Limitations and usefulness of maximum daily shrinkage (MDS) and trunk growth rate (TGR) indicators in the irrigation scheduling of table olive trees

Maximum daily trunk shrinkage (MDS) is the most popular indicator derived from trunk diameter fluctuations in most fruit trees and has been reported to be one of the earliest signs in the detection of water stress. However, in some species such as olive trees (Olea europaea L.), MDS does not usually change in water stress conditions and trunk growth rate (TGR) has been suggested as better indicator. Most of this lack of sensitivity to drought conditions has been related to the relationship between the MDS and the water potential. This curvilinear relationship produces an uncertain zone were great variations of water potential do not imply any changes of MDS. The MDS signal, the ratio between measured MDS and estimated MDS with full irrigation, has been thought to be a better indicator than MDS, as it reduces the effect of the environment.. On the other hand, though literature results suggest an effect of environment in TGR values, there are not clear relationship between this indicator and meteorological data. The aims of this work are, on one hand, to study the improvements of the baseline approach in the MDS signal and, on the other, study the influence of several meteorological variables in TGR. Three years’ data from an irrigation experiment were used in to carry out the MDS analysis and six years’ data for full irrigated trees during pit hardening period were used for TGR study. The comparison between MDS vs. water potential and MDS signal vs. water potential presented a great scattering in both relationships. Values of MDS signal between 1.1 and 1.4 were always identified with moderate water stress conditions (−1.4 to −2 MPa of water potential). However, since this MDS signal values are around the maximum in the curvilineal relationship with water potential, greater values of MDS signal (in the range of 1.1–1.4) were not necessary lower values of water potential. In addition, during low fruit load seasons MDS signal was not an accurate indicator. On the other hand, absolute values of several climatological measurements were not significantly related with TGR. Only daily increments explain part of the variations of TGR in full irrigated trees. In all the data analysed, the daily increment of average vapour pressure deficit was the best indicator related with TGR. The increase of this indicator decreased TGR values. In addition, the agreement between this indicator and TGR was affected for fruit load. Great yield seasons decrease the influence of VPD increment in TGR.Spanish Ministerio de Ciencia e Innovación, (AGL2010-19201-CO4-03 and AGL2013-45922-C2-1-R

Saving irrigation water as a tool to increase pomegranate fruit price and enhance the bioactive compound content

The non-climateric character of pomegranate (P. granatum) fruit underlines the importance of determining the optimum harvest time to improve fruit quality. The effect of irrigation withholding during 6, 15, 25 and 36 d before harvest was evaluated in order to clarify whether fruit ripening is critical or non-critical from the yield, fruit characteristics and composition point of view. The results indicated that this phenological period is critical because irrigation is essential during most of this phenological period to achieve maximum yield. However, a 6 d of irrigation restriction at the end of ripening period can be used as a tool to come early harvest time, saves irrigation water, enhances the bioactive compounds (anthocyanins, phenolic compounds, punicalagin and ellagic acid) and increases the price of the fruit without affecting marketable yield and fruit size

Deficit irrigation and emerging fruit crops as a strategy to save water in Mediterranean semiarid agrosystems

Water scarcity in Mediterranean climate areas will be progressively aggravated by climate change, population increase and urban, tourism and industrial activities. To protect water resources and their integrity for future use and to improve biodiversity, besides following advanced deficit irrigation strategies in fruit cultivation, attention could well be directed towards what are at present underused plant materials able to withstand deficit irrigation with minimum impact on yield and fruit quality. To this end, the state of the art as regards deficit irrigation strategies and the response of some very interesting emerging fruit crops [jujube (Zizyphus jujuba Mill.), loquat (Eriobotrya japonica Lindl.), pistachio (Pistacia vera L.) and pomegranate (Punica granatum L.)] are reviewed. The strengths and weaknesses of deficit irrigation strategies and the mechanisms developed by these emerging fruit crops in the face of water stress are discussed. The response of these crops to deficit irrigation, with special attention paid to the effect on yield but also on fruit quality and health-related chemical compounds, was analysed in order to assess their suitability for saving water in Mediterranean semiarid agrosystems and to analyze their potential role as alternatives to currently cultivated fruit crops with higher water requirements. Finally, the factors involved in establishing an identity brand (hydroSOS) to protect fruits obtained under specific DI conditions are discussed

Mejora de las propiedades de la capa superficial del suelo: fuerza impulsora para el laboreo de conservación bajo condiciones semiáridas

