Growth and production of garlic (Allium sativum L.) in the lowland on various types of mulch

This study aims to determine the effect of mulch treatment on the growth and production of garlic (Allium sativum L.) in the lowlands. The research was conducted in Lempong Village, Bola District, Wajo Regency located 78 m above sea level (asl) with an average temperature of 24ºC - 33ºC. This research was set using a Split Plot Design (SPD) with garlic varieties set as the main plots consisting of highland (var. Lumbu Hijau) and lowland varieties (var. Lumbu Putih) while mulch types were set as subplots consisting of control (no mulch), black silver plastic mulch, rice straw mulch, Gliricidia (Gliricidia sepium) leaves mulch, and banana leaves mixed with stem mulch. Each treatment combination was repeated 3 times. The results show that the Lumbu Putih variety had better growth and production than the Lumbu Hijau on the parameters of plant height, number of leaves, and number cloves per tuber. Straw mulch showed the best effect in suppressing soil temperature (28.5ºC). Banana leaves and stem mulch was the best type of mulch compared to control and other mulches on parameters of plant height, number of leaves, and number of cloves per tuber. The interaction between the Lumbu Putih variety and banana leaf and stem mulch produced the highest production per hectare (1.6 ton ha−1).


Introduction
Garlic belongs to the Liliaceae family and is popular in the world with its scientific name Allium sativum L., has high commercial value and is spread throughout the world [1].Consumption of garlic in the world ranks second after onions [2] and is an important vegetable commodity for Indonesian people.Garlic production in Indonesia in 2019 reached 88,816 tons, an increase from 2018 (39,300 tons) resulting in an increase in production of 49,516 tons.Garlic harvested area in Indonesia has increased in 2019.Harvested area in 2018 (5,013 ha) while in 2019 (12,280 ha), resulting in an increase of 7,267 ha from the previous year [3].Even though there was an increase in production in 2019, it was not yet able to meet domestic demand.
One of the conditions for growing garlic is to have an environment with a air temperature of around 20°C, hence it is most suitable grown in the highlands between 700 -1000 meters above sea level [2].Low temperature in garlic plant cultivation is necessary to get vernalization for bulb initiation and formation.The interaction between temperature and day length has an effect on tuber enlargement [4].Garlic cultivation in the highlands is limited because land use competes with conservation needs and the cultivation of other upland vegetables such as cabbage, potatoes and carrots.Meanwhile, planting in the lowlands is constrained by high temperatures.According to Oh et al [5], a growth temperature of 30C inhibits early growth of garlic, therefore efforts are needed to modify the microclimatic conditions in the lowlands to maintain soil temperature and moisture by using mulch, a material to cover the soil so that the humidity and temperature of the soil as a planting medium are maintained [2].Mulch also functions to suppress weed growth so that plants will grow better.
Applying mulch on the soil surface during the rainy season can prevent soil surface erosion on an area with slopes of 0° to 25° [6].Giving mulch to horticultural commodities can prevent rainwater splashing which causes infection at the splash point.In the dry season mulch will keep the sun's heat on the top soil surface.Evaporation suppression results in relatively low temperatures and humidity on mulched soil [7].
In general, mulch is divided into two types, namely inorganic and organic mulch.The use of inorganic mulches can accelerate plant production, increase yield per unit area, be efficient in the use of fertilizers and water, reduce erosion mostly due to rain, reduce pest and disease attacks, inhibit weed growth, prevent soil compaction and have the opportunity to plant on the same bed.more than once [8].
The application of organic mulch reduces soil temperature, moisture, cation exchange capacity, pH, organic C, soil organic matter, total N, availability of K and C/N ratio [9].The use of silver black plastic mulch has been known to suppress weed growth, maintain soil temperature stability and maximize photosynthesis.Organic mulch such as rice straw, Gliricidia sepium leaves, and banana leaf and stem, can be used and impact on reducing soil surface temperature, improve soil structure and texture, and produce organic matter that increases soil fertility [10].In addition, the Gliricidia and banana are usually used as a source of nitrogen and phosphorus nutrients.
The application of mulch on the soil surface provides an opportunity to utilize a variety of plant organic matter wastes, especially their relation to soil and water.The ability of mulch to minimize evaporation also helps to maintain soil temperature.Organic mulch can act as an insulating material for soil layers because it can lower soil temperature during high air temperatures and warm the soil during low air temperatures [11].
Modification is a change or addition of something, or modification is changing the initial conditions.Soil temperature is a broad concept, because it can be used to classify the thermal properties of a system [12].Soil temperature is an important factor in determine the physical processes that occur in the soil, as well as energy and mass exchange with the atmosphere, including evaporation and aeration processes.Soil temperature also affects biological processes such as seed germination, seed growth and development, root development, and microbial activity in the soil.A previous study showed that mulch can be used to modify soil temperature and the use of mulch provided a lower soil temperature compared to soil without mulch [13].Therefore, it is necessary to study the effect of using mulch on the growth and production of garlic when grown in the lowland.

