Key findings:

The study found that while the combination of irradiation duration and planting media did not significantly impact most observation variables, plants with additional LED light showed better growth than those without it. Root length was the only variable significantly affected by both factors in this urban farming experiment.

What is known and what is new?

Urban areas face limited agricultural land due to urban development, leading to the adoption of urban farming practices. Lettuce is a suitable crop for urban farming, offering high economic value. Factors affecting lettuce growth include planting media, irradiation duration, light type, humidity, and aeration. This study investigates the impact of irradiation duration and planting media on lettuce growth in urban farming. While most variables showed no significant interaction, the addition of LED light improved growth compared to plants without it.

What is the implication, and what should change now?

The study suggests that optimizing irradiation duration and planting media can enhance lettuce growth in urban farming, offering a solution to limited agricultural land. This can increase lettuce production in urban areas, providing a fresh and locally sourced vegetable supply. Urban farmers should consider using LED lights to supplement natural light for lettuce cultivation. Additionally, further research could explore other factors, such as humidity and aeration, to optimize lettuce growth in urban environments.

Agricultural land in urban areas is getting narrower as a result of building and infrastructure development, which has caused the concept of crop cultivation to change to urban farming. The concept of urban farming is the utilization of narrow land in urban areas that are converted into productive agricultural land carried out by city residents, both individually and in communities, as well as an effort to improve the environment. The concept of urban farming can be done outdoors or indoors on a household or commercial scale. One of them is the cultivation of plants carried out in front of a house terrace with minimal sunlight. This condition can be dealt with by using additional light in the form of LED lights which are expected to help the photosynthesis process of plants despite the lack of sunlight.

Lettuce (Lactuca sativa L.) is one of the commodities suitable for urban farming because basically lettuce is a leaf vegetable crop that has high economic value and has good benefits for consumers. Lettuce plants can grow well in tropical and sub-tropical climates. Demand for lettuce (Lactuca sativa L.) in Indonesia continues to increase, along with the increasing population and per capita consumption. The Central Statistics Agency (BPS) released the results of the 2020 National Socio-Economic Survey (Susenas). Susesnas conducted a survey in 37 provinces in Indonesia regarding the average monthly expenditure of the Indonesian population to buy fruit and vegetables. According to BPS, the daily per capita consumption of vegetables is 128.34 grams. This amount is still far from the threshold set by WHO and the Ministry of Health. WHO generally recommends the consumption of vegetables and fruits for a healthy life of 400 grams per person per day, which consists of 250 grams of vegetables (equivalent to 2 servings or 2 glasses of vegetables after cooking and draining) and 150 grams of fruit.

Lettuce growth is influenced by several factors including planting media, length of irradiation, type of light, humidity, and aeration. Based on this, research related to the length of irradiation and growing media is important. Light requirements within a 12-hour period should be maintained along with low humidity and good air circulation for lettuce plant growth. Growing media such as compost, cocopeat, and husk charcoal are lightweight and have high water and nutrient absorption. However, studies on the optimal media composition for indoor lettuce production are still limited [1]. Therefore, it is necessary to test to determine the composition of planting media and the appropriate length of irradiation on the growth and development of lettuce plants so as to get the best results.

This research was conducted from August to November 2022 at Wonorejo Seedling Farm, Surabaya, East Java. This research was conducted in a closed room with simulated porch light. Analysis of leaf chlorophyll of lettuce plants was carried out at the Biotechnology Laboratory I, Faculty of Agriculture, National Development University "Veteran" East Java, Surabaya, East Java.

The tools used in this study include polybags, spray bottles, measuring cups, mortar and pestle, ruler, LED lamp, micropipette, spectrophotometer, sentifuge, scissors, analytical scales, stationery, timer outlet, camera, and laptop for data processing. Materials used for this research include water, soil, compost planting media, cocopeat, firewood husks, lettuce seeds (Lettuce sativa L.).

This research is a factorial experiment arranged using a Divided Plot Design (RPT) or can be called Split Plot Design with the main plot, namely the length of irradiation or photoperiodicity of plants and subplots in the form of planting media, each treatment combination repeated three times.

