Carbon mineralization in an organic soil, with and without added grass litter, from a high-CO2 environment at a carbon dioxide spring

Both CO₂-C production and the decomposability of grass leaf litter in a gley soil from a naturally occurring CO₂ spring were previously shown to be influenced by the atmospheric CO₂ concentrations under which the soil and litter were sampled. Here we investigate C mineralization in an organic soil from very high CO₂ environments (range 1220-3900 μl l⁻¹) at the same spring, and the effect of added leaf litter on CO₂-C production. Carbon mineralization in the organic soil was unusual in two respects: (1) the proportion of labile components was very high, with more than 11% of the initial soil C being metabolized to CO₂-C after 56 d at 25 °C; (2) rates of CO₂-C production in autumn samples increased on incubation, after an initial decline. Decomposition was initially more rapid in C3 Holcus lanatus (Yorkshire fog) than in C4 Pennisetum clandestinum (kikuyu) litter, but differed little in samples from different atmospheric CO₂ concentrations. Overall, the effects of environmental variables on estimates of litter decomposability in the organic soil were similar to, although much less marked than, those in the gley soil. Results suggest that organic components in the organic soil were metabolized at least as readily as those of added litter during the later stages of the 56-d incubation.     

Carbon and nitrogen mineralization after maize harvest between and within maize rows: a microcosm study using 13C natural abundance

The sequestration of carbon in soil is not completely understood, and quantitative information about the rates of soil organic carbon (SOC) turnover could improve understanding. We analyzed the effects of the uneven distribution of crop residues after harvest of silage maize on C and N losses (CO₂‐C, dissolved organic carbon (DOC) and nitrogen (DON), and NO₃^–) from a Haplic Phaeozem and on the occurrence of priming effects induced by the decomposition of accumulated maize residues. Soil columns were taken from a continuous maize (since 1961) field after harvest i) between maize stalk rows (M_bare), ii) within the maize rows including a standing maize stalk (M_stalk), and iii) from a continuous rye (since 1878) field after tillage (rye stalk and roots were mixed into the Ap horizon). The soil columns were incubated for 230 days at 8 °C with an irrigation rate of 2 mm 10^–2 M CaCl₂ per day. Natural ¹³C abundance was used to distinguish between maize‐derived C (in SOC and maize residues) and older C originating from former C₃ vegetation. The uneven distribution of maize residues resulted in a considerably increased heterotrophic activity within the maize rows as compared with soil between seed rows. Cumulative CO₂ production was 53.1 g CO₂‐C m^–2 for M_stalk and 23.3 g CO₂‐C m^–2 for M_bare. The contribution of maize‐derived C to the total CO₂ emission was 83 % (M_stalk) and 67 % (M_bare). Calculated as difference between CO₂‐C release from M_stalk and M_bare, 19 % of the maize residues (roots and stalk) in M_stalk were mineralized during the incubation period. There was no or only a marginal effect of the accumulation of maize residues in M_stalk on leaching of DOC, DON, and NO₃^–. Total DOC and DON leaching amounted to 2.5 g C m^–2 and 0.16 g N m^–2 for M_stalk and to 2.1 g C m^–2 and 0.12 g N m^–2 for M_bare. The contribution of maize‐derived C to DOC leaching was about 25 % for M_stalk and M_bare. Nitrate leaching amounted to 3.9 g NO₃^–‐N m^–2 for M_stalk and to 3.5 g NO₃^–‐N m^–2 for M_bare. There was no priming effect induced by the decomposition of fresh maize residues with respect to CO₂ or DOC production from indigenous soil organic carbon derived from C₃ vegetation.     

