Development , Physiology and Productivity of the Common Bean Under Different Nitrogen Doses

Among nutrients, nitrogen is required in the greatest quantities by bean culture. The objective of this work was to evaluate growth, physiological responses and productivity of the common bean cultivar, ‘IAC Imperador’ under varying nitrogen doses in Brejo Paraibano. The experiment was carried out at Fazenda Experimental Chã-de-Jardim (Chã-de-Jardim Experimental Farm), of the Centro de Ciências Agrárias of the Universidade Federal da Paraíba, in the municipality of Areia, state of Paraíba. The treatments comprised 0, 50, 100, 150 and 200 kg of nitrogen ha, applied in coverage at 35 days after sowing. To assess growth, plant height, stem diameter and number of leaves were evaluated. For gas exchange, photosynthesis rate, internal CO2 concentration, transpiration, stomatal conductance, instantaneous water use efficiency and instantaneous carboxylation efficiency were evaluated. For chlorophyll “a” fluorescence, minimum leaf fluorescence, maximum leaf fluorescence, variable maximum fluorescence, potential quantum efficiency of PSII (Photosystem II) and ratio (Fv/F0) were evaluated. For the components of primary productivity, the height of insertion of the first pod, number of pods per plant and the number of grains per pod were evaluated. Nitrogen fertilization in coverage significantly affected most of the growth, gas exchange and productivity variables, with the dose of 200 kg ha being responsible for the highest values (p < 0.05). Chlorophyll fluorescence showed no significant differences among the nitrogen doses. The nitrogen doses influenced the growth, gas exchange and productivity of the common bean in the region of Brejo Paraibano.


Introduction
Beans (Phaseolus vulgaris L.) are one of the most economically important crops for Brazil (FAO, 2017), generating employment and income, and are an important source of protein for the population.The expected national production in 2017 exceeds 3.3 million tons (IBGE, 2017).However, the average productivity of 886 kg ha -1 (CONAB, 2017) is considered low and due mainly to the low level of technology employed (Nascente et al., 2012).
The management of fertilization is considered fundamental to achieving better grain yields (Arf et al., 2011), with nitrogen (N) being the most influential nutrient for bean crops.This macronutrient is of great importance to the physiology of bean plants because it acts on the composition of the chlorophyll molecule by transforming photoassimilates into grain, thereby increasing productivity (Soratto et al., 2006).When evaluating fertilization with nitrogen in coverage, Crusciol et al. (2007) found productivity above 3,000 kg ha -1 , and obtained significant responses for nitrogen doses up to a maximum of 120 kg ha -1 .High doses of nitrogen can stimulate vegetative growth and cause morphological changes in plants (Marschner, 1995).Growth assessment is essential for analyzing the effects of management systems on plants by providing information on plant productivity as a function of time, which is impossible to obtain from only grain yield (Urchei et al., 2000).
Several Brazilian ecosystems are favorable for bean cultivation, including the Brazilian semi-arid region, which possesses intrinsic edaphoclimatic conditions.However, there is a lack of studies in support of making the management of nitrogen fertilization and the use of more productive genotypes feasible for achieving satisfactory yields and results for producers.

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Study A
The resea (Chã-de-Ja Paraíba, in Aw', accor months of shown in F The bean c semi-erect Fusarium The prope Na + ; 5.49 1. 23  T5 (200 kg ha -1 ).The plots had a total area of 9.0 m² and a useful area of 6.0 m 2 , in which five plants were chosen, at random from three central lines of each plot, so that they could be evaluated.
The data were submitted to analysis of variance, according to the design adopted.In the study of the effects of N doses, data were submitted to regression analysis, with adjustment of representative curves, according to the evaluated characteristics (Soares et al., 2016).

