BLACK PEPPER RESPONSE TO DIFFERENT IRRIGATIONS DEPTHS

Objective: This study aimed to evaluate the effect of irrigation depths on development, productivity and water use efficiency of black pepper. Theoretical Framework: Irrigation management is a very important technique from an economic and environmental point of view in an irrigated agricultural activity. Proper irrigation management can save water and energy, increase crop productivity and improve product quality. Method : The experiment had five treatments, four replications, with depth irrigation replacement related to the crop evapotranspiration (ETc). The treatments were T1: 25% of ETc; T2: 50%; T3: 75%; T4: 100%; and T5: 125%. In the first year we evaluated: number of leaves per plant (NLP), plants height (PH), stem diameter (SD) and leaf temperature (LT). In the second year the number of bunches per plant (NBP) and the productivity of fresh grains (PFG) and dry grains (PDG). Results and conclusion: The best results were, respectively, 52.5 (NLP); 173.1 cm (PH) and 13.5 mm (SD), with 100% of ETc. The lowest values of leaf temperature were in the 100% treatment. The best results for NBP and PDG were found in 75% and 100% depths, respectively. The total evapotranspiration that promoted the highest PDG was 563.2 mm, with a yield of 875.2 kg ha -1 and 0.155 kg m -3 of water use efficiency. Implications of research: Producing satisfactorily with water use efficiency is essential for the sustainability of irrigated agriculture. Originality/value: Studies that evaluate the efficiency of water use and its relationship with crop yield are in evidence and need to be encouraged.


INTRODUCTION
Black pepper (Piper nigrum L.) is a climbing plant, belonging to Piperaceae family, of high productivity and one of the most valued spices in the world, with great economic value and also known as Indian pepper or black gold (Lima et al., 2010;Takooree et al., 2019).
Introduced in Brazil in the seventeenth century in the state of Bahia, and then brought to the States of Paraíba, Maranhão and Pará (Pedeag, 2016), black pepper presented economic importance only in 1993 year, when it was reintroduced in the state of Pará by the Japanese people.Currently, it has a major presence in the municipalities of the North of Espírito Santo state, making it the second largest producer and exporter at the national level, after Pará state.
The plantations in the North of the State are concentrated in the municipalities of São Mateus and Jaguaré, with more than 75% of cultivated area and production (Ramos, 2015).
Brazil is the fourth-largest producer of black pepper in the world (Faostat, 2020).Due to the good adaptation of the different types of soil, there are several commercially accepted cultivars of black pepper in Brazil, among them, Bragantina (Lemos et al. 2014;Pinho et al., 2020;Pannaga et al., 2021) Black pepper is the most used spice by Brazilian cuisine.It is mainly used in industrialized products (salami, sausage, mortadella, ham) and for food seasoning.Brazil consumes only 10% in the form of whole grains, the other 90% are used in the form of milled grains, in mixtures with other condiments (Duarte & Albuquerque, 2005).

THEORETICAL FRAMEWORK
The black pepper grain productivity is an indicative of profit for the farmers, being directly related to the crop profitability.Therefore, irrigated crops tend to be more profitable (Balana et al., 2020), since they can present a longer period of grain filling (flowering until maturation) and green leaf area to perform photosynthesis and remobilize the reserves, providing a greater supply of grain assimilates (Tao et al., 2021).
According to Bonomo et al. (2013), irrigation management is a very important technique from an economic and environmental point of view in an irrigated agricultural activity, because with proper irrigation management, we can save water, energy, increase crop productivity and improve product quality (González Perea et al., 2018;Saccon, 2018;Imran et al., 2019).
Therefore, irrigation practices are important to ensure production in the region's most susceptible to water deficit (Satriani et al., 2018).Based on this, it is essential to know the water requirement of the black pepper, cultivated under different irrigation depths, so that it has a good productivity and a better use of the applied water, avoiding excess or water deficit.
The objective of this study was to evaluate the effect of irrigation depths on the initial development and productivity of black pepper cultivar bragantina and to identify the percentage of irrigation that provides the best water use efficiency.

FIELD OF STUDY
The cultivation was carried out in a field, on a small farm, in São Mateus, Espírito Santo state, Brazil, at coordinates 18° 44' S and 40° 06' W, in an altitude of 77 m above sea level.

EXPERIMENTAL DESIGN AND TREATMENT
The experimental design was a randomized block design (RBD), with five treatments and four replications.Four useful rows were planted, spaced 2.5 m between rows and 2 m between plants.Six plants were planted for each treatment, two plants were considered as borders, and four useful plants, with 144 plants in the experiment, being 96 useful plants.