Methodology
This research was conducted in Lempong Village, Bola District, Wajo Regency during growing season from June to October 2019.The geographic location is between 3º39' -4º16' South Latitude and 119º53' -120º27' East Longitude and the altitude is 78 m above sea level (asl) with an average temperature of 24ºC -33ºC.

Experimental design
This research was conducted in the form of an experiment using Split Plot Design.The first factor as the main plot was variety (V) which consisted of 2 levels, namely the Lumbu Putih (variety adapted to the lowlands) and the Lumbu Hijau (variety adapted to the highlands).The second factor as subplots was the type of mulch (M) which consisted of 5 types, namely control (no mulch), silver black plastic mulch, rice straw mulch, Gliricidia leaves mulch, and banana leaves and stem mulch.Based on these two factors, 10 treatment combinations were obtained.Each treatment combination was repeated 3 times, hence there were 30 experimental units in total.

Mulch installation
Prior to mulch installation, land for trial was prepared by conducting soil tillage 17 days before planting.Soil was ploughed and hoed to a depth of ± 30 -40 cm and beds or experimental plots were made to a size of 100 cm x 120 cm, height ± 20 -30 cm, and distance between the beds of 50 cm.Cow manure was given to all plots at the time of tillage as basic fertilizer at a dose of 2.67 tons/ha The installation of mulch was carried out a day before planting the garlic.Silver black plastic mulch was installed during the day to facilitate the installation process.The organic mulch provided in the form of chopped dry organic matter, ± 5 cm thick per bed.The organic mulches were maintained during the study and replaced with new organic matter when 50-70% of the organic matter has weathered.

Soil temperature measurement
Soil temperature was observed during the plant growth using a digital soil temperature probe at the tillage depth of 20 cm.

Planting
This study used 2 types of varieties, namely Lumbu Putih, a variety that grows well in the lowlands and Lumbu Hijau, a highland variety.Prior to planting, the cloves were cut 1/3 at the top to stimulate shoot growth and then dipped in a Hormonic solution concentration of 25 ml/l water and sprayed with Dithane fungicide to prevent disease.Planting was carried out when the soil is moist by making a planting hole with a wooden planting stick with plant spacing of 10 cm x 15 cm then covered with soil.Each bed was planted with 80 plants, hence total population was 2,400 plants.Plant was fertilized at 25 days after planting (DAP) and 45 DAP using Phonska fertilizer at dosage of 255 kg/ha, respectively and at 75 DAP using ZA fertilizer of 170 kg/ha.Harvesting was carried out when the garlic leaves are starting to turn yellow and dry, about 50-60% of all garlic plants already look yellow and dry, the stems dry and the base of the stems hardens.

Data analysis
The data that has been collected is then analysed using analysis of variance (ANOVA) to test the effect of the treatment given, if there is a significant effect then it is continued with a further test using the Least Significant Difference (LSD) test at a level of 95%.

Effect of Much on Soil temperature
The results of variance showed that the type of mulch had a significant effect on soil temperature in garlic cultivation in the lowlands.The use of organic mulch during the growth period resulted in a much lower soil temperature compared to the control treatment and the use of silver black plastic mulch.Rice straw mulch showed the highest temperature decrease from 29.17 C to 28.50 C while the temperature of the soil in both plots without mulch and using silver black plastic mulch experienced a temperature increase of 1 C (figure 1).

