Data collected for soybean plants include: plant height, number of branches, pod color, seed shape, seed hilum color, trichome shape, number and length of trichomes on soybean leaves and pods, degree of damage to soybean leaves and pods due to S. litura armyworm attack, pod sucking R. linearis, and pod borer E. zinckenella, 100 seed weight and seed yield.

The damage level of soybean leaves due to S. litura attack in the plant age of 35 days after planting (dap), number of branches per plant at 45 dap, plant height in generative phase plant age of 50 dap, pod color, seed shape, seed hilum color, shape trichomes for the generative phase (50 dap), the number and length of trichomes on soybean leaves at 50 dap, and the damage level of soybean pods due to attack by S. litura and E. zinckenella at 70 dap are observed. Meanwhile, the weight of 100 seeds, pod color, seed shape, seed hilum color, and seed yield were all observed after harvesting the soybeans.

The rate of damage to the leaves is calculated based on the following formula (Apriani et al., 2021):

Scale value, v i :

Pod damage rate is calculated based on the formula:

All observed data were analyzed using ANOVA. The average ratio of leaf damage intensity caused by S. litura and the other parameters was tested using the Duncan test probability level of 5%.

There is no significant difference in plant height among the three planting designs. The plant size is varied by the number of branches per plant. The highest number of branches is observed in the three rows transplanting design (3.38 branches), whereas the lowest is in the farmers transplanting design (2.76 branches) (Table 1). The study results (Kuntyastuti et al., 2018) also showed that spacing had an effect on plant height, number of branches, and filled pods. Similarly, the results of the study (Agudamu Yoshihira and Shiraiwa, 2016) demonstrated that population density affects the response of branch formation and soybean yields on Hokkaido determinate and United States indeterminate soybean varieties.

Table 1 reveals that the Detap-1 variety exhibited the highest plant height at 52.13 cm, whereas the lowest height was observed in the Derap-1 variety at 45.11 cm. This result is in accordance with Indonesian Legume and Tuber Crops Research Institute (2016), which is mentioned in the Description of Varieties of Soybean Crops. The Detap-1 variety has a plant height of 68.70 cm, while Derap-1 has a plant height of approximately 59.00 cm. Parameter number of branches per plant is one of the factors that determine the high or low productivity of soybeans. In general, the more the number of branches, the higher the productivity. Table 1 reveals that Devon-1 variety had the highest number of branches (3.42 branches) Detap-1 (2.91 branches) and Derap-1 (2.93 branches) varieties had the lowest. This aspect is in contrast with the report of Indonesian Legume and Tuber Crops Research Institute (2016), which is mentioned in the Description of Varieties of Soybean Crops that the Devon-1 variety has approximately 2–3 branches per plant, while Detap-1 has approximately 3–6 branches per plant and Derap-1 has approximately 2–4 branches per plant.

Table 2 indicates no significant interaction between plant height and planting method as well as variety. According to Ayu Rahmasari and Sebayang (2016), this lack of interaction is due to the influence of the density level on the spacing treatment. The insufficient light on the plant causes the shape of the plant to be taller and weaker. This higher form of plants (etiolation) is due to the activity of the growth hormone, such as auxin (Harjadi and Yahya, 2007).

Figure 4 shows that several types of pests are common in soybean plants in Indonesia, including South Sulawesi. The armyworm S. litura (Figure 4A) is the pest that causes the most damage to soybean leaves in South Sulawesi. According to Marwoto and Suharsono (2008), S. litura is a polyphagous pest; hence, it is often found on plants other than soybeans. Spodoptera litura is one of the important pests on soybean plants and can attack on the primary host plants causing yield losses of 10–40% (Sundar et al., 2018). Spodoptera litura has high reproductive and migratory capacity (Dhaliwal et al., 2010).

Spodoptera litura activity appeared in mid to late August and peaked in mid to late September (Punithavalli et al., 2014). The pest is spread in almost all areas of soybean and horticultural crops in Indonesia. Armyworms have a wide host range (Marwoto and Suharsono, 2008; Fattah and Ilyas, 2016). This polyphagous nature allows pests to maintain their life cycle in nature throughout the year by obtaining food from other host plants when the primary host plant is not available. According to Fattah et al. (2020), S. litura pests can cause damage to soybean leaves approximately 16.24–45.00%.

