The northeastern region of Brazil exhibits a large diversity in terms of crops and, in regard to the irrigated crops, there are expressive improvements in productivity and quality of the products. In this region, the main hubs are in the semiarid, where there is a high water demand that is not fulfilled by natural precipitation, resulting in hydric deficits for long periods in the plant cycle, thus demanding the use of irrigation.

The fruticulture stands out in the semiarid region and the mango is among the main cultivated fruit trees, especially as exportation of fresh fruits. From the national production of mango in 2012, the northeast region accounted for 66.54%. Bahia is the largest producer with 54.04% of the regional production [1] wherein Juazeiro, Livramento de Nossa Senhora, Rio Corrente, Ceraíma/Estreito and Itaberaba can be highlighted as production hubs of mango located in the semiarid of Bahia, therefore the use of irrigation is required.

The Tommy Atkins was originated in the 1920s, in Fort Lauderdade, Florida, USA, as a progeny of Haden. This cultivar is a strong tree, of medium size and dense foliage. It exhibits high productivity, regular production, high attractiveness and resistance of the fruits [2] , and it responds well to flower induction [3] .

In water shortage conditions, irrigation management should be performed more accurately, maximizing water use and productivity, or increasing the productivity of water. The accuracy of management relates to the availability of information about the system water-soil-plant-atmosphere.

Research has shown that the interruption of irrigation on mango crops during the flower differentiation is an interesting option; however, the irrigation should be restarted soon after, in the panicle emergence stage. [4] - [7] point out that the reduction of 50% of the amount of water applied to the fruit setting significantly reduces yield, even if supplying the hydric demand over the growing and ripping stages of the fruits.

Management strategies of irrigation that prioritize the reasonable use of water have been adopted in some regions. Among these, two methods stand out from rest: RDI (Regulated Deficit Irrigation) and PRD (Partial Root-zone Drying) [4] - [8] .

Partial Rootzone Drying (PRD) or partial drying of the radicular system [8] , consists of alternating the irrigation on both sides of a plant, at a frequency previously set, which the most commonly used are seven, fourteen and twenty days [9] . PRD bases on biochemical responses from the plants to achieve a balance between the vegetative and reproductive development through the hydric stress, consequently, there is a significant improvement in yield by water unit applied [10] . The dryness on one side leads to a decrease of plant transpiration without exhibiting symptoms of severe stress. In mango crops, the PRD has already been subject of research by [11] - [13] , where the authors obtained positive results in water and electricity savings, improvement in the quality of the fruits and yield maintenance. However, these studies are still lack of consistent results that allow the producer to adopt the correct method for a specific edaphoclimatic condition, since the water requirement of crops relies on specific conditions (soil, climate and cultivar), thus justifying the conduction of studies on this subject.

In the north of Thailand [12] found out no significant reduction in yield and quality of mango and they affirmed that it was possible to obtain a sustainable production by using PRD at 50% of ETc. [13] mentioned that deficit irrigation from 30 to 50% resulted in higher use efficiency and savings of water. Similar results were found by [14] with PRD applied to a “Kent” mango orchard in the semiarid of Bahia. According to the authors, reduction of 50% in the volume of applied water results in no significant decreases of yield using PRD with alternation of 14 and 21 days.

Working with “Tommy Atkins” mango in the region of Petrolina PE, 15] observed that the yields under irrigation at 70%, 80% and 90% of evapotranspiration of reference (ETo) were significantly higher than the productivity at 100% of ETo. The authors concluded that the efficiency in water use, in the studied region, could be enhanced by setting the irrigation at 90% of ETo.

The adoption of irrigation management techniques that focuses on the sustainability with less water demand is of fundamental importance, mainly in semiarid regions, where the water requirement is high and the availability of this resource is smaller than that in other regions of the country [4] [5] . The practice of the efficient usage of water in irrigation should be adopted, once the agricultural sector demands high volume of water. In Brazil, irrigated crops consume 61% of the water [16] . There are evidences of waste in irrigated sites where irrigation is in general overly performed. Besides the higher waste of water, over watering can cause losses of yield, plant diseases, leaching and negative environmental impact.

Based on the above discussion and in view of the dearth of information in the literature about the use of PRD in the Brazilian semiarid, it is necessary more studies related to irrigation with reduced water depth in a specific production phase of the plant without causing any economical loss. This study aimed to evaluate the yield, water-use efficiency and physiological characteristics of “Tommy Atkins” mango under partial root-zone drying (PRD) in the semiarid of Bahia.

The use of PRD caused no significant reduction in the production (number of fruits per hectare and yield) of the “Tommy Atkins” mango compared to full irrigation (Table 2). The physiological variables measured in “Tommy Atkins” were not affected by treatments based on the PRD (P > 0.05). [7] point out that when the water deficit in the soil is not very sharp, changes in stomatal conductance follow the same trend of the plants without water deficit and the reduction by 50% of ETc in the mango crop does not cause significant reduction in transpiration. However, a reduction of 24.20% in transpiration in plants subjected to regulated deficit irrigation (RDI) compared to full irrigation in the fruit expansion phase.