光照与黑暗培养对亚热带区稻田及旱地土壤有机碳及其活性组分的影响

农田土壤的固碳潜力对于理解陆地生态系统碳循环和气候变化至关重要.分别选取亚热带区4种典型稻田和旱地土壤,设置裸土光照和裸土黑暗处理,探讨土壤有机碳(SOC)及其活性组分(可溶性有机碳(DOC)和微生物生物量碳(MBC))对光照和黑暗条件的响应。结果表明,与培养前相比,培养80 d后,光照和黑暗培养下稻田及旱地土壤SOC含量差异不显著,这可能与土壤SOC含量变化是一个缓慢的过程有关.光照和黑暗培养均显著提高了土壤DOC含量(与培养前相比,光照和遮光培养平均分别提高73.37%和80.58%),而MBC显著降低(与培养前相比,光照和遮光培养平均分别降低35.58%和32.32%)。相关分析表明,培养后的土壤DOC含量与土壤粘粒含量呈极显著正相关性(P<0.01),而与土壤原有碳氮水平呈极显著负相关;土壤MBC则恰好相反,MBC与土壤粘粒含量呈极显著负相关,而与土壤原有碳氮水平呈极显著正相关.本研究表明,短期(80d)的光照和黑暗培养对稻田及旱地土壤SOC含量变化影响不大,而显著改变了有机碳活性组分(DOC和MBC)含量,进一步说明了土壤活性有机碳是土壤中活性化学组分,随环境条件变化表现出强烈的变化趋势。     

不同种类有机肥碳、 氮矿化特性研究

本文采用室内培养法研究了陕西关中地区日光温室栽培生产中9个不同有机肥的碳、氮矿化特性。结果表明:不同有机肥碳、氮的矿化量和矿化率（矿化量占总有机碳或氮的比例）的动态变化存在明显差异,其中碳矿化率在22.24%～87.16%之间,变异系数达90.30 %;氮矿化率在29.07%～84.87%之间,变异系数达67.37 %;不同类型有机肥相比,鸡粪平均的碳、氮矿化累积量及矿化率显著高于猪粪和牛粪;猪粪与牛粪平均的碳、氮矿化累积量及矿化率无显著差异。同一种类有机肥,培养期间其碳、氮矿化累积量及矿化率也存在明显差异。供试有机肥碳、氮的矿化量与有机肥全氮含量均呈线性关系,表明有机肥氮含量是影响矿化量的主导因子。     

长期施用化肥和秸秆对水稻土碳氮矿化的影响

以长期定位试验的土壤为供试材料,通过室内培养试验,研究了长期施用化肥和秸秆对水稻土?C、N矿化和微生物生物量的影响。结果表明长期施用化肥和秸秆增加了土壤?C?矿化量,但降低了可矿化?C?在土壤有机?C?中的比例。长期施用化肥能够增加土壤?N?矿化量,而且增加了可矿化?N?在土壤全?N?中的比例,但配施秸秆不能继续增加?N?矿化量。长期施用化肥和秸秆能够显著增加土壤微生物生物量?C、N?含量,但微生物量在土壤中的比例变化不大。     

Carbon availability regulates soil respiration response to nitrogen and temperature

The response of soil CO₂ fluxes (R_soil) to interactions between carbon (C) and nitrogen (N) availability or C and temperature conditions is not well understood, but may increasingly affect future C storage under the combined anthropogenic impacts of N deposition and climate change. Here we addressed this uncertainty through a series of laboratory incubation experiments using soils from three contrasting ecosystems to investigate how changes in C, N, and temperature regulate R_soil through changes to Michaelis–Menten parameters (i.e. V_max and K_m). Results of this study demonstrate that R_soil response to N enrichment and changes in temperature are dependent on the C availability of soil substrates. N addition influenced R_soil through both the maximum rate (V_max) and the half saturation constant (K_m). The increase in K_m corresponded to a decrease in R_soil when C was limited. Alternatively, when C was abundant, N enrichment increased R_soil, which corresponded to an increase in V_max. Regulation of temperature sensitivity through V_max and K_m was also dependent on C availability. Both V_max and K_m demonstrated positive temperature responses, supporting the hypothesis of a canceling effect at low C concentrations. While temperature sensitivity was influenced by both C quantity and C complexity, our results suggested that C quantity is a stronger predictor. Despite strong differences in climate, vegetation, and management of our soils, C–N and C-temperature interactions were markedly similar between sites, highlighting the importance of C availability in the regulation of R_soil and justifying the use of Michaelis–Menten kinetics in biogeochemical modeling.     

