Growth, Yield, and Sugar Content of Different Varieties of Sweet Corn and Harvest Time

The demand for sweet corn has increased largely because of its superior tastes compared with common corn. This research was conducted to analyze the growth and yield and sugar content of sweet corn seed on different varieties and harvest times. This research was conducted in South Sulawesi, Indonesia, from April to August 2018. The research was designed under a split-plot design. The main plot consisted of planting systems (single row and twin-row), whereas subplots consisted of three varieties (Bonanza, Talenta, and Master Sweet) and three harvest times (65, 70, and 75 days after planting). Variables measured consisted of plant height, cob length, cob weight, estimation of cob weight per hectare, and sugar content. Significant varietal differences were observed in plant height, cob length, cob weight, and sugar content. Master Sweet variety had the greatest plant height and cob length, whereas Bonanza variety produced the greatest cob weight, cob weight per hectare, and sugar content. Harvest time at 75 days after planting (DAP) produced the greatest plant height in the twin-row system, cob diameter, cob weight, and cob weight per hectare, whereas that at 65 DAP had the greatest plant height in control and sugar content. The twin-row system produced the greatest cob weight per hectare (22.33 ton/ha). This study recommends the use of Bonanza variety and harvest at 65 DAP to produce the greatest sweet corn cob per hectare.


Introduction
Sweet corn is a variety of corn with high sugar content and has a high nutritional value [1,2]. In Indonesia, sweet corn was first known in the form of imported cans. In the 1980s, this corn variety was cultivated in Indonesia commercially on a small scale [3]. Furthermore, sweet corn is increasingly known and widely consumed; therefore, the demand for sweet corn has been increasing. Sweet corn production in Indonesia remained low with average production below 10 tons/hectares (Wibowo, 2017).
is situation led to an increase in imports from 1,010,178 tons in 2011 to 1,125,463 tons in 2014. Hence, developing superior, highyielding sweet corn varieties through plant breeding is necessary. Cultivation technologies such as enhancing cropping systems and selecting proper varieties are among efforts to increase domestic production. e potential of land for developing sweet corn cultivation in Indonesia is huge; however, in fact, the production was only reached 8.31 tons/ha or only one-third of the potential possessed [4]. e low sweet corn production in Indonesia is due to the development of sweet corn generally in the marginal dry land, whereas dry land is confronted with many issues such as limited water availability and low soil fertility [5,6].
erefore, sweet corn production should be increased, for instance, by enhancing appropriate cultivation technology [7]. An essential factor in enhancing cultivation technology is spacing and the selection of varieties. e selection of sweet corn varieties is a key process for increasing production [8].
Sweet corn has varying sugar levels. Local varieties have a sugar content of 9%-11%, whereas hybrid sweet corn varieties have a sugar content of 16%-18% [9]. e sweet corn quality is determined by the presence of sugar content of sweet corn kernels [10]. e sugar content of sweet corn is influenced by varieties and by harvest time [11]. e prompt harvest maturity is necessary to ensure quality corn sweetness [12]. Previous research has been conducted on relatively fertile land with organic systems [13]. Research conducted on marginal land with the application of the Legowo planting system has never been done. is research is designed to increase crop productivity through increasing plant populations by adjusting the spacing and to utilize the effects of edge plants, in which planting is done by reducing the distance of the plant in a row and widening the range between the plants.
e Legowo system is the twin-row system with wider space in between. It has a denser space within rows and a wider one between the twins to foster the yield. However, the application of the Legowo system to corn still shows inconsistent results compared with conventional systems. e present study aims to analyze the growth, yield, and sweet corn seed sugar content of various varieties and harvest times with the application of the Legowo spacing system.

