Decoupling factor, aerodynamic and canopy conductances of a hedgerow olive orchard under Mediterranean climate

CROP-CLIMATE COUPLING IN GREENHOUSES. CHARACTERIZATION AND ANALYSIS

Maize canopies under two soil water regimes: III. Variation in coupling with the atmosphere and the role of leaf area index

Steps toward an improvement in process-based models of water use by fruit trees: A case study in olive

Water status, gas exchange and crop performance in a super high density olive orchard under deficit irrigation scheduled from leaf turgor measurements

Maize canopies under two soil water regimes: II. Seasonal trends of evapotranspiration, carbon dioxide assimilation and canopy conductance, and as related to leaf area index

Assessing plant water status in a hedgerow olive orchard from thermography at plant level

Spring deficit irrigation promotes significant reduction on vegetative growth, flowering, fruit growth and production in hedgerow olive orchards (cv. Arbequina)

Online-monitoring of tree water stress in a hedgerow olive orchard using the leaf patch clamp pressure probe

Scheduling regulated deficit irrigation in a hedgerow olive orchard from leaf turgor pressure related measurements

Yield response of a mature hedgerow oil olive orchard to different levels of water stress during pit hardening

Effects of water stress on fruit growth and water relations between fruits and leaves in a hedgerow olive orchard

Citrus is a crop of major economic importance in Spain, cultivated during the dry season when irrigation is essential to guarantee yields of high quality. As water resources are progressively more insufficient, more effective water management in agriculture is crucial. Deficit irrigation in many agricultural crops has frequently proved to be an efficient tool for improving water-use efficiency. We hypothesise that, despite the effectiveness of deficit irrigation, the most suitable strategy in citrus orchards remains to be defined for Mediterranean environment. In this study, for the period from 2006 to 2008, a 12-year-old orange orchard, Citrus sinensis L. Osb. cv. Navelina, grafted onto Carrizo citrange, C. sinensis L. Osb. × Poncirus trifoliata L. Osb., were subjected under two deficit-irrigation strategies defined as follows: (1) low-frequency deficit irrigation applied according to the plant–water status, and (2) sustained-deficit irrigation with a water-stress ratio of 0.6, defined as the ratio of actual water-limited supply in this treatment related to the water supply of the control treatment. The control treatment was irrigated at 100% of ETC for the entire irrigation season (ETC: crop evapotranspiration). Midday stem–water potential (Ψstem) and stomatal conductance (gS) were used to estimate the water status of the trees. The lowest Ψstem and gS values were registered in the deficit-irrigation treatments with a seasonal pattern consistent with the irrigation dynamics applied in each case. Ψstem and gS values significantly differed from those of the control trees. Although the integrated stress levels were similar in deficit-irrigation treatments, differences in yield and fruit quality were found, having a more positive response to low-frequency deficit irrigation with an increase of 25% in yield in comparison to the sustained-deficit irrigation treatment. Here, we thus demonstrate the significant differences in water productivity. Indeed, water productivity parameter not only depends on the amount of water, but also on the irrigation strategy applied, which promoted substantial water savings without significant impact on yield. The present study highlights that low-frequency deficit irrigation should be adopted as a most appropriate strategy for achieving sustainable water management and attains reasonable yields and improves quality in citrus orchards under Mediterranean semiarid climate.

Soil moisture dynamics in a hedgerow olive orchard under well-watered and deficit irrigation regimes: Assessment, prediction and scenario analysis