Growth Analyses
Table 1 provides F-test results that show that nitrogen fertilization did not affect plant height, but significantly affected diameter and the number of leaves.The CVs of all of the variables analyzed were low.It should be emphasized that the experiment was carried out in the field.
Figure 3A shows mean plant height at 45 and 60 days after sowing.Height did not differ significantly among nitrogen doses, but maximum heights were obtained at doses of 0 and 200 kg ha -1 for both evaluation periods, with it being 8.3 cm at 45 days and 18.4 cm at 60 days.The dose of 100 kg ha -1 produced the shortest height for both evaluation periods.
These results are the opposite of those reported by Biscaro et al. (2012), who found a growth response up to the dose of 125 kg ha -1 , and for Cunha et al. (2013) andViana et al. (2013), where they obtained increases in growth due to the application of up to 136 and 108 kg ha -1 , respectively.However, the results of Valderrama et al. (2012), not found an effect of nitrogen fertilization on plant height, are similar to those of the present study.These differing results may be related to different edaphoclimatic conditions where the experiments took place.According to the edaphoclimatic conditions observed during the present experiment (Figure 2), accumulated value (495.8 mm) was higher than the water requirement of the crop, which ranged from 300 to 400 mm (Moreira et al., 2003).Souza et al. ( 2013) attributed these differences specifically to soil fertility levels and to the production systems adopted by the authors, in addition to irrigation.
Studying different bean genotypes under varying doses of nitrogen fertilizer, Sousa et al. ( 2012) found higher growth with the use of 80 kg ha -1 , and a constant growth until the dose of 150 kg ha -1 , with doses higher than this causing a negative effect on growth.Evaluating different doses of fertilization in different salinities, Sousa et al. (2013) did not find differences between the doses of nitrogen applied up to 190% of the recommended dose for bean crops.Similarly, working with sources and doses of N, on the surface and incorporated, Cunha et al. (2013) also observed an increase in bean height with nitrogen supply.
Studying organomineral fertilization, Nakayama et al. (2013) observed linear growth as a function of the application of nitrogen up to 250 kg ha -1 .These data are similar to those found by Salgado et al. (2012), who evaluated different bean cultivars in nitrogen poor and rich soils and found that growth was better in soils with high nitrogen concentrations.
Bean plant height did not respond well to fertilization even though it was expected that the increased availability of the nutrient would lead to greater absorption and height growth since adequate doses of nitrogen are associated with high photosynthetic activity and, consequently, vigorous vegetative growth (Souza et al., 2014).Nitrogen uptake and crop use are strongly influenced by meteorological conditions, so it is important to discuss agronomic characteristics in relation to precipitation, such as low soil water reserves and/or low precipitation, since these factors can substantially reduce nitrogen uptake, particularly immediately after fertilization (Vleugelsa et al., 2017), which indeed occured in the present study.
The studied bean 'IAC imperador', which is adapted to the region, may have developed a capacity for plasticity and translocated nutrients from other plant sites and invested in growth.This factor could lead to a reduction in other aspects of the plant, such as productivity.
The mean diameter of bean plants responded positively to the doses of nitrogen, mainly at 60 days after sowing.The dose of 200 kg ha -1 promoted the greatest growth in stem diameter, with an increase of 5% and 16% relative to the control treatment at 45 and 60 days post-sowing, respectively (Figure 3B).These data are similar to those found by Nakayama et al. (2013), who obtained linearly increasing values in diameter using nitrogen fertilizer up to a dose of 250 kg ha -1 .On the other hand, Salgado et al. (2012) and Sousa et al. (2013) did not find significant difference for stem diameter in situations of low and high availability of nitrogen in the soil, but confirm that differences can occur depending on the conditions of the growth environment or the use of different cultivars.
Studying nitrogen fertilization of up to 150 kg ha -1 at different times, Vleugelsa et al. (2017) did not find differences in plant diameter among applied doses.This may have been due to the fact that nitrogen is a very  2).Evaluating the effect of nitrogen fertilization on growth and gas exchange of bean plants, Soares et al. (2013), found a significant effect of nitrogen doses only for transpiration.
Figure 4 provides the mean values for the physiological responses of beans to the effects of N doses, specifically for photosynthetic rate (A), internal CO 2 concentration (Ci), transpiration (E), stomatal conductance (gs), instantaneous water use efficiency (IWUE) and instantaneous carboxylation efficiency (ICE).
Regarding gas exchange, the values for photosynthetic rate (A) exhibited an increasing linear response to the effect of the doses of N and, according to the regression equation, the values range from 15.552 µmol m -2 s -1 (control, 0 kg of nitrogen ha -1 ) to 17.891 µmol m -2 s -1 (200 kg of nitrogen ha -1 ) (Figure 4A).The dose of 200 kg of nitrogen ha -1 had the highest values of photosynthetic rate, which may be related to there being a sufficient amount of nitrogen since the nutritional state of plants influences photosynthesis.According to Taiz et al. (2017), the deficiency of some nutrients, such as nitrogen and magnesium, in the soil causes chlorosis in the leaves, which interferes with the process of photosynthesis.According to Larcher (2004), the highest photosynthetic rates are achieved through fertilization.
The results for transpiration (E) followed the same trend of stomatal conductance with a linear response to the effect of N doses, with values varying between 2.926 mmol m -2 s -1 (control, 0 kg of nitrogen ha -1 ) and 4.010 mmol m -2 s -1 (200 kg of nitrogen ha -1 ) (Figure 4B).The elevation of leaf transpiration rate not only increases water flow in the xylem, but also raises the concentration of cytokinin synthesized in the roots, which is an important mechanism for delaying leaf senescence, as evidenced in the present study (Larcher, 2004;Marschner, 1995;Soares et al., 2013;Taiz et al., 2017).
The internal carbon concentration (Ci) exhibited an increasing linear response to the effect of the doses of N and, according to the regression equation, increased the most with the dose of 200 kg of nitrogen ha -1 (Figure 4C).
The internal carbon values varied between 188.72 µmol m -2 s -1 (control, 0 kg of nitrogen ha -1 ) and 534.19 µmol m -2 s -1 (200 kg of nitrogen ha -1 ).Ferraz et al. (2012) analyzed gas exchange of cultivated beans in the field in the semi-arid region of Northeast Brazil, and found no significant responses to the different doses, with the most expressive results being 277.0 and 289.6 μmol m -2 s -1 .Evaluating the effects of nitrogen on gas exchange of the common bean, Anjos et al. (2014) found no significant effect of the different doses on internal carbon concentration.
Stomatal conductance (gs) exhibited a linear response among doses, with the lowest values being for the control (0 kg of nitrogen ha -1 ), which had values varying between 0.157 mol m -2 s -1 (control) and 0.264 mol m -2 s -1 (200 kg of nitrogen ha -1 ).This response may be related to a high degree of closure of the stomata at the lowest N doses in order to void losses to the water conduction system.Nitrogen is a nutrient involved in protoplasmic processes, enzymatic reactions and photosynthesis, causing an osmotic gradient that allows the movement of water, thereby regulating the opening and closing of stomata (Epstein & Bloom, 2006;Silva et al., 2013).
Regarding instantaneous water use efficiency (IWUE), a reduction of 28% was observed between the highest value of 102.50 [(µmol m -2 s -1 ) (mmol m -2 s -1 ) -1 ] for the 200-dose kg of nitrogen ha -1 , and the lowest value of 84.75 [(µmol m -2 s -1 ) (mmol m -2 s -1 ) -1 ] for the control (Figure 4E).The increase in IWUE for the 100-dose kg of nitrogen ha -1 may be associated with the already established benefits that this dose provides to gas exchange in bean plants, which provides better development of the photosynthetic process.This parameter is determined by the relationship between the rate of photosynthesis and the rate of transpiration (A/E), in which the values measured relate to the amount of carbon the plant receives for each unit of water it loses (Jaimez et al., 2005).
The instantaneous carboxylation efficiency (ICE), calculated by ratio A/Ci, differed among the different doses.
Plants that received the dose of 200 kg of nitrogen ha -1 had the highest instantaneous carboxylation efficiency, with 0.560 [(μmol m -2 s -1 ) (μmol mol -1 ) -1 ] (Figure 4F).The instantaneous carboxylation efficiency (ICE) obtained by Machado et al. (2005) bears little resemblance to the internal CO 2 and the carbon dioxide assimilation rate.Some authors, such as Silva (2012), have found high values for internal CO 2 concentration, associated with increased stomatal conductance, indicating an increase in the instantaneous carboxylation efficiency.Similar results were found in the present work, with ICE values varying among the doses of N applied (Figure 4F).Evaluating the effect of nitrogen fertilization on three bean-cultivars, Ferraz et al. (2012) recorded ICE values ranging from 0.03 to 0.08 [(μmol m -2 s -1 ) (μmol mol -1 ) -1 ].Note.ns, * Figure conducta  In relation to chlorophyll fluorescence, no significant differences were observed among doses applied and the analyzed variables (Table 3).The doses of nitrogen applied to the bean plants did not significantly interfere with minimum fluorescence (F 0 ), indicating all reaction centers were open (Figure 5A).According to previous experiments (Baker & Rosenqvst, 2004;Konrad et al., 2005;Suassuna et al., 2010), maximum fluorescence (F m ) represents the maximum intensity of fluorescence, when practically all the quinone is reduced and the reaction centers reach their maximum capacity of photochemical reactions.In the case of the present study, the doses of nitrogen applied did not interfere with the reduction of quinone.Maximum variable fluorescence (F v ), potential quantum efficiency of PSII (F v /F m ) and the ratio between maximum variable fluorescence and minimum fluorescence (F v /F 0 ) also did not differ significantly among doses (Table 3 and Figure 5).

