CONCENTRATION OF INJETION SOLUTION AND ITS EFFECTS ON SOIL AND ON YIELD OF FERTIRRIGATED BANANA CV TERRA MARANHÃO

The Fertigation is the combined application of water and nutrients to a crop. It can be adapted to all types of agricultural crops. The objective of this study was to evaluate the effect of urea concentration in irrigation water on electrical conductivity of the soil solution and saturation extract along the first cycle of banana cv. Terra Maranhão. The experiment followed a completely randomized design with six treatments and ten replications. Treatments regarded for using three urea concentrations (1.0; 2.5 and 4.0 g L) in irrigation water applied by two micro irrigation systems (microsprinkler and drip). Results showed that there was a linear elevation of electrical conductivity of saturation extract and soil solution with the increase on concentration of urea in the injection solution. Urea should be used under concentrations up to 2.5 g L in irrigation water without causing increase on electric conductivity of soil solution and saturation extract, considering 1.1 dS m as the tolerated value for the crop. Nitrate in the soil solution increased significantly with the increase of urea concentration in the injection solution. The maximum concentration of nitrate in the soil occurred for 4,0 g L concentration of the injection solution.


INTRODUCTION
The Fertirrigation is a technique that combines the application of water with fertilizers through certain irrigation systems.The use of this technique has made it possible to optimize the use of inputs in different irrigated crops, both in aspects related to productivity and the quality of the obtained products, being most notable its adoption in irrigated crops by localized irrigation systems (Oliveira et al systems., 2008(OLIVEIRA et al., 2008).Proper management should be used in order to maintain the values below the acceptable limits of soil salinity.Soil salinity has negative consequences for agricultural crops.About 900 million hectares are affected by salts (FAGERIA et al., 2010).Monitoring the soil salinity becomes crucial especially where fertirrigation is practiced.This misguided technique can raise the salinity of the soil, even if temporarily.The electrical conductivity of the soil can be used to quantify the salts in the soil.For purposes of fertirrigation electrical conductivity (EC) can be expressed as electrical conductivity of the soil solution (EC W ) in unsaturated conditions and the electrical conductivity of the saturation extract (EC se ), that is the CE of the soil solution when saturated.Studies using EC have pointed out their potential for measuring the nutrient content in the soil solution (ANDRADE NETO et al., 2012).
The effects of salinity on plants may be caused by the difficulty in water absorption, and toxicity of specific ions by interference of salts in the physiological processes (indirect effects), reducing the growth and development of plants (DIAS & BLANCO, 2010).This is because a higher salt concentration in the soil solution results in greater competition for water between the plant and the salts (osmotic effect), which impairs the essential metabolic processes of plants.The negative effect on plant development by salinity is due to the difficulty to absorbing water, the toxicity of the ions involved and the physiological effects caused by salts (GHEYI et al., 2010).The rational management of fertirrigation has give attention to monitoring the concentration of fertilizer in irrigation water and the injection solution.Different concentrations of salt in irrigation water provide different levels of electrical conductivity of the soil solution and the saturation extract.In this sense, promoting the direct monitoring of salinity in the root zone is recommended to evaluate the current situation and the effectiveness of various management programs in irrigated areas.Accordingly, the electrical conductivity of the stratum saturation (ECss) and soil solution (EC W ) are presented as tools to be used in monitoring the fertirrigation.Electrical conductivity values at certain levels can cause a decrease in productivity (BLANCO et al., 2008).
Among the most commonly used nitrogen sources are urea and ammonium sulfate.Nitrogen participates in various compounds considered essential for the growth and development of plants, especially proteins and chlorophyll (TAIZ & ZEIGER, 2009).Nitrate constitutes one of the inorganic forms of nitrogen in the soil and, together with the ammonia constitutes the final product of the mineralization of organic nitrogen.The objective of the present study was to evaluate the effect of the concentration of calcium nitrate and urea in the irrigation water on the electrical conductivity on soil solution, the saturation extract and nitrate content during the first cycle of the banana cv.Terra.

