EMERGENCE , GROWTH AND PRODUCTION OF SESAME UNDER SALT STRESS AND PROPORTIONS OF NITRATE AND AMMONIUM

In arid and semi-arid regions, the quality of irrigation water varies in geographic terms and during the year, and the occurrence of water with high concentrations of salts is common. In this context, this study aimed to evaluate the emergence, growth and production of sesame, cultivar CNPA G3, irrigated with saline water and fertilized with N of different carrier proportions by the ratio of nitrate and ammonium (NO3 -N and NH4 -N) in an experiment conducted in lysimeters arranged in a greenhouse in the municipality of Campina Grande-PB, Brazil. The treatments were distributed into randomized blocks using a 5 × 5 factorial scheme relative to levels of irrigation water salinity (ECw; 0.6, 1.2, 1.8, 2.4 and 3.0 dS m) and five proportions of NO3 -N/NH4 -N (200/0; 150/50; 100/100; 50/150 and 0/200 mg of N kg), with three replicates. The increase in ECw compromised the emergence, growth and production of sesame, cultivar CNPA G3, and the production components were the most sensitive variables. The highest growth in diameter was obtained with the proportion of 200/0 mg kg -1 of NO3 -N/NH4 -N. An ECw level of 3.0 dS m and fertilization with 0/200 mg kg of NO3 -N/NH4 -N promoted deleterious effects on the total mass of sesame fruits and mass of seeds. The interaction between water salinity levels and NO3 /NH4 + proportions significantly affected the number of leaves (at 50 and 70 days after sowing), the total mass of fruits and the mass of seeds.


INTRODUCTION
Sesame (Sesamum indicum L.) belongs to the Pedaliaceae family, and Africa is considered its center of origin due to the large number of species from the Sesamum genus on that continent (SOUSA et al., 2014).The oil extracted from its seeds can be used in the manufacturing of pies, margarine, perfumes, lubricants, medicines and soap.In addition, the high content of unsaturated fatty acids in the oil and digestive protein in the grains make sesame a food of high quality for human and non-ruminant domestic animals (AMABILE et al., 2001).
Besides the nutritional importance, sesame stands out in terms of good production stability relative to the water factor (low water requirement) compared to other cultivated species and constitutes an alternative source of income, especially for small and medium farmers in northeastern Brazil (ARAÚJO et al., 2014).
In this region, the occurrence of high temperatures, low rainfall, irregular rainfall distribution and intense evaporation is common.Combined with the variability in the water quality used for irrigation, in both spatial and temporal terms, the occurrence of water with high concentration of salts is common (ALVES et al., 2011).The use of water with high concentrations of salts limits the growth and production of vegetables, due to the reduction in the osmotic potential of the soil solution, and also may cause ionic toxicity, nutritional imbalances or both (FLOWERS, 2004).
Various studies have indicated the sesame crop to be sensitive to salinity (RHOADES;KANDIAH;MASHALI, 2000;SUASSUNA, 2013); however, there are reports pointing to it being moderately tolerant to salt stress (ABBASDOKHT et al., 2012;BAHRAMI;RAZMJOO, 2012).Therefore, it is evident that the use of saline water for irrigation is conditioned to the tolerance of crops to salinity and to the practices of both irrigation and fertilization management (LIMA et al., 2015); the tolerance level of plants to salinity may vary depending on the species and cultivars of the same species in addition to other factors, such as both type and concentration of salt as well as exposure time (GARCIA et al., 2010).
Among the management practices that can reduce the deleterious effects caused by salinity stress on sesame crops, N fertilization stands out (LIMA et al., 2012).In the soil solution, N can be found in the nitric and ammoniacal forms, but the rates of absorption by higher plants are influenced by factors such as the NO 3 -/NH 4 + proportion in the environment, temperature and concentration of carbohydrates in the roots, among others (TAIZ; ZEIGER, 2013).In addition, the interaction between N sources (nitric and ammoniacal) in plants has different effects on their growth and development (MASCLAUX-DAUBRESSE et al., 2010).
According to Ali, Sivakami and Raghuram (2007), the supply of N exclusively as NO 3 -may result in a decrease in dry matter production in plants with low capacity to reduce NO 3 -, because, for the N to perform its functions in the plant, it is necessary that it be reduced and incorporated into organic compounds.On the other hand, high levels of NH 4 + in the tissue cells can be toxic and cause negative effects on root and shoot growth (HACHIYA et al., 2012), leading to physiological and nutritional disorders (HOLZSCHUH et al., 2011).
Thus, this study aimed to evaluate the emergence, growth and production of sesame, cultivar CNPA G3, irrigated with saline water and fertilized with different proportions of NO 3 -and NH 4 + .

