氮沉降和施生物质炭对毛竹林土壤N2O通量的影响

本研究于2019年7月-2020年7月在浙江省杭州市典型毛竹林布置野外控制实验,采用静态箱-气相色谱法测定毛竹林土壤N2O通量,分析生物质炭(10 t·hm-2)、氮沉降(60 kg N·hm-2·a-1)、生物质炭+氮沉降混合处理对土壤N2O通量的影响,并探讨了土壤N2O通量与环境因子的关系.结果 表明:与对照相比,...     

Simultaneous quantification of N2, NH3 and N2O emissions from a flooded paddy field under different N fertilization regimes

Gaseous nitrogen (N) emissions, especially emissions of dinitrogen (N₂) and ammonia (NH₃), have long been considered as the major pathways of N loss from flooded rice paddies. However, no studies have simultaneously evaluated the overall response of gaseous N losses to improved N fertilization practices due to the difficulties to directly measure N₂ emissions from paddy soils. We simultaneously quantified emissions of N₂ (using membrane inlet mass spectrometry), NH₃ and nitrous oxide (N₂O) from a flooded paddy field in southern China over an entire rice‐growing season. Our field experiment included three treatments: a control treatment (no N addition) and two N fertilizer (220 kg N/ha) application methods, the traditional surface application of N fertilizer and the incorporation of N fertilizer into the soil. Our results show that over the rice‐growing season, the cumulative gaseous N losses from the surface application treatment accounted for 13.5% (N₂), 19.1% (NH₃), 0.2% (N₂O) and 32.8% (total gaseous N loss) of the applied N fertilizer. Compared with the surface application treatment, the incorporation of N fertilizer into the soil decreased the emissions of NH₃, N₂ and N₂O by 14.2%, 13.3% and 42.5%, respectively. Overall, the incorporation of N fertilizer into the soil significantly reduced the total gaseous N loss by 13.8%, improved the fertilizer N use efficiency by 14.4%, increased the rice yield by 13.9% and reduced the gaseous N loss intensity (gaseous N loss/rice yield) by 24.3%. Our results indicate that the incorporation of N fertilizer into the soil is an effective agricultural management practice in ensuring food security and environmental sustainability in flooded paddy ecosystems.     

Atmospheric CO2 and O3 alter competition for soil nitrogen in developing forests

Plant growth responses to rising atmospheric CO₂ and O₃ vary among genotypes and between species, which could plausibly influence the strength of competitive interactions for soil N. Ascribable to the size‐symmetric nature of belowground competition, we reasoned that differential growth responses to CO₂ and O₃ should shift as juvenile individuals mature, thereby altering competitive hierarchies and forest composition. In a 12‐year‐long forest FACE experiment, we used tracer ¹⁵N and whole‐plant N content to assess belowground competitive interactions among five Populus tremuloides genotypes, between a single P. tremuloides genotype and Betula papryrifera, as well as between the same single P. tremuloides genotype and Acer saccharum. Under elevated CO₂, the amount of soil N and ¹⁵N obtained by the P. tremuloides genotype common to each community was contingent on the nature of belowground competition. When this genotype competed with its congeners, it obtained equivalent amounts of soil N and tracer ¹⁵N under ambient and elevated CO₂; however, its acquisition of soil N under elevated CO₂ increased by a significant margin when grown in competition with B. papyrifera (+30%) and A. saccharum (+60%). In contrast, elevated O₃ had no effect on soil N and ¹⁵N acquisition by the P. tremuloides genotype common in each community, regardless of competitive interactions. Under elevated CO₂, the rank order of N acquisition among P. tremuloides genotypes shifted over time, indicating that growth responses to CO₂ change during ontogeny; this was not the case under elevated O₃. In the aspen‐birch community, the competitive advantage elevated CO₂ initially conveyed on birch diminished over time, whereas maple was a poor competitor for soil N in all regards. The extent to which elevated CO₂ and O₃ will shape the genetic structure and composition of future forests is, in part, contingent on the time‐dependent effects of belowground competition on plant growth response.     