CONDUCTING THE EXPERIMENT
Pepper seedlings were planted in December 2016 and conducted until the beginning of April 2018 for 470 days.The period was divided into two stages, the first from planting until day 199, called Year 1 (Vegetative stage), and the second, from day 200 to day 470, called Year 2 (Productive stage).The local soil has a sandy texture, field capacity of 18% (weight base), permanent wilting point of 9% (weight base), and bulk density of 1.15 g cm -3 .The effective root system depth considered was 0.4 m and the maximum allowable depletion of water for the crop (f factor) was 0.4.
For irrigation depths variation, we installed different numbers of emitters per plant, so that all irrigations were done at the same time.The treatments consisted of different irrigation depths, proportional to crop evapotranspiration (ETc), as follows: T1: 25% of ETc (1 emitter); T2: 50% (2 emitters); T3: 75% (3 emitters); T4: 100% (4 emitters); and T5: 125% (5 emitters).A microspray irrigation system was used, working at of 100 kPa-pressure and 10 L h -1 -flow rate.Figure 1 shows images of the experimental area, at planting time (A and B) and the production stage (C).After the installation of the irrigation system and the plots demarcation, we assessed the irrigation system, and calculated the Christiansen Uniformity Coefficient (93%) and the emitters flow rate (10 L h -1 ) (Thompson and Ross, 2011).For the irrigation system efficiency assessment, the treatment 4 (T4 -4 emitters) was used as a reference, applying 100% of irrigation depth related to the crop evapotranspiration.In the assessment, a 1,000 mL beaker and measuring cups were used, measuring the volume of water collected from each emitter, from a total of 16 emitters, at a time of 20 seconds.
Irrigation management was performed using a spreadsheet (Figure 2), determining the black pepper water demand, using coefficients of adjustment (soil moisture coefficient -KS and coefficient due to the location of the irrigation -KL) on the reference evapotranspiration (ETo).The values of KS were calculated with the logarithmic model (Mantovani et al., 2009).
The percentage of wetted area was 40%, resulting in a KL of 0.63, calculated by the method of Keller and Bliesner (1990).The gross irrigation depths were calculated by water balance, in which the inputs of water were irrigation and rainfall and the exit was crop evapotranspiration (ETc).We determined the soil moisture by the gravimetric method (Bernardo et al., 2019) to compare it to the calculated soil moisture.

Figure 2
Spreadsheet used to calculate evapotranspiration and water balance.For the ETo estimation method, the available meteorological elements (maximum and minimum air temperatures) were used, following the Hargreaves and Samani model (Allen et al., 1998).The temperature data used to calculate the evapotranspiration were obtained in a digital thermometer installed in the farm.The values of Kc used were 0.6 in the initial stage (21 days), 0.7 in the intermediate stage (314 days) and 0.9 in the final stage (136 days).

EXPERIMENTAL DATA
In the first year, we evaluated the number of leaves per plant (NLP), the plant height (PH), the stem diameter (SD) at soil level and the leaf temperature (LT), following the methodology described by Vieira et al. (2014), at 64, 138 and 199 days after planting (DAP).
In the second year, we evaluated the experiment at 353, 409, 445 and 470 DAP, measuring the number of bunches per plant (NBP), the productivity of fresh grains (PFG) (kg ha -1 ) and the productivity of dry grains (PDG) (kg ha -1 ).Leaf temperature values were compared graphically with the maximum temperature recorded on the day of measurement.
To calculate the water demand, the values of water depths applied in the two crop cycles were summed for all treatments.We calculated the water use efficiency for each treatment, using dry grains productivity data.

STATISTICAL ANALYZES OF DATA
To verify the assumptions for validation of the analysis of variance, the evaluated variables were submitted to the normality test (Shapiro Wilk).As the variables met the assumptions, it was adopted as a procedure for the decomposition of the degrees of freedom of the treatments in regression models by the orthogonal polynomial's method, being the choice of the model based on the coefficient of determination and the level of significance.For all procedures, the significance of variance analysis was presented in the graphs.