MATERIAL AND METHODS
The research was conducted in recipients adapted as lysimeters under greenhouse conditions at the Center of Technology and Natural Resources of the Federal University of Campina Grande, Campina Grande-PB, Brazil, situated at the local geographic coordinates 7°15'18" S, 35°52'28" W at a mean altitude of 550 m.
The experimental design consisted of randomized blocks in a 5 × 5 factorial scheme, with three replicates, totaling 75 experimental units, in which the treatments resulted from the combination of five levels of irrigation water electrical conductivity (ECw; 0.6, 1.2, 1.8, 2.4 and 3.0 dS m -1 ), associated with five proportions of NO 3 --N and NH 4 + -N (200:0, 150:50, 100:100, 50:150 and 0:200 mg N kg -1 of soil).The salinity levels (SL) of the water used in the irrigation of the sesame cultivar CNPA G3 were prepared in order to obtain a proportion equivalent to 7:2:1 of Na + :Ca 2+ :Mg 2+ , respectively, using the salts NaCl, CaCl 2 •2H 2 O and MgCl 2 •6H 2 O, adjusting them to the electrical conductivity values of the public-supply water available in the municipality of Campina Grande-PB (ECw = 1.35 dS m -1 ).The levels of 0.6 and 1.2 dS m -1 were obtained from a mixture of public-supply water and the rainwater (ECw = 0.02 dSm -1 ).After preparation and ECw calibration, the solutions were stored in 200-L plastic containers that were properly protected to avoid evaporation and entry of small insects as well as the entry and/or contamination with materials that could compromise the quality.
Plants were cultivated in lysimeters with a capacity of 20 L, with a hole at the bottom to allow drainage, connected to a transparent drain with diameter of 4 mm.The tip of the drain inside the lysimeter was fitted with a nonwoven geotextile (Bidim OP 30) to avoid clogging with soil material.The other tip of each drain was connected to a plastic bottle to collect the drained water and for estimating water consumed by the plants.The lysimeters were filled with a layer of 0.5 kg of crushed stone, followed by 24.5 kg of eutrophic Regolithic Neosol, of a sandy loam texture (0-20 cm), from the rural area of the municipality of Esperança-PB, properly crushed to break up clods, whose chemical and physical attributes (Table 1) were determined using the methodologies proposed by Donagema et al. (2011).
Table 1.Chemical and physical attributes * of the soil used in the experiment, prior to applying treatments.* Determined using the methodologies proposed by Donagema et al. (2011).OM -Organic matter: Walkley-Black wet digestion; Ca 2+ and Mg 2+ extracted with 1 M KCl, pH 7.0; Na + and K + extracted with 1 M NH 4 OAc, pH 7.0; ESP-Exchangeable sodium percentage; ECse -Electrical conductivity of the saturation extract; SL -Sandy loam; AW -Available water; AD -Apparent density; PD -Particle density.
The experiment used the sesame cultivar CNPA G3, which has medium size; a cycle between 90 and 100 days; a branched growth habit; and uniform flowering and maturation.It has one fruit/ axil and cream-colored seeds.It has resistance to angular leaf spot and susceptibility to Cercospora leaf spot and Macrophomina.It is indicated for the Brazilian semi-arid region, where angular leaf spot is the main disease of the crop (LIMA et al., 2013).
Prior to sowing, the soil received irrigation sufficient to achieve field capacity, using water according to the treatments.After sowing, irrigation was performed daily at 5 p.m. by applying water to each lysimeter according to the treatment in order to increase soil moisture to field capacity.The applied volume was determined based on the water requirements of the plants, estimated through the water balance: applied volume -volume drained in the previous irrigation.
Sowing consisted of planting 15 seeds of the cultivar CNPA G3 in each lysimeter.Thinning was performed in two steps: when the plants showed two and three pairs of true leaves at 20 and 30 days after sowing (DAS), respectively, leaving the most vigorous plant per plot.
Basal fertilization with K and P was based on the recommendation of Novais, Neves and Barros (1991).Calcium nitrate [Ca(NO 3 -) 2 •2H 2 O] was used as the source of NO 3 --N, while ammonium chloride (NH 4 Cl) was used as the source of NH 4 + -N.The treatments with proportions of NO 3 -/NH 4 + (PNA) were split; one-third of the recommended dose was applied as a basal amount and the other two-thirds in three equal applications, at intervals of 10 days, with the first one at 25 DAS.In order to inhibit/retard the nitrification of the ammoniacal N applied to the soil, in each application with ammonium chloride, a nitrification inhibitor (dicyandiamide [DCD]) was used at a dose of 10% in relation to the total nitrogen (NH 4 + ) (TRENKEL, 1997).To avoid possible deficiencies of macro-and micronutrients, Ubyfol was applied to the leaves at the beginning of the flowering stage (at 43 DAS) The emergence of sesame, cultivar CNPA G3, was evaluated through the determination of the percentage of emergence of normal seedlings (EP), emergence speed index (ESI) and growth through plant height (PH), stem diameter (SD) and number of leaves (NL) at 50 and 70 DAS.The production components corresponded to the total number of fruits (TNF), total mass of fruits (TMF), total mass of seeds (TMS) and hull dry mass (HDM).
The EP was obtained by daily counting of the number of emerged plants until establishment, adopting the criterion of the appearance of the epicotyl on the surface of the container.These data were used to determine the ESI via Equation 1, presented by Carvalho and Nakagawa (2000).
PH was measured as the distance from the base of the plant to the insertion of the apical meristem, SD was measured at 2 cm from the base of the plant and NL was obtained through the count of each plant.The values of total mass of fruits, seeds and hull were quantified on an analytical scale with a precision of 0.01 g and the TNF quantified after harvest.
The data were subjected to analysis of variance by a F test.When significant, polynomial regression analysis was applied to the water salinity level factor, and a test of comparison of the means (Tukey at 0.05 probability level) was applied to the proportions of NO 3 -and NH 4 + , using the statistical software SISVAR 4.2 (FERREIRA, 2011).

