Soil CO2 flux was measured monthly over a year from tropical peatland of Sarawak, Malaysia using a closed‐chamber technique. The soil CO2 flux ranged from 100 to 533 mg C m−2 h−1 for the forest ecosystem, 63 to 245 mg C m−2 h−1 for the sago and 46 to 335 mg C m−2 h−1 for the oil palm. Based on principal component analysis (PCA), the environmental variables over all sites could be classified into three components, namely, climate, soil moisture and soil bulk density, which accounted for 86% of the seasonal variability. A regression tree approach showed that CO2 flux in each ecosystem was related to different underlying environmental factors. They were relative humidity for forest, soil temperature at 5 cm for sago and water‐filled pore space for oil palm. On an annual basis, the soil CO2 flux was highest in the forest ecosystem with an estimated production of 2.1 kg C m−2 yr−1 followed by oil palm at 1.5 kg C m−2 yr−1 and sago at 1.1 kg C m−2 yr−1. The different dominant controlling factors in CO2 flux among the studied ecosystems suggested that land use affected the exchange of CO2 between tropical peatland and the atmosphere.

A B S T R A C T Soil CO 2 flux was measured monthly over a year from tropical peatland of Sarawak, Malaysia using a closed-chamber technique. The soil CO 2 flux ranged from 100 to 533 mg C m −2 h −1 for the forest ecosystem, 63 to 245 mg C m −2 h −1 for the sago and 46 to 335 mg C m −2 h −1 for the oil palm. Based on principal component analysis (PCA), the environmental variables over all sites could be classified into three components, namely, climate, soil moisture and soil bulk density, which accounted for 86% of the seasonal variability. A regression tree approach showed that CO 2 flux in each ecosystem was related to different underlying environmental factors. They were relative humidity for forest, soil temperature at 5 cm for sago and water-filled pore space for oil palm. On an annual basis, the soil CO 2 flux was highest in the forest ecosystem with an estimated production of 2.1 kg C m −2 yr −1 followed by oil palm at 1.5 kg C m −2 yr −1 and sago at 1.1 kg C m −2 yr −1 . The different dominant controlling factors in CO 2 flux among the studied ecosystems suggested that land use affected the exchange of CO 2 between tropical peatland and the atmosphere.

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Nitrous oxide (N 2 O) emissions were measured monthly over 1 year in three ecosystems on tropical peatland of Sarawak, Malaysia, using a closed-chamber technique. The three ecosystems investigated were mixed peat swamp forest, sago (Metroxylon sagu) and oil palm (Elaeis guineensis) plantations. The highest annual N 2 O emissions were observed in the sago ecosystem with a production rate of 3.3 kg N ha −1 year −1 , followed by the oil palm ecosystem at 1.2 kg N ha −1 year −1 and the forest ecosystem at 0.7 kg N ha. The N 2 O emissions ranged from -3.4 to 19.7 μg N m −2 h −1 for the forest ecosystem, from 1.0 to 176.3 μg N m −2 h −1 for the sago ecosystem and from 0.9 to 58.4 μg N m −2 h −1 for the oil palm ecosystem. Multiple regression analysis showed that N 2 O production in each ecosystem was regulated by different variables. The key factors influencing N 2 O emissions in the forest ecosystem were the water table and the concentration at 25-50 cm, soil temperature at 5 cm and nitrate concentration at 0-25 cm in the sago ecosystem, and water-filled pore space, soil temperature at 5 cm and concentrations at 0 -25 cm in the oil palm ecosystem. R 2 values for the above regression equations were 0.57, 0.63 and 0.48 for forest, sago and oil palm, respectively. The results suggest that the conversion of tropical peat swamp forest to agricultural crops, which causes substantial changes to the environment and soil properties, will significantly affect the exchange of N 2 O between the tropical peatland and the atmosphere. Thus, the estimation of net N 2 O production from tropical peatland for the global N 2 O budget should take into consideration ecosystem type.

Mulching materials from oil palm residues such as pruned palm fronds (OPF), empty fruit bunches (EFB), and Eco-mat (ECO; a compressed EFB mat) are often the recommended soil and water conservation practices (CP) for oil palm plantations on hill slopes. Another recommended CP is the construction of silt pits or trenches (SIL) across the hill slope to capture runoff and then return the water and nutrients into the surrounding soil. Although these four CP are recommended practices, their relative effects on improving soil physical properties and on increasing the soil water content have never been compared with one another. Consequently, the objective of this study was to fill in this knowledge gap. A threeyear field experiment was conducted in a non-terraced oil palm plantation, and soil samples from 0 to 0.15, 0.15 to 0.30, and 0.30 to 0.45 m depths were collected every three months and analyzed for their soil physical properties. Soil water content up to 0.75 m depth was also measured daily. EFB released the highest amount of organic matter and nutrients into the soil compared to OPF, ECO, and SIL. Hence, EFB was most effective to increase soil aggregation, aggregate stability, soil water retention at field capacity, available soil water content, and the relative proportion of soil mesopores. Due to these improved soil physical properties, EFB also gave the highest soil water content. Unlike ECO that concentrated more water in the upper soil layers, EFB distributed the soil water more uniformly throughout the whole soil profile, but SIL concentrated more soil water in the lower soil layers (>0.30 m) because the water levels in the pits were often below 0.30 m from the soil surface. The large opening area of the silt pits could have also caused large evaporative water losses from the pits. EFB mulching is recommended as the best CP, particularly for oil palm plantations on hill slopes.

The decomposition and nutrient release temporal patterns of three oil palm residues used as soil mulch were studied. Empty fruit bunches (EFB; 1000 kg plot−1), Eco-mat (processed EFB carpet; 30 kg plot−1), and pruned palm fronds (180 kg plot−1) were left to decompose (and sampled monthly) on the soil surface for 8 months. The frond's leaflets had the highest initial concentration for most nutrients, and the frond's rachis and Eco-mat the lowest. The order of residue quality and rate of residue mass loss were: leaflets > fronds > EFB > Ecomat > rachis. EFB however had a higher mass loss rate than the fronds. Residue mass loss and nutrient release rates were faster at the beginning than at the end of the decomposition period. Leaflets released the highest total amount of nutrients (except for K), and rachis the lowest. The fronds released either significantly higher (for N and Ca) or not significantly different (for P and Mg) total amount of nutrients than EFB. Converting EFB into Eco-mat had resulted in nutrient losses (e.g. N, K and Mg) and a residue quality reduction in Eco-mat. This study's results would aid in better soil and oil palm fertilisation management.

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