甜玉米/白三叶草秸秆还田的碳氮矿化研究

豆科/禾本科作物间套作后进行秸秆还田能补充土壤养分,缓解集约化农业生产对环境的压力.根据田间甜玉米/白三叶草套种各作物的秸秆产量,在恒温恒湿条件下进行室内培养,探讨秸秆不同方式还田后土壤微生物量碳、微生物量氮、呼吸产生的CO2和矿化产生的无机氮的变化规律.研究发现,各施肥处理的土壤微生物量碳、微生物量氮均在培养前期出现峰值,后期平稳降低;甜玉米秸秆和白三叶草绿肥同时还田的土壤微生物量碳、微生物量氮在各培养时期均最大,峰值分别达529.57 mg·kg-1和75.50 mg·kg-1,土壤呼吸产生的CO2最多;白三叶草绿肥单独还田有利于土壤无机氮的释放,培养第26 d 无机氮达到最大值,为29.81 mg·kg-1,之后一直在对照处理的1.60倍以上,第80 d达到2.48倍;甜玉米秸秆单独还田不利于土壤无机氮的释放,培养的第26 d至结束,甜玉米秸秆处理的无机氮为对照的13%～53%,最大为7.51 mg·kg-1;甜玉米秸秆配施尿素,短期内不利于土壤无机氮矿化.结果表明,施用有机物料能引起土壤有机质的短期快速转化,甜玉米秸秆和白三叶草绿肥配施有利于维持较大基数的土壤微生物量,单施白三叶草绿肥土壤微生物活性强,最有利于土壤速效氮的释放.     

上海地区水稻土氮素矿化模拟

Six paddy soils of Shanghai, China, were studied after 120 days of anaerobic incubation at 25 ℃ and 35 ℃. Four models, the effective accumulated temperature model, the one-component first-order exponential model (the one-pool model), the two-component first-order exponential model (the two-pool model), and the two-component first-order plus zero-order exponential model including a constant term (the special model), were fitted to the data of observed mineral-N during incubation using non-linear regression procedures. The two-pool model and the special model gave the best fits amongst the four models, and parameters in the special model were more reasonable than those in the other three. Results showed that the special model gave a better prediction of nitrogen mineralization under flooded conditions than the other three models.     

A comparison of different indices for nitrogen mineralization

Indices of N mineralization in soils of contrasting texture, pH, and organic matter contents were compared at different dates during the growing season. The indices were derived from a 12-week aerobic incubation, determination of the amount of microbial biomass at the start of the incubation, determination of the increase in NH ₄ ⁺ after boiling with 2 M KCl for 2h, and extraction of total soluble N with 0.01 M CaCl₂. Cumulative mineral N increased linearly with time in the course of the incubations. Rates of mineralization in soil samples taken in March 1989 and 1990 were significantly correlated with soluble organic N, while correlations between the mineralization rate and the increase in NH ₄ ⁺ after boiling with 2 M KCl for 2 h were poor for sandy soils and absent for loamy soils. Correlations between NH ₄ ⁺ after boiling with 2 M KCl for 2h and the soil N concentration were highly significant, but no general relationship was found between the mineralization rate and the soil N concentration. Neither biomass N nor biomass C was significantly correlated with the mineralization rate or with one of the chemical indices. Among the methods tested, soluble organic N extracted with 0.01 M CaCl₂ was the only method with any promise for routine measurement of the mineralization capacity of the individual sites.     