The first factor is the length of irradiation (main plot) of plants consisting of 3 levels, namely as follows:

1. P1 = 6 hours irradiation time (LED)

2. P2 = 9 hours irradiation time (LED)

3. P3 = 12 hours irradiation time (LED)

The second factor is the planting media used (sub plot) consisting of 3 levels, namely as follows:

1. M1 = Compost

2. M2 = Cocopeat

3. M3 = Fired husk

The technical implementation in the treatment of length of irradiation between P1, P2, and P3 is in the same place. For the treatment of P1, P2, and P3 are located in the green house, each of which uses white LED tube lights. Treatment irradiation starts at 18.00 WIB where P1 for 6 hours until 00.00 WIB. P2 for 9 hours until 18.00 WIB until 03.00 WIB and P3 for 12 hours, starting at 18.00 WIB until 06.00 WIB according to the treatment. All LED lights are sure to turn on and off with a timer outlet. The research plan from the randomization results can be seen in Figure 1.

Figure 1. Experiment Plan

Based on the treatment factors with each level that has been determined, 9 treatment combinations were obtained, which were repeated 3 times so that 27 experimental units were obtained. Each experimental unit consisted of three polybags, each polybag containing 1 seedling or 1 plant. Each experimental unit contained 3 plants for observation, resulting in a total sample of 81 plants.

Observation Parameters

Leaf Number Increase 

Observation of the number of leaves was carried out simultaneously with the measurement of plant height. The interval of observation of the number of leaves was every week from the age of 5 HST to 45 HST. The leaves that were observed were those that had opened completely.

Root Length Increase (cm)

Root length measurements were measured from the base of the root to the tip of the longest root using a ruler by pulling out the plant sample first during the harvest period. Removal of the sample was done carefully so as not to damage the roots. Root length observations were made after the plants had been harvested.

Plant Length Increase (cm)

Measurement of plant length is only done once in the research process, namely when the plants are already in the harvest phase. Plant length measurements were measured starting from the longest root neck to the longest leaf tops using a ruler as a measurement tool.

Plant Fresh Weight (gram)

Observations of fresh weight or wet weight of stalks were carried out by weighing all parts starting from the roots, stems, and leaves of the plant. The tool used in weighing is analytical scales. Weighing of plant samples is done after harvest.

Chlorophyll Content (µg/ml)

Plant quality parameters can be measured through chlorophyll content. Chlorophyll content measurements of each sample taken from three trays were measured using a spectrophotometer with wavelengths of 645 nm and 663 nm. The chlorophyll content test uses a solvent extraction method whose absorbance is read on a UV-Vis spectrophotometer. How to analyze leaf chlorophyll content (mg/g) according to Sestak (2014) can be calculated by the following formula:

Description:

A645      = Absorbance at wavelength 645 nm

A663      = Absorbance at wavelength 663 nm 

V             = Volume of solution (ml)

W            = sample weight (mg)

Leaf Number Increase 

The results of the interaction between the treatment of additional length of irradiation (photoperiodicity) of LED lights and various kinds of planting media on the increase in the number of leaves of lettuce plants during 45 HST. The treatment of providing additional length of irradiation showed no significant effect on all data on the number of leaves of plants. However, the growth of lettuce contained in Figure 2 (A and B) shows that the growth of lettuce that gets additional LED light irradiation shows better and faster growth results compared to plants that do not receive additional irradiation. The results of growth according to the data can be seen in the graph below that the growth of lettuce without using additional length of LED light irradiation has slow growth and stagnation.

Figure 2. Plant conditions without the addition of LEDs and the addition of LEDs with an average plant wet weight of 10.08 g/plant and 67.04 g/plant.

The treatment of the type of planting media gives a real influence on all the data results of the number of leaves. The average value of the increase in the number of leaves of lettuce plants due to the treatment of additional length of irradiation and the type of planting media is presented in Table 1.

