Peat mapping on a scale of 1:50,000 in oil palm plantation land, at the peat hydrological unit in Musi Banyuasin Regency and the implications of its use

. Oil palm cultivation on peatlands, one of which must be guided by the Ministry of Environment and Forestry Regulation Number P.10/2019 concerning Determination and Management of Peat Dome Based on Peat Hydrological Units (KHG). This paper aims to study the results of peat mapping on a scale of 1:50,000 in several KHGs associated with regulations for managing the Peat Ecosystem. The results on a scale of 1: 50,000 in Musi Banyuasin Regency, South Sumatra show that in the Sembilang -Lalan River KHG of an area of 6,973 ha, only 414 ha or 5.94% is peat soil. In the Lalan -Bentayan River KHG covering an area of 4,976 ha, no peat soil was found. In the Bentayan -Penimpahan River KHG covering an area of 8,025 ha, only 245 ha (3.05%) is peat soil. The mapping results show that even though an area is declared a KHG, it does not necessarily contain peat soil. Based on this, it is necessary to revise the location of the KHG-KHG, especially in South Sumatra based on the results of peat mapping. Thus, the rules regarding the management of oil palm plantations in these locations must be adjusted to the results of the 1:50,000 scale survey.


Introduction
About forty-five percent of tropical peatland is in Indonesia, the rest is in several Southeast Asian countries (Malaysia, Brunei, Vietnam, the Philippines, Papua New Guinea, and Thailand), Africa, the Caribbean, Central America, and South America [1].Peat soil is widely spread in Musi Banyuasin district, South Sumatra Province.Based on data from the Indonesian Centre for Agricultural Land Resource Research Development [2,3], peatlands in this district cover an area of 239,454 ha with depths varying from shallow (50 cm) to extreme deep (> 700 cm).There are many oil palm plantations in Musi Banyuasin Regency in the Peat Hydrological Unit (KHG).All oil palm plantations in Musi Banyuasin Regency in 2020 covering an area of 43,071 ha, consisting of plantations that have not yet produced, are in production and are not producing because they are old [4].
In an effort to protect and manage the peat ecosystem, including the area and distribution of peat, it is regulated in Government Regulation no.71 of 2014 in conjunction with Government Regulation No. 57 of 2016, while the Peat Hydrological Unit (KHG) is regulated by the Minister of Environment and Forestry (LHK) in the Minister of Environment and Forestry Regulation No. 14 of 2017.Through the Decree of the Minister of LHK No. 129 of 2017, the National Peat Hydrological Area (KHG) Map with a scale of 1:250,000 was established.The boundaries of the peat ecosystem map can be verified using swamp distribution maps, quaternary geological maps, DEM maps, and field surveys.The boundaries of the Peat Hydrological Unit can be delineated manually (on screen) from the overlay between the peat ecosystem map and the river network map.If there are difficulties in delineating the boundaries of the Peat Hydrological Unit, especially in the upstream part, it can be assisted by using DEM Maps or high resolution satellite imagery [5].Although the extent and boundaries of the KHG scale of 1: 250,000 are regulated by the government, they are still considered inaccurate.The area of peat distribution listed in the attachment to the Government Regulation has a significant difference with the actual conditions in the field [6].
The Peat Hydrological Unit in South Sumatra has an area of 445,676 Ha (73.42%) with a Peat Ecosystem Protection Function covering an area of 268,939 Ha (44.29%) and a Peat Ecosystem Cultivation Function 176,737 Ha (29.13%).Meanwhile, the distribution of peat based on the results of the survey and mapping of the Tidal Rice Field Clearing Project (P4S) only has an area of 137,670 Ha (22.6%).The results of the comparison between the two maps show that there is a difference in area, the Peat Hydrological Unit map is 3 times wider than the peat distribution map from the P4S mapping.This shows that there are weaknesses and inaccuracies in drawing Peat Hydrological Unit boundaries in the study area [6].
To find out the exact area of a Peat Hydrological Area (KHG) in Musi Banyuasin Regency, peatland mapping at a scale of 1: 50,000 has been carried out in 3 KHG locations, namely KHG S. Sembilang -S.Lalan S. Lalan-S.Bentayan, KHG S. Bentayan-S.Penimpahan.The purpose of this paper is to present the results of peat mapping at a scale of 1: 50,000 in three KHGs in Musi Banyuasin Regency in relation to regulations for managing the Peat Ecosystem.