Effects of long-term litter manipulation on soil carbon,nitrogen, and phosphorus in a temperate deciduous forest

Changes in above-ground litterfall can influence below-ground biogeochemical processes in forests. In order to examine how above-ground litter inputs affect soil carbon (C), nitrogen (N) and phosphorus (P) in a temperate deciduous forest, we studied a 14-year-old small-scale litter manipulation experiment that included control, litter exclusion, and doubled litter addition at a mature Fagus sylvatica L. site. Total organic C (TOC), total N (TN) and total P (TP), total organic P (TOP), bioavailable inorganic P (Pi), microbial C, N and P, soil respiration and fine root biomass were analyzed in the A and in two B horizons. Our results showed that litter manipulation had no significant effect on TOC in the mineral soil. Litter addition increased the bioavailable Pi in the A horizon but had no significant effect on N in the mineral soil. Litter exclusion decreased TN and TP in the B horizon to a depth of 10 cm. In the A horizon of the litter exclusion treatment, TP, TOP and bioavailable Pi were increased, which is most likely due to the higher root biomass in this treatment. The high fine root biomass seems to have counteracted the effects of the excluded aboveground litter. In conclusion, our study indicates that aboveground litter is not an important source for C in the mineral soil and that P recycling from root litter might be more important than from above-ground litter.     

氮素补充对高寒草甸土壤团聚体有机碳、全氮分布的影响

土壤结构的稳定性对高寒草甸生态系统有重要意义。为研究不同水平氮素补充对高寒草甸草地土壤团聚体、有机碳和全氮含量及分布格局的影响,于2012-2014年在青藏高原东部夏河县进行3 a的试验研究。试验为随机区组设计,包括0(对照)、50(低氮)、100(中氮)和200(高氮)kg/hm2 4个氮素补充水平。研究结果表明:低、中、高水平氮素补充处理显著提高了0~30 cm土层≥0.25 mm大团聚体质量分数(P0.05),比对照分别提高了4.74%、6.42%和1.96%;较之对照,低、中水平氮素补充处理显著增加了≥5 mm、≥2~5 mm粒级团聚体含量;低、中水平氮素补充处理显著提升了0~30 cm土壤团聚体平均质量直径,分别比对照提升了9.79%和12.63%。不同水平氮素补充处理有机碳、全氮含量大小排序分别为:中氮≈低氮对照高氮、中氮低氮≈高氮对照。不同粒级团聚体中0.25 mm微团聚体有机碳含量最高而全氮含量最低、≥0.25~2 mm粒级有机碳含量最低而全氮含量最高;低、中水平氮素补充提高了不同粒级团聚体0~30 cm土层有机碳含量而高水平氮素补充处理显著降低了有机碳含量;低、中、高水平氮素补充增加了不同粒级团聚体全氮含量,其中中水平氮素补充处理最高,低水平氮补充次之。不同粒级团聚体含量是影响团聚体养分贡献率的主要原因,≥2~5 mm粒级团聚体含量与相应粒级团聚体有机碳含量呈显著正相关关系,≥5 mm和≥2~5 mm粒级团聚体含量与相应粒级团聚体全氮含量分别呈极显著正相关、显著正相关关系。研究表明连续每年补充50~100 kg/hm2氮可以改善高寒草甸土壤结构并提高土壤肥力状况。     

岳桦和暗针叶林两种植被类型下土壤碳氮元素的转化过程

Soil samples were taken from an Ermans birch (Betula ermanii)-dark coniferous forest (Picea jezoensis and Abies nephrolepis) ecotone growing on volcanic ejecta in the northern slope of Changbai Mountains of Northeast China, to compare soil carbon (C) and nitrogen (N) transformations in the two forests. The soil type is Umbri-Gelic Cambosols in Chinese Soil Taxonomy. Soil samples were incubated aerobically at 20℃ and field capacity of 700 g kg^-1 over a period of 27 weeks. The amount of soil microbial biomass and net N mineralization were higher in the Ermans birch than the dark coniferous forest (P < 0.05), whereas the cumulative C mineralization (as CO₂ emission)in the dark coniferous forest exceeded that in the Ermans birch (P < 0.05). Release of the cumulative dissolved organic C and dissolved organic N were greater in the Ermans birch than the dark coniferous forest (P < 0.05). The results suggested that differences of forest types could result in considerable change in soil C and N transformations.     

