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Introduction
The cauliflower (Brassica oleracea var botrytis L.) is a vegetable that has good potential for being developed in Central Kalimantan because of its high price and high demand. Initially, the cauliflower was known as a cold-climate (sub-tropical) vegetable, but biotechnological advances have enabled the production of cauliflower varieties that can grow and produce flowers in the lowlands, 5 to 200 masl. Newly developed cauliflower varieties are also resistant to high temperatures; for example, Widiatningrum and Pukan (2010) report varieties able to grow and bloom at temperatures up to 30 °C.
Central Kalimantan is one of the Indonesian provinces located in an equatorial area; its elevation in the swamp area ranges from 0 to 50 masl and in the hills from 51 to 100 masl. Data from 2016 revealed that the Central Borneo region has average solar radiation of 55.79 % with temperatures described as quite hot. Daytime temperatures can reach 35.06 °C, while the average temperature is 27.40 °C (Badan Pusat Statistik [BPS], 2017). Environmental factors in tropical lowland regions (elevation and temperature) do not favor the growth of cauliflower plants, which limits their cultivation (Widiatningrum & Pukan, 2010). Nuryadin, Nugraha, and Sumekar (2016) state that temperatures of 29 °C inhibit the growth and development of cauliflower plants.
Cauliflower plants require more specific environmental conditions than other cabbage types; its cultivation in an unsuitable environment requires climate modification to meet the requirements of the different stages of plant growth (Elahi et al., 2015). The intercropping system is a cheap and simple alternative that helps to reduce the ambient temperature. This type of system can be used to generate temperate microclimates, such as those that exist in the tropics, by protecting crops with low growth habits, such as cauliflower, with taller plants (Belel, Halim, Rafii, & Saud, 2014).
The combination of planting time and spacing in an intercropping system is intended to suppress the competition between plants for growth factors, especially during the critical period for the plant. The success of an intercropping system is strongly influenced by planting time, which significantly affects yield (Purnamasari, Maghfoer, & Suminarti, 2014). Plant spacing maximizes complementarity and minimizes competition because each plant has sufficient growing space. The objective of this research was to evaluate the effect of planting time and plant spacing on the growth and yield of cauliflower plants in an intercropping system with sweet corn under high-temperature conditions in Central Kalimantan, Indonesia.
Materials and methods
Study area location and materials
The study was conducted on peatlands in Kalampangan, Palangka Raya City, Indonesia, located at an elevation of 35 masl with an average temperature of 27-32 °C. The materials used in this study were corn seeds cv. Bonanza (PT East West Seed Indonesia, Purwakarta, Indonesia), cauliflower seeds cv. PM 126 (PT East West Seed Indonesia, Purwakarta, Indonesia), chicken manure compost, inorganic fertilizers (urea, SP-36, and KCl) and ash.
Experimental design
The study was performed using a split-plot design with three replicates. The main plot corresponded to the sweet corn planting time; W1 = four weeks prior to cauliflower transplantation; W2 = two weeks prior to cauliflower transplantation and W3 = simultaneous planting with cauliflower. The sub-plot was the spacing between sweet corn plants: J1 = 60 cm, J2 = 30 cm and J3 = 20 cm.
Field experiment
To condition the soil, 10 t·ha-1 of chicken manure compost and 10 t·ha-1 of ash were added after soil tillage; that is, two weeks before planting. Cauliflower was planted 60 cm x 60 cm apart in a 3.0 x 5.4 m experimental plot. The spacing between sweet corn rows was 120 cm, and plant spacing in the rows was according to each treatment. The cauliflower plants were fertilized with inorganic fertilizer consisting of 200 kg·ha-1 of urea (46:0:0), 250 kg·ha-1 of SP36 (0:36:0), and 150 kg·ha-1 of KCl (0:62:0). SP-36 fertilizer and KCl were applied simultaneously at seven days after planting (dap), and urea was applied at 7 and 21 dap. The sweet corn was fertilized with 200 kg·ha-1 of urea, 100 kg·ha-1 of SP-36 and 100 kg·ha-1 of KCl. SP-36 and KCl were applied at 7 dap, while urea was applied at 7, 28 and 49 dap (66.67 kg·ha-1 each).
