Irrigation under different soil surface wetted areas and water depths for banana cv . Grand Naine

1 Agricultural Engineering, Embrapa Mandioca e Fruticultura, C.P. 07, Cruz das Almas, BA, Brazil. 2 Agricultural Engineering, Instituto Federal Baiano Campus Guanambi, C.P 009. Zona Rural, Distrito de Ceraíma, Guanambi, BA, Brazil. 3 Agricultural Engineering, Universidade Federal de São João Del-Rei, Campus de Sete Lagoas. Rod. MG 424 km 47, CEP: 35701970 Sete Lagoas, MG, Brazil. 4 Agricultural Engineering, Epamig Norte. Rodovia MGT 122 km 155, Zona Rural, CEP: 39527-000 Nova Porteirinha – MG, Brazil.


INTRODUCTION
Brazil is in the fifth position in the global ranking of banana production and, according to FAOSTAT (2015), in 2014, the production was 6,946,567 tons, with emphasis for the northeast and southeast regions, which account for 66.91% of the production (IBGE-SIDRA, 2016).The state of Minas Gerais is the second largest *Corresponding author.E-mail: eugenio.coelho@embrapa.br.Tel: +55 (75) 33128021.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License producer in the southeast region, with 47.48% of the production concentrated in its northern portion (IBGE-SIDRA, 2016), a semi-arid region, recently identified by the trademark "Região do Jaíba", constituted for characterization as an area of geographic indication for the production of quality fruits.
In the Brazilian semi-arid region, the mean annual rainfall is lower than 800 mm, with irregularity of spatial and temporal distribution and aridity index between 0.2 and 0.5.Since the water requirement of the banana crop is higher than the natural rainfall and with regular distribution, the use of irrigation becomes necessary to fulfill water needs during the periods of water deficit in the soil even in humid regions (Vanhove et al., 2012;Ravi et al., 2013;Muthusamy et al., 2014;Kissel et al., 2015).However, it is necessary to attempt for precision of irrigation mainly in semiarid regions of tropics and subtropics more subjected to climate changes (Surendar et al., 2013(Surendar et al., , 2015)).
Micro-sprinkler irrigation has been predominant in the localized irrigation of banana in the production centers of the semi-arid region.There are different micro-sprinklers available in the market, in terms of both structure and nominal flow rate.Flow rates are related to the radius of throw and, consequently, the generated soil surface wetted area.The soil surface wetted area is associated with the region of root development; the higher it is, the greater the lateral expansion of the root system.However, larger soil surface wetted diameters also imply greater areas under evaporation, with reduction of application efficiency.Rocha (2009) evaluated the effect of the percentage of soil surface wetted area on physiological, production and fruit quality variables of "Tahiti" lime (transpiration, stomatal conductance and leaf temperature) and observed no differences in these aspects for the evaluated soil surface wetted area percentages.
The knowledge on the water requirement of the banana crop has increased in the last years and results have been found for different climate conditions (Coelho et al., 2013;Silva;Bezerra, 2009;Montenegro et al., 2008;Teixeira et al., 2002) for different cultivars in different physiographic regions.However, considering microsprinkler irrigation as the trickle system most used in the production centers of irrigated banana in Brazil, studies that associate levels of irrigation water and soil surface wetted area for water application by micro-sprinklers are scarce.
The emitter radius of throw determines soil surface wetted area, which is dependent upon its flow rate and pressure.The emitter precipitation intensity, in turn, depends on their physical characteristics.The wetted area on the soil surface due to the application of water is a determinant factor in the mean moisture content of the wetted volume and in its dimensions, with implications on root distribution, on water and nutrient uptake and also on soil water losses through evaporation and percolation.Farmers usually do not know which emitter to choose for optimal production and market offers types with different flow rates.Moreover, morphological, production and fruit quality factors of the banana crop may be influenced by the soil surface wetted area, in isolation or in interaction with the applied water depths.This study aimed to evaluate the effect of different irrigation water depths and soil surface wetted areas applied by a micro-sprinkler system on yield, fruit physical characteristics and on leaf area of "Grand Naine" banana during three production cycles in Northern Minas Gerais, Brazil.

