Pengaruh Kedalaman Muka Air Tanah dan Dosis Terak Baja terhadap Hidrofobisitas Tanah Gambut, Emisi Karbon, dan Produksi Kelapa Sawit
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Date
2015Author
Winarna
Murtilaksono, Kukuh
Sabiham, Supiandi
Sutandi, Atang
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Development of oil palm plantation requires drainage to support growth and production of the oil palm. The excessive drainage would cause the peat dryness of as well as hydrophobicity and thus decreasing its capacity to retent water, soil infiltration, surface erossion. It can limit oil palm growth. The application of water management and soil amandment must be performed to avoid the decrease of peat soil quality and to improve the productivity of oil palm. This series research was designed to: 1) evaluate the peat soil hydrophobicity under oil palm plantation area, 2) study the effect of the ground water level depth and stell slag dose on the peat soil hydrophobicity and other soil physical changes, 3) study the effect of the ground water level depth and the steel slag dose on CO2 emission from peat soil, and 4) study the effect of ground water level depth and steel slag dose on the growth and production of oil palm. The first study has utilized sapric and hemic peat soil samples taken from the 6-year Panai Jaya Oil Palm Plantation (PAJ) and the 20-year Meranti Paham Oil Palm Plantation (MEP). Peat soil samples were heated at a temperature of 50°C with a time interval and the effects on hydrophobicity were recorded. Hydrophobicity of the peat soil was evaluated by Water Drop Penetration Time (WDPT) method. After the hydrophobicity of all peat soil samples had been observed, a number of soil properties, including soil water content (SWC), total acidity, carboxylic content (COOH) and phenolic-OH were then analyzed. Critical water content (CWC) of the peat soil. The point at which hydrophobicity occurred, was determined using exponential relationship between soil water content and the probability of the occurrence of soil hydrophobicity, the point at which the probability of the occurrence of hydrophobicity was between 60% and 80%. Fourier Transform Infra Red (FTIR) spectrometer was used to evaluate peat soil hydrophobicity by knowing the functional groups in peat soil. The second experiment was carried out in laboratory by application of various steel slag level (0; 7.17; 14.81; dan 22.44 g pot-1) on two peat type (sapric dan hemic) with two soil moisture conditions including wet and dry (hydrophobic). Peat soil samples that has been added with steel slag incubation for 60 days and observation of soil properties, FTIR analysis, and wettability by WDPT method. The field experiment was carried out in 6 years-oil palm block of PAJ. Research plots was designed using a split plot design with three replications. Plots treated with three treatments of ground water level (MAT-1, MAT-2, and MAT-3) as main plots and four level of steel slag application (0; 3.15; 6.51; 9.86 kg pohon-1) as a subplot. MAT-1 is ground water level (GWL) at depths of 30-50 cm, MAT-2 is GWL at depths of 60-75 cm, and WLM-3 is GWL at depths 70-90 cm below the soil surface. The research observation consists actual soil water content, actual v hydrophobicity, oil palm growth and production, subsidence, and accumulation of heavy metals in fruit. The results shown that hydrophobicity of peat soil in this study was negatively related to soil water content (SWC), total acidity, content of carboxylic and phenolic-OH. The decrease in SWC, total acidity, carboxylic content, and phenolic-OH content will increase the hydrophobicity. SWC leads to an increase in the ratio of hydrophobic component on the hydrophilic component, and peat soil experiences hydrophobicity. Based on the exponential model between hydrophobicity and soil water content, critical water content (CWC) of peat soil hydrophobicity is obtained. CWC of PAJ hemic> PAJ sapric> hemic MEP> MEP sapric, is 201-223%, 293-307%, 118 -126%, and 184 – 213%, respectively. Hemic will experience hydrophobicity faster than sapric. Likewise PAJ peat will require higher water content than MEP peat to keep the peat soils still hydrophilic. The GWL in the peat soil of this study indicated that the treatment of MAT-1 and MAT-2 (30-70 cm) was able to keep the actual SWC in the top layer, while the decrease of GWL depth up to >70 cm below the soil surface (MAT-3) significantly influenced the decrease of SWC to the top layer (0-10 cm). The GWL that is too deep (>70 cm) could potentially cause the hydrophobicity in the upper layers of soil (0-10 cm), especially in dry season. Combination of steel slag application has not shown any significant effect on the increase of the water content in the soil, but it affects the improvement of soil properties such as soil pH, ash content, and water retention. The measurement of CO2 emission was 28.33, 37.92, and 50.23 ton ha-1 year-1 respectively to the conditions on of MAT-1, MAT-2, and MAT-3. The decrease of GWL up to >70 cm could significant increase the CO2 emissions. The application of steel slag had not significantly reduced the CO2 emissions. This research obtained a relationship between CO2 flux and peat soil water content ranges from dry to wet, which is a peat soil ranged hydrophilic to hydrophobic. In the hydrophilic, the CO2 emissions of peat soil decreased with the increase of soil moisture. The highest CO2 emission could be achieved on the conditions of soil moisture content ranging from CWC to field capacity. The hydrophobic condition caused a decline in active functional groups (carboxylic, hydroxyl), a decrease in biochemical processes; moreover, drying peat material occured so that the decomposition of peat and producing CO2 emissions would decline. The GWL treatment significantly affected fresh fruit bunches (FFB) production (6 years old). The FFB production of GWL of MAT-1 > MAT-2 > MAT-3. The decrease of GWL depth that was deeper than 70 cm significantly reduced the production of FFB up to 8-11% on the treatment of GWL in the range of 30-70 cm. The application of various level of steel slag had not significantly influenced the FFB production in the first year of the study. The application of various level of steel slag could improve the physical and chemical properties of peat soil of Panai Jaya. The implication of this research was that the application of good water management on the peat soil in the oil palm plantations by regulating the ground water level in the range of 30-70 cm that was adequate of keeping the soil moist until the top layer of peat soil could prevent hydrophobicity, reduce CO2 emissions, and improve the growth and production of oil palm.
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