不同施氮量对麦田土壤水稳性团聚体和N2O排放的影响

过量施氮可破坏农田土壤结构,增加温室气体排放量。为揭示不同施氮量对土壤团聚体和N₂O排放的影响,于2018—2020年基于氮肥定位试验,设置秸秆原位还田条件下施氮 0 (N₀)、120 (N₁₂₀)、180 (N₁₈₀)、240 (N₂₄₀)、300 (N₃₀₀)、360 kg·hm^-2 (N₃₆₀) 6个处理,研究不同施氮量对麦田土壤N₂O排放、土壤充水孔隙度(WFPS)、土壤温度、硝态氮、铵态氮含量、水稳性团聚体的组成及稳定性的影响。结果表明: 土壤N₂O排放量与氮肥用量之间呈显著正相关关系,WFPS与施氮量之间无显著相关关系,0~10 cm土壤温度随氮肥施用量的增加而显著降低,土壤硝态氮、铵态氮含量与氮肥施用量间存在显著正相关关系。随氮肥施用量的增加,直径>2 mm的水稳性团聚体含量降低,直径<0.5 mm的水稳性团聚体含量增加,土壤水稳性团聚体的粒径也逐渐减小。氮肥施用量与团聚体平均重量直径(MWD)、几何平均直径之间呈显著负相关关系,但与分形维数之间并无显著相关性。MWD (x)与N₂O排放通量(y)之间的拟合方程为:y=3928.3e^-2.171x (R²=0.55,P<0.001),表明当MWD减小时,N₂O排放量将会剧烈升高。可见,麦田施氮量的增加会降低0~10 cm土壤温度,增加土壤硝态氮和铵态氮含量,减小耕层土壤水稳性团聚体的平均粒径,降低团聚体的稳定性,增加N₂O的排放量。     

DMPP reduced nitrification,but not annual N2O emissions from mineral fertilizer applied to oilseed rape on a sandy loam soil

Direct field emissions of nitrous oxide (N₂O) may determine whether biodiesel from oilseed rape (Brassica napus L.) fulfills the EU requirement of at least 50% reduction of greenhouse gas emissions as compared to fossil diesel. However, only few studies have documented fertilizer N emission factors (EF) and mitigation options for N₂O emissions from oilseed rape cropping systems. We conducted a field experiment with three N levels (0, 171, and 217 kg/ha), where the N fertilizer was applied as ammonium sulfate nitrate with or without the nitrification inhibitor 3,4‐dimethylpyrazole phosphate (DMPP). N₂O fluxes were measured using static chambers technique and soil samples were analyzed for water and mineral N content during a monitoring period of 368 days. The DMPP treatments showed a significantly increased level of ammonium () for up to 18 weeks after spring fertilization as compared to the treatments without DMPP. However, this difference did not result in a corresponding decrease in soil content, and no differences in cumulative N₂O emissions were found between any fertilized treatments with or without DMPP (mean, 1.26 kg N₂O‐N ha^?1 year^?1). More field experiments are needed to clarify whether DMPP‐coated mineral fertilizers could mitigate N₂O emissions under different weather conditions, for example, under conditions where fertilization events concurred with rainfall events increasing water‐filled pore space to the assumed 60% threshold for denitrification. Emission factors for mineral N fertilizer were 0.28%–0.36% with a mean of 0.32% across the fertilized treatments. These data concur with recent European studies suggesting that the EF for mineral N fertilizers in oilseed rape cropping systems may typically be lower than the default IPCC value of 1%. Further studies are needed to consolidate an EF for oilseed rape under temperate conditions, which will be determining for the sustainability of Northern European oilseed rape cultivation for biodiesel.     

生物炭施用3年后对稻麦轮作系统CH4和N2O综合温室效应的影响

本试验对比观测研究了在稻田土壤中经3年陈化后的生物炭(B_3)和新施入生物炭(B_0)对稻麦轮作系统CH_4和N_2O综合温室效应和温室气体强度的影响,旨在明确生物炭对土壤温室气体排放的长期效应.田间试验设置4个处理,分别为对照(CK)、施用氮肥不施用生物炭(N)、施用氮肥和新生物炭(NB_0)以及施用氮肥和陈化生物炭(NB_3)处理.结果表明:NB_0和NB_3处理均显著提高了稻田土壤pH值、有机碳和全氮含量,并且显著影响与温室气体排放相关的微生物潜在活性.与N处理相比,NB_3处理显著增加了作物产量,增幅14.1%,并且显著降低了CH_4和N_2O排放,降幅分别为9.0%和34.0%;而NB_0处理显著增加作物产量,增幅9.3%,显著降低N_2O排放,降幅38.6%,但增加了CH_4排放,增幅4.7%;同时NB_0和NB_3处理均能降低稻麦轮作系统的综合温室效应和温室气体强度,且NB_3处理能更有效地减少温室气体的排放并提高作物产量.在土壤中经3年陈化后的生物炭仍然具有固碳减排能力,因此,施用生物炭对稻麦轮作系统固碳减排和改善作物生产具有长期效应.     

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

Labelled fertilizer N applied to winter wheat as Na¹⁵NO₃ and (¹⁵NH₄)₂SO₄ at a total N dressing of 100kg ha⁻¹ was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO₃ and 32.3%, 48.4% and 52.5% for the NH₄ carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO₃ and 51.7%, 63.5% and 66.1% for the NH₄ carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO₃−N and to 22.5%, 12.7% and 15.2% of the applied NH₄−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.