In addition to the S. litura pest that attacks soybean crops in South Sulawesi, E. zinckenella is a pod borer pest that causes huge losses to soybean seed yields. Yield losses of soybean caused by pod borers, such as E. zinckenella (Figure 4C), are difficult to estimate because they are influenced by genotype susceptibility, control technology used, farmers’ socioeconomic conditions, and other environmental conditions (Oliveira et al., 2014). The pod borer is considered to be the most difficult soybean pest to control due to its larval feeding behavior. Larvae spend most of their time in the pods consuming seeds (Apriyanto et al., 2009).

Another pest that causes huge damage to soybean pods in South Sulawesi is the brown ladybug. The farmer gave the name brown ladybug because the adult ladybug has a brownish color. Young ladybugs (nymphs) are similar to black ants (Figure 4B). Both young ladybugs (nymphs) and adult ladybugs both damage soybean pods by sucking up the liquid in the pods while filling the seeds. Apart from attacking soybean pods, brown ladybugs also attack several other legume crops, such as long beans and green beans (Marwoto et al., 2013).

As shown in Table 3, it is evident that the lowest incidence of S. litura infestation occurred in Devon-1 (11.87%), followed by Detap-1 (14.89%) and Derap-1 (15.51%). The lowest attack rates of R. linearis and E. zinckenella on Derap-1 varieties were 9.07 and 10.01%, respectively, followed by Detap-1 (10.08 and 12.45%) and Devon-1 (12.58 and 13.77%). In Indonesia, the resistance test of soybean varieties to S. litura in the unselected test showed an intensity of pest attack of 34–64 and 19–57% in the selected test (Adie et al., 2020).

The results showed that all cropping design had no significant effect on S. litura attack, with an attack rate of 13.44–14.21% (Table 4). Meanwhile, the attack rates of R. linearis and E. zinkenella were significantly different for each cropping design tested. Similarly in E. zinckenella attacks, the 20 cm × 20 cm horn jajar planting design had the highest number of insects (12.55%), followed by 2 Legowo (12.18%) and 3 Legowo (11.58%). In general, the attack rates of S. litura, R. linearis, and E. zinckenella were the lowest compared with the other two cropping designs (Table 4). The high migratory and feeding ability of S. litura led attacks on soybeans with different varieties and cropping patterns, which was significantly different from one another.

In general, soybeans are planted in rainfed lowland rice fields in Indonesia during the peak of the dry season, from June to October. At this time, the population of pests that attack the pods increases (Krisnawati and Adie, 2019). Riptortus linearis is one of the most damaging pod-sucking insects in South Sulawesi, apart from Nezara viridula L. (Hemiptera: Pentatomidae) and Leptocorisa acuta Fabricius (Hemiptera: Alydidae) (Rahayu et al., 2018).

Table 3 shows that the level of damage to the pod borer on Detap-1 and Derap-1 is lower than that on Devon-1. The number of trichomes in the pods affects soybean resistance to borers. Trichomes also play a role as a factor of soybean resistance to pod borer because trichome density affects the number of E. zinckenella eggs laid and the intensity of attack (Sari and Suharsono, 2010; Poniman et al., 2020). As shown in Table 5, the number of trichomes in the Detap-1 and Devon-1 pods was more numerous and significantly different from the number of trichomes in the Derap-1 pods. The more the number of trichomes in the pods, the greater the number of eggs laid, so the higher the intensity of the attack. This aspect is consistent with the study by Susanto and Adjie (2008); the pod borer prefers to lay eggs in soybean pods, which have a higher number of trichomes and are longer. The aforementioned can damage and result in losses to the larval stage. The characteristic of long trichomes also inhibits the mechanism for borers to attack pods. Conversely, Table 6 shows that the Detap-1 variety has the highest pod trichome length and is significantly different from other varieties, and this factor has an effect on the lower percentage of pod borer attacks compared with Devon-1.

