Physical properties and ash content of post-fire Sumatra coastal peat soil in Sei Kepayang District, Asahan Regency, North Sumatra

Fires in peatland have numerous detrimental effects as regards degradation of the environment especially changes of soil properties. The purpose of this study is to ascertain how drying and rewetting peatlands affects the physical and chemical characteristics of post-fire peat soil with two depths. This research was carried out in Dusun XIII, Perbangunan Village, Sei Kepayang, Asahan Regency. The factor was drying and re-wetting of the past fire peatland, namely: unburnt peat in wet conditions (P-nw), post-burnt peat in dry conditions (P-bd), and post-burnt peat in wet conditions (P-bw) within 2 tiers namely: 0-30 cm and 30-60 cm respectively. This research data analysis used a descriptive method presented through tables and graphs. The findings indicate that post-fire peat experience changes in moisture content, degree of decomposition, bulk density, soil color, and ash content. In conclusion, there are changes in peat properties in post-fire peat due to drying and rewetting.


Introduction
Approximately 420 million hectares make up the world's peatlands, of which 30 to 45 million hectares are found in tropical regions [1].Papua, Sulawesi, and other tiny islands make up 35%, 32%, and 30%, respectively, of Indonesia's 14.9 million hectares of tropical peatlands; only around 30% of these areas are suitable for agriculture [2].
North Sumatra has the fourth largest peatland area in Indonesia at 325,296 ha, located on the east coast in Labuhan Batu and Asahan districts, 192,000 ha (59%) and 24,000 ha (7.4%) respectively.About 70% is medium peat, 15.3% is deep peat and 14.5% is shallow peat [3].
Deforestation, peatland fires, excessive drainage, and overuse of forest land in Indonesia are the main causes of Indonesia's peatland degradation [4].Severe peatland fires that have occurred in Indonesia were in 1997, 1998, 2002, and 2006, in each case about 1.5-2.2 million ha of peatland burned in Sumatra and Kalimantan.Peatland fires can consist of ground fires, surface fires and crown fires [5].Peatland fires change peat soil's physical, biological, and chemical characteristics, affecting the ecosystem around them [6].According to [7] peat soil taken from Sei Kepayang Village, has a moisture content of 645%, organic matter content of 75%, ash content of 25%, and fiber content of 23%.
In the Asahan District's Sei Kepayang Sub-district, no research has ever been done on post-fire peat soils.These factors make it important to evaluate the post-fire peat soil properties in Sei Kepayang Subdistrict, Asahan District.

Materials and Methods
The research was conducted on lowland peatland in Perbangunan Village, Sei Kepayang District, Asahan Regency [3.447491, 98.The study employed an ex-post facto survey approach, which investigates the causes and effects of unmanipulated items or in accordance with field circumstances.Sampling using purposive sampling technique or taking based on certain criteria in the field.There are three conditions for soil sampling namely: P-nw: Unburned in wet condition; P-bd: Post-burn in dry condition; P-bw: Post-burn and rewetted at four replications for each sample site, at depths of 0-30 and 30-60 cm, respectively.
The parameters observed were the physical properties of peat including: Degree of Decomposition (Von Post Method), Bulk Density (Ring Sample), Moisture Content (Gravimetric method), Peat Color (Munsell Soil Color Chart), and additionally Ash Content (Combustion Method).
Sampling of disturbed soil was carried out using a hoe at several points based on two sample depths, namely 0-30 cm and 30-60 cm, which were then composited per depth.The soil was taken and put into a plastic bag.Then, the samples were labeled.For bulk density determination, undisturbed soil samples were taken using a ring sample.