Variables evaluated
Cauliflower growth was determined at four time-points: at 10, 20, 30 and 40 dap, in terms of leaf area (dm2) and plant dry weight (g). At harvest, the variables evaluated were curd weight (g), curd yield per hectare (t·ha-1) and curd diameter (cm). Temperatures (°C) in the cauliflower canopy were recorded each week between 14 and 49 dap as supporting data. The data obtained were subjected to an analysis of variance in the DSAASTAT program (EXCEL®, VBA add-in), and when the effect of the treatments was observed, a comparison of means was conducted using the least significant difference test (LSD, P ≤ 0.05). Additionally, a regression analysis was performed in Excel®.
Results
As shown in Table 1 and 2, the highest values for cauliflower leaf area and dry weight were obtained with sweet corn that was planted two weeks before the cauliflower (W2), although in the case of leaf area, this treatment did not differ statistically from W3 at 30 and 40 dap. This may be because the intensity of sunlight was sufficient for optimal photosynthesis.
Table 1 Means comparison of leaf area of cauliflower plants treated with different transplant times and spacing between sweet corn plants.
| Treatment | Days after planting | |||
|---|---|---|---|---|
| 10 | 20 | 30 | 40 | |
| Planting time of SC1 | ||||
| W1 (four weeks before CF) | 1.42 | 4.40 az | 32.18 a | 61.02 a |
| W2 (two weeks before CF) | 1.53 | 5.81 b | 34.77 b | 67.94 b |
| W3 (simultaneously with CF) | 1.45 | 4.88 a | 33.11 ab | 64.12 ab |
| LSD | ns | 0.88 | 1.7 | 4.98 |
| Plant spacing of SC | ||||
| J1 (60 cm) | 1.56 b | 6.00 b | 34.99 b | 70.21 b |
| J2 (30 cm) | 1.49 b | 5.45 b | 34.19 b | 70.47 b |
| J3 (20 cm) | 0.066 a | 3.63 a | 30.88 a | 52.41 a |
| LSD | 0.07 | 0.57 | 1.21 | 6.67 |
1SC = sweet corn; CF = cauliflower; LSD = least significant difference; ns = not significant. zMeans with the same letter within each column do not differ statistically (P ≤ 0.05).
Table 2 Means comparison of dry weight of cauliflower plants treated with different transplant times and spacing between sweet corn plants.
| Treatment | Days after planting | |||
|---|---|---|---|---|
| 10 | 20 | 30 | 40 | |
| Planting time of SC1 | ||||
| W1 (four weeks before CF) | 1.11 | 3.71 az | 10.01 a | 32.62 a |
| W2 (two weeks before CF) | 1.17 | 4.54 c | 17.16 c | 44.06 c |
| W3 (simultaneously with CF) | 1.15 | 3.99 b | 14.99 b | 39.66 b |
| LSD | ns | 0.16 | 1.33 | 2.11 |
| Plant spacing of SC | ||||
| J1 (60 cm) | 1.22 b | 4.86 b | 17.24 c | 44.55 c |
| J2 (30 cm) | 1.13 a | 4.40 b | 14.47 b | 40.60 b |
| J3 (20 cm) | 1.08 a | 2.99 a | 10.44 a | 31.20 a |
| LSD | 0.09 | 0.69 | 1.7 | 1.82 |
1SC = sweet corn; CF = cauliflower; LSD = least significant difference; ns = not significant. zMeans with the same letter within each column do not differ statistically (P ≤ 0.05).
Figure 1 shows that leaf area is strongly related to the dry weight of cauliflower plants (R2 = 96 and 97 %). Based on the results of the regression curves, it was observed that the highest dry weight of cauliflower plants per unit of leaf area was found with the W2 treatment, followed by W3. The ability of cauliflower to produce large leaves was lower with the W1 treatment, which influenced dry weight. Leaf area is smaller probably because there was less photosynthesis.