Carbon and nitrogen mineralization of sewage sludge compost in soils with a different initial pH

Soil properties may affect the decomposition of added organic materials and inorganic nitrogen (N) production in agricultural soils. Three soils, Potu (Pu), Sankengtzu (Sk) and Erhlin (Eh) soils, mixed with sewage sludge compost (SSC) at application rates of 0 (control), 25, 75 and 150 Mg ha⁻¹ were selected from Taiwan for incubation for 112 days. The aim of the present study was to examine the effects of SSC application rates on the carbon decomposition rate, N transformation and pH changes in three soils with different initial soil pH values (4.8–7.7). The results indicated that the highest peaks of the CO₂ evolution rate occurred after 3 days of incubation, for all treatments. The Pu soil (pH 4.8) had a relatively low rate of CO₂ evolution, total amounts of CO₂ evolution and percentage of added organic C loss, all of which resulted from inhibition of microbial activity under low pH. For the Pu and Sk soils, the concentration of NH₄⁺-N reached its peak after 7–14 days of incubation, which indicated that ammonification might have occurred in the two soils with low initial pH values. NO₃⁻-N rapidly accumulated in the first 7 days of incubation in the Eh soil (pH 7.7). The direction and extent of the soil pH changes were influenced by the N in the SSC and the initial soil pH. Ammonification of organic N in the SSC caused the soil pH to increase, whereas nitrification of mineralized N caused the soil pH to decline. Consequently, the initial soil pH greatly affected the rate of carbon decomposition, ammonification and nitrification of SSC.     

土壤健康与农业绿色发展: 机遇与对策

  目的  为探明有机物料还田配合优化施氮对石灰性潮土土壤有机碳（SOC）及其活性组分、土壤团聚体的形成与稳定性的影响。  方法  依托长期定位试验,设置农民习惯施氮（CF_N）、优化施氮（OF_N）、秸秆还田 + 优化施氮（S_N）和生物炭 + 优化施氮（BC_N）四个处理开展土壤有机碳固定效果与机制的研究。  结果  四种施肥方式下,BC_N处理对土壤有机碳的提升效果最明显,达到18.68 g kg⁻¹,其次依次为S_N、CF_N和OF_N处理。与CF_N处理相比,有机物料还田配合优化施氮能够显著增加土壤微生物量碳（MBC）、可溶性有机碳（DOC）、颗粒态有机碳（POC）和易氧化有机碳（EOC）的含量,增幅分别为128.26%、96.62%、219.72%和45.42%;同时,> 0.25 mm团聚体的比例与土壤团聚体平均重量直径（MWD）显著提高,S_N与BC_N较CF_N处理> 0.25 mm团聚体的比例分别增加132.44%和91.45%,MWD值分别增加89.79%和66.87%。这主要得益于土壤交换性Ca^{2 +} 、Mg^{2 +} 、K ⁺ 和Na ⁺ ,以及铁铝氧化物含量的改善对大团聚体形成与稳定的驱动作用。OF_N处理较CF_N处理显著减少了氮肥投入量（261 vs. 480 kg N hm⁻² yr⁻¹）,但所测定的各指标均未表现出显著差异。  结论  尽管长期（12年）秸秆与秸秆生物炭等碳量还田配合优化施氮提高土壤有机碳含量、改善土壤团聚体结构的效果存在差异,但均显著优于单施氮肥处理。研究结果可为华北平原石灰性潮土农田碳氮协同调控策略促进土壤健康提供理论支撑。     