RESULTS AND DISCUSSION
According to the summary of the analysis of variance by the F test (Table 2), the interaction between factors (SL ×NAP) promoted a significant effect (p<0.01) on the variable NL in both evaluated periods.When analyzing the factors separately, the saline levels significantly affected (p<0.The process of germination was evaluated through EP and ESI, and, under saline water irrigation, these variables were significantly affected at the 0.05 and 0.01 probability levels, respectively (Table 2).According to Figure 1, the increase in ECw linearly reduced the variables, promoting decreases of the order of 4.65% for ESI and 7.52% for EP per unit increase in ECw (i.e., losses of 11.16% and 18.05% in ESI and EP, respectively, between plants irrigated using water of 3.0 and 0.6 dS m -1 , respectively, with negative effects on speed index and on the total emergence of normal sesame seedlings).When studying the effects of NaCl on emergence, growth and production of castor bean, Nobre et al. (2013) detected significant effects on ESI and EP, and, as observed in the present study, these variables showed linear decreases of 3.62% and 3.35%, respectively, per unit increment in ECw.According to Voigt et al. (2009), the reduction of these variables can be attributed to the lower water absorption caused by the increase in the concentration of soluble salts in the soil as well as by the absorption of ions in concentrations sufficient to cause toxicity to the embryo and/or cells of the endosperm membrane.These authors claim that high concentrations of Na + and Cl -ions damage the processes of cell division and differentiation; activity of enzymes; and acquisition and distribution of nutrients and may cause delay in seedling emergence and in mobilization of reserves.
As observed in ESI and EP, the concentrations of salts in the irrigation water significantly affected (p<0.01)PH and SD of sesame (Table 2), with linear reductions (Figure 2).The increase in water salinity reduced by 12.41% and 14.06% the growth in height of sesame plants per unit increase in ECw, at 50 and 70 DAS, respectively, and the lowest values of PH were estimated to be 104.82 and 139.58 cm for plants irrigated with 3.0 dS m -1 , which represented reductions of 29.78% and 33.74%, respectively, in both evaluation periods (Figure 2A).SD decreased by 11.05% and 13.76% per unit increase in ECw, which corresponded to losses of 30.87% and 38.75% in the SD of plants irrigated with water of 3.0 dS m -1 compared to the controls, respectively, whose values decreased by 4.24 at 50 DAS and 6.55 mm at 50 and 70 DAS, respectively (Figure 2B).In addition, the stress caused by water salinity on these variables was more intense at 70 DAS, denoting the effect of the accumulation of salts in the soil due to irrigation with saline water over time.According to Nobre et al. (2010), the increase in the concentration of salts in the soil solution, due to the supply from the irrigation water, negatively affects water absorption by plants, due to the reduction in the soil osmotic potential, compromising the photosynthetic and metabolic processes and, consequently, affecting the growth in height and SD.
Based on the values of SD of sesame, cultivar CNPA G3, under different NO 3 -/NH 4 + proportions, there was significant difference between the treatments at 70 DAS (Figure 3 In studies with interaction of NO 3 -and NH 4 + on the growth of peanut, Ribeiro et al. (2012) did not find significant effects of the treatments on SD, but the authors observed that the best responses occurred for the NH 4 + /NO 3 -ratios of 25/75 and 0/100, respectively.These results demonstrate that the peanut crop responds to the different ratios of the NH 4 + and NO 3 -ions in the nutrient solution, and, like sesame, this crop responds better to a supply of N in the nitric form compared to the ammoniacal form.
The results of the F test for the data (Table 2) reveal that the interaction between the studied factors (irrigation water salinity and NO 3 -/NH 4 + proportions) significantly influenced at the 0.01 probability level the NL at 50 and 70 DAS, evidencing that the studied factors act interdependently.According to Figures 4A and 4B, there is similar behavior of the variable in the studied periods, such that when sesame plants were subjected to different proportions of NO 3 -/NH 4 + , there were significant differences between the means only in the plants irrigated with water of lower (0.6 dS m -1 ) and higher salinity (2.4 and/or 3.0 dS m -1 ), at 50 and 70 DAS, respectively.+ proportion of 150/50 mg kg -1 showed the highest NL (143.33 and 319.66 leaves plant -1 , respectively, at 50 and 70 DAS).Furthermore, the lowest number of leaves (43.33 leaves plant -1 ) occurred at 50 DAS (Figure 4A) in plants irrigated with water of 2.4 dS m -1 and subjected to fertilization with 200/0 mg kg -1 of NO 3 -/NH 4 + .When comparing the means of the studied treatments (Figure 4B), sesame plants irrigated with water of higher ECw (3.0 dS m -1 ) and fertilized with 0/200 mg kg -1 of NO 3 -/ NH 4 + obtained the lowest NL (61.00 leaves plant -1 ), at 70 DAS.When analyzing the results obtained for NL in both studied periods together (50 and 70 DAS), the crop has greater preference for the absorption of N in the nitric form.Ribeiro et al. (2012) observed that the use of NH 4 + n greater proportions (100/0 and 75/25) inhibited the production of leaves, and, according to these authors, this effect can be attributed to the fact that the carbohydrates translocated from leaves to roots are preferentially used as skeletons of carbon and energy for the process of NH 4 + assimilation, to avoid its accumulation to toxic levels, and not for the processes associated with the growth of this organ.Holzschuh et al. (2011) observed, through the analysis of the xylem sap, that NH 4 + negatively affects the absorption of K, Ca and Mg ions, in magnitudes that depend on their concentrations in the environment.