Figure 1 Relationship between leaf area and dry weight of cauliflower plants as a function of sweet corn transplanting time. W1 = four weeks prior to cauliflower transplantation; W2 = two weeks prior to cauliflower transplantation and W3 = simultaneous planting with cauliflower.
As a result of the above, in Table 3 it can be seen that the curd yield per hectare in cauliflower planted four weeks after sweet corn (W1) had the lowest value (2.61 t·ha-1) compared to other times, as well as the lowest temperature (Table 4). The W2 planting time had the highest yield (4.18 t·ha-1) as well as an intermediate temperature (between 25.3 and 25.90 °C) compared to the rest of the treatments (Table 4).
Table 3 Yield of cauliflower plants treated with different planting times and sweet corn spacing.
| Treatment | Curd weight (g) | Curd yield (t·ha-1) | Curd diameter (cm) |
|---|---|---|---|
| Planting time of SC1 | |||
| W1 (four weeks before CF) | 117.61 az | 2.61 a | 8.61 a |
| W2 (two weeks before CF) | 188.15 c | 4.18 c | 9.73 c |
| W3 (simultaneously with CF) | 156.09 b | 3.47 b | 9.06 b |
| LSD | ns | 0.45 | 0.53 |
| Plant spacing of SC | |||
| J1 (60 cm) | 228.19 c | 5.07 c | 11.7 c |
| J2 (30 cm) | 165.83 b | 3.69 b | 9.73 b |
| J3 (20 cm) | 67.83 a | 1.51 a | 4.60 a |
| LSD | 12.57 | 0.53 | 0.49 |
1SC = sweet corn; CF = cauliflower; LSD = least significant difference; ns = not significant. zMeans with the same letter within each column do not differ statistically (P ≤ 0.05).
Table 4 Air temperature in the canopy of cauliflower crops treated with different planting times and plant spacing in the sweet corn.
| Treatment | Days after planting | |||||
|---|---|---|---|---|---|---|
| 14 | 21 | 28 | 35 | 42 | 49 | |
| Planting time of SC1 | ||||||
| W1 (four weeks before CF) | 26.9 | 26.2 az | 25.9 a | 25.5 a | 24.4 a | 24.1 a |
| W2 (two weeks before CF) | 27.8 | 27.1 ab | 26.5 ab | 25.9 b | 25.3 b | 24.7 b |
| W3 (simultaneously with CF) | 28.1 | 27.6 b | 27.4 b | 26.5 c | 26.3 c | 25.1 b |
| LSD | ns | 1.1 | 1 | 0.42 | 0.9 | 0.5 |
| Plant spacing of SC | ||||||
| J1 (60 cm) | 28.2 | 27.5 b | 27.0 b | 26.8 c | 26.2 c | 25.2 c |
| J2 (30 cm) | 27.3 | 26.9 ab | 26.6 ab | 25.9 b | 25.4 b | 24.6 b |
| J3 (20 cm) | 27.3 | 26.5 a | 26.2 a | 25.2 a | 24.5 a | 24.1 a |
| LSD | ns | 0.7 | 0.5 | 0.7 | 0.5 | 0.4 |
1SC = sweet corn; CF = cauliflower; LSD = least significant difference; ns = not significant. zMeans with the same letter within each column do not differ statistically (P ≤ 0.05).
Discussion
Leaf area and dry weight
The results of the analysis of the cauliflower-sweet corn intercropping system showed no interaction between planting time and plant spacing of sweet corn regarding the leaf area and dry weight of cauliflower plants (Table 5). The significant effect occurred in each treatment separately (Tables 1 and 2). The planting time of sweet corn had a significant effect on cauliflower leaf area and dry weight at 20 to 40 dap, while the plant spacing of sweet corn had a significant effect during the entire observation period (10 to 40 dap). Planting time is an essential factor in crop cultivation that will affect subsequent growth rates and crop yields (Nulhakim & Hatta, 2008). Plant spacing in intercropping systems is important because appropriate spacing arrangements will optimize resource utilization, such as total light interception, and nutrient and water uptake by both types of plants (Gebru, 2015).
