flux (LE) over a drip-irrigated olive (cv. Arbequina) orchard located in the Pencahue Valley, Maule Region, Chile (35°25′S; 71°44′W; 90 m above sea level). For this study, a helicopter-based unmanned aerial vehicle (UAV) was equipped with multispectral and infrared thermal cameras to obtain simultaneously the normalized difference vegetation index (NDVI) and surface temperature (Tsurface) at very high resolution (6 cm × 6 cm). Meteorological variables and surface energy balance components were measured at the time of the UAV overpass (near solar noon). The performance of the RSEB algorithm was evaluated using measurements of H and LE obtained from an eddy correlation system. In addition, estimated values of Rsi and Rn were compared with ground-truth measurements from a four-way net radiometer while those of G were compared with soil heat flux based on flux plates. Results indicated that RSEB algorithm estimated LE and H with errors of 7% and 5%, respectively. Values of the root mean squared error (RMSE) and mean absolute error (MAE) for LE were 50 and 43 W m−2 while those for H were 56 and 46 W m−2, respectively. Finally, the RSEB algorithm computed Rsi, Rn and G with error less than 5% and with values of RMSE and MAE less than 38 W m−2. Results demonstrated that multispectral and thermal cameras placed on an UAV could provide an excellent tool to evaluate the intra-orchard spatial variability of Rn, G, H, LE, NDVI and Tsurface over the tree canopy and soil surface between rows.

Partitioning of net radiation and evapotranspiration over a superintensive drip-irrigated olive orchard

To evaluate the partitioning of net radiation (Rn) and actual evapotranspiration (ETa), measurements of Rn, sensible heat flux (H), soil heat flux (G), latent heat flux (LE), reference evapotranspiration (ETo), transpiration (Tp) and soil evaporation (Es) were taken during the 2009/2010 and 2010/2011 growing seasons on a flat and uniform olive (cv. Arbequina) orchard, located in the Pencahue Valley, Region del Maule, Chile (35°23′ LS; 71°44′ LW; 96 m above sea level). Olive trees were trained on a triangular hedgerow system with a plant density of 1333 trees ha−1 (superintensive). An eddy covariance system, sapflow sensors and microlysimeter were used to measure ETa, Tp and Es, respectively. Results indicated that the eddy covariance measurements showed a lack of the energy balance closure of 12.8 %. Values of LE, H and G were between 28–47, 34–68 and 2–6 % of Rn, respectively, while ratios of Tp and Es to ETa ranged between 0.64–0.74 and 0.26–0.36, respectively. During two growing seasons, the single crop coefficient (Kc = ETa/ETo) was between 0.27 and 0.66, while the dual crop coefficient (Tp/ETo + Es/ETo) ranged between 0.26 and 0.56. According to these results, H and Tp were the main component of Rn and ETa, respectively, for the particular conditions of the drip-irrigated olive orchard with a fractional cover of 30 % and wetted area of 4.5 %.

Evaluation of three semi-empirical approaches to estimate the net radiation over a drip-irrigated olive orchard

The use of actual evapotranspiration (ETα) models requires an appropriate parameterization of the available energy, where the net radiation (Rn) is the most important component. Thus, a study was carried out to calibrate and evaluate three semi-empirical approaches to estimate net radiation (Rn) over a drip-irrigated olive (Olea europaea L. 'Arbequina') orchard during 2009/2010 and 2010/2011 seasons. The orchard was planted in 2005 at high density in the Pencahue Valley, Maule Region, Chile. The evaluated models were calculated using the balance between long and short wave radiation. To achieve this objective it was assumed that Ts = Tα for Model 1, Ts = Tv for Model 2 and Ts = Tr for Model 3 (Ts is surface temperature; Tα is air temperature; and Tv is temperature inside of the tree canopy; Tr is radiometric temperature). For the three models, the Brutsaert's empirical coefficient (Φ) was calibrated using incoming long wave radiation equation with the database of 2009/2010 season. Thus, the calibration indicated that Φ was equal to 1.75. Using the database from 2010/2011 season, the validation indicated that the three models were able to predict the Rn at a 30-min interval with errors lower than 6%, root mean square error (RMSE) between 26 and 39 W m-2 and mean absolute error (MAE) between 20 and 31 W m-2. On daily time intervals, validation indicated that models presented errors, RMSE and MAE between 2% and 3%, 1.22-1.54 and 1.04-1.35 MJ m-2 d-1, respectively. The three R„-Models would be evaluated and used in others Mediterranean conditions according to the availability of data to estimate net radiation over a drip-irrigated olive orchard planted at high density.

