**4.1. Olive**

between canopy and air, a threshold of 0.5 was found to trigger irrigation [74]. It was also

A number of indicators related to plant water status of grapevines have been discussed in the

poorly in detecting grapevine water stress in Alto Douro vineyards in Portugal [82]. This can be eventually explained by the fact that either the cultivar displayed an anisohydric behavior [51] or the relative conductance was not used. According to Acevedo-Opazo et al. [83] and Lanari et al. [84], Ψleaf or Ψstem are reported to correlate well with both soil water content and net photosynthesis, and they are suitable to perform irrigation scheduling on grapevines under DI. In other studies, a better performance was obtained by using this variable measured at predawn [56, 79, 85]. According to Silvestre (2018, personal communication), there is some

experimental evidence that Ψstem is not a good indicator in vineyards under high VPD.

Measurements of vegetative growth, when applied to grapevines, can offer simplicity, sensitivity to water stress over extended periods [86], as tissue expansion underlying vegetative growth responds to water status, and are interrelated with crop yield and quality. The stage development of shoot tips can be used reliably to estimate vineyard water status and manage irrigation, given that moderate water stress is primarily affected by soil water content [86]. An experiment to evaluate the visual assessment of shoot tip stage as a method to estimate the water status of vineyards and its utility in vineyard management showed that calculation based on the tip stage [87] is fast, nondestructive, and does not require special skills or equip-

Brillante et al. [80] observed that canopy temperature was an important predictor in determining the water stress experienced by grapevine, especially at midday. These positive results are not always observed: due to excessive wind and turbulence in SW of Portugal, the significant differences in DI treatments could not be identified using proximal radiative canopy temperature [88]. Bellvert et al. [89] emphasized the influence of VPD in using airborne thermal imagery in vineyards. Canopy temperature and derived parameters such as the empirical CWSI [59] have also been used in vineyards by Grant et al. [90] and King and Shellie [91] to

Sap flow performed satisfactorily in detecting grapevine water stress in Alto Douro [82], and in a study developed by Selles et al. [92], diameter changes proved more sensitive than water potentials. Again, many different results were obtained in South Portugal, where differences in DI could not be distinguished using SDV, but were quite clear regarding sap flow records for different treatments [56]. If a single indicator based on sap flow or SDV did not reflect the grapevine response, according to Oliveira et al. [93], their combination could provide more

In general, threshold values for DI in vineyard based on water potential have been abundantly suggested, but in the case of vine production, the quality issues are crucial; therefore,

[76, 77], Ψp, or Ψstem [78–81], sap flow and SDV-derived variables. Being

and Ψp, cor-

at the time of measurement performed

found that it is possible to identify a threshold in the relationship between gs

responding to a change in the plant behavior, equal to Ψpd = −0.45 MPa [75].

very sensitive to transient meteorological conditions, gs

ment and it is independent of prevailing weather conditions [86].

**3.4. Grapevines**

58 Irrigation in Agroecosystems

literature such as gs

monitor plant water stress.

detailed information.

#### *4.1.1. Vegetative growth and production cycle*

Shoots growth and fruits development are cyclical and both are repeated on an annual basis, but only vegetative growth is completed in the same year, while olives production needs two consecutive seasons [96]. In the first one, the formation of the buds and their floral induction take place. In the following year, flower development occurs as well as flowering, fruit set, growth, and oil accumulation. In Mediterranean climate conditions of northern hemisphere, shoot growth takes place from March until the middle of July, although a second flow of growth can occur in late August, when olive trees are fully irrigated, or at the beginning of autumn rainfall [97]. Water deficit reduces shoots growth and has a negative effect on the potential production of the following year. Flowering occurs at the end of spring, and it is very sensitive to water deficit [63], or at high temperatures. Fruit set is very sensitive to water deficit and fruit growth has a double sigmoid behavior [96, 98] with three main stages, as follows. Phase I is the fast-growing, when both the cell division and expansion contribute to the size increase, the endocarp being the main tissue in development, reaching 80% of the volume of the olives [98] with full expansion about 8 weeks after full bloom [99]. The occurrence of water deficit in this stage results in a small endocarp and extreme water stress can compromise the viability of the fruit. Phase II, of slow-growth, is less sensitive to water deficit [100], when the endocarp progressively hardens and both the embryo and the endocarp reach their final size [98]. During phase III, of fast growing, parenchyma cells of the mesocarp experience a large increase in size, entirely due to cell expansion, and the oil biosynthesis begins [98]; so water availability for the fruit determines its size and the accumulation of oil. Thus, water deficit may produce small fruits and the mesocarp/endocarp ratio is reduced due to decreased weight of the mesocarp.

