Agronomic performance of arugula/nira intercropping in different cultivation arrangements

Spatial planning of cultivation arrangements is essential to ensure the superiority of intercropping when compared with monocrop. Thus, the aim of this study was to evaluate the agronomic performance of arugula/nira intercropping in different cultivation arrangements. The experiment was carried out in a randomized block design, in a split plot scheme, the plots represented the cultivation arrangements and the subplots the production cycles (winter and spring). The arrangements were T 1 = arugula monoculture; T 2 = two rows of arugula alternating with three rows of nira (2R:3N); T 3 = two rows of arugula alternating with two rows of nira (2R:2N); T 4 = two rows of arugula alternating with one row of nira (2R:1N); T 5 = nira monoculture. Productive traits and agronomic performance indexes of the intercropping systems were evaluated. Single arugula cultivation and 2R:1N intercropping achieved similar productivity, 2R:1N intercropping showed the highest productive efficiency, with land-use efficiency of 1.16%, though arugula showed a relative contribution of in production yield of the system. We concluded that 2R:1N intercropping can be used to optimize the use of productive inputs in arugula cultivation.


Scientific communication
Horticultura Brasileira 38 (3) July -September, 2020 I ntercropping is a technique in which two or more species are grown simultaneously in the same area, during, at least, part of the life cycle of each crop (Silva et al., 2011;Hendges et al., 2017). Intercropping increases productivity and profits per area, making production systems more sustainable, since the grown area and other available resources (soil, water, light and nutrients) are more appropriately used. This agriculture method also reduces economic risks due to the possibility of crop diversification (Lira & Edilson, 2013;Damasceno et al., 2016;Hendges et al., 2017). However, in order to maximize the use of the resources in intercropping, the crops must be adjusted in a way to maintain the greatest complementarity between each other.
Arugula (Eruca sativa) is a shortcycle leafy vegetable, widely used in Brazilian cuisine. Despite little technical information about its cultivation, arugula has been widely grown throughout all Brazilian regions (Oliveira et al., 2015). In Brazil, this is one of the main leafy vegetables and, despite being traditionally grown in monocrop, it has excellent potential use in intercropping (Nunes et al., 2013). GUIMARÃES

ABSTRACT
Spatial planning of cultivation arrangements is essential to ensure the superiority of intercropping when compared with monocrop. Thus, the aim of this study was to evaluate the agronomic performance of arugula/nira intercropping in different cultivation arrangements. The experiment was carried out in a randomized block design, in a split plot scheme, the plots represented the cultivation arrangements and the subplots the production cycles (winter and spring). The arrangements were T 1 = arugula monoculture; T 2 = two rows of arugula alternating with three rows of nira (2R:3N); T 3 = two rows of arugula alternating with two rows of nira (2R:2N); T 4 = two rows of arugula alternating with one row of nira (2R:1N); T 5 = nira monoculture. Productive traits and agronomic performance indexes of the intercropping systems were evaluated. Single arugula cultivation and 2R:1N intercropping achieved similar productivity, 2R:1N intercropping showed the highest productive efficiency, with land-use efficiency of 1.16%, though arugula showed a relative contribution of 84.3% in production yield of the system. We concluded that 2R:1N intercropping can be used to optimize the use of productive inputs in arugula cultivation.
Palavras-chave: Eruca sativa, Allium tuberosum, uso eficiente da terra, produtividade. "Nira" (Allium tuberosum), although not being popular in Brazil, is one of the main condiment crops in Asia. This species shows high potential to be used in intercropping with vegetables: it can increase productivity and also contributes to reducing pest infestation (Souza & Macedo, 2007;Porto, 2008).
Nevertheless, it is necessary to establish an appropriate growing arrangement in order to obtain high production and intercropping efficiency (Oliveira et al., 2015). It is essential that plant size, root system and canopy density be studied previously in order to identify if the interaction is possible (Sugasti et al., 2013). Thus, the aim of this study was to evaluate agronomic performance of arugula/nira intercropping in different cultivation arrangements.

