Data from: Soil nitrogen-cycling responses to conversion of lowland forests to oil palm and rubber plantations in Sumatra, Indonesia

Rapid deforestation in Sumatra, Indonesia is presently occurring due to the expansion of palm oil and rubber production, fueled by an increasing global demand. Our study aimed to assess changes in soil-N cycling rates with conversion of forest to oil palm (Elaeis guineensis) and rubber (Hevea brasiliensis) plantations. In Jambi Province, Sumatra, Indonesia, we selected two soil landscapes – loam and clay Acrisol soils – each with four land-use types: lowland forest and forest with regenerating rubber (hereafter, “jungle rubber”) as reference land uses, and rubber and oil palm as converted land uses. Gross soil-N cycling rates were measured using the 15N pool dilution technique with in-situ incubation of soil cores. In the loam Acrisol soil, where fertility was low, microbial biomass, gross N mineralization and NH4+ immobilization were also low and no significant changes were detected with land-use conversion. The clay Acrisol soil which had higher initial fertility based on the reference land uses (i.e. higher pH, organic C, total N, effective cation exchange capacity (ECEC) and base saturation) (P≤0.05–0.09) had larger microbial biomass and NH4+ transformation rates (P≤0.05) compared to the loam Acrisol soil. Conversion of forest and jungle rubber to rubber and oil palm in the clay Acrisol soil decreased soil fertility which, in turn, reduced microbial biomass and consequently decreased NH4+ transformation rates (P≤0.05–0.09). This was further attested by the correlation of gross N mineralization and microbial biomass N with ECEC, organic C, total N (R=0.51–0. 76; P≤0.05) and C:N ratio (R=-0.71 – -0.75, P≤0.05). Our findings suggest that the larger the initial soil fertility and N availability, the larger the reductions upon land-use conversion. Because soil N availability was dependent on microbial biomass, management practices in converted oil palm and rubber plantations should focus on enriching microbial biomass.

受全球需求持续增长驱动，印度尼西亚苏门答腊岛目前正因棕榈油与橡胶产业扩张而经历快速森林砍伐。本研究旨在评估森林转换为油棕（Elaeis guineensis）与橡胶（Hevea brasiliensis）人工林后，土壤氮（N）循环速率的变化情况。在印度尼西亚苏门答腊占碑省，我们选取了两种土壤类型——壤质黏绨土（Acrisol）与黏质黏绨土（Acrisol）——每种土壤类型下设置四种土地利用方式：以低地森林及再生橡胶林（以下简称“次生橡胶林”）作为对照用地，橡胶林与油棕园作为转换用地。采用¹⁵N池稀释法结合土柱原位培养技术，测定土壤总氮循环速率。在肥力较低的壤质黏绨土中，微生物生物量、总氮矿化速率与铵态氮（NH₄⁺）固持速率均处于较低水平，且土地利用转换未引发显著变化。相较于壤质黏绨土，黏质黏绨土的初始肥力更高——基于对照用地的分析显示其pH、有机碳（C）、全氮（N）、有效阳离子交换量（ECEC）以及盐基饱和度均更高（P≤0.05~0.09），其微生物生物量与NH₄⁺转化速率也显著更高（P≤0.05）。在黏质黏绨土中，将森林与次生橡胶林转换为橡胶林与油棕园会降低土壤肥力，进而削弱微生物生物量，最终降低NH₄⁺转化速率（P≤0.05~0.09）。总氮矿化速率与微生物生物量氮与ECEC、有机C、全氮（R=0.51~0.76；P≤0.05）以及碳氮比（C:N）（R=-0.71~-0.75，P≤0.05）之间的相关性进一步验证了这一结论。本研究结果表明，初始土壤肥力与氮素可利用性越高，土地利用转换后相关指标的降幅便越大。由于土壤氮素可利用性依赖于微生物生物量，因此针对转换后的油棕与橡胶人工林的管理措施应将提升微生物生物量作为核心方向。