The effect of long term conservation tillage (CT) application on soil organic carbon (SOC) concentration, and on stratification ratios (SR) of SOC, soluble organic carbon (SOCs), microbial biomass carbon (MBC) and protease activity (PA) has been studied. The SR was established dividing values of these variables at 0-5 cm depth by values at 10-25 cm depth. The results were compared with those obtained under traditional tillage (TT). The study was conducted in a wheat-sunflower crop rotation established in 1991 under rainfed conditions in south-west Spain. The results showed here correspond to the years 2001 (sunflower) and 2002 and 2004 (wheat). Despite a slight increase in SOC and the SR of SOC under CT compared to TT, noticeable and significant increases of SR of SOCs, MBC and PA were recorded in CT compared to TT. These increases reveal that the stratification of SOC under CT have consequences on soil functions beyond that of potentially sequestering more C in the soil. CT also improved soil quality by softening the loss of CaCO3, compared to TT.Se han estudiado a largo plazo los efectos del laboreo de conservación (LC) sobre la concentración de carbono orgánico (CO) y las razones de estratificación (RE) del CO, CO soluble, C de la biomasa microbiana y actividad enzimática proteasa. Las RE se establecieron dividiendo los valores de estas variables en la profundidad de 0-5 cm por los valores obtenidos en la profundidad de 10-25 cm y los resultados se compararon con los obtenidos bajo laboreo tradicional (LT). El estudio se realizó sobre una rotación trigo-girasol establecida en 1991 bajo condiciones de secano, en el sur de España; los resultados presentados corresponden a los años 2001 (girasol) y 2002 y 2004 (trigo). El aumento de CO y estratificación del CO en LC sólo fue moderado respecto al registrado en LT. Sin embargo, los aumentos de los valores de estratificación de CO soluble, C de la biomasa microbiana y actividad proteasa fueron notables y significativamente más altos en LC que en LT. La estratificación del CO en LC no sólo refleja una acumulación de CO, sino que afecta a las funciones (dinámica) del suelo. El LC también mejoró la calidad del suelo mitigando, respecto a LT, las pérdidas de CaCO3

Addition of compost changed responses of soil-tree system in olive groves in relation to the irrigation strategy

Intensification of olive production could suppose an increase of natural resources consumption as well as an acceleration of soil degradation. Studies of soil and trees combining different strategies of water management and fertilization to solve these drawbacks are scarce and contradictory. The aim of this work was to describe the effect of organic and inorganic fertilization in soil parameters (water availability, physico-chemical properties and greenhouse gas emissions) and tree development (fruit and crown growth pattern) in rainfed and irrigated conditions in two different olive systems (hedgerow and intensive). The solid olive-mill by-product called “Alperujo” compost (AC) was added as organic fertilization in both systems and two irrigation managements (full and deficit) at the hedgerow sites were also considered. The addition of AC tended to increase soil water retention and soil organic matter (SOM), displaying on average about 15% and 20% more respectively in soils treated compared to their controls in both experiments. Irrigation rather than compost addition was the factor controlling the evolution of both fruit and tree growth. However, AC seemed influenced fruit production specially at the hedgerow system that yielded 30% and 41% more for the deficit and full irrigation management with compost than their respective controls. Emissions of GHE did not generally increase with the AC addition and showed a marked seasonal character in both sites. Regardless irrigation, at the hedgerow site, the full irrigation regimen tended to increase CO2 and CH4 soil fluxes. The agronomic use of organic wastes combined with a deficit irrigation strategy proved to be an efficient tool for nutrient recycling, and promoting a zero waste circular economy and a water conservation strategy

New approach for olive trees irrigation scheduling using trunk diameter sensors

Trunk diameter fluctuations (TDFs) have been suggested as an irrigation-scheduling tool for several fruit trees, but the works in olive trees has not obtained successful results with any of the indicators (maximum daily shrinkage (MDS) and trunk growth rate (TGR)) that are calculated from the daily TDF curves. No studies of olive trees have ever used reference trees to reduce the influence of the environment, as in work for other fruit trees. In this work, we compare different continuous and discrete water status measurements in a drought cycle. We suggest the calculation of a new and related indicator (DTGR), the difference between the TGR of stressed trees, and the TGR of reference trees. Negative DTGR values always indicate water stress conditions. The current work describes the variations of this new indicator (DTGR) in relation to water stress, and compares DTRG to the midday stem water potential, maximum leaf conductance and to the MDS. The midday stem water potential and the maximum leaf conductance describe the stress cycle clearer than the trunk diameter fluctuation indicators. No significant differences were found in the values of MDS between stressed and reference trees. On the other hand, the DTGR pattern values were near that of the stem water potential, though positive values were recorded in some dates during the water stress cycle. These variations indicate that DTGR is not a cumulative water stress indicators, as is water potential. Therefore, according to our data, water potential is a better indicator than the TDF parameters when no deficit irrigation scheduling is performed in olive trees. DTGR seems to be a good indicator of water stress from a threshold value around -1.4 MPa in olive trees. In addition, higher variability of DTGR than stem water potential may also be reduced with the increase in the number of sensors.Leaf conductance Maximum daily shrinkage Stem water potential Trunk diameter fluctuations Trunk growth rate Water relations

Deficit irrigation and emerging fruit crops as a strategy to save water in Mediterranean semiarid agrosystems

Water scarcity in Mediterranean climate areas will be progressively aggravated by climate change, population increase and urban, tourism and industrial activities. To protect water resources and their integrity for future use and to improve biodiversity, besides following advanced deficit irrigation strategies in fruit cultivation, attention could well be directed towards what are at present underused plant materials able to withstand deficit irrigation with minimum impact on yield and fruit quality. To this end, the state of the art as regards deficit irrigation strategies and the response of some very interesting emerging fruit crops [jujube (Zizyphus jujuba Mill.), loquat (Eriobotrya japonica Lindl.), pistachio (Pistacia vera L.) and pomegranate (Punica granatum L.)] are reviewed. The strengths and weaknesses of deficit irrigation strategies and the mechanisms developed by these emerging fruit crops in the face of water stress are discussed. The response of these crops to deficit irrigation, with special attention paid to the effect on yield but also on fruit quality and health-related chemical compounds, was analysed in order to assess their suitability for saving water in Mediterranean semiarid agrosystems and to analyze their potential role as alternatives to currently cultivated fruit crops with higher water requirements. Finally, the factors involved in establishing an identity brand (hydroSOS) to protect fruits obtained under specific DI conditions are discussed