Materials and Methods
is research was conducted in Gowa Regency, South Sulawesi Province, Indonesia, from April to August 2018. e climate characteristic in the study site was classified as C2 (according to Oldman's classification), monthly rainfall ranges from 0-560 mm, with an altitude of 10 m above sea level. Soil type was alluvial with moderate pH and C-organic content, while the nitrogen content was low (Table 1). ree varieties of sweet corn (Bonanza, Talenta, and Master Sweet) were used in the present study as these hybrid varieties had high yield potential (Surtinah, 2015;Abadi and Sugiharto, 2019).
is study adopted a split-split plot design, which consists of the two main plots, three subplots, and three subsub plots (Figure 1). e main plot consisted of planting treatments as follows: P0 � control (single row planting system with a spacing of 70 cm × 25 cm) P1 � treatment (Legowo planting system or twin-row with a spacing of 50 cm × 25 cm and between twins of 100 cm) e subplots consisted of varieties: Land preparation was done by hoeing the soil and cleaning the weeds and roots. e land was divided into two blocks: control and treatment. Each block was split into three subplots each represented varieties, while a subsubplot represented different harvest times. Corn seeds of all varieties were planted in the subplots randomly.
inning was done at 14 DAP, leaving one plant for each hole and 9 plants in each sub-subplots. Fertilizers consisted of 350 kg/ha of urea, 150 kg/ha of phosphate, and 150 kg/ha of potassium chloride were applied for all the treatments. Application of two-thirds of urea, phosphate, and potassium chloride was done a week after planting, while onethird application of urea was done a month after planting. Watering was performed manually every week during the plant growth phase. Weeds were controlled by applying the herbicide on 21 and 40 DAP. Harvesting was done by sampling three plants in each subplot at the age of 65, 70, and 75 DAP. e variables observed were plant height, cob length, cob diameter, cob weight, cob weight per hectare, and seed sugar content observed in the form of total dissolved solids. Measurement of plant heights for all treatments was conducted at 56 DAP, while the length, diameter, and weight of cobs were measured directly at harvest time. Cob lengths and diameter were measured by a caliper. Cob weight was measured using a digital balance. e cob weight per hectare was extrapolated by multiplying cob weight with the corn population per hectare (56800 stalks/ha in control and 60000 stalks/ha in treatment). e sugar contents of harvested corns were measured using Refractometer. e corn beans were squeezed out, and the corn liquid was put onto the glass prism of the refractometer. e result was seen through the eyepiece. e data obtained were calculated using analysis of variance followed by the least significant difference (LSD) multiple range test (p < 0.05) using SPSS 20.

Effect of Spacing System, Sweet Corn Variety, and Harvest Time on Different Plant Growth and Yield Parameters.
Planting system (P) significantly affected cob weight per hectare, variety (V) significantly affected all variables except cob diameter, and harvest time (H) significantly affected all variables except cob length. e interaction between spacing the system and variety did not affect any variable. e interaction between the planting system and harvest time significantly affected the cob weight and cob weight per hectare. Interaction between variety and harvest time (V * H) as well as interaction among all factors (P * V * H) did not significantly affect all variables ( Table 2). e results of the analysis of plant height on various varieties and harvest times showed that the variety had a significant effect on the height of sweet corn plants. As shown in Table 3, the highest sweet corn plant height was found in the Master Sweet variety (171.67 cm), whereas the lowest was found in the Talenta variety (130.83 cm).
e planting system did not affect the plant height, whereas varieties and harvest time had a significant effect. e best harvest time with the Legowo system was produced at 75 DAP (162.8 cm), whereas the regular system was at 65 DAP (161 cm).

Cob Length.
Analysis of the data on the effect of the spacing system, corn variety, and harvest time on cob length showed that the effect of corn variety was statistically significant, whereas those of the others were not significant. e interactions between factors were not significant, indicating that the cob length was solely affected by variety. e Master Sweet variety had the longest cob (28.08 cm), whereas the Talenta variety had the shortest (25.33 cm) ( Table 4).

Cob Diameter.
e results of observations on the cob diameter of sweet corn showed that the effect of harvest time was significant. e longest diameter of the cob was found in the Bonanza variety (6.18 cm), whereas the shortest was found in the Talenta variety (5.96 cm). e harvest at the age of 75 DAP produced the largest cob diameters, both in control (6.22 cm) and in the Legowo system (6.33 cm). e effect of the spacing system and variety on the cob length was not significant. ere was no significant interaction between the factors (Table 5).

Cob Weight.
e results of the cob weight analysis showed that the weight of sweet corn cobs was influenced by variety and harvest time. e Bonanza variety produced the heaviest cob (374.17 g/cob), whereas the Talenta variety produced the lightest (310.83 g/cob). ere was a significant effect of interaction between the planting system and harvest   Table 2: Summary of F statistic followed by the probability of the effect of the spacing system, variety, and harvest time on growth, yield, and sugar content of sweet corn.

