Nitrous oxide (N 2 O) fluxes from tropical peatland soils were measured at a grassland, three croplands, a natural forest, a burned forest and a regenerated forest in Central Kalimantan, Indonesia. Only croplands received fertilization (665-1278 kg N ha −1 year −1 ). Mean annual N 2 O emissions from croplands were 21-131 kg N ha −1 year −1 in 2002-2003 and 52-259 kg N ha −1 year −1 in 2003-2004, and were significantly higher than the emissions from other comparable sites. Cropland N 2 O emissions were among the highest values reported from cultivated tropical, temperate and boreal organic soils. Mean annual N 2 O emissions were 7.1 (2002-2003) and 23 (2003-2004) kg N ha −1 year −1 from grassland, and were significantly higher than in natural, regenerated and burned forests (0.62, 0.40 and 0.97 kg N ha −1 year −1 in 2002-2003 and 4.4, 4.0 and 1.5 kg N ha −1 year −1 in 2003-2004, respectively). Annual N 2 O emissions did not differ significantly between forests in 2002-2003, but were significantly lower in burned forest in 2003-2004. Annual N 2 O emission was significantly correlated between years. Regression analysis revealed that annual N 2 O emissions in 2003 -2004 were 1.9-fold the corresponding 2002-2003 value (annual precipitation of 2339 and 1994 mm, respectively). N 2 O fluxes were higher during the rainy season than during the dry season at all sites except the regenerated forest. N 2 O fluxes in cropland and grassland were significantly lower when the water-filled pore space (WFPS) was less than 60-70%, and increased with an increase in soil NO 3 -N concentration when WFPS exceeded this threshold. Thus, changes in soil moisture were important in controlling seasonal changes in N 2 O emission. Our results suggest that changing land use from forestry to agriculture will increase N 2 O production. The effect of forest fires on N 2 O emission from these soils was not clear. N 2 O emissions from Indonesian peatlands 663

Our previous research showed large amounts of nitrous oxide (N 2 O) emission (4200 kg N ha À1 year À1 ) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N 2 O fluxes and the source of nitrogen (N) substrate for N 2 O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N 2 O and carbon dioxide (CO 2 ) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N 2 O emission from two treatments, contribution of the N source for N 2 O was calculated. Nitrous oxide concentrations at five depths (5-80 cm) were also measured for calculating net N 2 O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607 kg N ha À1 year À1. There were no significant differences in between N 2 O fluxes in the two treatments at each site. Annual N 2 O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858 kg N ha À1 year À1 , respectively. However, there was also no significant difference between annual N 2 O emissions in the two treatments at each site. This suggests most of the emitted N 2 O was derived from the decomposition of peat. There were significant positive correlations between N 2 O and CO 2 fluxes in bare treatment in two croplands where N 2 O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N 2 O was mainly produced in the surface soil down to 15 cm in the soil. The logarithmic value of the ratio of N 2 O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N 2 O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N 2 O was mainly produced by denitrification at high range of WFPS in surface soil.

To clarify the microbiological factors that explain high N 2 O emission in an arable peat soil in Central Kalimantan, Indonesia, a substrate-induced respiration-inhibition experiment was conducted for N 2 O production. The N 2 O emission rate decreased by 31% with the addition of streptomycin, whereas it decreased by 81% with the addition of cycloheximide, compared with a non-antibiotic-added control. This result revealed a greater contribution of the fungal community than bacterial community to the production of N 2 O in the soil. The population density of fungi in the soil, determined using the dilution plate method, was 5.5 log c.f.u. g -1 soil and 4.9 log c.f.u. g -1 soil in the non-selective medium (rose bengal) and the selective medium for Fusarium, respectively. The N 2 O-producing potential was randomly examined in each of these isolates by inoculation onto Czapek agar medium (pH 4.3) and incubation at 28°C for 14 days. Significant N 2 O-producing potential was found in six out of 19 strains and in five out of seven strains isolated from the non-selective and selective media, respectively. Twenty-three out of 26 strains produced more than 20% CO 2 during the 14-day incubation period, suggesting the presence of facultative fungi in the soil. These strains were identified to be Fusarium oxysporum and Neocosmospora vasinfecta based on the sequence of 18S rDNA, irrespective of the N 2 O-producing potential and the growth potential in conditions of low O 2 concentration.

ABSTRACT

Peatland is an important ecosystem in Indonesia. But in almost every dry season, drained peatlands have been subject to detrimental wildfires. As a response, the government has explicitly prohibited the burning of land since 2016. To clear the land of crop residues and conduct zero burning practices, one alternative method is to utilize the waste biomass to support the cultivation of earthworms (vermiculture). This study examined the quality of liquid fertilizers and compost produced from vermiculture using a completely randomized factorial design, consisting of two treatment factors. The first factor was worm type, with two species used in this research named Lumbricus rubellus and Eudrilus eugeniae. The second factor was the type of feed provided to the worms, comprising no feed (control), vegetable waste, and crop residue waste resulting from zero burning land preparation. The type of feed significantly affected the pH value of the liquid fertilizer produced by the vermiculture but did not significantly affect the nutrient contents (N, P, and K). The combination of the types of earthworms and types of feed significantly affected the pH value of the vermicompost. The combination of worm types and feed types had a significant effect on exchangeable Ca, but not on exchangeable Mg, Na, and K. In combination, green vegetable waste and Lumbricus rubellus produced the greatest effect on soil CEC. However, for Base Saturation, the control (no food) and Eudrilus eugeniae showed the highest value. Types of worms and types of feed had a significant effect on the exchangeable Mg, while the other three parameters made no significant differences. Zero burning waste and Eudrilus eugeniae provide a better exchangeable Ca and Mg. In contrast, no-feeding and Eudrilus eugeniae have a better effect on exchangeable Na and K. Types of worms and types of feed did not significantly affect the weight of worm colonies, but the addition of feed increased the weight of worms with the highest weight resulting from the use of zero burning waste feed. The results showed that crop residue wastes were potentially good as a feed for earthworms.