MATERIALS AND METHODS
The experiment was carried out in the Northern Unit of the Agricultural Research Company of Minas Gerais -EPAMIG, in the municipality of Nova Porteirinha, Minas Gerais State, Brazil (Figure 1).The area is inserted in the Brazilian semi-arid region, at the geographical coordinates of 15° 46' 38.98"S, 43 17' 22.06" W and altitude of 537 m, and its climate is Aw, according to Köppen"s classification.The soil of the experimental area was classified as dystrophic Red Yellow Latosol and its physical-hydraulic characteristics are presented in Table 1.
The experiment was conducted from 2003 to the beginning of 2006, comprehending three production cycles of "Grand Naine" banana, with planting spacing of 3.0 m × 2.7 m under microsprinkler irrigation, maintaining the soil covered by the straw of the plants.The experimental design was randomized blocks with four replicates, in a split-plot arrangement, with three soil surface wetted areas in the plots and five irrigation depths in subplots.
Irrigation water depths were determined by the ETc fractions of 0.70, 0.85, 1.00, 1.15 and 1.30 of ETc, considering the efficiency of the irrigation system of 0.85, with daily irrigations.Crop evapotranspiration (ETc) between two irrigations was obtained based on the potential evapotranspiration (ETo) determined by the Class-A pan method and on crop coefficients (Kc) established as a function of those suggested by Allen et al. (1998).The wetted area on the soil surface was determined by the radius of throw of the micro-sprinklers, according to their flow rates, through water collectors positioned in a grid (0.50 × 0.50 m) in an area with four plants (5 m × 4 m), and the emitter in the center.The soil surface wetted area 1, with 10.17 m 2 , was obtained using emitter with flow rate of 20 L h -1 and radius of throw of 1.8 m; the soil surface wetted area 2, with 23.74 m 2 , was obtained using emitter with flow rate of 63.6 L h -1 and radius of throw of 2.7 m, and the soil surface wetted area 3, with 28.26 m 2 , was obtained using emitter with flow rate of 60 L h -1 and radius of throw of 3.0 m.
The process of soil surface wetted area determination was also used to obtain the mean precipitation intensity, based on the mean water depth of the collectors divided by the time (h) of the test, which was performed periodically.The mean precipitation intensity was used in the determination of irrigation time.Irrigation depths and soil surface wetted areas were differentiated in the controller through valves corresponding to each one of the factors, totaling 15 sub-main lines.Rainfall and class A pan evaporation were measured in a conventional weather station, installed close to the experiment.
Soil water status was evaluated through soil water tension, measured with a tensiometer using an analog tensimeter, before irrigations.Leaf area was evaluated based on the length and width of the third leaf during flowering period.Yield (t ha -1 ) and the variables of fruit physical quality (mean length, weight and diameter of the central fruit from the second hand) were evaluated at harvest.Distance and effective depth of the root system were observed by opening soil pits in the plots, between the plant and the micro- Table 1.Soil physical-hydraulic characteristics: Texture, density and water contents corresponding to the potentials obtained in the soil water retention curve (Nova Porteirinha-Minas Gerais, Brazil).

Layer (m)
Sand Silt Clay Soil density (Mg m -3 ) Soil moisture (cm 3 cm -3 ) at tension (kPa) (g kg sprinkler, and by removing the roots from the soil in monoliths at the distances of 0.25, 0.50, 0.75 and 1.00 m from the plant and along the soil profile from the surface to 0.80 m, every 0.10 m.The images were processed according to Sant"ana et al. ( 2012), allowing the determination of root length at each distance and soil depth between the plant and the micro-sprinkler.Distance and effective depth of the roots corresponded to those with 80% of the cumulative total length from the plant and from soil surface (Sant"ana et al., 2012).The data of mean length, weight and diameter of the central fruit of the second hand, leaf area and yield were submitted to analysis of variance in each cycle.The means of dependent variables were compared by Tukey test at 0.05 probability level for the independent variable soil surface wetted area.Regression analysis evaluated depended variables as a function of irrigation depths.Regression models were also fitted to the data of cumulative root length as a function of the distance from the plant and soil depth, referring to each soil surface wetted area.