Quantitative analysis of soil water content in young drip-irrigated olive orchards

The present work was carried out in northern Tunisia (36°40’ N, 10°16’ E) during a single growing season in order to examine how water is distributed within young drip-irrigated olive orchards on the basis of distance to trunk and depth. Soil water content was measured by using a time domain reflectometer (TDR) and a neutron probe calibrated by concurrently measuring soil water content gravimetrically. Measurements were made below the canopies, along the line of drippers and out of the projected canopy area, at distances of 1.4 m, 2.2 m, 2.8 m and 4.2 m from trunks (Compartments G1, G2, G3 and G4), taking into account the heterogeneous distribution of roots. Results showed significant and positive correlations between the series of data collected simultaneously with the PVC and aluminum access tubes and those collected using the different methods and apparatus, demonstrating that any device may be employed, depending only on their availability. Results showed significant changes in soil water contents and stocks according to the season, depth and distance to trunk. During the rainy period, the stocks of water increased homogeneously within all soil compartments, but varied consistently during the dry season with lower values recorded within the upper soil layers. The area situated at 4.2 m from trunks was the driest in summer but it was the wettest during the rainy period. No roots were found at this distance while maximum root densities were observed at 0.4 m from trunk within the upper layers. The lack of water recorded after June affected tree height and fruit growth rates, although irrigation application was sufficient to meet the seasonal crop water needs.

Short-term dynamics of soil chemical parameters after application of alperujo in high-density drip-irrigated olive groves in Argentina

Two-phase olive oil mills generate a semi-solid waste made of olive pulp, olive stone, and vegetation water commonly called ‘alperujo’. Lack of disposal alternatives drives many Argentinean olive oil producers to apply it directly as soil amendment to the olive orchards. Even though this practice has been widely evaluated in Mediterranean countries, there is little agreement on the environmental impact that it may produce. In this work a surface layer of alperujo was applied to a high-density, drip-irrigated olive orchard, and different parameters were monitored. This report summarises the dynamics of soil chemical properties during the first 200 days after application. The results obtained showed that soil amended with alperujo increased total organic matter (OM), nitrogen (N) and available potassium (K), without affecting soil electrical conductivity (EC), pH and C/N ratio. The results suggest that surface application of alperujo may represent an attractive alternative to disposal under conservationist management. Further research evaluating long term effects on chemical and biological indicators must be performed to ensure the sustainability of alperujo as soil amendment.

Validation of a Two-Layer Model to Estimate Latent Heat Flux and Evapotranspiration in a Drip-Irrigated Olive Orchard

A two-layer model was evaluated to simulate latent heat flux (LE) and evapotranspiration (ET) of a drip-irrigated olive orchard during the 2009-2010 and 2010-2011 growing seasons. This orchard is located in the Pencahue Valley, Maule Region, Chile (35 23' S; 71 44' W; 96 m above mean sea level). A constant canopy size was maintained during the two study periods, with leaf area index (LAI) and fractional cover (fc) ranging between 1.29 and 1.34 m2 m-2 and between 0.29 and 0.30, respectively. In addition, the olive orchard was maintained under non-water-stressed conditions, with a midday stem water potential greater than -1.96 MPa. The LE and ET obtained from the eddy covariance (EC) system were used to validate the performance of the two-layer model. The validation including the two study periods indicated that mean values of root mean square error (RMSE) and index of agreement (Ia) for latent heat flux were 28 W m-2 and 0.98, respectively, while the RMSE and Ia values for olive evapotranspiration were 0.52 mm d-1 and 0.84, respectively. This study also indicated that the two-layer model overestimated LE and ET by about 2% and 6%, respectively. Finally, results indicated that the model was very sensitive to errors in the measurements of stomatal conductance and LAI. Major errors of the two-layer model to simulate ET directly were associated with very dry atmospheric conditions (vapor pressure deficit between 3.5 and 4.5 kPa) observed during the afternoon. However, the main errors did not significantly affect the overall performance of the two-layer model.

Efficacy of a hydroxytyrosol-rich preparation from olive mill wastewater for control of olive psyllid, Euphyllura olivina, infestations

Olive mill wastewater (OMW) is a problematic by-product in Mediterranean countries. Despite this, it is a raw material that is an unfailing source of bioactive molecules. A hydroxytyrosol-rich preparation (HRP) (49.6% weight:dry weight) was extracted from fresh OMW using a hydrolysis and post-hydrolysis purification process. The field efficacy of HRP as a spray treatment (2500 l ha −1) against olive psyllid, Euphyllura olivina (Hemiptera: Psyllidae), was evaluated in 2008 and 2009 in a drip-irrigated olive orchard. The HRP showed strong insecticidal activity against E. olivina at a concentration of 2 g l −1 hydroxytyrosol. Application of HRP resulted in 41.1 and 72.1% control of nymphs and adults, respectively. However, HRP application did not reduce egg hatch. Neither phytotoxicity nor toxicity to auxiliary-fauna was recorded with concentrations of 1.25 g l −1 or 2 g l −1 HRP. But, the 2.5 g l −1 concentration was slightly phytotoxic, especially at the E and F floral phenological stages of the grapes. HRP offers a natural and effective extract for control of olive psyllid and opens a new opportunity for the reuse of OMW.