Rev
The interaction between the irrigation water salinity levels and the NO 3 -/NH 4 + proportions significantly affected the mass of fruits and mass of seeds of sesame.On the other hand, the number of fruits harvested and HDM responded to the isolated effects of irrigation water salinity (Table 3).According to the F test, the production components of the crop respond differently to the effects of the interaction between the studied factors (SL ×NAP), but all respond to the effects of irrigation water salinity.
Table 3. Summary of F test results for total number of fruits (TNF), hull dry mass (HDM), total mass of fruits (TMF) and total mass of seeds (TMS) of sesame plants, cultivar CNPA G3, irrigated with saline water and fertilized with different proportions of NO 3 -and NH 4 + .
The total number of fruits per plant of sesame decreased linearly with an increase in ECw, showing a reduction of 31.45% in the number of fruits per unit increase in ECw (Figure 5A).When analyzing the behavior of this phenomenon, there was a reduction of 93.79% (106.74 fruits plant -1 ) between the highest (ECw = 3.0 dS m -1 ) and lowest (ECw = 0.6 dS m -1 ) levels of irrigation water salinity, and it can be concluded that the increase in water salinity directly interferes with the number of fruits and, consequently, the mass of seeds.As observed for TNF, HDM also decreased linearly with an increase in saline water level, showing a reduction of 32.22% per unit increase of ECw in the studied interval.Santos et al. (2012) claimed that this trend could be attributed to the fact that the plant, in order to adjust osmotically, uses a certain amount of energy for the accumulation of sugars, organic acids and ions in the vacuole, and this energy could be used for growth and production.Nobre et al. (2013) reported that the stresses caused by excess ions, in general, reduce CO 2 assimilation, stomatal conductance, transpiration and photosynthesis and, consequently, reduce crop production.
The interaction between the studied factors (irrigation water salinity and NO 3 -/NH 4 + proportions) significantly influenced, at the 0.01 probability level, the masses of fruits and seeds, reinforcing the fact that the studied factors do not act only in isolation on these variables.According to Figure 6A and 6B, there is a similar behavior of these variables, such that when the sesame plants were subjected to different proportions of NO 3 -/NH 4 + , a significant difference occurred only when the plants were irrigated with water of lower salinity (0.6 and 1.2 dS m -1 ).On the other hand, when the plants were subjected to irrigation with water of 1.8, 2.4 and 3.0 dS m -1 , regardless of the NO 3 -/NH 4 + proportion, there was no significant effect (p>0.05) of this interaction on the TMF or TMS variable.Columns with different letters in the same level of salinity differ by Tukey test at p<0.05.As observed in the results for NL (Figure 4A  and 4B), the highest values of total masses of fruits and seeds (48.84 and 26.04 g) were obtained in sesame plants irrigated with an ECw level of 0.6 dS m -1 and fertilized with an NO 3 -/ NH 4 + ratio of 150/50.On the other hand, although there was no significant influence on the total masses of fruits and seeds, plants subjected to an ECw of 3.0 dS m -1 and fertilized using proportions with larger amounts of ammonium chloride obtained the lowest TMF and TMS (1.69 and 0.55 g).According to the results, as the ECw levels increased, the dose of NH 4 + above the 100/100 ratio (NO 3 -/NH 4 + ) intensified the deleterious effects on plant production, indicating that the sesame crop absorbs more N in the form of NO 3 -.In a study with peanut plants, Ribeiro et al. (2012) also found a reduction in the development of this crop, which resulted in damage to its production, when the crop was subjected to higher proportions of NH 4 + (100/0 and 75/25 of NH 4 + /NO 3 -).This reduction was attributed to restrictions in the water flow of the plant, due to the effects of salinity caused by the NH 4 + ion, which promotes a reduction in the activity of the nitrate reductase enzyme, according to Silva et al. (2011).These authors claim that the effects of NH 4 + toxicity are attributed to the reduction or inhibition of the absorption of cations, especially K, as a consequence of the imbalance of ions.
When analyzing the effects of different proportions of NO 3 -/NH 4 + on cotton, cultivar BRS Topaz, under saline stress, Lima et al. (2016) found that fertilization with a higher NO 3 -dose (75/25 mg of NO 3 -N/ NH 4 + -N) promoted lower production of cotton seed mass (5.64 g plant -1 ), but when the plants were subjected to the proportions of 25/75 and 0/100 (mg of NO 3 -N/NH 4 + -N), they obtained the highest values of cotton seed mass (26.53 and 27.94 g plant -1 , respectively).Araújo et al. (2012) also found the largest numbers of panicles per plant in two rice cultivars when the proportion of the forms of N was 75% NO 3 -and 25% NH 4 + , and maximum grain production was observed when the ratio was equal to 78% and 77% for the cultivars BRS Colosso and BRSMG Conai, respectively.