Table 1. Average Num0ber of Leaves of Lettuce Plants in the Treatment of Additional Length of Illumination and Various Planting Media

Description: Numbers followed by the same letter indicate no significant difference in the BNT test at the 5% level; tn = not significantly different; HST = Days After Planting

The average results of the increase in the number of leaves of lettuce plants at the age of 45 HST (Table 1.) showed that the treatment of providing additional length of irradiation for 6 hours, 9 hours, and 12 hours showed significant differences in each other on the increase in the number of leaves of plants. The treatment of cocopeat planting media increased the percentage of the number of plant leaves by 16.5% compared to the marang husk media. The highest average plant results were found in the treatment of husk charcoal planting media which amounted to 8.81. The growth rate of the number of leaves can be seen in the following diagram in figure 3 and 4.

Figure 3. Lettuce plant development additional length of irradiation treatment

Figure 4. Development of lettuce plants in the planting media treatment

The treatment of additional length of LED light irradiation on lettuce plants (Lactuca sativa L.) gives a significantly different effect on the parameters of plant length and plant water content. The treatment of P3 or additional length of LED light irradiation for 12 hours showed the highest results on the increase in the length of lettuce plants which amounted to 37.43 cm. The provision of irradiation treatment shows that the longer the additional irradiation, the more rapid the growth of plant length. 

Root Length Increase (cm)

The results of the Variety Analysis showed that the interaction between the combination of the treatment of additional length of irradiation and various kinds of planting media showed results that significantly affected the increase in root length of lettuce plants. The average value of lettuce root length increase due to the treatment of additional length of irradiation and various kinds of planting media is presented in Table 2.

Table 2. Average Root Length Increase (cm) of Lettuce Plants in the Treatment of Additional Length of Illumination and Various Planting Media

Description: Numbers followed by the same letter indicate not significantly different at the 5% level of BNT test; tn = not significantly different; HST = Days After Planting

The combined treatment of additional irradiation and planting media in table 4.2. Table 4.2 shows significantly different results on the root length of lettuce plants. The highest average root length increase of lettuce plants is found in the combination of 9 hours of irradiation and cocopeat planting media, which is 10.94 cm. The lowest root increment was found in the combination of the treatment of the addition of the length of irradiation of LED lights for 6 hours and cocopeat planting media which amounted to 7.06 cm. The combination treatment of the addition of 6 hours of irradiation and cocopeat planting media increased the percentage of root length by 35% compared to the combination treatment of the addition of 6 hours of LED light irradiation with cocopeat planting media.

Plant Length (cm)

The results of the Analysis of Variance showed that the interaction of the treatment of additional length of irradiation did not give a significant effect on the length gain of lettuce plants, while the treatment of various kinds of planting media showed results that had a significant effect on the length gain of lettuce plants. The average value of length gain of lettuce plants due to the treatment of additional length of irradiation and various kinds of planting media is presented in Table 3.

Table 3. Average Length Increase of Lettuce Plants (cm) in the Treatment of Additional Length of Illumination and Various Planting Media

Description: Numbers followed by the same letter indicate no significant difference in the BNT test at the 5% level; HST = Days After Planting

The treatment of providing additional length of irradiation and planting media in Table 3 shows that the results of the treatment of additional length of LED light irradiation are not significantly different from each other. The treatment of the use of planting media shows that the treatment of compost and cocopeat is not significantly different while the treatment of husk charcoal planting media shows significantly different results on the length of lettuce plants. The average plant length was 55.56 in the treatment of husk charcoal planting media, while the lowest plant length increase was 42.39 in the treatment of cocopeat planting media. The cocopeat planting media treatment experienced a percentage increase of 31% compared to the husk charcoal planting media treatment.

Plant Fresh Weight (gram)

The results of the Analysis of Variance showed that the interaction of the treatment of additional length of irradiation did not give a significant effect on the wet weight of lettuce plants, while the treatment of various kinds of planting media showed results that significantly affected the wet weight of lettuce plants. The average value of fresh weight gain of lettuce plants due to the treatment of additional length of irradiation and various kinds of planting media is presented in Table 4.

