Tropical deforestation for fertilizer-based agriculture has greatly increased in the last decades resulting in significant greenhouse gas (GHG; carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O)) emissions. Unfortunately, empirical studies on soil GHG fluxes from African deforestation hotspots are still limited, creating uncertainties in global GHG budgets. Therefore, we assessed how soil GHG fluxes along with their auxiliary controls (water filled pore space (WFPS), temperature, and mineral nitrogen (N)) differed between the forest and sugarcane plantations. This assessment was based on monthly (forest) and intensive (sugarcane) GHG and auxiliary measurements between May 2019 and June 2020. Measurements were conducted in four reference forest plots and 12 sugarcane plots randomly assigned to three fertilization treatment groups (low, standard, and high), representing the fertilization gradient used by sugarcane farmers in Uganda. Despite the use of different fertilization rates as treatments for the sugarcane experiment, neither auxiliary controls nor soil GHG fluxes significantly differed among the treatments. Soil CO₂ effluxes were higher under sugarcane (17.6 ± 0.0 Mg C ha^-1 yr^-1) compared to forest (14.5 ± 0.1 Mg C ha^-1 yr^-1; p < 0.001) because of the higher autotrophic respiration from the sugarcane’s fine root biomass and the microbial decomposition of the sugarcane’s larger soil organic carbon (SOC) stocks. Conversely, soil CH₄ uptake under sugarcane (−1.1 ± 0.0 kg C ha^-1 yr^-1) was three times lower than under forest (−3.1 ± 0.0 kg C ha^-1 yr^-1; p < 0.001), owing to the likely alteration of methanotroph abundance upon conversion. Likewise, soil N₂O emissions were smaller under sugarcane (1.3 ± 0.0 kg N ha^-1 yr^-1) compared to forest (1.8 ± 0.0 kg N ha^-1 yr^-1; p < 0.001) because excess N from fertilizer addition in the sugarcane was either lost through leaching or taken up by the sugarcane crop. Only seasonal variability in WFPS, among the auxiliary controls, affected CH₄ uptake at both sites (p < 0.001) and soil CO₂ effluxes under sugarcane (p = 0.018). Noteworthy, soil N₂O fluxes from both sites were unaltered by the seasonality-mediated changes in auxiliary controls. We conclude that even with the increased SOC sequestration and the lower N₂O emissions under sugarcane compared to forest, the forest-sugarcane conversion resulted in a yearly net C loss of 2.8 Mg CO₂-eq ha^-1 from soils to atmosphere, largely arising from the higher soil CO₂ effluxes and to a smaller extent from a reduced CH₄ uptake under sugarcane.

在过去的几十年中，以化肥为基础的农业的热带森林砍伐大大增加，导致大量温室气体（GHG；二氧化碳（CO ₂）、甲烷（CH ₄）和一氧化二氮（N ₂O)) 排放。不幸的是，对来自非洲森林砍伐热点的土壤温室气体通量的实证研究仍然有限，这给全球温室气体预算带来了不确定性。因此，我们评估了森林和甘蔗种植园之间的土壤温室气体通量及其辅助控制（充水孔隙空间 (WFPS)、温度和矿物氮 (N)）的差异。该评估基于 2019 年 5 月至 2020 年 6 月期间每月（森林）和密集（甘蔗）温室气体和辅助测量。测量在四个参考森林地块和 12 个甘蔗地块中进行，随机分配到三个施肥处理组（低、标准和高），代表乌干达甘蔗农民使用的施肥梯度。尽管使用不同的受精率作为甘蔗实验的处理方法，辅助控制和土壤温室气体通量在处理之间均无显着差异。土壤二氧化碳^{与森林 (14.5 ± 0.1 Mg C ha -1} yr ^-1 )相比，甘蔗(17.6 ± 0.0 Mg C ha ^-1 yr ^{-1 ) 下的}_{2 个}流出量更高， 因为甘蔗细根的自养呼吸作用更高甘蔗较大的土壤有机碳 (SOC) 储量的生物量和微生物分解。相反，甘蔗下土壤 CH ₄吸收（-1.1 ± 0.0 kg C ha ^-1 yr ^{-1 ）比森林下（-3.1 ± 0.0 kg C ha -1} yr ^-1；p < 0.001）低三倍 ，这是由于转化后甲烷氧化菌丰度的可能变化。同样，土壤 N₂ O 排放量在甘蔗下（1.3 ± 0.0 kg N ha ^-1 yr ^-1）比森林（1.8 ± 0.0 kg N ha ^-1 yr ^-1 ; p  < 0.001）要小，因为甘蔗中添加的过量氮是要么通过浸出丢失，要么被甘蔗作物吸收。在辅助控制中，只有 WFPS 的季节性变化会影响两个地点的CH _4吸收（ p < 0.001）和甘蔗下的 土壤 CO _2流出（ p  = 0.018）。值得注意的是，土壤 N ₂来自两个站点的 O 通量不受辅助控制中季节性介导的变化的影响。我们得出结论，即使与森林相比，甘蔗下的 SOC 固存增加和 N ₂ O 排放量较低，森林-甘蔗转化导致土壤到大气的年净碳损失为 2.8 Mg CO ₂ -eq ha ^-1 ，主要是由较高的土壤 CO ₂流出量和较小程度的甘蔗下CH _{4吸收减少引起。}