Chloro
There have been other studies relating fertilization to fluorescence efficiency in beans.Studying different irrigation levels and fertilization of the eggplant, Silva et al. (2014) found similar values of F m , where increased irrigation depth and nitrogen doses did not interfere with F m .Therefore, in the present study (Figure 5B), the highest values of F m found, although not significant, may be related to the availability of water during the conduction of the experiment being favorable for the development of the crop (495.8 mm), thus showing that it did not cause deficiency in quinone A (QA) photoreduction and the flow of electrons between photosystems (Tatagiba et al., 2014).
All of the values for potential quantum efficiency of PSII were greater than 0.75 electrons quantum -1 (Figure 5D), indicating that the photosynthetic apparatus is intact and performing all its functions.Previous works carried out with stress from fertilization and irrigation levels have verified that this is the threshold for a good response of plants to photosynthetic potential with no damage being caused (Reis & Campostrini 2008;Santos et al., 2010;Suassuna et al., 2010).
The ratio F v /F 0 is usually used in studies to evaluate different factors in several species, among them fertilization, shading and water stress.When studying the effects of salinity and fertilization on fluorescence parameters of P. vulgaris, Zanandrea et al. (2006) observed a maximum value of 4.578 electrons quantum -1 when 80 mmol L -1 of NaCl was applied.Studying gas exchange and chlorophyll fluorescence in six legume cultivars under aluminum stress, Konrad et al. (2005) found that the Fv/F0 ratio did not differ significantly among the six cultivars evaluated.In view of this, it can be seen that the type and dose of nitrogen can affect the physiological behavior of plants, but soil nitrogen my have been sufficient to supply the minimum fluorescence needs of the bean in this experiment (Figure 5E).