MATERIAL AND METHODS
The study was conducted in the experimental field of Embrapa Cassava and Tropical Fruits, located in Cruz das Almas -BA (12º48`S ; 39° 06`W; 225m).The climate is classified as humid to sub-humid with an average annual rainfall of 1,143 mm.The soil of the experimental area is classified as Oxisol with free texture.Featuring humidity corresponding to field capacity and the permanent wilting point of 0.2312 m 3 m -3 and 0.1645 m 3 m -3 , respectively 10 replications.The treatment means were compared by t test at 5% probability.The micro sprinkler system consisted of an emitter flow 43.0 L h -1 for four plants; the drip irrigation system involved a lateral line per plant row, with three emitters of 4.0 L h -1 per tussock of plants.The depth of irrigation water replacement between two irrigations was calculated by crop evapotranspiration estimated from A pan evaporation method.Fertirrigation occurred in a weekly frequency where the solution volume (water and solutes) and concentration of the injection solution was determined as recommended by COELHO (2009).Samples of the solution injection were collected in the solution tank and outlets of the emitters on the fertirrigation days.The irrigation time for micro sprinkler system was: 1 hour and 20 minutes; 33 minutes and 20 minutes respectively for concentrations of 1.0; 2.5 and 4.0 g L -1 .In the drip system, the average time for irrigation was 58 minutes; 24 minutes and 14 minutes, respectively for concentrations of 1.0; 2.5 and 4.0 g L -1 .Samples of soil solution were collected monthly at each plot for monitoring soil electrical conductivity (ECs), using water samplers installed near the dripper at depths of 0.20 and 0.40 m.Soil sample was also collected for for monitoring soil electrical conductivity of the saturation extract (ECs)at 0.30 m of plant near the dripper, with three replications per plot.The samples were collected with a Dutch auger type 0.030 m diameter, air-dried, and sieved on 0.002 m mesh.Then saturation paste was processed following EMBRAPA (1997) methodology from which was obtained the saturation extract that was used for determining the electrical conductivity using a table electrical conductivity meter.The solution samples were analyzed in kits of quick read "Horiba Card" for reading nitrate content.The kit was initially calibrated using solutions of known concentrations, presenting reliability of using, as COELHO et al. ( 2014) (Figure 1).Plant height, pseudo stem diameter at 0.20 m from soil surface and total leaf area (LA) were evaluated for growth analysis.Leaf area was estimated from the reading of the length and width of third leaf according to ALVES et al. (2010).Measurements of variables production were: productivity of hands, number of fruit per bunch, length and the diameter of the median fruit of the second hand.Average soil solution electrical conductivity and saturation extract as a function of urea concentrations were subjected to regression analysis and were compared between the irrigation systems by the Tukey test at 5% probability.

RESULTS AND DISCUSSION
Except for the concentration of 1.0 g L -1 there were no significant differences between means of EC se or EC s observed for the two irrigation systems.As for EC se under concentration of 1 g L -1 , the absolute averages for micro sprinkler system were superior to the averages obtained for the drip system.It was observed that for both systems the average EC s was equal to 0.9 times the EC se .These results are similar to those found by COSTA et al (2009).This superiority of EC se was also observed by (SANTANA et al., 2006).TABLE 2. Electrical conductivity averages of the saturation extract (EC s e ) and soil solution (EC s ), fertirrigated with urea by drip and micro sprinkler system.
There were linear increases in electrical conductivity of the saturation extract and soil solution as concentration of urea increased (Figure 2).For both electrical conductivities the angular coefficient of the linear function was higher for drip indicating greater increase in electrical conductivity per unity increase in the concentration of the solution in relation to micro sprinkler system.The effect of ions concentration in the soil solution or in the saturation extract resulting from the application of an ionic or saline solution is more pronounced on drip, since the solution is concentrated in a smaller volume of soil compared to micro sprinkler.The data of the electrical conductivity in the saturation extract (EC se ) and soil solution (EC s ) during the crop cycle, showed no continuous increase or decrease with time in any of the two systems studied (Figure 3).The values of the electrical conductivities EC se and EC s were higher for the concentration of 4.0 g L -1 followed by concentrations of 2.5 and 1.0 g L -1 .The increase on concentration of the fertilizer in irrigation water corresponded to the increases in the EC s and EC se .
The electrical conductivity of the soil solution (EC s ) and saturation extract (EC se ) were above 1.1 dS m -1 at irrigation water concentration of 4.0 g L -1 in both micro sprinklers and drip, in part of the crop cycle.The use of this concentration may cause damage to the crop as under drip as under micro sprinkler where 50% and 33% of the data of EC se exceed 1.1 dS m -1 , respectively, based upon the recommendation that the cultivation of banana should be done in soil with electrical conductivity of the saturation extract below 1.1 dS m -1 (OLIVEIRA, 1999).Banana is a glycophyte plant and therefore very sensitive to soil salinity (OLIVEIRA et al., 2000).The recommendation of OLIVEIRA (1999) is very close to those of other authors (DOOREMBOS & KASSAN, 1983;SILVA, 2002).DOOREMBOS & KASSAN (1983) claimed that banana need soil with EC se <1.0 dS m -1 .Based on these latter authors we should be careful with the concentration of 4.0 g L -1 , which resulted in values of EC se higher than 1.0 dS m -1 , in large part of the crop cycle for the two irrigation systems.ISRAELI et al. (1986), however, found average levels of salinity of water and soil of 3.6 and 3.0 dS m -1 , respectively, to cause delay in growth and decline in the banana production.No analysis of concentrations reached near the track of 3.0 dS m -1 .The layer of 0.20 m presented, except for the concentration solution of 1.0 g L -1 , higher concentrations of NO 3 -compared to the layer of 0.40 m for both the micro-sprinkler and for the drip.These results are expected since the process of infiltration and redistribution is more intense in the layer closest to the ground surface.Statistical difference was found between the average concentrations of NO 3 -of irrigation systems at both depths (P <0.05),where drip showed higher concentration of NO 3 -in the soil solution at both depths for all urea concentrations applied in the irrigation water (Table 3).This is due to the smaller wet volume under drip which affects larger volume of solution per volume of soil in relation to micro-sprinkler, in addition to the larger root growth expected in these wet volume.
The evaluation of the NO 3 -concentration in the soil solution, resulting from fertirrigation with urea application along the crop cycle in two depths resulted in elevated levels of NO 3 -in the soil solution as the concentration of urea increased in water irrigation (Figure 5).There was no definite trend of increasing or decreasing of nitrate concentration in the soil solution with time for all concentrations of urea throughout the crop cycle for both micro sprinklers and drip.On average, the levels of NO 3 -in soil solution ranged from 137.5 to 344.4 mg L -1 in the drip system and from 115.0 to 312.5 mg L -1 for micro sprinklers in the 0.20 m layer.In the 0.40 m layer, the variations were from 154.4 to 209.0 and 142.5 to 277.0 mg L -1 respectively for the drip and micro sprinklers.These tracks were next to those also found by ALVES et al. (2007) who studied different combinations of urea and calcium nitrate over the same crop and obtained levels of NO 3 -in soil solution between 3.5 to 225.0 mg L -1 and were similar to those obtained by KAISER (2010) that obtained levels of nitrate in the soil solution between 8 to 226.0 mg L -.The variations obtained were higher than the range of concentrations found by MONTEIRO (2007) who studied the spatial distribution of fertilizer ions (nitrate and potassium), using solution extractors and found values between 16.0 and 171.0 mg L -1 for Oxisol.No significant effect of urea concentration in irrigation water was observed on plant height, pseudo stem diameter and leaf area, and as the concentration increased, no increase was observed in growth parameters evaluated (Table 4).The leaf area reduction due to the increase of the salt levels is a common response in various banana genotypes (SILVA et al., (2009); WILLADINO et al., (2011).However for the salinity levels of the soil solution (less than 2.0 dS m -1 ), this reduction was not observed with increasing salt concentration in the irrigation water as a result of the treatments.There was effect of salt concentration on the characteristics of banana production for two used irrigation systems.The behavior of productivity as a function of concentration of irrigation water indicated that the concentration of the injection solution was different in the two irrigation systems (Figure 6), according to the concavity, but overall there was a declining trend in productivity with increasing concentration.The average productivity of treatments varied from 38.72 t ha -¹ to 53.86 t ha -¹ on drip, whereas treatment with 1.0 g L -1 showed higher productivity.The average productivity among irrigation systems did not differ for the concentration of 1.0 g L -1 (Table 5), the concentration of 2.5 g L -1 showed higher productivity, although with value closes to concentration of 1.0 g L -1 for treatments applied through micro sprinkler.The results are in agreement with those found by MEDEIROS et al (2008), who observed differences in productivity with increasing salt concentration in the irrigation water.There was no effect of concentration of the injection solution in production variables, length and diameter of the median fruit from the second hand (Table 5), which was also observed by ANDRADE NETO et al. (2011).These variables (length and fruit diameter) were not affected by the irrigation system (Table 5).

