Impact of planting distances to arthropods abundance on kangkong

Kangkong (Ipomoea reptans Poir) is the favourite green vegetable especially most of Asian people. The important factors affecting production of kangkong is the planting distance. The optimal planting distance create an ideal microhabitat around crop and potential to suppress development of insect pests. The research purpose is to study the impact of planting distance to arthropods abundance on kangkong. The research was conducted in Somba Opu District, Gowa Regency, South Sulawesi from February to May 2020. The arthropods identification was carried out at the Pest Laboratory, Department of Plant Pest and Diseases, Faculty of Agriculture, Hasanuddin University Makassar. The study was conducted in four treatments of planting distance, P1= 5 cm x 5 cm; P2 = 5 cm x 10 cm, P3 = 5 cm x 15 cm and P4 = the seeds was spread (without planting distance), respectively. Each treatment was repeated four times, the arthropods was caught by pitfall trap. The sampling method used the diagonal pattern. Observation of arthropods began when the kangkong 7 days after planting with interval 7 days until harvest. The arthropods results divided into two group (insect pest and natural enemies) showed that: 1) the highest number of insect pests in the pitfall trap was found in treatment P4 (Valanga sp. 1.25 individual); 2) the highest natural enemies number from Hymenoptera (Formicidae); and 3) the highest harvest number in the treatment P1 (13.1 kg) and the lowest in P4 (11.3 kg). Conclusion of the research: grasshopper Valanga sp. (Orthoptera: Acrididae) as the dominan insect pest in P4 (1.25 individual). Dominant arthropods as natural enemies in the kangkong field as Formicidae in P3 (14.5 individual). The highest harvest in kangkong field at P1 (13.1 kg) and the lowest in P4 (11.3 kg).


Introduction
Kangkong (Ipomoea reptans Poir) family Convolvulaceae as the popular green vegetable in the world wide.Kangkong as the familiar vegetable consumption in Indonesia and few country in South-East Asia.Beside cabbage, carrot and many economical important commodity, kangkong including in the circle of marketing because contain vitamin, mineral that useful increasing human healthy.The lowest price of kangkong and easy to consumption made them as famous green vegetable in Indonesian fork.Kangkong production in South Sulawesi in the periods of 2018, 2019 and 2020 is 130.50 quintal/ha; 149.37 quintal/ha and 126.69 quintal/ha, respectively.In 2021, kangkong production in South Sulawesi increasing become 254.142quintal/ha, more higher than the past [1, 2].
In the kangkong farming, the optimalize production inhibit by presence of pests and plant diseases.Beside presence of insect causing damage of the plant, planting distance also affects agricultural plant 1230 (2023) 012103 IOP Publishing doi:10.1088/1755-1315/1230/1/012103 2 productivity.The advantages using planting distance for cultivated plants are: minimize the damage occur during weeding, the plants have enough space to grow, also nutrients are evenly distributed for each plant [3,4,5,6].Few research results shown the effect of planting distance able increasing the plant productivity.In case, planting distance 30 cm for spinach effectively increased the number of leaves, plant height and biomass.The spinach productivity has strong related to fertilizers availability and suitable planting distance [7,8].Related to the planting distance, another research reported the planting distance used 55 cm x 55 cm in cabbage given the highest result to plant height around 64.13 cm, than without planting distance only 49.2 cm.Another parameter of cabbage showed of planting distance 55 cm x 55 cm is 59.02 cm, then without planting distance is 28.96 cm.In other hands showed, planting distance increasing the average weight of cabbage with planting distance 55 cm x 55 cm is 2.08 kg and 1.27 kg on the cabbage without planting distance [9,10].
Beside planting method, the arthropods abundance level has relationship to planting distance and nutrition suitability of its host.Commonly insects as plant feeder taking benefit from wide variety of host and non-host plant.Insect pest increasing their development by consumption of its host.Sometimes presenting insect pest protecting plant from another herbivorous insect.This is very unique interaction between herbivorous insect and hosts [11,12,13].Related to number of abundance and ecosystem, another researcher reported that host plant selection by insects involving visual behavioral and ability detecting of chemical cues, assessment of host plant size, and many abilities to navigate and identify hosts in their habitat.The visual and chemical stimuli playing important roles in host plant location and acceptance process.Number of insect develop on its host depend on its suitability as the source of food [14,15,16,17,18].Commonly farmers growing kangkong with spread methods and never applied in the filed used planting distance.In the future, the researcher hope the observation result a recommendation methods planting distance for kangkong to avoid insect pests used different planting distance.