MATERIAL AND METHODS
The experiment was carried out from July to November 2017, in the experimental area at Horta Didática, Universidade Federal do Ceará (UFC), Fortaleza-CE (3º44'17"S, 38º34'29"W, 21 m altitude). The local climate is 'As', dry summer tropical climate, average annual temperature is 26°C and 1,450 mm rainfall (Alvares et al., 2014). During the experiment (July 17 to November 18), the average temperature was 28°C, minimum 23ºC and maximum 32°C, relative humidity 66% and accumulated rainfall 79.5 mm.
The experimental design was randomized blocks, arranged in split plot scheme subdivided in time (5x2), considering some plots as cultivation arrangements and subplots the two production cycles (winter and spring), with four blocks. The arrangements (treatments) consisted of single cultivation and arugula/nira intercropping cultivation described as: T 1 = arugula monoculture; T 2 = two rows of arugula alternating with three rows of nira (2R:3N); T 3 = two rows of arugula alternating with two rows of nira (2R:2N); T 4 = two rows of arugula alternating with one row of nira (2R:1N); T 5 = nira monoculture.
The experimental plot consisted of an area covering 2.0 m 2 (1.0x2.0 m). Spacings were 0.2x0.2 m for arugula and 0.1x0.1 m for nira. In the intercropping systems, nira plants were spaced 0.20 m from the arugula cultivation rows. The useful area of the plot consisted of four central rows of arugula and two central rows of nira, measuring 1.0 m 2 . The authors evaluated 20 plants per crop per replicate.
Nira was vegetatively propagated using tillers of plants which were already produced in the didactic vegetable garden of UFC. Tillers were separated, roots were partially eliminated and shoots were cut (leaving approximately 3-cm leaves). Then tillers were transplanted. Two cultivation cycles for arugula and one cultivation cycle for nira were carried out.
Irrigation was performed daily, through micro-sprinkler irrigation with operating pressure of 110 mca (meter of water column) in the morning and afternoon, in order to keep appropriate soil moisture. Weeds were controlled manually (hoeing or hand-picking), as required. Top-dressing fertilizations were performed by applying 5 kg m -2 of organic compost, followed by scarification, at seven and 21 days after transplanting (DAT) of arugula seedlings. Pests were visually monitored at weekly intervals.
Arugula was harvested at 30 DAT in the first and second cycle, and the following agronomic parameters were evaluated: plant height (PH, cm), number of leaves (NL), leaf area (LA, cm 2 ), marketable fresh mass (MFM, g), marketable dry mass (MDM, g) and productivity (PROD, t ha -1 ). The marketable part was characterized by leaves without apparent damages and leaves showing apparent damages were classified as non-marketable. Nira was harvested at 90 days after planting (DAP), and plant height (PH, cm), average number of tillers per plant (NTPP), number of leaves (NL), shoot fresh mass (SFM, g), shoot dry mass (SDM, g) and productivity (PROD, t ha -1 ) were evaluated.
Height was determined with the aid of a graduated scale. For arugula plant, the height was measured from the stem until the leaf priomordia, for nira, from the soil to the end of the leaf. Masses were quantified using a digital scale with centesimal precision. In order to quantify dry mass, the fresh vegetables were placed in an oven with forced air circulation at 65°C, until constant mass. Leaf area was measured using a benchtop model LI-3100C, LI-COR.
Using the productivity parameters of the crops, we calculated the following indexes: land use efficiency index (LUE), relative contribution of arugula to LUE (RCC), area time equivalent ratio (ATR) and system productivity index (SPI).
The land use efficiency index (LUE) was calculated using the formula proposed by Willey (1979): where, Yab is the production of "a" crop intercropped with "b" crop, Yba is the production of "b" crop intercropped with "a" crop, Yaa is the production of "a" monoculture and Ybb is the production of "b" monoculture.
RCC was calculated using the formula proposed by Souza & Macedo (2007): where, I is the individual relative productivity; LUE is land-use efficiency index.
SPI standardizes the yield of the secondary crop in relation to the main crop, being calculated according to Odo's methodology (1991): in which: Yaa is the yield of "a" in monoculture, Ybb is the yield of "b" in monoculture; Yab is the yield of "a" crop intercropped; Yba is the yield of "b" crop intercropped.
Data were submitted to Shapiro Wilk's test (normality test) and, then, the authors performed ANOVA F test and averages were compared through Tukey test at 5% significance, using Sisvar software (Ferreira, 2011).