RESULTS AND DISCUSSION
Figure 3 shows the calculated and measured soil moistures, irrigation, rainfall and soil water limits (field capacity, permanent wilting point, and safety soil moisture) during the experimental period for the T4 treatment (100% of ETc).In this treatment, the soil moisture was, in the majority of experimental period, kept above the safety limit, i.e. closer to the field capacity, however, in some moments there were decrease of soil moisture to values below the limit (green line).The measured moisture values served as a reference for adjustments of the values used in the irrigation management at the beginning of the experiment and for validation of the calculations from the third month.In the figures 4 (A), (B), (C) and (D), we can see the number of leaves per plant (NLP), the plant height (PH), the stem diameter (SD), and the leaf temperature (LT), respectively.
There was a linear behavior for all variables NLP, PH, and SD, for the evaluations at 138 and 199 DAP, where the best averages were obtained in the water depth referring to 100% of the crop evapotranspiration (346.2 mm).For the LT variable, the highest value was obtained in the 25% of ETc (304.8 mm) at 64 DAP.For the variables NLP, PH, and SD, the evaluations at 64 DAP did not present significant results, because at this initial stage, the plants were in the field acclimation stage, therefore irrigation did not influence its initial development, since the contact between the roots and the soil provided a surface area for the absorption of water.Therefore, transplanted plants demand greater protection against water losses as soon as they go to the field, because in this period, the new roots that are being emitted will restore their root-soil connection, which may take a few days until this process occurs totally, causing then water stress.
There are many factors that are considered critical when plants are submitted to water stress, such as photosynthesis (Zhang et al., 2018), stomata behavior (Tsai et al., 2020), reserve mobilization (Prats-Llinàs et al., 2019), leaf expansion and growth (Anjum et al., 2017;Shafique et al., 2020).Thus, one of the first processes that are affected in the plant with water deficit is the division and the cellular expansion (Small & Degenhardt, 2018), where the growth of the leaves and stems diminish considerably before it becomes severe, causing the stomata to close (García-Tejero et al., 2018;Klein, 2014) and cause photosynthesis decreasing (Zandalinas et al., 2018;Vieira and Ferrarezi, 2021).
We verified that 25 and 52.5 leaves per plant were obtained at 138 DAP and 199 DAP, respectively.A similar result was found by Martins et al. (2006), working with Conilon coffee (Coffea canephora).They observed that the increase of the applied water depth provided greater fresh matter production of the plants and that the low availability of water caused a smaller roots development.
At 138 DAP, an average plant height of 116 cm was observed and at 199 DAP, it was observed 173 cm.Alves et al. (2000), when working with Conilon coffee, observed that the average plant height values maintained an upward trend as a function of the applied irrigation depth, which is similar to the results found in this study, where the highest plant height was found in treatments applying 100 to 125% of ETc at 199 DAP.
We measured, at 138 DAP, 9.2 mm of SD and at 199 DAP, 13.5 mm.Rodrigues et al. (2009), when working with castor beans, observed that there was an increase in the SD, with greater sensitivity in the initial phase of growth, deducing that plants cultivated without water restriction should be more resistant to tipping due to the sturdier stalks.It was also noticed that the smaller the depth applied, the smaller the diameter of the stem, a result similar to that found in this study.Papazoglou et al. (2020) did not observe the same trend for castor beans with moderate water scarcity.
There was a trend to decrease the leaf temperature as we increased the irrigation depth at 138 and 199 DAP, besides there was no statistical adjustment for the polynomials (P>0.05).
Comparing the leaf temperature values with the maximum air temperature recorded on the days of measurements, a closer approximation is observed in the treatments with the lowest irrigation depths (lower ETc values).These results corroborate with those of Trentin et al. (2011) and Vieira and Ferrarezi (2021), in greenhouse studies with sugarcane and citrus, respectively, in which plants maintained under adequate water supply had lower temperatures, when compared to those under conditions of severe water stress.
The increase in leaf temperature causes a reduction in stomatal conductance (Fauset et al., 2019), a process in which the stomata open allowing the vapor escaping and the diffusion of the carbon dioxide from the atmosphere to the interior of the leaf (Peak et al., 2023), which is the raw material of photosynthesis.Another factor that contributes to the variation in the stomatal and transpiratory behavior of the plant is the variation of the angle of exposure of the leaves to the solar rays (Krukowski et al., 2020), being, therefore, an important mechanism of plants' defense, that occurs mainly in periods of water stress, decreasing the leaf temperature and, consequently, stomatal transpiration (Oliveira et al., 2005).The stomata opening is also related to the water condition of the soil (Kangur et al., 2021) and not only by solar radiation.
Apparently, the plant seeks to reduce leaf area to reduce transpiration (Cruz et al., 2019) without abruptly affecting water absorption capacity by roots.
The number of bunches per plant (NBP), productivity of fresh grains (PFG) and productivity of dry grains (PDG) are presented in Figures 5 (A), (B), and (C).The linear model was chosen to represent the phenomenon due to the higher values of significance for all variables, where the best averages were observed close to the depth of 100% ETc.

