Broccoli Production With Regulated Deficit Irrigation at Different Phenological Stages

The objective of this study was to evaluate the effects of different levels of soil water replacement in each phenological stage of broccoli crop cultivated in a protected environment. The experiment was conducted in a protected environment in the municipality of Maringá, Paraná, Brazil. The experimental design used was in randomized blocks 4 by 3 having four levels of water replacement (55, 70, 85, and 100% of crop evapotranspiration) applied in three phenological stages (initial, intermediate, and final), and four replications. Productivity, inflorescence fresh matter, leaf fresh matter, stem fresh matter, number of leaves, stem diameter, inflorescence height, inflorescence diameter, plant height, leaf area, inflorescence dry matter, stem dry matter and leaf dry matter were evaluated. The data were submitted to variance analysis and compared by Scott-Knott test and regression analysis. Deficit of 30% of the ETc during the final stage of the broccoli crop, reduced productivity by 7%, on the other hand for the initial and intermediate stages, there was a drop of 30% and 23% respectively. The water deficit caused significant losses in broccoli production during the first phenological stages, but the final stage was less critical.

and 542 m altitude). The climate, classified according to Koppen, is of the subtropical mesothermal humid type, with annual average precipitation of 1500 mm and average value for temperature close to 28 to 29 ºC (Nitsche et al., 2019). The protected environment features arched ceiling, coated with low density polyethylene film (150 μm thick) and protected sides with white anti-fid screen.
A randomized block design was used in a 4 × 3 factorial scheme, with four levels of water replacement (55,70,85, and 100% of crop evapotranspiration (ETc)) applied in three phenological stages (initial stage: from planting to 7 to 10 leaves; intermediate stage: from 7 to 10 leaves until the inflorescence appearance in the meristem; final stage: from the inflorescence emergence to harvest), with four replications. Phenological stages were defined according to Allen et al. (1998).
Broccoli seedlings, hybrid BRO 68®, produced in polystyrene trays (200 cells) with coconut fiber substrate, and housed in a greenhouse until transplantation. Transplanting for definitive site was performed when the seedlings presented three to four definitive leaves, with spacing of 1.0 m between row and 0.5 m between plants. The experimental unit consisted of six plants and the two central plants were evaluated.
The soil of the experimental area is classified as Nitossolo Vermelho distroférrico correlated with Ultisol in the soil taxonomy classification (Santos et al., 2018b). A composite sample was collected at a depth of 0-20 cm for chemical characterization of the soil (Table 1).
The Penman-Monteith method, standardized by FAO according to Allen et al. (1998), was used to estimate the reference evapotranspiration (ETo), using weather station data present inside the protected environment. The crop coefficients of 0.7 (initial stage), 1.05 (intermediate stage) and 0.95 (final stage) were used to determine crop evapotranspiration.
Water replacement was performed every two days at 8 o'clock. The irrigation system used was drip microirrigation, containing in each site 10 self-compensating flow drippers 4 L h -1 spaced at 0.25 m and operating at a pressure of 100 kPa. During 14 days after transplanting (DAT), 100% of the ETc was redone for the establishment of the crop. Pest control was performed with deltamethrin (25 g L -1 ) according to recommendations for the culture. Weeds were manually controlled.
At 81 DAT, the stem diameter, number of leaves and plant height were determined in the field. The plants sectioned near the soil surface and sent to the laboratory to determine the diameter and height of the inflorescences, inflorescence fresh matter, stem fresh matter and leaf fresh matter. The inflorescence dry matter, stem dry matter and leaf dry matter was determined after samples were submitted in a forced air circulation oven at 65 ºC until reaching constant weight. The leaf area was determined using the LI-3100 equipment. Crop yield was estimated in kg m -2 .
The data were submitted to variance analysis, being compared by the Scott-Knott test and regression analysis with 5% significance, using the statistical software SISVAR (Ferreira, 2019). Table 2 shows the duration of the phenological stages, the longest was the initial stage resulting in a longer period of exposure to water deficit.  The variables productivity, inflorescence fresh matter, leaf fresh matter, inflorescence diameter, plant height, leaf area, inflorescence dry matter and leaf dry matter of broccoli crop were influenced by applied water depths, it was possible to adjust quadratic regression models, significant at the level of 5% probability as shown in Figure  1.

Results and Discussion
jas.ccsenet. The increase of water depths provided increased productivity, inflorescence fresh matter, leaf fresh matter, inflorescence diameter, plant height, leaf area, inflorescence dry matter and leaf dry matter ( Figure 1). According to Taiz et al. (2017) the most prominent response of plants to water deficit, is the decrease in leaf area production, stomata closure, acceleration of senescence and leaf abscisc, culminating in decreased production. Although mechanisms such as the decrease in stomatic conductance, help in the maintenance of turgor, they lead to the reduction of gas exchange of the plant, reducing the photosynthetic rates and, consequently, the accumulation of fresh and dry matter (Nawaz et al., 2015).
According to Figure 1, the highest productivity value was obtained with a replacement of 100% of the ETc with a yield of 3.06 kg m -2 , it was 30% higher than that obtained with a replacement of 55% of the ETc. Similar results were reported by Ayas et al. (2011), when irrigation depths of 75 and 100% of ETc were applied to broccoli culture, the obtained values were 2.75 and 2.92 kg m -2 , respectively. Tangune et al. (2016) observed that the highest yield value of single-head broccoli production was 2.65 kg m -2 when irrigations were performed at the strain of 15 kPa at 0.2 m depth. Deficit irrigation causes a reduction in yield according to the stress level that the plant is subjected to (Hachmann et al., 2019;Wenneck et al., 2021). Erdem et al. (2010) reported a maximum marketable yield of 0.81 kg m -2 when broccoli irrigation with 50% of ETc and an irrigation interval of 7 days. Silveira et al. (2016) evaluating the production of branchy broccoli submitted to different levels of soil water replacement, obtained the highest productivity of 0.46 kg m -2 with replacement of 100% of ETc. These yield differences can be attributed to several factors, including differences of cultivars, climatic conditions, management methods adopted and regions.
The morphological variables of broccoli culture were influenced by the differentiation of phenological stages, and it was possible to apply the Scott-Knott test at the level of 5% probability, as shown in Table 3. Table 3. Components of broccoli culture as a function of phenological stage Productivity was influenced by phenological stage (Table 3). The final stage presented average productivity of 2.70 kg m -2 being significantly higher than the initial stage (2.41 kg m -2 ) and intermediate stage (2.54 kg m -2 ). There was a significant effect of water depths for the three phenological stages, the increase in water deficit tends to reduce productivity ( Figure 2). jas.ccsenet.

Figure
The increa 30% of the stress can occurs in a production s. In the water ological stage a y higher than t 3). Silva, Bisc li with differe Vol. 13,No. 12; nological stage e, and the defic y ( Figure 2 Vol. 13, No. 12; Deficit of 30% of the ETc at the final stage of the broccoli culture, there was a 7% drop in productivity, with a drop of 30% and 23% in the initial and intermediate stages, respectively.
The RDI response is very dependent on the timing and severity of water deficits. More research is needed to elucidate the basis of the observed responses, given the interactions between water stress and crop yield and quality.