RESULTS AND DISCUSSION
Based on ANOVA F test, the authors verified interaction effect (p≤ 0,01) between cultivation arrangements and production cycles for number of leaves (NL), leaf area (LA), marketable fresh and dry mass (MFM and MDM) and productivity. Plant height showed significant difference only between the production cycles.
For NL, the authors observed that 2R:3N and 2R:1N arrangements showed the greatest number of emissions in the first cycle. In the second cycle, the single arugula and 2R:1N arrangement showed the greatest NL (Table 1). Leaf area in the first cycle of arugula was higher in intercropping systems, whereas in the second cycle, the plants from single cultivation and intercropped with an alternated row of nira showed the highest LAs.
For marketable fresh and dry mass, in the first cycle, arugula plants from intercropping treatments were always superior to the ones produced in the single cultivation (Table 2). In the second cycle, single arugula and 2R:1N intercropping was superior to the other treatments.
This differentiated behavior in cultivation systems in the two production cycles can be related to the fact that in the second cycle of arugula, nira plants showed to be higher, which can have caused greater interference on the arugula, mainly when more rows of nira, between rows of arugula, were used. Thus, an interspecific competition for space between these crops probably occurred in the second cycle.
In general, interspecific competition can be justified by greater plant density which leads to increased competition for growth factors such as solar radiation, water and nutrients limiting leaf expansion (Zanine & Santos, 2004). Besides that, canopy formation speed and leaf architecture of the intercropping can also modify complementarity between crops when associated, according to observed in lettuce/ cucumber intercropping, in which the 2R:3N = two rows of arugula alternated with three rows of nira; 2R:2N = two rows of arugula alternated with two rows of nira; 2R:1N = two rows of arugula alternating with one row of nira. Averages followed by the same lowercase letter in the column and uppercase in the line do not differ statistically among each other (p≤0.05) by Tukey test.

Figure 1. Productivity of arugula plants in different cultivation arrangements with nira
and production cycle (winter and spring). Averages followed by the same lowercase letter between cultivation arrangements and uppercase letters between production cycles do not differ statistically from each other, by Tukey test, p≤0.05}. Fortaleza, UFC, 2017.
cucumber caused greater restriction of solar radiation on lettuce (Rezende et al., 2010). Melo et al. (2015) evaluated the viability of Chinese cabbage/beet intercropping and noticed that in the intercropping with alternating row arrangement, interspecific competition was noticed, influencing negatively on the productivity of both species. Arugula productivity was higher in 2R:1N arrangement in the first production cycle, whereas in the second cycle, aragula monocrop showed higher productivity (Figure 1).
The authors could verify that the lowest relative population density of nira in 2R:1N arrangement contributed to a better performance, being similar behavior observed in nira monocrop. This fact can be explained due to a greater interspecific competition for spaces in other intercropping arrangements observed on account of a greater number of nira plants. In the second cycle, the highest productivity of arugula monocrop was probably due to a greater development of nira plants, which caused greater shading on the arugula, in addition to a lower incidence of rainfall, which caused less damage to plants. Similarly, Camili et al. (2013), working with lettuce/taro intercropping, observed that rapid growth of taro and, consequently, rapid formation of leaf area interfered in lettuce productivity in the second cycle of intercropping.
For nira, cultivation arrangements only influenced on the marketable dry mass (MDM) and productivity (p≤0.05) ( Table 3). For nira MDM, 2R:1N intercropping showed the greatest average. In other treatments, population pressure of the highest densities of nira may have caused a more intense competition for environmental resources such as solar radiation, resulting in less accumulation of dry mass in the shoot of nira. According to Taiz et al. (2017), a decrease in light intensity causes a reduction in photosynthetic activity, with a concomitant decrease in the production of photoassimilates by the plant, which reduces the accumulation of mass in the plants.
Productivity of nira was higher under monoculture, considering the highest relative population density by area. In  2R:3N = two rows of arugula alternated with three of nira; 2R:2N = two rows of arugula alternated with two of nira; 2R:1N = two rows of arugula alternated with one of nira. Averages followed by the same letter in the columns do not differ statistically from each other, using Tukey test, p≤0.05. average, single cultivation showed yield 381.2% above the intercropped crops.
For agronomic performance indexes of arugula/nira intercropping systems, we observed greater efficiency in land use in the 2R:1N intercropping, which showed efficiency 16% above the monocrop of arugula and nira (Table 4). Therefore, we can infer that the effects of cooperation or compensation between intercropped crops contributed to the advantages of the intercropping (Barros Júnior et al., 2011).
Land use efficiency of 2R:1N intercropping was observed mainly to a high productive performance of arugula, which contributed significantly for LUE, with approximately 84.3%. This fact leads to greater productive stability of the system, considering the system productivity index, which was 16.55% higher than the single arugula crop. According to Heredia Zárate et al. (2007), the increase in production per unit area is one of the most important reasons for cultivating two or more associated crops as it allows better use of land and other available resources, resulting in greater economic yield. However, to make it possible, the arrangement of plants in the growing area should be done in the most favorable way for both crops.
The intercropping system of two rows of arugula cultivation alternated with one row of nira made it possible to obtain productivity similar to single arugula cultivation, with greater agronomic efficiency in the use of productive resources when compared to the other arrangements, though.