Parameter
Planting system (P) International Journal of Agronomy time on the cob weight, where the results of the Legowo system at 75 DAP produced the highest cob weight (372.22 ton/ha), whereas a regular system with 65 DAP produced the lowest (298.89 ton/ha) ( Table 6).

Estimation Cob Weight per
Hectare. e results of data analysis showed that all factors influenced the cob weight per hectare. As shown in Table 7, the highest estimation cob weight per hectare was significantly produced by the Bonanza variety (21.86 ton/ha), and the lowest was produced by the Talenta variety (18.17 ton/ha). ere was a significant effect of interaction between the planting system and harvest time on the cob weight, in which the Legowo system at 75 DAP produced the highest cob weight (22.33 ton/ha), whereas a regular system with 65 DAP produced the lowest one (16.98 ton/ha).

Sugar Content.
e results of the analysis of sugar content observed based on total dissolved sugar levels showed that the variety and harvest time were significantly affected by the sugar content. e highest corn sugar content was found in the Bonanza variety (22.75°Brix), whereas the lowest was found in the Talenta variety (20.08°Brix). Harvesting at 65 DAP produced the highest sugar content (22.83°Brix), whereas the lowest was produced at 70 DAP (Table 8).
e growth and yield of sweet corn were influenced by the variety and the harvest time. e Master Sweet variety had the greatest plant height and cob length, whereas the Bonanza variety produced the greatest cob weight, cob weight per hectare, and sugar content. is difference indicated that the Master Sweet variety produced long and slim cob, whereas the Bonanza variety produced shorter but corpulent cob.
is means that the Bonanza variety had   greater cob lateral growth capability, so it has a longer diameter. Plant growth is an interaction between genetic and environmental factors [14]. erefore, the difference in plant growth in the same environment, meaning that a greater genetic factor influences. Maize species pose different phenotypic character variations between one variety and other varieties. is result was consistent with the previous studies which reported high growth differences in corn plants from various genotypes tested [15][16][17]. e high production of Master Sweet and Bonanza varieties was supported by the size of the diameter of both, as well as on the cob length variable. A larger cob diameter and a longer cob allow the number of rows of seeds and allow the product produced per unit area to be heavier too. is is in line with another study that revealed the variable of fresh cob weight is positively correlated with the results obtained [18]. e difference in the production of the tested varieties is related to the genetic potential of each variety tested. Variety is one of the aspects to be considered for plant development because achieving high productivity is determined by genetic potential [19]. e high yield of the Bonanza varieties was also supported by better plant growth. is is consistent with the results obtained by Ahmad et al. [20], who concluded that maize yields positively and is significantly correlated with plant height, cob height, and yield components. High plant growth contributes to the possibility to leaf more [6]. With the presence of more leaves, capturing more solar energy is possible. is may accelerate the process of photosynthesis more rapidly and ultimately will produce plants with higher growth and production.
e Legowo system produced higher chlorophyll content than did the conventional system when phosphor was added [21]. Our result is consistent with another study that shows that the Legowo system supports higher production than the conventional system [22]. By contrast, another study showed that the Bonanza variety has low to moderate yield and late-maturing when planting in the organic system [13].
e results of the analysis of sweet corn sugar levels showed that the sugar content is influenced by the variety and the harvest time. e highest sugar content was found in Bonanza and Master Sweet varieties, at 70 DAP. is is in Note. e numbers followed by different letters indicate the significant difference by LSD (p < 0.05).  International Journal of Agronomy line with the study by Haddadi [23], who proposed that the sugar and the harvest time are influenced by the variety used and added that sweet corn is harvested at the mature stage of milk. e differences in varieties and differences in harvest time affect the sugar content, in which the delay in harvest time will cause the concentration of water and sugar levels to decrease but the starch content to increase [24]. Conversely, the sweet corn harvest age is 60-70 DAP for planting in the lowlands [25].

Conclusions
Variety significantly influenced plant height, cob length, cob weight, cob weight per hectare, and sugar content. e Master Sweet variety had the greatest plant height and cob length, whereas the Bonanza variety produced the greatest cob weight, cob weight per hectare, and sugar content. Harvest time at 75 DAP produced the greatest harvest, while at 65 DAP produced the best sugar content.
is study recommends the use of the Bonanza variety twin planted with the twin-row system to produce the greatest sweet corn harvest.
Data Availability e authors state that all data generated or analyzed during this study are included in this article. e full data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that there are no conflicts of interest regarding the publication of this paper.