Site of research
The research was conducted in farmers field at Somba Opu District, Gowa Regency, South Sulawesi, Indonesia from February to May 2020.

Preparing the plot
The tillage has been finished a week before planting the agricultural commodity.The field free weeds and made four plot with measurement 150 cm x 90 cm, respectively.Height of the plot 25 -30 cm to avoid flooding and distance between plot 50 cm.

Seed screening
The commercial kangkong seeds used in the research from Panah Merah.The seeds soaked water to dormancy break and separated floating seeds.The sinking seed as important indicator of healthy seeds ready plating in the field.

Planting seed and fertilizing
The kangkong research treatment used planting distance: P1= 5 cm x 5 cm; P2= 5 cm x 10 cm; P3 = 5 cm x 15 cm; P4= spread the seeds.Kangkong seeds planting with direct methods.Every holes in P1, P2 and P3 filling with 1 -3 seeds and watering (exception P4 kangkong seed was spread).The research used manure as based fertilizer spread in the plot surface together with tillage.The first fertilizer when kangkong 14 days after planting used urea, SP-36 and KCl mixed water 15 L for all of the plots.The second and third fertilizer in the 20 and 30 days after planting, respectively.

Arthropods collection
The observation of insect pests and another arthropods as their natural enemies in kangkong began at 7 days after planting with interval 7 days after planting (total observation 4 times until harvest).The arthropods from kangkong field was collected by pitfall trap made from plastic cup, filling mixture water and liquid detergent.Pitfall trap was planted diagonally in each plot used 5 pieces of the tools.Pitfall traps were installed in the morning and after 24 hours, they were collected by separating the arthropods according based the physical perform order/genera.The arthropods identification was carried out at the Pest Laboratory, Department of Plant Pest and Diseases, Faculty of Agriculture, Hasanuddin University Makassar.The identification of samples used literature [19].

Harvest
The harvest was conducted after kangkong age around 30 days after planting (last day after observation).Kangkong was harvested by pulling up to the roots.After that, the kangkong weighed for all treatments.

Data analysis
Data analysis in the research used ANOVA in the Least Significance Difference level 5%.

Result
Based the collected of arthropods in the field, the sample material divided into two main group (insect pest and natural enemies).Valanga sp. as the dominant insect pest in every treatment (highest in the P4 = 1.25 individual).Beside Valanga sp. the result showed almost similar number of insect pest in every treatment (table 1).Commonly kangkong harvest after 30 days after planting when the mature plant ready for human consumption.The highest harvest weight of kangkong showed in the treatment P1 then the lowest in the P4 (figure 1).

Discussion
Based table 1, the kind of potential insect pest attacked kangkong from order: 2 family of Orthoptera (Acrididae, Pyrgomorphidae), 3 family of Lepidoptera (Noctuidae, Pyralidae, Crambidae), Coleoptera (Chrysomelidae) and Hemiptera (Coreidae).Valanga sp. as the dominant pest attacked kangkong and highest in P4 (1.25 individual).The result of LSD test showed there are not significance difference of insect pest in every treatment.Based research of [6,16] stated that more sunlight can inhibit insect development because their potential increasing microclimate temperature and finally caused dehydration.Insect pests able to detect the nutritional quality of plant with the olfactory organs found in the antennae and mouth.Overall, P1 showed that planting distance seems limiting insect development and deserve as recommendation treatment for farmer in the field.
The dominant arthropods as natural enemies from Hymenoptera (Formicidae) found in all of the treatment, The number of natural enemies increased followed the plant age and availability of prey surrounding the plant.P1 showed the lowest number of natural enemies.It means that planting distances closest between plant not suitable for supporting of natural enemies activities.Natural enemies prefer more open space under the sunlight in purpose foraging the prey.The result of research [4,5,18] showed that presence of prey and environment quality determine success of the natural enemies life.Kangkong with treatment spread of the seeds at P4 showed highest number of natural enemies.This is reality on field, insect pest develop very well and attracted natural enemies as biological control in nature.
The highest of kangkong harvest in P1 (13.1 kg) then the lowest in P4 (11.3 kg).The highly harvest of kangkong at P1 showed the plant is growing by adapting optimally to its environment.The closest planting distance improves the optimization of nutrient uptake needed by plants.On the other hand, the P4 (spread the seeds) not preparing space for growth optimally such as another treatment.Research from [7,8] showed the importance planting distance improving quality of harvest.Plant growth optimal if the environment supporting nutrients, light, water and growing space.The result of research was showed P1 the best planting distance for kangkong growth in the field.

Table 1 .
Number of insect pest in the different treatment (individual)