CONCLUSIONS
The increase in irrigation water salinity compromises the emergence, growth and production of sesame, cultivar CNPA G3, and the production components are the variables most sensitive to saline stress.
The greatest growth of sesame, cultivar CNPA G3, evaluated by SD is obtained when plants are fertilized with a NO 3 -/NH 4 + ratio of 200/0 mg kg -1 .
An ECw level of 3.0 dS m -1 and fertilization with 0/200 mg kg -1 of NO 3 -/NH 4 + promotes deleterious effects on the TMF and mass of seeds in the sesame crop.
The interaction between saline water levels and NO 3 -/NH 4 + proportions significantly affects the NL (at 50 and 70 DAS), the TMF and the mass of seeds.
01) the ESI, EP, PH, SD and NL at 50 and 70 DAS.Regarding the proportions of NO 3 -and NH 4 + , only SD at 70 DAS was significantly affected (p<0.05).Table 2. Summary of the F test for emergence speed index (ESI), emergence percentage (EP), plant height (PH), stem diameter (SD) and number of leaves (NL) of sesame plants, cultivar CNPA G3, irrigated with saline water and fertilized with different proportions of NO 3 and NH 4 + , at 50 and 70 DAS.ns,**, *not significant, significant at p < 0.01 and p < 0.05, respectively.

