Kuantifikasi modal dan distribusi karbon dalam sistem tebang bakar pada lahan berlereng di Rantau Pandan, Jambi

Land clearing by slash and burn is practised in large parts of Sumatra to convert forest land into agricultural use or to renew agroforest at the end of
production cycle. The heat will change of physical, chemical and or biological aspect of soil depending on the temperature of the burn. An Indirect impact of
slash and burn is the erosion process that is caused by the disappearance of vegetation. Eroded material will sediment inside or Outside slash and burn field
Nutrients that are carried away by erosion oil sloping land or In the lower part or the field contribute to the indirect impact of slash and hum system on soil fertility.

This study investigates the influence or slash-and-burn practices on: C-stock of above and belowground biomass, the amount of nutrient added due to the burning system, the redistribution of nutrients caused by erosion and sedimentation processes, and the impact or the soil fertility pattern on growth of upland rice.

The study was conducted by on farm with four treatments plot which were Forest I, Forest I slashed and burned, Forest II, Forest II only slashed without
burn. The influence of slash and burn on the change of carbon stock was quantified by measuring trees, wood/branches, stem, under-storey, woody litter,
leaves, litter, roots (0-5 cm) and soil organic matter fraction. Observations of physical and chemical soil properties, the changes on nutrient pattern by erosion and sedimentation, involved: pH, Corg Ntot P, K, Ca, Na, Mg, bulk density and texture. A laboratory experiment to study the influence of temperature and heat duration on C and N status of forest soil was carried out with temperatures of 50 derajat C 75 derajat C 100 derajad C 125 derajat C and 150 derajad C with a duration of 5 and 10 minutes. Sediment weight and the nutrient content in overland flow were investigated which sampled across the slope. The influence of erosion and sedimentation due
to slash-and-burn practice on the growth of upland rice planted by farmer was recorded to study it's relation with sedimentation pattern.

The study result indicate that slash and burn practises decreased total carbon stock of forest I by 52 Mg ha-1 or 66 %, slashing alone (forest II) decreased
carbon stock by 24 Mg ha-1 or 22%.

The soil pH, and the content off C and N were not significantly affected by the slash and burn event (p<0.05), but the topsoil content of available P, and exchangeable K, Ca, Na, Mg changed significantly (p<0.05). At a depth 5- 10 cm no significant change in soil chemical properties (1)<0.05) were found The field that was slashed only showed no significant differences (p<0.05) in soil chemical properties, except for P. Neither system showed a significant effect (p<0.05) on soil bulk density.

Macro-organic matter fractions were 63 % reduced in the 0 5 cm layer after slashing and burning of forest 1, and 18 5'0' reduced in 5 - 10 cm layer. The reduction in the field that was only slashed was 36 % in 0-5 cm and 40 in 5-10 cm layer.

The impact of ash input in a field experiment with and without bottom trays treatment, showed that carbon content was significantly different (p<O.05) in 0-5 cm, but for Nitrogen content was not significantly different (p<0.05). In forest I the average of sediment collection in one month period yielded the equivalent of
74 kg ha' in lower slope, 23 kg ha-1 in middle slope and 16 kg ha-1 in the upper slope. The highest amount of sediment in forest I that was slashed and burned was found in middle slope that is 9656 kg ha-1 or higher 10-30 times that) values found in lower and upper slope. The highest amount of sediment in forest It was found in middle slope that is 69 kg ha-1, 16 kg ha-1 in lower slope and 11 kg ha-1 in upper slope. The highest amount of sediment in forest I that only slashed was found in lower slope (47 kg ha-1 39 kg ha-1 in middle slope and the lowest was 22 kg ha-1 in upper slope. Most of chemical observed showed the sediment was enriched relative to the top soil (0-5 cm). The result of dry weight sediment captured non confined on PVC trap showed that the highest sediment was In the middle slope,

The best growth of the upland rice crop (the highest value of plant height and dry weight) were found in the in middle slope.

The overall conclusion is that erosion and sedimentation following slash and burn resulted in a Substantial redistribution of soil fertility from upper and higher position to middle and lower position oil the slope, but there was no evidence for sediment transfer to the river.