Table 5 Significance of the interaction between the two factors studied (planting time and sweet corn plant spacing) and the variables evaluated in cauliflower plants.
| Variables | F-value |
|---|---|
| Leaf area 10 dap1 | 2.554 |
| Leaf area 20 dap | 1.167 |
| Leaf area 30 dap | 0.544 |
| Leaf area 40 dap | 0.220 |
| Dry weight 10 dap | 2.554 |
| Dry weight 20 dap | 0.780 |
| Dry weight 30 dap | 0.771 |
| Dry weight 40 dap | 0.788 |
| Curd weight | 0.830 |
| Curd yield | 0.830 |
| Curd diameter | 0.924 |
| Air temperature 14 dap | 0.485 |
| Air temperature 21 dap | 0.048 |
| Air temperature 28 dap | 0.120 |
| Air temperature 35 dap | 0.041 |
| Air temperature 42 dap | 0.779 |
| Air temperature 49 dap | 0.615 |
1dap = days after planting; Ftable 5 % = 3.26; Ftable 1 % = 5.41
Kamara et al. (2017) note that intercropping systems have the positive effect of blocking excessive sunlight. In this case, the shade of the sweet corn plants had a positive effect on the cauliflower, as the temperature around the cauliflower canopy was reduced to about 26.5-28 °C, which is suitable for the development of leaf area and increases the dry weight of cauliflower plants. Sufficient sunlight and a suitable temperature in a hot area could increase the success of cauliflower cultivation according to the growth stage of the plants.
The W1 treatment resulted in lower leaf growth and dry weight in cauliflower plants. This was because the sweet corn leaves eclipsed the cauliflower plants, so the intensity of sunlight received by them was low, as well as the temperature (from 27.6 to 25.9 °C, between 7 and 28 dap, respectively). The lack of sunlight directly decreases canopy temperature and lowers nutrient and water uptake, inhibiting cauliflower growth. In addition, low temperatures during the initial phase of cauliflower growth slow the plant’s growth and development (Gebru, 2015).
The factors that influence the success of intercropping are plant spacing and plant population (Ofori & Gamedoagbao, 2005). Plant biomass decreases with increasing crop density in the intercropping system (Sutharsan & Srikrishnah, 2015). The lowest value of leaf area and dry weight of cauliflower was recorded with the J3 treatment, which represents the shortest distance. With a broader spacing of sweet corn plants, the leaf area and dry weight of the cauliflower plant also increased, although there were no significant statistical differences between treatments J1 and J2 (Table 1).
Relationship between leaf area and dry weight
Intercropping cultivation of high and low plants can reduce the intensity of sunlight and air temperature while increasing the relative humidity of the canopy (Zafaranieh, 2015). The W2 treatment resulted in a temperature between 26.5 and 28.0 °C, which was suitable for the growth of cauliflower plants. This is reflected in the leaf area and dry weight values obtained with this treatment, which were higher than in W1. Leaf area plays an important role because the formation of plant biomass is determined by the interception of sunlight by the leaves and its effectiveness, in which light interception is used to increase the dry weight of the plant (Belel et al., 2014).
Efforts to increase the success rate when planting in an intercropping system involve adjusting the appropriate spacing between component plants. This research study found that sweet corn plant spacing of 60 cm (J1) and 30 cm (J2) is the most suitable planting distance for the growth of cauliflower plants. The results of regression analysis showed that the increase in dry weight per unit of leaf area with treatments J1 and J2 was greater than with J3 until the end of vegetative growth (Figure 2). Good spatial arrangement in an intercropping system can decrease crop competition and thus improve crop growth (Sutharsan & Srikrishnah, 2015).
Cauliflower yield
Cauliflower plants that grow in hot areas require special treatment to stimulate flowering. The transition from the vegetative phase to the generative phase in the cauliflower plant is a complicated morphogenetic process. To produce an edible flower, the cauliflower plant needs low temperatures; in addition, the induction of flowering and therefore yield are affected by light, temperature, water availability, nutrients and chemicals, such as hormones and growth regulators (Cebula, Kalisz, & Kunicki, 2005; Kałużewicz et al., 2012). Therefore, it is important to adjust the timing of sweet corn planting to have adequate sunlight and temperature levels when the vegetative growth and generative stage of cauliflower plants occur.
