Assessment of Soil Enzyme activities in multiple land use in Central Kalimantan, Indonesia

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Peat swamp forest is one of the most important ecosystems in Southeast Asia, particularly in Indonesia. Tropical peat swamp forests contain a high number of valuable timber species and provide numerous ecosystem services all over Southeast Asia, including in Central Kalimantan, Indonesia. However, in recent years a severe decline in the peat swamp forest ecosystems has been reported due to anthropogenic influences. During the last 20 years the coastal peat swamp forests in Kalimantan have undergone a rapid deforestation and conversions predominantly into oil palm plantation and agriculture. Agroforestry has been proposed as an alternative land management strategy to overcome the conflict between economic needs and peat swamp forest decline. The establishment of agroforestry is also believed to improve soil quality. Soil enzymes respond to land use management. However, literature is limited on studies evaluating peat swamp forest ecosystems especially comparing agroforestry practices in peat areas with other land use practices on enzyme activities. The objective of this study was to compare soil quality, particularly focused on soil enzyme activities among four land use systems common in the peat swamp forest ecosystems: natural peat swamp forest, palm oil, conventional monoculture agriculture, and homegarden agroforestry system in Central Kalimantan, Indonesia. The study was conducted at three different villages in Seruyan Regency i.e. Kuala Pembuang, Muara Dua, and Telaga Pulang. Two soil depths (0-15 cm and 15-30 cm) were evaluated for three enzyme activities (phosphomonoesterase, urease, and cellulase), C/N ratio, and soil microbial respiration. The soil enzyme activities were measured colorimetrically and quantified using spectrophotometer. Carbon percentage and N percentage were measured using a dry combustion method. Peat soil respiration was measured by alkali absorption method. Vegetation analysis was also conducted to compare with the measured soil data. The results showed that enzyme activities, percentages of C and N, and also soil respiration were significantly different (α 0.05) among land use practices within the soil depths (0-15 cm and 15-30 cm). The highest urease enzyme activity was found in natural forest for the 0-15 cm depth (569.69 μg N-NH4/g/hr) and followed by the activity at homegarden system (515.99 μg N-NH4/g/hr) for the same soil depth. The lowest urease activity was found at palm oil site for 0-15 cm and 15-30 cm soil depths (137.69 μg N-NH4/g/hr and 155.2 μg NNH4/g/hr). The highest carbon level of 35.99% was found at natural forests in the 15-30 cm soil depth followed by 21.68% at homegarden system on 0-15 cm soil depth. The lowest carbon level was found at palm oil on 0-15 cm soil depth (1.32%). The highest nitrogen level was found at natural forest (1.23%) for 15-30 cm soil depth and followed by agriculture site at 0-15 cm (1.15%). The lowest soil nitrogen level was found at palm oil plantation for both soil depths (0.43% and 0.21%). The highest C:N ratio was found at agriculture site for 0-15 cm soil depth in Telaga Pulang (36.3) and followed by C:N ratio at agriculture site in Muara Dua for 0-15 cm soil depth (34.66). The lowest C:N ratio was found at palm oil site for 15-30 cm soil depth (0.00). For soil respiration, the highest rate (0.72mgCO2/h) was recorded in natural forest in the 0-15 cm soil depth followed by palm oil plantation for 0-15 cm soil depth (0.69 mgCO2 h-1). The outcomes of this study will help formulate land management recommendations for landowners, palm oil management, government agencies, and communities around the study areas to maintain soil quality for long-term sustainability of the peat forest ecosystems. Homegarden systems can be recommended as the most appropriate alternative land management in Seruyan District, Central Kalimantan based on soil enzyme activities, soil nitrogen, soil carbon, and soil respiration. Long-term research on microbial community identification and characterization for more comprehensive studies with soil enzyme activities of tropical peat swamp forests may help develop better land management plans for improved ecosystem services including soil health and economic benefits.

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