Carbon Mineralization and Water-Extractable Organic Carbon and Nitrogen as Predictors of Soil Health and Nitrogen Mineralization Potential

ABSTRACT

The United States Department of Agriculture Natural Resources Conservation Service (NRCS) launched a national “Soil health initiative” in 2012; as a part of that effort, a soil health index (SHI) has been developed. The SHI is calculated using results of three soil tests: 24-h carbon mineralization following rewetting of air-dried soil (C_min, by the “Solvita” proprietary method) and water-extractable organic carbon (C) and nitrogen (N). These tests are being promoted both as the inputs into the SHI calculation and as predictors of soil N mineralization potential. Soil was collected from 35 California fields in annual crop rotations; 20 fields were under certified organic management and the other 15 under conventional management, to provide a range of soil properties and management effects. Carbon mineralization was determined by the Solvita method, and by a comparison method utilizing head space carbon dioxide (CO₂) monitoring by infrared gas analyzer (IRGA); additionally, two soil wetting protocols were compared, capillary wetting (the Solvita method) and wetting to 50% water-filled pore space (WFPS). Both water-extractable C (WEOC) and N (WEON) were determined using NRCS-recommended protocols. Net N mineralization (N_min) was also determined after a 28-day aerobic incubation at 25°C. Solvita C_min was highly correlated with the IRGA method using capillary wetting (R² = 0.81). However, capillary soil wetting resulted in high gravimetric water content that significantly suppressed C_min compared to the 50% WFPS method. N_min was correlated with Solvita C_min (r = 0.54) and with WEOC and WEON (r = 0.62 for each comparison); combining these three measurements into the SHI slightly improved the correlation with N_min. The organically managed soils scored higher than the conventional soils on the SHI, with a minority of organic soils and the majority of conventional soils scoring below the NRCS target threshold. SHI and soil organic matter were correlated, suggesting an inherent bias that would complicate the application of a national SHI standard.     

高寒草甸土CO2流通和氮矿化之间的关系以及对外加碳或氮的响应

In nutrient-limited alpine meadows,nitrogen(N) mineralization is prior to soil microbial immobilization;therefore,increased mineral N supply would be most likely immobilized by soil microbes due to nutrient shortage in alpine soils.In addition,low temperature in alpine meadows might be one of the primary factors limiting soil organic matter decomposition and thus N mineralization.A laboratory incubation experiment was performed using an alpine meadow soil from the Tibetan Plateau.Two levels of NH4NO3(N) or glucose(C) were added,with a blank without addition of C or N as the control,before incubation at 5,15,or 25 ℃ for 28 d.CO2 efflux was measured during the 28-d incubation,and the mineral N was measured at the beginning and end of the incubation,in order to test two hypotheses:1) net N mineralization is negatively correlated with CO2 efflux for the control and 2) the external labile N or C supply will shift the negative correlation to positive.The results showed a negative correlation between CO2 efflux and net N immobilization in the control.External inorganic N supply did not change the negative correlation.The external labile C supply shifted the linear correlation from negative to positive under the low C addition level.However,under the high C level,no correlation was found.These suggested that the correlation of CO2 efflux to net N mineralization strongly depend on soil labile C and C:N ratio regardless of temperatures.Further research should focus on the effects of the types and the amount of litter components on interactions of C and N during soil organic matter decomposition.     

不同种植年限水田与旱地土壤有机氮组分变化

在浙江慈溪地区,由于不同时期围海造田形成了具有长时间尺度序列的典型水稻土和旱地土壤,为研究长期的土壤氮素生物地球化学循环过程提供了很好的对象。本研究运用封管水解Bremner法测定了不同种植年限下土壤氨基酸氮、氨基糖氮、氨态氮、未知氮等酸解性有机氮组分,以探究不同种植年限和种植方式对土壤有机氮组分的影响。结果显示,旱地土壤的不同氮组分含量仅为水稻土相对应氮组分含量的50%~60%,水稻种植较旱地更利于土壤氮素的保存和利用。从长时间尺度来看,除氨基酸氮和水稻土氨基糖氮外,有机氮各组分含量随时间呈指数变化趋势,水稻土主要呈增加趋势,而旱地土壤则表现为降低趋势。该地区土壤氨基酸氮占全氮比例为23.5%~29.3%,氨基糖氮比例为6.0%~7.6%,氨态氮为21.0%~28.8%,未知氮为13.0%~21.1%,不同种植方式和种植年限对土壤主要有机氮组分所占全氮比例影响不大。     

