Irrigation Depth and Nitrogen Fertilization on Production and Quality of Cherry Tomatoes

Nitrogen fertilization and water supply are determinant factors for production and physical-chemical quality of cherry tomato. The objective of this study is to evaluate the productivity and quality of cherry tomatoes, cultivar Carolina, produced under different irrigation depth and nitrogen treatments. The experiment was conducted in a protected environment in randomized blocks and a 5 × 3 factorial design with three replications. The treatments were integrated by the combination of five irrigation depth consisting of 50, 75, 100, 125 and 150% of replacement of the reference evapotranspiration (ETo), and three nitrogen treatments fertilization (common urea, urea with urease inhibitor and without the application of nitrogen). The productive and qualitative characteristics of tomato fruits were evaluated. Productivity was better responsive with the 125% ETo depth. The 100% ETo depth provided the highest titratable acidity. Nitrogen treatments did not promote differences in productivity and quality of tomatoes.


Introduction
Brazil is the eighth largest tomato producer in the world (FAO, 2015).This crop stands out because of its social and economic relevance.It may be cultivated in all regions of Brazil by the adoption of different techniques of cultivation and management during the whole year (Vilela, Melo, Boiteux, & Clemente, 2012).The mini-tomato (Lycopersicum esculentum Mill) is mainly produced in the Center-West and Southeast regions of Brazil (Cunha, Sandri, Vieira, Cortez, & Oliveira, 2014).These authors emphasized that farmers in these regions constantly need new crop, water and nutritional management options, which would make it possible to maximize profitability.
The cherry tomatoes have satisfactory market values according Maciel, Fernandes, Melo and Oliveira (2016).Thus, they have been more interested in farmers who spread their cultivation in a protected environment.However, for better yields and economic profitability, it is necessary that the factors inherent to nutrition, correct use of water, genetics and sanity be at adequate levels (Silva et al., 2013).
The water is one of the factors that present the greatest influence on tomato growth and development characteristics (Andrade, Noronha, Azevedo, Silva, & Santos, 2017).Santana, Vieira and Barreto (2010) mentioned water deficiency as the factor that affects tomato production the most.Andrade, Noronha, Azevedo, Silva, and Santos (2017) indicated that fruit quality also responds negatively to both water excess and deficit, as well as inadequate fertilization.According to Soares et al. (2012), one of the main demands of producers is precisely to know the water requirement of tomatoes, and alternatives sources of N.
Thus, irrigation should be adequately managed respecting the water requirement of the crop during its cycle, and the estimation of evapotranspiration is important in this determination (Xie & Zhu, 2013).Recent studies have been carried out to evaluate the effects of drip irrigation depth on productivity and/or quality of tomato fruits, be it for industrial processing (Moreira et al., 2012;Silva et al., 2013) or for in natura consumption (Campagnol, Abrahão, Mello, Oviedo, & Minami, 2014;Brito et al., 2015).However, studies correlating irrigation depth with the production and quality of cherry tomatoes are still scarce.Source: Doorenbos and Kassan (1994).
Tomato Carolina was a cultivar selected for this study.It has a habit of indeterminate growth, a cycle of 100 to 115 days, tolerance to some diseases and high productivity of tasty fruits.Twenty-five days after sowing, cherry tomatoes were transplanted into pots with a volumetric capacity of 6 L of substrate.A soil representative of the Brazilian Cerrado region was used, it classified as Oxisol with a clayey texture.The pots were arranged 1.0 m apart between rows and 0.50 m apart between plants, as recommended.Soil acidity and nutrient supply were corrected based on chemical analysis (Table 2), as recommended by Ribeiro, Guimarães and Alvarez (1999).
Table 2.Chemical characterization of the soil used as substrate for cherry tomato cultivation in a protected environment Phosphate and potassium fertilization were performed for all treatments using the triple superfostate and potassium chloride sources, respectively.In contrast to nitrogen, different treatments (CU, UI and WN) were used according to the respective treatments.Both nitrogen and potassium were applied in cover using a split-plot design every 15 days throughout the crop cycle until the 8 th week, according to Table 3.The phosphorus was applied at total dose at the time of transplanting tomato seedlings.Note.The analyzed variables were productivity (Prod), fruit transverse diameter (TD), longitudinal fruit diameter (LD), number of fruits per plant (NF pl -1 ), fruit mass per plant (FM pl -1 ), total soluble solids (TSS), total titratable acidity (TTA), ratio and water use efficiency (WUE).
The TD and LDs of three representative fruits of each plant were measured using a digital caliper.For the determination of productivity (Prod) we counted NF pl -1 and obtained FM pl -1 on an analytical bullet.Afterwards, we extrapolated the results to yield per hectare, since the spacing adopted between plants was the same used in the field.
The TSS content was determined using a portable sugar refractometer and the results were expressed in ºBrix, and the TTA was obtained by titration with 0.1 N NaOH.The ratio of TSS per TTA, called ratio (TSS/TTA), was calculated for the different samples.These analyses were performed after extraction of the broth from five tomatoes randomly selected from each plot, manually macerated and sieved.The relation between the average productivity of each plot and the irrigation depth applied throughout the crop cycle determined the WUE.