The reduction in transpiration rate in leaves of plants under water deficit can be explained by adaptation of the crop to avoid water loss [7] . [21] points out that as the soil water becomes scarce, the plant begins to reduce its transpiration rate to decrease the loss of water and to save available water in the soil. This probably occurs because of the stomatal closure caused by a signal emitted by the roots, synthesis of the plant hormone abscisic acid (ABA) and transport to the shoot via the xylem in response to water deficit in the soil. [22] emphasizes that this mechanism keeps the water in the plant, however interferes with the assimilation of CO₂, and hence in yield. In this study, it was found that with higher water deficit, associated with switching, that is PRD at 40% of ETc,

Means followed by the same letters in the line do not differ significantly at 5% probability by Tukey test. FI―full irrigation, 100% of ETc; 02―100% of ETc, alternation of the irrigation side (FA) at every 15 days; 03―80% of ETc with FA of 15 days; 04―60% of ETc with FA of 15 days.

there was no reduction in yield. It is a very important fact from a sustainable standpoint, because productivity was satisfactory, enabling high and greater water-use efficiency, reaching up an increase of 77.10% in the WUE compared to full irrigation; i.e. increasing water productivity.

The rise in stomatal conductance (gs) causes increase in transpiration, photosynthesis and in carboxylation efficiency. The gs is responsible by the entering of CO₂ and the release of water by the stomata; the larger is its opening, the smaller is the stomatal resistance and, consequently, there is increase in transpiration [22] .

The eco-physiological behavior is a result of the balance of several environmental factors and not a single factor. The optimal temperature for the carboxylation of CO₂ by the enzyme rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase is 22˚C. This enzyme prevails in plants with photosynthetic mechanism C₃, such as the mango tree. The balance between the activities of carboxylase and oxygenase of the rubisco is maintained by the kinetic properties of the enzyme, temperature, and concentration of CO₂ and O₂. Under concentration of environmental CO₂, an increase in the temperature modifies the kinetic constants of the rubisco and increases the oxygenation rate, preferably, the carboxylation [22] , that is, it increases the photorespiration with decrease in the net photosynthesis rate of the plant. In general, below 30˚C, the quantum productivity of the photosynthesis, mol of CO₂ fixed per absorbed quantum, in C₃ plants is usually high and, above this limit, it falls significantly.

The results of production obtained in this study are in accordance with the ones showed by [11] , who worked with PRD in a “Kent” mango orchard in the semiarid of Bahia and a reduction of 50% of applied water was accomplished without any significant reduction in yield with alternation of PRD of 14 and 21 days. This research also agrees with [12] [13] who claim that is possible to obtain a sustainable production with the use of PRD at 50% of the ETc and a deficit irrigation at 30% to 50% results in a high efficient use of water with big savings of this resource. Table 2 indicates that the treatment 05 (PRD with 40% of ETc) with productivity of 17.00 t∙ha⁻¹ results in higher efficiency of water use.

The study demonstrates that the partial rootzone drying (PRD) with 40% of ETc and alternation of the watered side at every 15 days do not cause significant reduction in productivity and increase a water use efficiency (WUE) (P < 0.05 by Tukey test, as can be seen in Table 2). The use of PRD, with different hydric replenishments did not significantly affect the photosynthetically active radiation incident on the leaf, Qleaf; leaf temperature Tl; internal concentration of CO₂, Ci; transpiration, E; stomatal conductance, gs; photosynthesis, A; carboxylation efficiency, A/Ci; quantum efficiency of photosynthesis, A/Qleaf and instant water-use efficiency, A/E. The increase in leaf temperature causes reduction in A/Qleaf and A/E, however, increasing transpiration. The increase in gs results in higher E, A and A/Ci (Figures 4(d)-(f)).

The theory of using partial rootzone drying bases on the fact that the hydric deficit in the soil induces the production of abscisic acid (ABA) by the roots that is transported through the vascular system, concentrating in the shoot, promoting the partial closing of the stomata, controlling the vegetative growth and, consequently, reducing the water loss to the atmosphere. This fact is partially verified by the values of stomatal conductance―gs and transpiration―E (Table 2), in which, despite not differing statistically, the means of gs and E fall as the applied water reduces in the PRD.

It can be concluded with the present paper that the use of PRD with 40% of ETc causes no interference on the gas exchange in “Tommy Atkins” mango, maintaining the yield and increasing the efficiency of water use.

The authors are grateful to the Instituto Federal Baiano for the financial support and the IF Baiano Campus Guanambi for providing the area, materials and its staff to enable the conduction of this study.

Marcelo Rocha dos Santos,Breno Rosa Neves,Bismarc Lopes da Silva,Sérgio Luiz Rodrigues Donato, (2015) Yield, Water Use Efficiency and Physiological Characteristic of “Tommy Atkins” Mango under Partial Rootzone Drying Irrigation System. Journal of Water Resource and Protection,07,1029-1037. doi: 10.4236/jwarp.2015.713084