RESULTS
Climatic attributes were not similar during the three crop cycles.Irrigation water depths applied in each treatment (fraction of ETc) were different for each cycle (Table 2), because of the variation in the maximum evapotranspiration (ETo) and crop evapotranspiration (ETc).
The lowest irrigation water depth value recorded in cycle 1 was above 800 mm and, in cycles 2 and 3, above 990 mm and for the treatment 0.85 ETc, the irrigation water depths in all cycles were higher than 997 mm.These depths of water corresponded to values near to the ones observed by Bassoi et al. (2004) for maximum yields in the semi-arid of Petrolina, Pernambuco State whose aridity indexes were smaller than the ones of the Nova Porteirinha.
According to the analysis of variance (Table 3), there was no interaction between the factors soil surface wetted area x water depth during the three cycles for the evaluated dependent variables of "Grand Naine" banana.There was effect of soil surface wetted area on central fruit length (CFL) in cycles 1 and 3, central fruit diameter (CFD) in cycle 2, central fruit weight (CFW) in cycle 3, total leaf area (TLA) in cycles 1 and 3 and yield (Y) in the three cycles.The irrigation depths influenced, independently, only central fruit length (CFL) in cycle 3.
The mean length of the central fruit of the second hand was the highest for the soil surface wetted area of 23.74 m 2 in cycle 1 (Table 4), and the lowest for the soil surface wetted area of 10.17 m 2 in cycle 3.The irrigation water depths did not influence mean diameter and weight of the  , 2006) the largest soil surface wetted area resulted fruits of length within the class of length greater than 22 cm and smaller than 26 cm, with mean of 24.30 cm.The smallest soil surface wetted area led to fruits within the class of length greater than 18 cm and smaller than 22 cm in the third cycle.
"Grand Naine" banana showed lower leaf area for the smallest soil surface wetted area (10.17 m 2 ) in cycles 1 and 3 (Table 5), as well as lower yield for this wetted area in all production cycles.Means of leaf area from larger soil surface wetted areas, 23.74 and 27.18 m 2 , were not different between themselves for all cycles.The mean yields for these same conditions differed only in the first cycle (Table 5).Irrigation water depths did not influence both leaf area and yield in the range of 990 mm (0.7 ETc) to equivalent to 1840 mm (1.30ETc).
The increase of soil surface wetted area was equal to 133% from 10.17 to 23.74 m 2 and to 18% from 23.74 to 28.26 m 2 .These wetted volumes allowed greater effective lateral distance from plant and depth of roots (Figure 3).Effective distance from plant and effective depth were 0.84 and 0.53 m, respectively for soil surface wetted area of 10.17 m 2 .The effective distances were 1.11 and 1.36 m and the effective depths were 0.53 and 0.58 m for the areas of 23.7 and 28.2 m 2 , respectively (Figure 3), demonstrating that the wetted areas on the soil surface promote larger volume of soil for the distribution of roots.

