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Universidade Federal de Viçosa Brazil (2009)

Otimização da irrigação localizada em pomares de manga no semi-árido baiano

Cotrim Carlos Elizio

Titre : Otimização da irrigação localizada em pomares de manga no semi-árido baiano

Optimization of the located irrigation in mango orchards in semi-arid baiano

Auteur : Cotrim Carlos Elizio

Université de soutenance : Universidade Federal de Viçosa

Grade : Doctor Scientiae 2009

Résumé
The objective of this work was evaluate the use of the regulated deficit irrigation (RDI) as an alternative of irrigation management in mango orchard in order to optimize water use efficiency (WUE), in semi-arid, and to determine the crop transpiration and WUE for each irrigation management tested. The research was developed in a 9 years old Tommy Atkins mango crop orchard of 8 x 8 m spacing under microsprinkler and of 8 x 4 meters under drip, located in Guanambi, southwest of the Bahia, during two productive crop cycles. In the first one, between 07/18 and 11/07/2006, the regulated deficit irrigation management and the crop productivity had been monitored, and in the second one, during the period of 06/20 and 10/11/2007, besides these parameters, also soil water content, soil water potential (ψm), stem water potential (Ψstem) and plant sap flow (SFp) were measured. Deficits had been applied in phases I, II and III of fruit growth, that corresponded respectively 60, 31 and 20 days in 2006 and the 51, 31 and 31 days in 2007. In 2006 an entirely random experimental design was used, in plots consisted of a mango plant, with 10 treatments and five replications, under trickle, and with 10 treatments and three repetitions, under microsprinkler. In 2007 treatments were reduced to 8 and the design and replications were kept. In 2006 the treatments consisted in control (T0) and in application of the regulated deficit irrigation (RDI) with 40 (T1, T2 and T3), 60 (T4, T5 and T6) e 80% of the Etc (T7, T8 and T9) in the phases I, II and III of fruit development. In 2007 the control with irrigation of 100% of the ETc in all phases (T2) and treatments under RDI with 60% of the Etc (T3, T4 and T5) were kept. Treatments without irrigation (T1) and under RDI with 30% of the Etc (T6, T7 and T8) in the phases I, II and III were increased. Ψm was determined by using tensiometers, with weekly readings, before and after the event of irrigation and the Ψstem was determined weekly using a pressure chamber of Scholander. The soil water content was determined in several locations of two vertical plans perpendicular each other through the time domain reflectometria (TDR). The first one, of 1.0 m x 1,0 m, with a grid of 0.25 x 0.25 m, with the origin in the trunk and transversal direction to plant row and the second one, of 0.75 m x 0.75 m, with the same grid, with the origin in the trunk and longitudinal direction to plant row. The readings, obtained by probes were stored each 15 minutes during one week per phase, by a TDR/ datalogger set. Two treatments always were monitored simultaneously, where T2 and T3 in phase I, T2 and T4 in phase II and T2 and T5 in phase III, with and without covering the shaded area around plants. Crop evapotranspiration (ETc) was estimated by the soil water balance using soil water content data. The sap flow in the plant (SFp) was estimated through the heat dissipation probe method from the difference of temperature among the probes of 16 sensors that were installed in 16 plants. The difference of temperature was registered every 15 minutes in a datalogger / multiplexer set. At the end of each productive cycle, fruits were harvested and evaluated according to quality. They were also quantified and weighed, for the calculation of WUE. In all treatments with RDI, ψm remained between 0 and -11 kPa, not characterizing water deficit condition. ψm varied between -30 and -75 kPa, characterizing short water deficit only for treatment T1. The Ψstem varied between -0.83 and -1.53 MPa for T2, between -1.33 and - 1.83 MPa for T1 and between -0.83 and -1.70 MPa for the treatments with RDI. The treatments T1, T7 and T8 were statistical different from the others by the test of Tukey (p <0.05) that showed that the differences in the RDI management was evidenced by this parameter (Ψstem). The estimated ETc by the soil water balance varied between 2.14 and 4.18 mm day-1 for the T2 treatment, while plant water absorption varied between 2.11 and 3.47 mm day-1. For treatments T3, T4 and T5 the estimated ETc values remained between 1.19 and 2.43 mm day-1 and the plant water absorption ones remained between 0.90 and 1.83 mm day-1. The estimated FSp varied between 0.76 and 1.42 L m-2 day- 1 for T2, between 0.39 and 0.79 L m-2 day-1 for T1 and was in average about 0.82 L m-2 day-1 for treatments T3, T4 and T5, and about 0.71 L m-2 day-1 for T6, T7 and T8. The mango productivity as well as the WUE calculated had not showed significant difference among treatments, by test of Tukey (p < 0.05) in the two evaluated years. The results show the possibility of reduction of the levels of irrigation applied currently, by application of controlled deficits in the irrigation during the phases of fruit growth without providing damages in fruit quality or significant losses of mango orchard yield.

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