Data were submitted to analysis of variance associated with F test at a significance level of 5%.For the evaluation of the irrigation depth, a regression analysis was used, and for the comparison between the nitrogen treatments, a Tukey test at 5% probability was performed.The statistical software SISVAR was used for statistical analyses (Ferreira, 2011).
Qualitative and quantitative characteristics had a significant effect on irrigation depth, except for the LD, TSS and Ratio variables.TD and TTA were significant at 5% probability.On the other hand, Prod, FM pl -1 , NF pl -1 and WUE were significant at 1% level.For nitrogen treatments, Prod., FM pl -1 and NF pl -1 were significant at 1% probability, and TD and LD were significant at 5% probability.In the interaction of factors between IB and NS, only the characteristics NF and WUE were significant at 5% probability.
The NF pl -1 , in function of the irrigation depth in the treatment with CU, presented a higher value with the depth of 126.24% of ETo, in which it reached the average of 37.41 of fruits per plant (Figure 2A).Regarding the UI treatment, the mean number of fruits per plant was 32.62 and the depth that allowed this average was 112% of the ETo.In the WN treatment, the fruit average was below the other treatments, reaching only 24.7 fruits per plant, requiring an irrigation depth of 118.38% of ETo.This low number of fruits found in the treatment without N (Table 5) reinforces the idea of the centrality of this nutrient for the increase in tomato fruit production.ence.
e (IB) mmon 100% ysical to the 75%, Vieira 34.28 aried dium between 25 and 30 mm, large between 30 and 35 mm and giant when greater than 35 mm (Fernandes, Corá and Braz, 2007).In this study, therefore, the cherry tomato class would be between medium and large.
By observing Table 5, it was found that, for the TD and LD of the fruits, only the treatment with urease inhibitor differed from that without nitrogen.The factor irrigation depth influenced the TD of fruits.For higher values, an intermediate depth was required, in which it reached 22.15 mm in diameter using a 78.5% ETo depth regardless of the nitrogen treatment used (Figure 3A).Silva et al. (2013) analyzed the cultivation of the Caline IPA 6 tomato in a protected environment under different evapotranspiration replacement rates and observed that the transversal diameter maintained its averages between 28.5 and 45.5 mm for depth between 33 and 166% of ETo.In this study, the behavior was quadratic, with the vertex facing downwards, indicating that intermediate irrigation depth presented smaller fruits, were verified with application of these irrigation depth.
For the optimum irrigation depth, 127.06% of ETo, regardless of the nitrogen treatment, there was a mean fruit mass per plant of 212.75 g, as observed in the Figure 3C.On the other hand, Silva et al. (2013) found that the irrigation depth that provided the best yield of fruit mass per plant was the 128% of the ETo for the cultivar Caline IPA 6.A similar result was found in this study.Regarding productivity, the CU treatment obtained the best fit between the estimated and the observed data.
Feltrin, Pott, Furlani and Carvalho (2005) reported that the TTA reaches the maximum value when still with a yellow coloration, and this value reduces as the tomato fruit matures.Ferreira et al. (2010) stated that the tomato harvested in the first flowering tend to present a higher TTA, an observation also made by Vieira, Cardoso, Dourado, Caliari and Soares Júnior (2014) and observed in this study.The mean value of 0.374% TTA of cherry tomatoes in a conventional and organic cultivation was within the range found in this study, whose values varied between 0.30 and 0.68%, but did not show differences in function of nitrogen fertilization.For the TTA of 0.55%, a depth of 100% of ETo was applied regardless of the nitrogen treatment used (Figure 3B).
Regarding the physical-chemical quality of cherry tomatoes, TSSs reflect the sweetness of the product, indicate maturity/ripeness level and may be expressed in ºBrix (Pineli, 2009).Ramos et al. (2013) stated that fertilization, temperature, irrigation and the genetic influenced the character of the cultivar.According to Schwarz et al. (2013), a fruit with values higher than 3 ºBrix is recommended for marketing in natura.In this study, the content of TSS varied from 4.0 to 8.0 °Brix, with the lowest values observed in the treatment without addition of N (Table 5).
According to Moura et al. (2017), studies reporting the water use efficiency for cherry tomatoes are scarce.The WUE showed an inverse behavior of productivity; Santana, Vieira, and Barreto (2010) observed the same behavior upon analyzing the response of irrigated tomatoes to levels of water replacement in the soil.Based on the equations of each treatment of N (Figure 2B), it is observed that the reduction rate of WUE was 77, 47 and 23 g mm -1 , for UI, CU and WN, respectively.Efficiency of water use is directly related to productivity.The higher the productivity, as even water consumption, the greater the effectiveness of water use.

Table 1 .
Tomato crop coefficient (Kc) for each stage of development, and number of days at each stage

Table 3 .
Fertilization times and nutrient doses applied throughout the cultivation of cherry tomatoes in protected environment

Table 5
Moura et al. (2017)4)found different WUEs for cherry tomato cultivars: 'Swett Milion' had 29.1 kg m -3 and 'Sweet Grape' had 22.3 kg m -3 .According toMoura et al. (2017), the differences in water use efficiency values may be attributed to the cultivars studied, local climatic conditions and planting spacing, and in this study, it was observed that nitrogen fertilization also exerts a great influence.