The results of the analysis showed that there was no significant interaction between planting times and distances between sweet corn plants and cauliflower yield. However, the treatments separately affected the yield components of the cauliflower plant: curd weight, curd yield and curd diameter. W1 treatments had the lowest curd weight (117.61 g) and smallest curd diameter (8.61 cm) (Table 3); this was due to excessive shading in cauliflower plants from the onset of growth. The high shade levels blocked the sunlight and caused lower temperatures in the canopy; this affected the rate of photosynthesis, which also reduces the photosynthate that translocated to the curd.
The success of cauliflower production depends on the climate, especially temperature, and this relationship is very intensive and complex (Farzana, Muhammad-Solaiman, & Amin, 2016). Extremely high or low temperatures are less suitable for curd formation in a lowland environment because the curd will be less compact or disconnected. Cauliflower planted in high temperatures produces small and low-quality curds; in addition, if heat-resistant cauliflower varieties enter the flowering phase at temperatures that are too low and shade levels too high, the resulting curd will be small and have low quality (Ajithkumar, Karthika, & Rao, 2014; Thakur, 2014).
Figure 3 shows that leaf area had an effect of 78 % (R2 = 0.78) on curd weight, which means that 78 % of the curd weight was affected by the leaf area, while other factors influence 22 %. The W2 treatment presented the highest curd yield (4.18 t·ha-1), curd diameter (9.73 cm) and curd weight (188.15 g) (Table 3). This is due to the fact that under this treatment the appropriate temperature was produced (Table 4) for the flowering process of lowland cauliflower growing in the tropics of Central Kalimantan. Having the light and temperature levels required at each cauliflower plant growth stage increases the success of planting in hot areas.
Appropriate crop density is vital in intercropping systems to balance the temperature of the canopy, which can increase leaf area and light absorption and thus improve yield (Zafaranieh, 2015). The results showed that closer spacing of sweet corn plants resulted in low curd weight and low yield, and that increasing spacing between plants from 20 cm (J3) to 60 cm (J1) also increased curd weight and yield (Table 3). The highest cauliflower curd yield was obtained with the J1 treatment (5.07 t·ha-1), while the lowest yield was obtained by J3 (1.51 t·ha-1). The plant spacing arrangement is intended to allow each plant to evenly obtain available resources, such as light, water and nutrients, and thereby reduce the level of competition among plants. Suitable spacing for intercropped plants has been reported to increase crop yield (Cebula et al., 2005).
The highest curd diameter and weight were obtained with the J1 treatment, with values of 11.7 cm and 228.19 g, respectively. Figure 4 shows the relationship between curd diameter and curd weight, where the effect is 90 % (R2 = 0.90), which means that the magnitude of the curd diameter is 90 % influenced by the weight per curd while other factors cause the other 10 %. The level of competition for resources, such as sunlight, nutrients and moisture, can be minimized to form plant organs and leaf area used for photosynthesis. This leads to more significant assimilate translocation from source to sink, resulting in improved crop yields (Hadidi, Sharaiha, & Debei, 2011).
The setting of the spacing in an intercropping system is closely related to the leaf area produced by the plant, where close spacing will produce a smaller leaf area. Treatment J3 caused high competition among plants, as well as reducing sunlight intensity and temperature. Those conditions affected the growth process, so the cauliflower produced small and lightweight curds that were not compact. As seen in Figure 3, leaf area and curd weight are related; that is, a larger leaf area increases the photosynthesis process, which increases curd weight.
Conclusions
The optimal planting time and spacing between sweet corn plants in an intercropping system with cauliflower reduces the air temperature of the cauliflower canopy. Planting sweet corn two weeks before planting cauliflower, with 60-cm spacing, is more suitable for increasing leaf area and dry weight of cauliflower plants. In addition, under these conditions, a curd yield of 5.07 and 4.18 t·ha-1 can be obtained in the lowlands of Central Kalimantan.