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The lowest averages were observed in the depth of 25% ETc (470.2 mm), with the productivity-increasing proportionally to the increase of the applied depth, up to the 100% ETc (547.8 mm).These higher averages occurred due to the water supply in quantities adequate to the crop needs, mainly in the pre-flowering stages until the ripening of the grains, when the water stress could affect the translocation of sap in the plant and its productivity (Ramadan et al., 2022;Othibeng et al., 2022).
For the NBP, the reduction of the observed productivity was due to the low applied depths.According to Santos and Carlesso (1998) and Rotili et al. (2021), the limitation of the water availability in the soil during the pre-flowering period affects the development of vegetative structures of the plants, reducing the biomass production capacity by the crop (Viciedo et al., 2019).In this way, the low depths applied in the pepper affected the production and permanence of the inflorescences in the plant, occurring its abortion.
Another important factor that interferes directly in the production is the amount of leaf area present in the evaluated plants.According to Ojeda et al. (2018), the increase of the applied depths provides greater production of fresh matter of the plants, i.e., the larger the depth applied, the greater the leaf area, providing greater photosynthesis (Lawson & Vialet-Chabrand, 2019), that is, greater production of chemical energy.However, when submitted to high temperatures and low water availability, as in the case of treatments with 25% and 50% ETc, they tend to close their stomata (Caser et al., 2017), reducing stomatal conductance (Ahumada-Orellana et al., 2019) and consequently reducing the raw material of photosynthesis (Zhao et al., 2020).
For the PFG and PDG variables, the highest averages were also obtained on the 100% ETc depth.This is due to the higher water availability for the processes of cell expansion and, consequently, the formation of the grain.On the other hand, the lowest rates of accumulated matter are the result of the low water availability for the initial process of grain formation, occurring low cell expansion, which can be limited to small grains or few grains per bunch, which justifies the low productivity in treatments with the smallest depths.Parallel to this process, the production of photosynthesis provides greater amounts of photoassimilates that are used in the formation and grains development, in which after completing cell expansion, accumulation of dry matter occurs in the developing grains.Bergamaschi et al. (2004), when working with maize plants, reported that the reduction in the harvest was a consequence of the lack of rainfall that occurred in December and January, when the great majority of the corn plantations of the Espírito Santo State was in the critical period, that is, from the pennon formation to the beginning of grain filling.Similar fact was reported by Bassoi et al. (2011), when evaluating grapevine plants, where they observed that the water deficit between anthesis (opening of flowers) and veraison (beginning of berries ripening) decreases the final size of the berry irreversibly, even if there is a wetting after the veraison.This fact corroborates Santos and Carlesso (1998), who affirm that the grain formation stage is that of greater dependence on assimilates.According to the author, this dependence is due to the low reserve that the plant has, and may not complete the grain development, that is, the grain reaches maturity with a low dry matter rate or is detached from the plant before of maturation.
Table 1 presents data of crop evapotranspiration, irrigation depths applied during the cycle, crop productivity, and water use efficiency, i.e., the relationship between yield (obtained by PDG) and crop evapotranspiration, for each treatment, in the second year.As the irrigation depths increase and consequently higher crop evapotranspiration, the crop yield increases, reaching values of up to 875.2 kg ha -1 for the evapotranspiration of 563.2 mm.This productivity is lower than the average found in commercial crops in Brazil (2,230 kg ha -1 ); however, it is worth mentioning that the crop cycle was reduced, harvesting only the first bunches.The best efficiency of water use occurred in the 100% replacement of the ETc, with the production of 0.159 kg of dry pepper per 1,000 L of evapotranspirated water.

CONCLUSION
In the first year of cultivation of Bragantina pepper, the application of irrigation depths for 100% ETc treatment (346.2 mm) promoted the higher plant height, stem diameter, and number of leaves per plant, as well as the smaller leaf temperatures.From the second year of cultivation, the irrigation depth that provided the highest averages for the number of bunches per plant (NBP), productivity of fresh grains (PFG) and productivity of dry grain (PDG) was 13 the irrigation depths of 100% of ETc (548.8 mm).The total evapotranspiration that promoted the highest PDG was 563.2 mm, with a yield of 875.2 kg ha -1 and 0.155 kg m -3 of water use efficiency.

Figure 1
Figure 1Experimental area at planting time (A and B) and in the production stage (C).

Figure 3
Figure 3Calculated and measured soil moistures, irrigations performed, rainfall, and soil water limits during the experimental period, for T4 treatment (100% ETc).

Figure 4
Figure 4 Number of leaves per plant (A), plants height (B), stem diameter (C), and leaf temperature (D) of black pepper plants submitted to different irrigation depths.

Figure 5
Figure 5 Number of bunches per plant (A), productivity of fresh grains (B) and productivity of dry grains (C) of black pepper plants submitted to different ETc.

Table 1
Treatments and applied depths, water demand and water use efficiency in the second year of crop development in each treatment.