Methods
The peatland mapping method is based on Articles 13 and 14 of the Regulation of the Minister of Environment and Forestry Number P.14 of 2017 [11].The implementation of the Peat Ecosystem inventory at this location is carried out to obtain increased accuracy and intensity or the level of depth of data/information on the Peat Ecosystem map by using: a. Map of Rupabumi Indonesia (RBI) scale 1:50,000 [9]; b.Map interpretation of high resolution remote sensing imagery; and c.Based on the topographical map of Indonesia and the interpretation map of remote sensing imagery and the results of the field survey, delineation of the boundaries of the Peat Hydrological Unit was carried out.
The field survey was conducted to obtain data on the characteristics of physics, chemistry, biology, hydrotopography, and types of sediment under peat by observing the systematic grid method consisting of longitudinal and transverse transects: a. the distance between transects is 2 (two) kilometers long, with an observation distance between points of 500 (five hundred) meters; b. the distance between transects is 3 (three) kilometers, with an observation distance between points of 1,000 (one thousand) meters; and c. the starting point of the two transects was determined from one of the peat dome.d.Soil observations in the field follow the standard guidelines [12] From the results of the field survey, the following data and information were obtained: a. the location, existence, and area of the Peat Hydrological Unit; b. characteristics of physics, chemistry, biology, hydrotopography, and types of sediment under peat include: Based on the data and information at the observation points, an interpolation analysis was carried out between the observation points to produce spatial information including: a. Peat Ecosystem boundaries; b. limit per Peat Ecosystem characteristics; and/or c. the combined boundary of the characteristics of the Peat Ecosystem.
The Peat Ecosystem Boundary is presented in the form of a Peat Hydrological Unit map at 1:50,000 scale mapping location.

Soil maps of KHG S. Sembilang-S. Lalan
The mapped land is part of KHG S. Sembilang-S.Lalan.Based on the map of the determination of the National Peat Hydrological Unit, this KHG has a total area of 84,670 ha [13], and what is mapped in this activity is 6,973 ha with 87 observation points.This land is a national private oil palm plantation, and the entire land has been planted with oil palms of various ages which are already producing oil palm plantations (Figure 2).The results of soil mapping in KHG are based on the national soil classification [14] consisting of Organosol, Regosol, Aluvial, Gleisol and Kambisol soil or based on the Soil Taxonomy classification system [15] consisting of: Histosols, Entisols and Inceptisols.Organosol soil or peat soil covers an area of 414 ha or 5.94%.The remaining 6,559 ha or 94.06% consists of mineral soils (Regosol, Aluvial, Gleisol and Kambisol).Organosols found have 3 depth classes, namely shallow (50 -< 100 cm), medium (100-<200 cm) and deep (200 -< 300 cm).The decomposition rates are all classified as hemic (Table 1).The main soil morphology at this location (Gleisol) is presented in Figure 3 and the distribution of the soil is presented in the soil map (Figure 4).

Soil Map of KHG S. Bentayan -S. Penimpahan
Based on the National Peat Hydrological Unit Map, KHG S. Bentayan -S.Penimpahan, total area is 42,999 ha [13].The land mapped at the KHG is 8,025 ha with 99 observation points.The mapped land is oil palm plantation land by a national private company, most of the land has been planted with oil palm with the oldest age being 7 years (Figure 5).The results of soil mapping in KHG based on the national soil classification [14] consisting of Organosol, Aluvial, and Gleisol or based on the Soil Taxonomy classification system [15] consisting of: Histosols, Entisols and Inceptisols.Organosol soil or peat soil covers an area of 245 ha or 3.05%.The remaining area of 7,780 ha or 96.95% consists of mineral soils (Aluvial and Gleisol).Organosols found have one depth class, namely shallow (50 -< 100 cm).The decomposition rate is classified as hemic and fibric on the surface (Table 2).The map of the land that was mapped from this activity is presented in Figure 6.

