Biomass and carbon stock potential of Gliricidia Sepium as an alternative energy at Timor Tengah Utara Regency, East Nusa Tenggara Province, Indonesia

The utilization of biomass from plants is one efforts for the fulfillment an availability of alternative energy in indonesia. Gliricidia sepium is a tolerant species that can grow in dry land. However its utilization as renewable energy source is non-optimized. This study aims to analyze the potential carbon stocks and biomass from Gliricidia sepium as a raw material for alternative energy in East Nusa Tenggara. This study was conducted in November 2015 and located in Humusu Sainiup, Timor Tengah Utara Regency, East Nusa Tenggara Province. The method used in collecting data was applied in three different land-use, namely monoculture Gliricidia sepium, polyculture between Gliricidia sepium and Leucaena leucocephala, and polyculture between Gliricidia sepium and Zea mays. We used the allometric equation from Ketterings namely B = 0.11ρD2+0,62 and C = 0.5 x B. The results showed that the different land-use will give different value of carbon stocks which is in this study the biggest value of carbon stocks was found in monoculture of Gliricidia sp (35.35 tC ha-1) compared with Gliricidia sp + Leucaena sp (18.83 tC ha-1), and Gliricidia sp + Zea mays (13.79 tC ha-1). The value of biomass and carbon stocks was influenced by wood density, trees density, and diameter at breast height (dbh).


Introduction
Population growth encourage increased energy needs for the improvement of human wellbeing from year to year. Increased energy consumption caused by two factors: population growth, which reached more than 20% and the improvement of living standards that drive energy consumption per capita increased by almost 40%.
The need for energy is a crucial issue for national development requires the availability of sufficient energy, safe, quality, and diverse and spread evenly throughout Indonesia affordable. The high growth of industry and population resulted in a gap between demand and supply of energy. This can lead to an energy crisis. Indonesia has energy resources 2 1234567890 ''"" which consist of non-renewable energy sources and renewable energy sources. The energy source has an important role in development as a crucial factor for other sectors such as industry, transport, households, commercial, and others [1].
Law No. 30 of 2007 on Energy [2] and Government Regulation No. 78 of 2014 on National Energy Policy [3] has been set up management and utilization of energy resources. National energy policy mandates a target of achieving an optimal mix of primary energy in 2025 that the role of renewable energy at least 23% and by 2050 at least 31%. Utilization of Indonesia's energy consumption has increased with an average growth of 1.9% per year which is still dominated by fossil fuels, the increase was due to higher activity in the transportation, industrial, and household [4]. The energy problem faced by Indonesia, which are: energy subsidies increased to Rp 255.6 trillion in 2011, the number of people who do not have access to electricity was 87.69 million population, limitations of domestic infrastructure challenges and problems in meeting domestic energy needs. Dependence on oil is still dominant reached 49.7%, while the utilization of renewable energy was approximately 6% [5]. Indonesia has the landscape and geographical location on the equator have some type of alternative energy sources that can be developed such as solar energy, wind energy, geothermal energy, ocean thermal energy and biomass energy. Among the sources of alternative energy, biomass energy is an alternative energy source that needs to be given priority in development compared with other energy sources.
Efforts to comply with the availability of alternative energy is the utilization of biomass plants. Biomass-based energy sources have the advantage in ensuring the availability of alternative energy sources as energy needs. Gliricidia plants is one of the renewable energy sources available in Indonesia, particularly in the province of East Nusa Tenggara.
Gliricidia have a place to grow tolerant characteristics in upland and utilization of renewable energy sources is not optimal. This study aims to analyze the potential of carbon stocks and biomass in G. sepium.

Materials and Methods
The study was conducted in October 2015 in the secondary forest in Humusu Sainiup, Timor Tengah Utara Regency, East Nusa Tenggara Province. Location of the study there are three types of land cover, namely on G. sepium monoculture, polyculture between G. sepium and L. leucochepala, and polyculture between G. sepium and Z. mays.
The materials used for the observation and measurement of the vegetation is in a location that includes seedlings, saplings, poles, trees. The equipment used for to conduct of research include GPS, Compass, Roll-meter, Meter Sewing, Hagameters, Tally Sheet,, Cameras, and Stationery.
The type of experimental plot is square with 20x20 cm, then made 3 subplot each sized 10x10 cm, 5x5 cm, and 2x2 cm. Plot with sized 20x20 cm be destined for tree, 10x10 cm for poles, 5x5 cm for stakes, and 2x2 cm for seedlings. Each type of land cover has made 5 experimental plots. After determining and make the plot as the sample plot, then do inventary to obtain data and information carefully according to circumstances on the ground in each plot were made, the variety of data and information is the location plots, plant species, and the diameter breast height (1.3 m). Biomass data analysis done using the allometric equation B = 0.11 ρ D 2+0.62 [6] and C = 0.5 x B [7].