#### *4.1.2. Olive response to water deficit*

Many studies had showed that high soil water availability increments yield components such as fruit number, fruit fresh weight, fruit volume, pulp:stone ratio, and oil content; therefore, increasing fruit and oil yields [12, 63] and that water scarcity can have a negative effect, depending on its level. In addition, irrigation regime can influence the relationship between vegetative and reproductive growth [101].

Hernandez-Santana [102] observed that olive trees prioritize fruit growth and oil content accumulation over vegetative growth, suggesting a higher sink strength for reproductive growth than vegetative growth. In the initial years of orchard establishment, when rapid vegetative growth is desirable in order to quickly obtain optimum tree size and canopy, as well as to begin fruit production as soon as possible, it is critical not to depress vegetative activity. For this reason, in commercial orchards, DI is commonly implemented only once, trees are fully grown to avoid negative effects on the formation of tree structure during the training period [102]. DI at early stages of tree development may result useful not only for water saving but also for controlling vigor in super high-density (SHD) orchards, in particular in regions where local conditions lead to excessive vegetative growth, such as in northern Argentina [103]. The choice and success of DI strategy is conditioned by tree density and rootzone size. It seems that SDI is more interesting when trees explore large volumes of soil, as in low-density orchards that maximize the availability of stored soil water per tree, compared to higher densities [97, 104]. Moreover, the success of SDI as compared to FI depends on the crop load of olive. About this issue, Martín-Vertedor et al. [105, 106] conducted a long term studied in "Morisca" orchard (417 trees ha−<sup>1</sup> ), in the Southwest of Spain. They observed that SDI (75% ETc) reduced yield in "on" years. Nevertheless, they reported that this DI could be advisable during "off" years, when a lower water use is observed, and trees are less sensitive to water deficit with low-crop load. There is still uncertainty about which DI strategies are better, regarding SDI or RDI [58, 101].

affect oil production [110], while a reduction of 72% (30 RDI) resulted in 26% less oil yield and

Deficit Irrigation in Mediterranean Fruit Trees and Grapevines: Water Stress Indicators and Crop…

http://dx.doi.org/10.5772/intechopen.80365

61

Fernández et al. [19] and Padilla-Díaz et al. [111] applied RDI in a SHD olive orchard using a strategy of 45% of the total irrigation requirements (IN) in total distribution, according to the vegetative phase: period 1–100% IN, before and during bloom; period 2–80% IN, during the maximum rate of pit hardening (6–10 weeks after bloom) that coincide with the phase of flower induction; period 3–100% IN at the end of pit hardening until the last week of September, and 20% IN during fruit maturity. During the end of June and till the last week of

Marra et al. [112] conducted a study in west of Sicily (Italy) in a SHD orchard (cv "Arbequina"), where five irrigation treatments were tested: 100% of IN, three SDI treatments with 75, 50, and 25% of IN, and a nonirrigated "rainfed" control. They found that oil yield increased with higher irrigation amounts up to a certain level (50 SDI) and a further increase in irrigation level improved crop load on the one hand, but decreased vegetative growth and increased the severity of biennial bearing. They conclude [112] that irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load. With regard to PRD, Wahbi et al. [108] analyzed the effect of applying PRD (50% of ETc) to "Picholine marocaine" olive trees in Marrocos in field grown conditions. They reported a yield reduction of 15–20%, achieved with 50% ETc, and that WP increased by 70% in PRD treatments. However, the lack of comparison between PRD and RDI did not clarify whether the effects observed were specifically triggered by PRD or if they were simply associated with general water deficits. Later, Aganchich et al. [113] addressed this question by comparing the effects of PRD and RDI in the same cultivars grown in spots. They reported that plant vegetative growth was substantially reduced under both PRD and RDI, more pronounced in PRD, compared with FI, as expressed by lower values of shoot length, leaf number, and total leaf area. In many cases, PRD treatment has been compared to a FI treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a DI treatment. In addition, not always a PRD treatment has been found advantageous as compared to a RDI treatment [66]. Taking into account that an irrigation system suitable for the PRD approach is more expensive and difficult to manage, the literature suggests that there are no agronomical advantages on PRD as compared to RDI [66]. It is of great importance to bear in mind that results depend mainly on cultivar, orchard characteristics, environmental conditions and agronomic practices, and to the large variability in rainfall, climate, and soil types between the various growing regions. Consequently, caution must be taken when applying

the findings reported by different authors to a particular orchard.

are considered for each product largely differ from one another.

The concept of quality in fruit products is wide, complex, and dynamic. In the case of olive trees, two main products are obtained from olive fruits: virgin olive oil (the juice of the fruit) and table olives; both are staple foods of the Mediterranean diet. The quality attributes that

*4.1.3. Effect on fruits and olive oils quality*

a best balance between water saving, tree vigor, and oil production was achieved [19].