Soil Map of KHG S. Lalan -S. Bentayan
Based on the National Peat Hydrological Unit Map, KHG S. Lalan -S.Bentayan the total area is 21,118 ha [13], and the land mapped in this KHG is 4,976 ha with 58 observation points.Almost all of the land is planted with productive oil palm (Figure 7).The results of soil mapping in KHG are based on the national soil classification [14] consisting of Aluvial, Gleisol, Kambisol and Podsolik soils or based on the Soil Taxonomy classification system [15] consisting of: Entisols, Inceptisols and Ultisols.No peat soil or Organosol found, all including mineral soil.In this KHG the area is not only in the form of swamp land, but in the form of dry land (Table 3).The soil map resulting from this activity is presented in Figure 8.Based on the definition in the Decree of the Minister of LHK No. 129 of 2017, KHG is a peat ecosystem located between two rivers, between a river and the sea, and/or in a swamp.Based on this, it seems that there is only a very small amount of peat soil and the location is on the northern edge, so this area by definition does not meet the requirements as a peat ecosystem.Therefore, this area, although as a whole is a swamp with little peat soil, so that this area's status as a peat ecosystem area needs to be reviewed.Especially in KHG S. Lalan -S.Bentayan, all the land is classified as not peat or mineral soil.Of course, it will be related to the way of management which as a whole is not a peat ecosystem.
One of the soils found in the three locations studied is a potential acid sulfate soil (Alluvial Sulfik and Gleisol Sulfik).Potential acid sulfate soils are soils that have a layer of sulfidic material in reduced conditions at a depth of 0-50 cm, pH > 4.0, and are included in the Alluvial soil classification (Entisols), while actual acid sulfate soils are soils that have a sulfuric horizon or pyrite that has been oxidized at a depth of 0-50 cm, pH <3.5, and included in the soil classification Gleisols (Inceptisols) [16].In the development of agriculture in acid sulphate swamps, location-specific technology components are required, including water management and land management.One way of managing water in swamps is the polder system [17].The advantage with this polder system is that it maintains the water level according to the needs of the plant, so that the pyrite is not oxidized and the acidity of the soil does not harm the plants.

Conclusion
Soil mapping in three KHG locations in Musi Banyuasin Regency has been carried out at the semi-detail level (scale 1: 50,000).The land is oil palm plantations.Most of the locations are swamp land, but only a few peat soils are found, namely 3.05 percent, 5.94 percent and 0 percent.The results of the peat mapping in these three locations show that the peat area is very small.The results of this mapping can be used to correct the National Peat Hydrological Unit Map (Decree of the Minister of Environment and Forestry of the Republic of Indonesia Number SK.129/MENLHK/SETJEN/PKL.0/2/2017).Based on the results of this mapping (scale 1 : 50,000), in these three KHGs the management of existing oil palm plantations cannot be guided by the way of managing peat ecosystems, but still must be guided by the way of managing swamp land in general.
Authors wishing to acknowledge assistance or encouragement from Head of Center for Agricultural Land Resources Research and Development; Management of PT Banyu Kahuripan Indonesia, and PT Surya Cipta Kahuripan.R. Bambang Heryanto and Sukarman are the main contributor to this paper.

Fig. 1 .
Fig. 1.Map of the location of KHG with mapped soils.

Fig. 5 .
Fig. 5. Oil palm plantations, drainage canals and the results of measuring the pH of canal water.

Table 1 .
Soil types and soil characteristics in the KHG S. Sembilang-S Lalan area

Table 2 .
Soil types and soil characteristics in the KHG S. Bentayan-S.Penimpahan.

Table 3 .
Soil types and soil characteristics in the KHG S. Lalan -S.Bentayan.