DISCUSSON
The results indicate that the soil surface area wetted influences the physical quality of fruits (F test), with evidence for mean fruit length, whose influence repeated for two of the three cycles evaluated, while the mean fruit weight was only influenced in cycle 3.Fruit dimensions such as length, diameter as well as fruit weight, are important attributes for genetic improvement and especially for market, because they interfere with the preference of the consumer and affect the yield of the fruit (Oliveira et al., 2013).
Fruits produced under the three soil surface wetted areas showed diameter values above 32 mm that is considered as the extra category for Cavendish bananas.These results do not agree with those reported by Figueiredo et al. (2006), who did not observe influence of soil surface wetted area, using one and two lateral lines of drippers, on the length of the central fruit of the second hand of "Prata-Anã" banana.The influence of soil surface wetted area upon fruit length "should be related to water and nutrient uptake, since water depth influenced it only on the third cycle in which means were close each other (Table 5).Therefore, the lateral root expansion due to the soil surface wetted area explains better the result.
Results of the range of mean diameter above 32 mm and weight of the central fruit above 180.36g in all cycles, regardless the irrigation depths agree and disagree with others authors (Figueiredo et al., 2006;Coelho et al., 2006) due to factors not considered as sources of variation in the statistical model.Despite the statistical influence of soil surface wetted area on some physical attributes for one or two crop cycles, the results are not enough to conclude that soil surface wetted area and irrigation water depth affects all attributes of physical quality of banana fruits for general purposes.
Irrigation water depth did not influence leaf area and yield because the range of irrigation water depths from 0.70 to 1.30 ETc corresponded to the one in which the yield rate begins to decrease as irrigation depth increases.Larger yield rate reduction occurred for irrigation water depths in between 1.0 and 1.25 ETc, as observed in studies that evaluated banana yield as a function of irrigation depths (Costa et al., 2014;Coelho et al., 2006;Figueiredo et al., 2006).In addition, the noneffect of the irrigation water depth on leaf area and yield may be due to the range of irrigation water depths close to or higher than 0.85 ETc, considering cycles 2 and 3. Mean water contents varied in this range from 80% (-27 kPa) to 88% (-18 kPa) with minimum from 67% (-70 kPa) to 75% (-37 kPa) of available water in the layer of 0.00 to 0.20 m during part of the cycles 2 and 3 (Figure 2).A  20% depletion of soil water availability is the limit for beginning stress for banana crop (Robson and Bower, 1987).The yields obtained in cycle 3 for the soil surface wetted area of 23.74 m 2 were similar to the "Grand Naine" yields reported by Goenaga and Irizarry (1986), who observed maximum estimated value of 47.9 t ha -1 for the water depth correspondent to 1.0 of class A pan evaporation.On the other hand, even with lower leaf area in cycle 3, the yield was higher than in the other cycles, suggesting the existence of other factors that may have influenced the increase in yield.The values of leaf area in cycles 1 and 2 are similar to those found by Coelho et al. (2006) for "Grand Naine" banana.An exception occurred for leaf area in cycle 3, which showed the lowest value (8.00 m 2 ).However, this value is similar to that obtained by Oliveira et al. (2013), who reported maximum leaf area of 9.35 m² for "Grand Naine" banana, 10 months after planting, with an estimated irrigation depth of 1,276 mm cycle -1 , in the Coastal Plains of Cruz das Almas, Bahia.The higher values of leaf area and yield of "Grand Naine" banana, cultivated under irrigation configurations with the greater soil surface wetted areas, 23.74 and 28.26 m 2 , are associated with the larger wetted volume of soil to which these superficial soil surface wetted areas corresponded.Fifteen percent of roots were at distance of 0.15 m and 100% of roots at 1.36 m from plant for surface wetted area of 10.17 m 2 while less than 20% of roots were at 0.15 m from plant and 100% of roots was also at 1.36 m for 28.2 m 2 (Figure 3).A hundred percent of roots were found at depth of 0.75 m for surface wetted area of 10.17 m 2 while for 28.2 m 2 they were found at 0.90 m depth (Figure 3).Larger expansion of the root system as in distance or in depth represents more nutrients and water uptake per unit of soil volume.Therefore, it increases nutrient in plants (Donato et al., 2010), promotes higher vigor to the plants (Donato et al., 2013) contributing to the increment of fruit physical quality and yield of banana crop as observed in the present study.

Conclusions
1. Central fruit diameter and weight, leaf area and yield of "Grand Naine" banana are not altered by irrigation depths from 821 to 1,525 mm for a total evapotranspiration in the cycle of 1,108 mm, as well as for irrigation depths equal to or higher than 991 mm and total crop evapotranspiration in the cycle equal to or higher than 1,466 mm; 2. Larger soil surface wetted area promotes greater expansion of the root system, higher leaf area, higher fruit length and higher yield in "Grand Naine" banana; 3. The use of micro-sprinklers with greater radius of throw, equal to or higher than 2.70 m, promoted wetted volume with better moisture conditions for the production of "Grand Naine" banana, considering fractions of the required water depths between 0.85 and 1.15 of ETc or water depths between 897 and 1,349 mm for 1,108 mm of ETc during the cycle, between 1,204 and 1,629 mm for 1,466 mm of ETc during the cycle and between 1,813 and 2,353 mm for 2,097 mm of ETc during the cycle.

Figure 1 .
Figure 1.Experimental area located at Nova Porteirinha County in the Northern of Minas Gerais, Brazil.

Figure 2 .FFigure 3 .
Figure 2. Soil water tension referring to the different water depths applied through irrigation during the second cycle.

Table 2 .
Rainfall, crop evapotranspiration and total water depths required by the plants, according to the applied treatments (Nova Porteirinha-MG, Brazil).

Table 4 )
. Irrigation water depth has affected central fruit length (F test) but any regression model did not relate these variables.Based on fruit length classification (PBMH; PIF

Table 3 .
Analysis of variance of the studied variables.

Table 4 .
Mean central fruit length (CFL), diameter (CFD) and weight (CFW) of fruits for the different soil surface wetted and under different irrigation water depths for the three evaluation cycles.Means followed by equal uppercase letters in the column do not differ by Tukey test at 0.05 probability level.

Table 5 .
Leaf area and yield for the different wetted areas and under different irrigation water depths for the three evaluation cycles.Means followed by equal uppercase letters in the column do not differ for each cycle by Tukey test at 0.05 probability level.