August IA was 20% of IN.

Lavee et al. [107] suggested that the most efficient schedule for RDI irrigation was to withhold water till the end of endocarp hardening and then to apply full irrigation from that stage till 2 weeks prior to harvest.

The literature provides results, for low-density orchards (300–600 trees ha−<sup>1</sup> ) under FI [63], SDI [12], RDI [11], and PRD [108] and for SHD olive orchards >1500 trees ha−<sup>1</sup> [109].

Often, DI strongly reduces vegetative growth, but only slightly reduces the final fruit volume. Water stress caused a higher reduction in fresh fruit yield than oil yield due to a higher oil concentration in DI irrigated trees "in Picual" (Spain), without differences between SDI and RDI [11]. Moreover, Iniesta et al. [11] observed that WP for oil production has tripled for a 25% decrease in total water applied. They conclude that both irrigation strategies may be used with moderate reductions (about 15%) in oil yield. Similarly, Fernandes-Silva et al. [12] ("Cobrançosa," Portugal) reported that for a SDI at 30% ETc, WP for oil is higher or very close to FI, depending on the year, and is more than double the one obtained in rainfed conditions; oil yield is reduced only 35% as compared to FI, while saving 60% of water applied. Nevertheless, oil concentration on a dry matter basis (DM) in SDI was 7–19% higher as compared to FI, hence oil yield reduction was lower than yield of fruit (DM). The higher oil yield observed in FI is mainly due to higher number of fruits, although under SDI, fruits have slight higher values of mesocarp (>3–5%) as compared to FI olives, mainly attributed to a higher crop load in FI olive trees. Fernandes-Silva et al. [12] founded a good relationship between the oil amount per mesocarp dry mass (g) (y = 0.83 × −0.17, r2 = 0.97). This may be useful in supporting the decision of the most suitable time for harvest to optimize oil productivity.

Irrigation is particularly an important component in SHD orchards as the trees are expected to have more reduced volume of the rootzone. There is not a consensus on the best irrigation approach for SHD olive orchards. A reduction in water applied up to 16% in July did not affect oil production [110], while a reduction of 72% (30 RDI) resulted in 26% less oil yield and a best balance between water saving, tree vigor, and oil production was achieved [19].

Fernández et al. [19] and Padilla-Díaz et al. [111] applied RDI in a SHD olive orchard using a strategy of 45% of the total irrigation requirements (IN) in total distribution, according to the vegetative phase: period 1–100% IN, before and during bloom; period 2–80% IN, during the maximum rate of pit hardening (6–10 weeks after bloom) that coincide with the phase of flower induction; period 3–100% IN at the end of pit hardening until the last week of September, and 20% IN during fruit maturity. During the end of June and till the last week of August IA was 20% of IN.

Marra et al. [112] conducted a study in west of Sicily (Italy) in a SHD orchard (cv "Arbequina"), where five irrigation treatments were tested: 100% of IN, three SDI treatments with 75, 50, and 25% of IN, and a nonirrigated "rainfed" control. They found that oil yield increased with higher irrigation amounts up to a certain level (50 SDI) and a further increase in irrigation level improved crop load on the one hand, but decreased vegetative growth and increased the severity of biennial bearing. They conclude [112] that irrigation scheduling in the new SHD orchards should be planned on a 2-year basis and corrected annually based on crop load.

With regard to PRD, Wahbi et al. [108] analyzed the effect of applying PRD (50% of ETc) to "Picholine marocaine" olive trees in Marrocos in field grown conditions. They reported a yield reduction of 15–20%, achieved with 50% ETc, and that WP increased by 70% in PRD treatments. However, the lack of comparison between PRD and RDI did not clarify whether the effects observed were specifically triggered by PRD or if they were simply associated with general water deficits. Later, Aganchich et al. [113] addressed this question by comparing the effects of PRD and RDI in the same cultivars grown in spots. They reported that plant vegetative growth was substantially reduced under both PRD and RDI, more pronounced in PRD, compared with FI, as expressed by lower values of shoot length, leaf number, and total leaf area. In many cases, PRD treatment has been compared to a FI treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a DI treatment. In addition, not always a PRD treatment has been found advantageous as compared to a RDI treatment [66]. Taking into account that an irrigation system suitable for the PRD approach is more expensive and difficult to manage, the literature suggests that there are no agronomical advantages on PRD as compared to RDI [66]. It is of great importance to bear in mind that results depend mainly on cultivar, orchard characteristics, environmental conditions and agronomic practices, and to the large variability in rainfall, climate, and soil types between the various growing regions. Consequently, caution must be taken when applying the findings reported by different authors to a particular orchard.