Results and Discussion
Table 1 shows that the drying and rewetting of peatlands did not show a significant difference in the maturity level of either post-fire peat or normal peat under wet conditions in Sei Kepayang Sub-district, Asahan District.However, at each depth the soil samples showed different degrees.There are Sapric at 30-60 cm depth and Hemic at 0-30 cm depth.The effect of peat drying and rewetting and soil sample depth on peat bulk density is presented in fig. 3. The highest BD value was found in unburned peat in wet conditions (P-nw).Meanwhile, post-fire peat in wet condition (P-bw) and post-fire peat in dry condition (P-bd) were reducing BD but not significantly different.
The effect of drying and rewetting post-fire peatlands and the depth of soil samples on peat moisture content is presented in fig. 4. Post-burnt peat in wet conditions (P-bw) has the highest moisture content value.Meanwhile, the lowest value is found in unburned peat in wet conditions (P-nw).The 30 -60 cm depth has the highest water content, while the 0-30 cm depth has the lowest water content.Table 2 shows that the drying and rewetting of peatlands show light differences in dark color (red to reddish brown and reddish black) between post-fire peat and unburned peat under wet conditions in Sei Kepayang Sub-district, Asahan District.However, at each depth the soil samples showed a difference in color.The dominant color variations are very dusky red at 0-30 cm depth and reddish black at 30-60 cm depth.The effect of peatland drying and rewetting and soil sample depth on peat ash content is presented in fig. 5. Unburnt peat in wet conditions (P-nw) has the highest ash content, while the lowest ash content is found in post-burnt peat in dry conditions (P-bd).The more decomposed the peat, the higher of BD would be [10].Continuous drying of peat can reduce the porosity value of peat, but in peat with a low degree of decomposition, the decrease in porosity value tends to be small [11].However, post-fire peat soil in dry conditions in this study had a lower BD value than unburned peat soil.This could be due to the fact that the mass of the post-fire peat material decreased as a result of some biomass turning into ash, while the volume of the peat soil did not change significantly, so the BD of the soil actually increased.
The fire decreased the peat soil's ability to store water, particularly in the top layer (0-30 cm), since some of it had already irrevocably dried up.In the deeper layers (30-60 cm), this process had not yet taken place.
Fire causes an increase in the decomposition process of peat material, so that the oxidation process can also increase the decomposition of the peat more quickly.Peat soils with a higher degree of decomposition cause the color of the peat to become darker as shown by the decrease in the chroma.
Ash content indicates the amount of inorganic peat material contained in the biomass as the parent material of the peat soil and is an indicator of the fertility of the peat soil.Ash content is not determined by the maturity of the peat, so it does not change the ash content of the peat soil significantly.

Conclusion
Peat fire causes changes to degree of decomposition, bulk density, moisture content, peat color, and ash content in Perbangunan Village, Sei Kepayang Sub-district, Asahan Regency, North Sumatra.Drying the post-fire peat decreased the bulk density at depths of 0-30 and 30-60 cm while rewetting post-fire peat increased the bulk density at depths of 0-30 and 30-60 cm.
703559].From March to June 2023, soil samples were analyzed at the University of Sumatera Utara's Research and Technology Laboratory and the Soil Physics and Classification Laboratory of the Faculty of Agriculture.The materials used were peat samples that had experienced fires in dry locations and had experienced rewetting at depths of 0-30 and 30-60 cm at the research location.The tools used are the Global Positioning System, Munsell Soil Color Chart, sample ring, sample box, oven, and other instruments in the laboratory.

4 Figure 3 .
Figure 3.The bulk density of burnt peat soil in dry and rewetted condition in Sei Kepayang, Asahan Regency

Figure 4 .
Figure 4.The moisture content of burnt peat soil in dry and rewetted conditions in Sei Kepayang, Asahan Regency

Figure 5 .
Figure 5.The ash content of burnt peat soil in dry and rewetted conditions in Sei Kepayang, Asahan Regency

Table 1 .
The Degree of Burnt Peat Decomposition in Dry and Rewet Condition Based on Von Post Humification Scale.

Table 2 .
The Color of Burnt Peat Soil in Dry and Rewet Conditions a YR is Yellow-Red hue in Munsell Soil Color Chart