Table 4. Average Wet Weight of Lettuce Plants (grams) in the Treatment of Additional Length of Illumination and Various Planting Media.

Description: Numbers followed by the same letter indicate not significantly different at the 5% BNT test level; tn is not significantly different; HST: Days After Planting

The treatment of providing additional length of irradiation and planting media on the average wet weight (table 4.) shows that the results of the treatment of providing additional length of lamp irradiation are not significantly different from each other, while the treatment of providing planting media shows that each treatment shows significantly different results on the measurement of wet weight of lettuce plants. The average wet weight was 40.04 in the treatment of husk charcoal planting media, while the lowest increase in plant length was 12.63 in the treatment of cocopeat planting media.

Chlorophyll Content (µg/ml)

The results of Chlorophyll Test Analysis using a spectrophotometer at wavelengths 646 and 663 obtained the total chlorophyll content of the treatment combination of additional irradiation duration and the type of growing media, using the calculation method of Harborne, 1987.

Figure 5. Total Chlorophyll Content of Lettuce Plant Leaves (µg/ml).

Based on the results of the total chlorophyll test analysis, it shows that the largest total chlorophyll is found in the treatment combination of P2M3 (9-hour irradiation duration and husk charcoal planting media) and P3M1 (12-hour irradiation duration and compost planting media), which is 39.08 and 38.84, respectively. While the smallest chlorophyll results were found in the treatment combination P3M2 (12 hours of irradiation and cocopeat planting media) which amounted to 22.70 as shown in Figure 4. Based on the results of the chlorophyll test analysis of lettuce plants, it shows that the higher the amount of chlorophyll value in plants, the more it affects the production yield [2].

The Effect of Providing Additional Duration of LED Lighting on the Growth of Lettuce Plants

The treatment of additional length of LED light irradiation on lettuce plants (Lactuca sativa L.) gives a significantly different effect on the parameters of plant length and plant water content. The treatment of P3 or additional length of LED light irradiation for 12 hours showed the highest results on the increase in the length of lettuce plants which amounted to 37.43 cm. The provision of irradiation treatment shows that the longer the additional irradiation, the faster the plant growth. 

The results of this observation can be proven in the statement Salma, et, al. (2020) [3] that the treatment of irradiation duration exceeding the optimal limit of plant irradiation makes the photosynthesis process not take place efficiently. The increase in plant height is closely related to the rate of photosynthesis and photosynthate produced. One of the factors that influence it is the appropriate amount of light intensity. According to Hamim (2018) [4] the more light energy that can be converted into chemical energy, the greater the reduction of CO2 into sugar, meaning the higher the photosynthate produced.  However, an increase in light intensity does not correlate with an increase in photosynthesis, but is parabolic. That is, when the light intensity increases at low intensity until the optimum level, it will increase the photosynthesis rate, but when the intensity exceeds the optimum limit, it has little effect on increasing photosynthesis. Therefore, lettuce plants with the longest irradiation cannot be said to have the best growth.

The Effect of Providing Different Types of Planting Media on the Growth of Lettuce Plants

Observations of different planting media treatments on lettuce plants (Lactuca sativa L.) significantly affect several observation parameters including plant length, number of leaves, fresh weight, and water content. The highest plant was owned by M3 or husk charcoal planting media treatment which amounted to 30.80 cm. In contrast to the number of leaves where the treatment of planting media was significantly different starting from the observation interval of 5 HST to 45 HST (harvest). The treatment that has the highest average number of leaves is in M3 or husk charcoal planting media with a value of 8.81 then followed by M1 compost planting media and the last M2 cocopeat planting media.

The planting media of husk charcoal (M3) gave a good effect on the parameters of plant length, plant fresh weight, and plant water content. This is probably because the composition of husk charcoal is most occupied by the content of nutrients Nitrogen, Phosphorus and Potassium in husk charcoal and supports the improvement of soil structure. In accordance with the statement Septiani (2012) [5] husk charcoal has porous properties, light, not dirty, but has a low ability to absorb water and good porosity is very beneficial if used as a planting medium because it supports the improvement of soil structure through better aeration and drainage. 