Inventory of biomass and carbon storage on monoculture G. sepium
Inventory of biomass and carbon storage on monoculture G. sepium is located at coordinates S 09 0 29' 16" E 124 0 56' 05" and at an altitude of 333 meters above sea level. Inventory made on 5 experimental plots, inventory data for biomass and carbon storage of data obtained by the above ground biomass that include categories stakes, poles, and trees. . This is because the sample plots commonly found plants that fall into the category pole density and very high frequency, which resulted in having the potential of biomass and carbon storage are greatest when compared to a stake or a tree well. Biomass and carbon storage value depends heavily on the density and frequency contained in each respective category in field trials. The higher level of density and frequency in a region, the greater the value of the biomass and carbon storage in the region. Based on study conducted by Fuwape and Akindele [8] obtained the results of research on Gamal plant biomass of 37.4 tons / ha. The value of biomass and carbon stock depends greatly on the density and frequency levels found in each category on the experimental field.

Inventory of biomass and carbon storage on intercropping G. sepium and L. leucochepala
Inventory of biomass and carbon storage on intercropping G. sepium and L. leucochepala is located at coordinates S 09 0 27' 51" E 124 0 57' 65" and at an altitude of 148 meters above sea level. Inventory made on 5 experimental plots, inventory data for biomass and carbon storage of data obtained by the above ground biomass and carbon storages that include categories stakes, poles, and trees.  [9] in Nunukan stated that the diversity of the size of the diameter, the presence of trees with a diameter >30 cm in a land use systems, contributing to significant biomass to the total carbon storage. This causes that the biomass content at the level of the tree has a value greater than the rate of saplings and poles.

Inventory of biomass and carbon storage on intercropping G.sepium and Zea mays
Inventory of biomass and carbon storage on intercropping G.sepium and Zea mays are on the coordinates S 09 0 29' 43" E 124 0 56' 86" and at an altitude of 281 meters above sea level. Inventory made on 5 experimental plots, inventory data for biomass and carbon storage of data obtained by the Biomass stand up (Above Ground Biomass) and carbon deposits that include categories stakes, poles, and trees. Table will present the results of the inventory of biomass and carbon storage contained in Gamal and corn fields. According to the table 3, the results of the calculation of the largest biomass and carbon storage is at stake category of 25,426.81 kg / ha, equivalent to 25.42 tonnes / ha, while for carbon deposits generates 12,713.41 kg / ha, equivalent to 12.71 tonnes / ha. This result is obtained because the sample plots G. sepium and Z. mays crops is very much a crop plant regeneration. The sample plots are also found Z. mays, because when the research was ongoing planted corn has been harvested by the local community. The difference in the acquisition of biomass is influenced by the density of vegetation, the diversity of its diameter size and density distribution of vegetation [9]. Data on the ground suggest that the category of the stake has a number of stands more than the category resulting poles and tree biomass and carbon storage values obtained at different stake levels much to the value of biomass and carbon storage in small trees and tree level. Tree growth is determined by the interaction between three factors namely genetic factors, environmental factors and cultivation techniques or silviculture techniques applied [11]. Genetic factors and cultivation techniques can be manipulated through tree breeding and the selection of appropriate cultivation or silviculture techniques that can increase tree productivity that is closely related to increased tree biomass and carbon storage.
All this time, Gliricidia are used as garden barriers, as firewood, as ruminant animal feed, and some studies have explained that Gliricidia have high carbon stores that can reduce air pollution, as well as large biomass and calorific values that can be developed as materials raw alternative energy. Based on study conducted by Amirta et al [12] showed that calorific value of Gliricidia higher than another fast growing species. Gliricidia has calorific value amounted to 4026.77 kCal/kg. These result explained that Gliricidia has a high calorific value compared to other fast growing species. In addition to, with the advantages of tolerant and one of the fast growing species, Gliricidia is one of raw materials that can be cultivateed in dry land and also has a low electrification ratio as an alternative energy.