Root length density and soil water distribution in drip-irrigated olive orchards in Argentina under arid conditions

Several studies have evaluated many above-ground aspects of olive production, but essential root system characteristics have been little examined. The objective of our study was to evaluate root length density (RLD) and root distribution relative to soil water content in three commercial orchards (north-west Argentina). Depending on the orchard, the different drip emitter arrangements included either: (1) emitters spaced continuously at 1-m intervals along the drip line (CE-4; 4 emitters per tree); (2) 4 emitters per tree spaced at 1-m intervals, but with a space of 2 m between emitters of neighbouring trees (E-4); or (3) 2 emitters per tree with 4 m between emitters of neighbouring trees (E-2). All of the orchards included either var. Manzanilla fina or Manzanilla reina trees (5–8 years old) growing in sandy soils, although the specific characteristics of each orchard differed. Root length density values (2.5–3.5 cm/cm3) in the upper soil depth (0–0.5 m) were fairly uniform along the drip line in the continuous emitter (CE-4) orchard. In contrast, roots were more concentrated in the E-4 and E-2 orchards, in some cases with maximum RLD values of up to 7 cm/cm3. Approximately 70% of the root system was located in the upper 0.5 m of soil depth, and most of the roots were within 0.5 m of the drip line. For each of the three orchards, significant linear relationships between soil water content and RLD were detected based on 42 sampling positions that included various distances from the trunk and soil depths. Values of RLD averaged over the entire rooting zone and total tree root length per leaf area for the three orchards were estimated to range from 0.19 to 0.48 cm/cm3 and from 1.8 to 3.5 km/m2, respectively. These results should reduce the uncertainty associated with the magnitude of RLD values under drip irrigation as intensively managed olive orchards continue to expand in established and new growing regions.

Soil evaporation from drip-irrigated olive orchards

Evaporation from the soil (Es) in the areas wetted by emitters under drip irrigation was characterised in the semi-arid, Mediterranean climate of Cordoba (Spain). A sharp discontinuity in Es was observed at the boundary of the wet zone, with values decreasing sharply in the surrounding dry area. A single mean value of evaporation from the wet zone (Esw) was determined using microlysimeters. Evaporation from the wet zones of two drip-irrigated olive orchards was clearly higher than the corresponding values of Es calculated assuming complete and uniform soil wetting (Eso), demonstrating the occurrence of micro-scale advection in olive orchards under drip irrigation. Measurements over several days showed that the increase in evaporation due to microadvection was roughly constant regardless of location and of the fraction of incident radiation reaching the soil. Thus, daily evaporation from wet drip-irrigated soil areas (Esw) could be estimated as the sum of Eso and an additive microadvective term (TMA). To quantify the microadvective effects, we developed variable local advective conditions by locating a single emitter in the centre of a 1.5 ha bare plot which was subjected to drying cycles. Esw increased relative to Eso as the soil dried and advective heat transfer increased evaporation from the area wetted by the emitter. The microadvective effects on Es were quantified using a microadvective coefficient (Ksw), defined as the ratio between Esw and Eso. A model was then developed to calculate TMA for different environmental and orchard conditions. The model was validated by comparing measured Esw against simulated evaporation (Eso+TMA) for different soil positions and environmental conditions in two drip-irrigated olive orchards. The mean absolute error of the prediction was 0.53 mm day–1, which represents about a 7% error in evaporation. The model was used to evaluate the relative importance of seasonal Es losses during an irrigation season under Cordoba conditions. Evaporation from the emitter zones (Esw) represented a fraction of seasonal orchard evapotranspiration (ET), which ranged from 4% to 12% for a mature (36% ground cover) and from 18% to 43% of ET for a young orchard (5% ground cover), depending on the fraction of soil surface wetted by the emitters. Estimated potential water savings by shifting from surface to subsurface drip ranged from 18 to 58 mm in a mature orchard and from 28 to 93 mm in a young orchard, assuming daily drip applications and absence of rainfall during the irrigation season.