Measurements of xylem sap flow (SF) and its response to soil and plant water status and climatic parameters can help to develop better water status indicators, which may help to manage irrigation based on orchard specific conditions. SF was measured with thermal dissipation probes in drip irrigated 12 years old nectarine (Prunus persica var nectarine) trees in Northern Israel. SF probes, automatic sensors for monitoring soil and plant water status, and a meteorological station were installed in standard irrigated plots and in a separate plot for experimental drying and wetting. Mid-day stem water potential (MSWP) was monitored periodically in all plots. SF and leaf conductance increased with leaf area development at the beginning of the season. Variations observed in the drying and wetting plot during four drying cycles before, and one after harvest, were instrumental in finding relationships between SF and canopy conductance and soil and plant water status and climate variables. SF was more variable and less sensitive than other water status measures. During drying, SF decreased by up to 40 % and relative to ET0 it decreased by up to 60%. When expressed relative to the irrigated trees SF decreased by up to 35%, and MSWP by 70%. Similar responses were observed in the post-harvest period. Signal to noise ratios were calculated for the sensors. During the drying cycles SF and conductance were significantly correlated with MSWP, and responses to reduced soil water were quantified. INTRODUCTION Differences in nectarine (Prunus persica var nectarine) sensitivity to water stress at different developmental stages are challenging for irrigation scheduling, similar to other deciduous fruit trees (Ortuno et al., 2004; 2006; Conejero et al., 2007, Fernandez et al., 2011, Biel et al., 2011). For improving agricultural irrigation efficiency it is critical to quantify plant and soil water status. The former can be monitored with manual tools, such as the pressure chamber for measuring leaf water potential, porometry for leaf conductance or with automatic soil and plant sensors (Jones, 2008). For automatic irrigation scheduling it is necessary to replace the manual tools, even though they are believed to be the most precise for setting irrigation timing in fruit trees (Casadesus et al., 2012). The growing shortage of water available for irrigation in many parts of the world increases the need for savings and increased efficiency in water use (Chalmers et al. 1986; Matthews et al., 1990; Fereres et al., 2003; Naor, 2006; Kanety, 2010; Casadesus et al., 2012). For this we need to have better automatic irrigation tools that can quantify water status more precisely (Remorini and Massai, 2003). One automated water status indicator could be the measurement of SF in the tree trunk (Naor and Cohen, 2003; Ortuno et al., 2006; Biel et al., 2012) but few studies have compared the performance of SF and other sensors with tree water status parameters like stem water potential (e.g. Biel et al., 2012).

Canopy conductance (gc) of an old boreal aspen forest and a west coast Douglas‐fir forest was calculated from the inversion of the Penman‐Monteith (PM) equation with above‐canopy water vapour flux measurements. Values of aspen gc agreed reasonably well with those obtained by scaling up from leafstomatal conductance measurements. Comparison of values of gc obtained from the CLASS (Canadian LAnd Surface Scheme) parametrization with values of Douglas‐fir gc in 1983 and 1984 calculated from the PM equation showed that the CLASS parametrization (based on the Jarvis‐Stewart (JS) model) worked well at high soil water potential (ψ), but underestimated gc at low ψ. In the case of the aspen forest during a wet growing season in 1994, the CLASS parametrization underestimated gc for high values of incident photosynthetic photon flux density. The effectiveness of three parametrizations of gc, developed using linear or non‐linear least squares analysis, was evaluated for the two forests. The first (based on the JS model), related gc to the product of several independent limiting functions, the second (based on the Ball‐Woo‐drow‐Berry (B WB) model related gc to the product of canopy net assimilation rate and canopy surface relative humidity divided by canopy surface CO2 concentration, and the third (based on a modified form of the BWB (MBWB) model) was the same as the second except that the relative humidity was replaced by the reciprocal of air vapour pressure deficit. For both forests, the JS parametrization gave the highest r2 and lowest root mean square (RMS) error. The RMS error of the MBWB parametrization was less than that of the BWB parametrization because the latter underestimated gc during the morning. With the incorporation of the new JS and MBWB parametrizations into CLASS, better estimates of the latent heat flux (QE) from the aspen and Douglas‐fir forests were obtained on half‐hourly and daily bases than with the original CLASS parametrization. The JS parametrization gave better estimates than the MBWB parametrization. Both models parametrized using 1994 data from the aspen forest were successfully applied to the same stand in 1996, which also had a relatively wet growing season. Both models parametrized using data from the Douglas‐fir forest were also applied to four other similar‐aged Douglas‐fir forests but with different values of the leaf area index. Under conditions of minimal water stress, better estimates of QE were obtained for three of the four forests using both parametrizations. In the case of the fourth forest, none of the parametrizations gave satisfactory estimates. This was likely because the initial conditions of soil water content and ψ used in CLASS for the gravelly soil was significantly overestimated as a result of not taking the stone content into account. For conditions of high water stress, which occurred in two of the forests, none of the parametrizations gave satisfactory estimates. However, when the ψ limiting function in the JS parametrization was replaced by that developed from measurements made in the other two forests, the JS parametrization gave reasonable estimates of QE. In the case of the MBWB parametrization, we were unable to adjust the ψ limiting function due to the lack of measurements of canopy net assimilation rate at these two sites.