Studies have shown that the use of husk charcoal as a growing medium can also have a positive impact on plant growth, especially in terms of increasing the number of leaves. The porous nature of husk charcoal and its good water-holding ability allows for proper accumulation of nutrients and moisture around the plant roots. This provides optimal conditions for root growth and nutrient absorption, which in turn stimulates the development of healthy shoots and foliage. In addition, husk charcoal also has a high cation exchange capacity, which helps provide the nutrients necessary for chlorophyll synthesis and vigorous leaf growth. Another factor is also found in research which states that husk charcoal has a high content of organic compounds and minerals, especially potassium in fertilizing plant growth. Therefore, as a planting medium, husk charcoal can provide better results in terms of increasing the number of leaves on plants.

The Effect of Additional Treatment of LED Lamp Illumination Length and Planting Media on Lettuce Growth

The treatment of providing additional length of LED light irradiation and differences in planting media on the results of lettuce plant growth (Lactuca sativa L.) Provides a real interaction on several observation parameters including plant length, root length, and water content. 

Observations of plant length treatment parameters showed the results did not significantly affect the growth of lettuce plants. This is because at the time of observation at the research location has uncertain whether (cloudy and rainy) so that growth does not increase significantly and is not significantly different at the time of observation. In contrast to the number of leaves where the treatment of planting media was significantly different starting from the observation interval of 5 HST to 45 HST (harvest). 

The average number of leaves at 20 and 30 HST showed an interaction between the additional duration of LED lighting and planting media, but did not show significantly different results at other observation times. This is caused by external factors, namely the weather as well as other observations that have similar results. The research time included a change of season from dry to rainy so that there were some observations that were not uniform. The treatment that has the highest average number of leaves is in M3 or husk charcoal planting media with a value of 8.81, followed by M1 compost planting media of 8.22 and M2 cocopeat planting media of 7.56. 

Observations of root length parameters showed an interaction between the additional duration of LED lamp irradiation and planting media. The highest observation value was found in the combination of P2M2 or 9 hours of irradiation and cocopeat planting media at 10.94 cm, while the lowest observation value was found in the combination of P1M2 or 6 hours of irradiation and cocopeat planting media at 7.06 cm. According to Lindawati, et al. (2015) [6] roots do not always grow lengthwise to reach the nutrients needed by plants for growth.  If the growth of the upper plant is optimal, the growth of the roots will also be good so that the amount of photosynthetic products that are translocated to all parts of the plant including the roots is also optimal.

The moisture content parameter shows that P2M3 is also still the best compared to other parameters at 39.08. The combination of husk charcoal planting media and 9 hours of LED light irradiation showed that the combination was the best interaction in this study. This is supported by the statement of (Mariana, 2017) [7] that husk charcoal is a porous planting medium and has a high carbon (C) content that makes this planting medium loose. The black-colored husk charcoal due to the combustion process has a high heat absorption capacity that can raise the temperature and accelerate germination.

Based on the results of observations and discussion in this study, it can be concluded that there is no interaction between the addition of length of irradiation and planting media on all observation variables except root length . Plants that do not get additional LED light irradiation give unsatisfactory results compared to plants that get LED light, while the effect of the length of LED irradiation does not show a real effect on the growth and yield of lettuce plants. Planting media showed the best effect on the growth and yield of lettuce plants is M3 treatment (husk charcoal planting media). 

ACKNOWLEDGEMENT

The author would like to thank my lecturers Ir. Hadi Suhardjono, MTP. and Dr. Ir. Yonny Koentjoro, MM. In addition, the author would like to thank Mr. Yudi, who facilitated the greenhouse for research and observation in Kebun Bibit Wonorejo, East Java.

Conflict of Interest:

The authors declare that they have no conflict of interest.

Funding: No funding sources 

Ethical approval: The study was approved by the Institutional Ethics Committee of Universitas Negeri Makassar

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