Meanwhile, there was no significant difference in the effect of the length of the trichomes on the leaves against armyworm attacks. Meanwhile the effect of length and number of trichomes on leaves on armyworm attacks is not significantly different. Based on the description of the varieties, Detap-1 and Devon-1 are sensitive to armyworm attack while Derap-1 exhibits partial resistant. Currently, there is no soybean variety that is fully resistant to armyworm (Sundari and Sari, 2015). The frequency of armyworm attacks on soybean leaves is caused by other factors, such as growing season and temperature. The intensity of armyworm attacks is generally high at the end of July or mid-August to October, where generally the temperature increases and the humidity is low (Uge et al., 2021).

In Table 4, the results illustrate the evaluation of pod damage levels attributed to R. linearis infestation. Derap-1 planted with a 3-row Legowo pattern showed the least damage (8.02%) followed by Derap-1 with a 2-row Legowo planting pattern (9.13%), Detap-1 Legowo pattern 3 rows (9.20%), Detap-1 Legowo pattern 2 rows (9.92%), Derap-1 horn pattern jajar 20 cm × 20 cm (10.05%), Detap-1 horn pattern jajar 20 cm × 20 cm (11.13%), Devon-1 Legowo pattern 3 rows (11.90%), Devon-1 Legowo pattern 2 rows (12.43%), and the highest damage was in Devon-1 horn pattern jajar 20 cm × 20 cm (13.43%) (Table 4). According to the study of Patu et al. (2021), the Detap-1 variety has a thick pod skin of 0.64 mm. The attack rate of R. linearis was high in the 20 cm × 20 cm (11.54%) horn soybean cropping design, followed by jajar 2 Legowo (10.49%) and 3 jajar Legowo (9.71%) (Table 4). The morphological characteristics of the thick shell of the pods are strongly related to the intensity of attack by R. linearis. The thicker the soybean pod shell, the lower the intensity of attack by pod-sucking pests. Pod trichomes are a part of the defense system against pests, which can inhibit the process of the stylet penetration of pod-sucking pests. Patu et al. (2021) stated that there was a relationship between the length of the pod trichomes and the intensity of the attacks. The longer the pod trichomes, the higher the attack intensity of sucking pests. On the one hand, long trichomes can withstand attack by pod-sucking pests, but on the other hand, long pod borer trichomes are an ideal medium for imago pod borer pests to lay eggs because eggs laid on long trichomes will prevent predators from preying on the eggs, so the percentage of eggs is very high. Similarly, trichomes can be ideal places for some pests to lay their eggs, which are not easily damaged by environmental disturbances.

In Figure 5, it can be observed that among the three soybean planting design tested, the double rows planting design (Figure 5B) and the three rows transplanting design (Figure 5C) result in a more regular appearance of the plant rows and provide empty or open space. This open or empty space or place has many benefits, making it easier for farmers to spray insecticides (pest and disease control) and liquid fertilizer in plants. Apart from that, another benefit is that it is easier for farmers to collect S. litura eggs and larvae and other pests. The two design transplanting (Figures 5B,C) is friendly technology. According to Poniman et al. (2020), the environmentally friendly technological innovation is the Legowo planting system using superior varieties. Similarly, as mentioned in the study by Mardian et al. (2019), the Legowo cropping design has a much better population and productivity when compared with the conventional cropping design. One way to control soybean pests in rainfed rice fields is to carry out appropriate cultivation management using pest-resistant varieties (Aryati and Ulina, 2023). The management of spacing is an environmentally friendly technology design that has a positive impact on the environment and the sustainability of plant productivity (Yan et al., 2020; Singh and Krishnaswamy, 2022).