Figure 1 .
Figure 1.Emergence speed index (ESI) (A) and emergence percentage (EP) (B) of sesame plants, cultivar CNPA G3, as a function of irrigation water salinity (ECw) and fertilization with different proportions of NO 3 and NH 4 + .
the other proportions did not differ.The excess of NH 4 + -N in the plant tissues, according toBritto and Kronzucker (2005) andHolzschuh et al. (2011), leads to toxicity in the plants because NH 4 + causes depolarization of the plasma membrane and the tonoplast; acidification of cell organelles in the attempt to maintain the electrical potential of the membranes; changes in the status of carbohydrates of the plants; decoupling of phosphorylation; and, consequently, physiological disorders that lead to the death of the cells and tissue.

Figure 3 .
Figure 3. Stem diameter (SD) of sesame, cultivar CNPA G3, as a function of fertilization with different proportions of NO 3 -and NH 4 + at 70 days after sowing (DAS).

Figure 4 .
Figure 4. Number of leaves (NL) of sesame, cultivar CNPA G3, at 50 (A) and 70 (B) days after sowing (DAS) as a function of the interaction between irrigation water salinity (ECw) and different proportions of NO 3 and NH 4 + .

Figure 5 .
Figure 5. Number of fruits per plant (A) and hull dry mass (HDM) (B) of sesame, cultivar CNPA G3, as a function of irrigation water salinity.

Figure 6 .
Figure 6.Total mass of fruits (TMF) (A) and total mass of seeds (TMS) (B) of sesame, cultivar CNPA G3, as a function of the interaction between irrigation water salinity and different proportions of NO 3 -and NH 4 + .