Effect of Mulch on growth and production of garlic.
The results of analysis of variance showed that the type of mulch had a very significant effect on plant height and number of leaves of garlic plants.Table 1 shows the use of banana leaf and stem mulch resulted in the highest average plant height (31.92 cm), not significantly different from the silver black plastic mulch and straw mulch, but significantly different from the Gliricidia leaves mulch and control or without mulch.The lowest plant height (21.73 cm) was found in the control treatment.Similarly, banana leaves and stem mulch produced the highest average number of leaves, namely 4.71 leaves, not significantly different from the silver black plastic mulch and straw mulch, but significantly different from Gliricidia leaves mulch and control.The least number of leaves (3.73) were found in the treatment without mulch.There was no significant difference between the two varieties used in this study in terms of plant height, but the Lumbu Putih variety showed a higher number of leaves than the Lumbu Hijau.The results of variance showed that the variety and type of mulch had a very significant effect on the number of cloves per tuber, but only the type of mulch had a significant effect on the diameter of the garlic bulbs.Straw mulch had the largest average tuber diameter (2.05 cm) which was not significantly different from banana leaves and stem mulch, Gliricidia leaves mulch, and silver black plastic mulch, but significantly different to control.The smallest bulb diameter (1.42 cm) was found in the control treatment or without mulch as shown in table 2. On the parameter number of cloves per bulb, use of straw mulch, banana leaves and stem mulch produced the highest average number of cloves per bulb (2.33 cloves) which was significantly different from control, silver black plastic mulch, and Gliricidia leaves mulch.The lowest number of cloves per bulb (1.50The results of variance showed that variety had a significant effect, while the type of mulch and the interaction between the two factors had a very significant effect on bulb production per hectare.The results of the LSD test of 0.05 (figure 2) showed that the lumbu putih variety using banana leaves and stem mulch produced the highest bulb production per hectare (1.641 ton ha -1 ) which was significantly different from other types of mulch.The Lumbu Putih variety using banana leaves and stem mulch was significantly different from the Lumbu Hijau variety using the same type of mulch.The lowest bulb production per hectare (0.325 ton ha -1 ) was found in the Lumbu Hijau variety using silver black plastic mulch, which was significantly different from other types of mulch, but still the same as the Lumbu Hijau variety in the control treatment or without mulch.

Discussion
Mulching treatment in this study has been shown to have a significant effect in reducing soil temperature and on the bulb diameter.In addition, mulching also significantly affect the plant height, number of leaves, the number of cloves per bulb and the productivity of garlic.Nevertheless, different was found between garlic varieties in response to mulch treatments.The Lumbu Putih variety had higher production than the Lumbu Hijau, this was influenced by the suitability of the growing habitat between the two varieties.The Lumbu Putih variety can grow well in the lowlands with an altitude of 6 -200 meters above sea level, while the Lumbu Hijau variety can only grow well at an altitude of 900 -1,100 meters above sea level, hence when planting in lowland, the Lumbu Hijau variety showed higher production when using organic mulch in the lowlands compared to control (figure 2).Difference in temperature from its natural habitat for varieties adaptive to highland will have impact on the bulb development process of the Lumbu Hijau variety.Variety plays an important role in production because achieving high yields is largely determined by its genetic potential.Yield potential in the field is influenced by the interaction between genetic factors and management of environmental conditions.If the management of the growing environment is not carried out properly, the high yield potential of these superior varieties cannot be achieved [14].The ecology of the experimental planting which is not in accordance with the natural habitat of garlic, which requires cold temperatures around 20 ºC.Low temperatures in garlic cultivation are necessary so that the plants get vernalization to initiate tuber formation [15].The interaction between temperature and day length has an effect on tuber enlargement.
The results of this study indicated that the best mulch for garlic cultivation was leaf and banana stem mulch compared to no mulch, silver black plastic mulch, straw mulch, and Gliricidia leaves mulch.Stems, midribs and banana leaves have good fiber making them suitable for use as mulch [16].Research conducted by Firli et [17] showed that plant height and tuber diameter showed an increase after applying banana leaf mulch.The ability of mulch to minimize evaporation also helps to maintain soil temperature.Organic mulch can act as an insulating material for soil layers because it can lower soil temperature during high air temperatures and warm the soil during low air temperatures [11].The application of mulch on the soil surface provides an opportunity to utilize a variety of plant organic wastes which have many benefits, especially their relationship to soil and water.Giving mulch in the dry season will keep the sun's heat on the top soil surface.Evaporation suppression results in relatively low temperatures and humidity on mulched soil [7].

Conclusion
Based on the research results that have been obtained, it can be concluded as follows • The Lumbu Putih variety showed better growth and production than the Lumbu Hijau on the parameters: the highest number of leaves (4.63 leaves), and the highest number of cloves per tuber (2.60 cloves).• Banana leaf and stem mulch is the best type of mulch compared to no mulch, silver black plastic mulch, straw mulch and Gliricidia leaf mulch on parameters: soil temperature (28.83 ºC), plant height (31.92 cm), number of leaves (4.71 leaves) and the number of cloves per tuber (2.33 cloves).

Table 1 .
Effect of mulch on growth of garlic on lowland.
cloves) was in the control treatment or without mulch.The LSD test in table 2 also shows that the Lumbu Putih variety produced the highest average number of cloves per tuber, which is 2.60 cloves, which is significantly different from the Lumbu Hijau variety, which produced the lowest number of cloves, namely 1.33 cloves.

Table 2 .
Effect of Mulch on the production of garlic on lowland.Productivity of two varieties of Garlic grown in lowland using different types of Mulch.