CONCLUSIONS
Urea can be used in concentrations up to 2.5 g L -1 in irrigation water without causing increases in electrical conductivity of the soil solution and the saturation extract above the amount considered appropriate for the crop 1.1 dS m -1 .
As the concentration of the injection solution increases, the concentration of NO3 -increases significantly in the soil solution with maximum at concentrations of 4.0 g L -1 .
The concentrations of urea in the injection solution has no effect on the pseudo stem diameter and height of the plant, as well as on length and diameter of the fruit of second hand, but has effect on productivity.

FIGURE 1 .
FIGURE 1. Calibration curve of the device Horiba Card.

FIGURE 2 .
FIGURE 2. Electrical conductivity of the saturation extract (a) and soil solution (b) as a function of concentration of the inject solution.

FIGURE 3 .
FIGURE 3. Values of electrical conductivity of the saturation extract (a and b), the soil solution (c and d), for fertirrigation with urea in two irrigation systems (drip and micro sprinkler).

FIGURE 4 .
FIGURE 4. Nitrate concentration in the soil solution as a function of concentration of the injection solution to (a) 0.20 m and (b) 0.40 m depth.

FIGURE 5 .
FIGURE 5. Concentration of NO 3 -in the soil solution at depth of 0.20 m (5 a) and 0.40 m (5 b) in fertirrigation with urea applied in two irrigation systems (drip and spray).

FIGURE 6 .
FIGURE 6. Productivity of banana cv.Terra Maranhão as a function of concentration of the injection solution.

TABLE 1 .
The chemical characteristics of the soil at the beginning of the experiment.

TABLE 3 .
NO3 -average in soil solution at depths of 0.20 and 0.40 m in drip and micro sprinkler system fertirrigated with urea.

TABLE 4 .
Averages plant height, pseudo stem diameter and leaf area of banana cv.Terra Maranhão.
* Letters compare irrigation systems on the same line (p = 0.05).

TABLE 5 .
Average productivity, length and diameter of the fruit of the banana cv.Terra Maranhão.
* Letters compare irrigation systems on the same line (p = 0.05).