Generally, the soybean planting distance implemented using a 25 cm × 25 cm tiling system. Double spacing (Legowo 2:1) can be done in an effort to increase production because soybean plants require sufficient light. Spacing is one of the cropping systems by adjusting the pattern of spacing between plants in crop cultivation, which includes the distance between rows and rows of each plant (Karokaro et al., 2015). Setting spacing can increase production because it is related to the availability of nutrients, sunlight which affects photosynthesis, and space for plants to grow. Double spacing (Legowo 2:1) is one of the spacing arrangements that is widely applied in Indonesia, especially for food crops, where the arrangement is alternate between two rows of plants, and there is one empty row, which is not planted. The jajar Legowo 2:1 system with 25 cm × 50 cm produces 213,333 rice clumps per plant compared with the 25 cm × 25 cm upland system, which produces 160,000 clumps; in addition to that, a double cropping system (Legowo) makes maintenance processes, such as fertilizing and maintenance, become easier (Ikhwani et al., 2013). Legowo is a method of growing soybeans that maximizes the utilization of sunlight, water, and nutrients. Legowo increases the soybean yield by 17% compared with a single row; hence, it is a recommended technology package using jajar Legowo to obtain higher yields (Haryati et al., 2021).

The weight of 100 seeds is an indicator of the size of the soybean seeds. The heavier the measurement of 100 soybeans, the larger the size of the soybeans. Table 6 shows that the highest weight of 100 seeds was observed in Derap-1 (17.94 g) and Detap-1 (17.30 g) while the lowest was in Devon-1 (16.33). In accordance with research conducted by the Indonesian Legume and Tuber Crops Research Institute (2016), which is mentioned in the Description of Varieties of Soybean Crops, the weight of 100 seeds for a variety, while Derap-1 is around 17.62 g, Detap-1 is about 15.37 g, and Devon-1 is about 14.30 g.

Soybean seed yield is the main target of farmers in the farming system. Each variety has different seed yields, and this is determined by genes and environmental factors. Based on data from Table 6, it can be observed that there was no significant difference in the seed yields of the three varieties, namely, Detap-1, Devon-1, and Derap-1. According to the report of Indonesian Legume and Tuber Crops Research Institute (2016), which is mentioned in the Description of Varieties of Soybean Crops, the average seed yield of the Detap-1 variety is approximately 2.70 t ha⁻¹, Derap-1 is approximately 2.82 t ha⁻¹, and Devon-1 is approximately 2.75 t ha⁻¹. According to Vlachostergios et al. (2021), the selection of cultivars and planting systems is an important factor for maximizing the yield of soybean seeds. The results of the study (Purwaningrahayu, 2023) showed the variability of the response of each genotype to different planting methods. Based on the productivity per hectare, there are nine accession numbers 2, 3, 5, 6, 8, 9, 11, 13, and 15, which are likely to produce soybean productivity above 3.0 tons/ha, with a double row planting of 50 cm × (30 cm × 15 cm) and more than a single row size of 40 cm × 15 cm.

Table 7 shows that there is no significant difference in the weight of 100 seeds among the three varieties with the three transplanting methods. The lack of significant difference is attributed to the fact that the three tested varieties possess large and nearly identical seed sizes. In Indonesia, soybeans are classified as large (weight > 14 g 100 seeds⁻¹), medium (10–14 g 100 seeds⁻¹), and small (<10 g 100 seeds⁻¹) (Indonesian Legume and Tuber Crops Research Institute, 2016). This classification aligns with the findings by Faizah and Yuliani (2019), which indicates that Detap-1, Devon-1, and Derap-1 varieties have relatively large seed sizes as their weights exceed 14 g 100 seeds⁻¹. One of the things that affects the size of the seeds is the height of the plants. Plant height can lead to a reduction in branches and subsequently affect seed size, as indicated by research results, involving the farmers transplanting method and the method of transplanting double rows with Detap-1, Devon-1, and Derap-1 varieties, in accordance with the findings by Krisnawati (2017). However, the outcomes of the method of transplanting three rows treatment on Detap-1 and Devon-1 varieties did not align with the results presented by Krisnawati (2017). Moreover, the implementation of a dual row spacing measuring 50 cm × (30 cm × 15 cm) has been proven to augment the productivity of soybeans by 11% in comparison with a singular row spacing of 40 cm × 15 cm (Purwaningrahayu, 2023).