基于不同林分类型下土壤碳氮储量垂直分布

以辽东大伙房水库周边防护林典型林分针阔混交林(落叶松-油松-刺槐混交林)、油松林、落叶松林、刺槐林为研究对象,对其土壤养分含量进行测定,研究了不同林分土壤剖面上有机碳、全氮、有机碳储量的分布规律。结果表明:随着土层深度的增大,4种林分的土壤有机碳、全氮含量均逐渐降低;4种林分土壤剖面有机碳含量大小顺序为落叶松林(24.16g/kg)刺槐林(23.07g/kg)针阔混交林(16.06g/kg)油松林(15.76g/kg);全氮含量大小顺序为刺槐林(5.23g/kg)落叶松林(4.57g/kg)油松林(3.45g/kg)针阔混交林(2.42g/kg);C/N平均值大小顺序为落叶松林(7.36)针阔混交林(6.51)油松林(4.67)刺槐林(4.57);4个林分0-40cm土层的有机碳储量大小为落叶松林(112.94t/hm~2)刺槐林(107.40t/hm~2)针阔混交林(105.42t/hm~2)油松林(89.89t/hm~2);4种林分土壤pH无明显差别,各土层土壤pH随土层深度增加而增大;4种林分土壤容重由高到低顺序依次为针阔混交林(1.73g/cm~3)油松(1.65g/cm~3)落叶松(1.64g/cm~3)刺槐(1.56g/cm~3)。4个林分土壤有机碳含量与土壤全氮含量互相间均存在极显著正相关关系,土壤有机碳、全氮含量与C/N之间则没有明显相关关系;在针阔混交林中,土壤容重、土壤全氮含量和土壤pH与土壤有机碳之间存在线性数量关系,而其他纯林则没有这种关系。     

过量施氮对旱地土壤碳、氮及供氮能力的影响

【目的】过量施氮会影响土壤有机碳、氮的组成与数量,进而改变土壤供氮能力,但关于西北旱地长期过量施用氮肥后土壤有机碳、氮及土壤供氮能力变化的研究尚缺乏。本文在长期定位试验的基础上,通过分析不同氮肥水平特别是过量施氮条件下土壤硝态氮,有机碳、氮和微生物量碳、氮的变化,探讨长期过量施氮对土壤有机碳、氮及供氮能力的影响。【方法】长期定位试验位于陕西杨凌西北农林科技大学农作一站。在施磷(P2O5)100kg/hm2的基础上,设5个氮水平,施氮量分别为N 0、80、160、240、320 kg/hm2。重复4次,小区面积40 m2,完全随机区组排列。种植冬小麦品种为小堰22。本文选取其中3处理,以不施氮为对照(N0)、施氮量N 160 kg/hm2为正常施氮(N160),施氮量N 320 kg/hm2为过量施氮(N320),分别于2012年6月小麦收获后和10月下季小麦播前采集土壤样品,进行测定分析。【结果】过量施氮导致下季小麦播前0—300 cm各土层硝态氮含量显著增加,平均由对照的2.8 mg/kg增加到15.5 mg/kg;同时,0—60 cm和0—300 cm土层的硝态氮累积量分别由对照的47.2和108.9 kg/hm2增加到76.5和727.7 kg/hm2。过量施氮也增加了夏闲期间0—300 cm土层土壤有机氮矿化量,由对照的72.4 kg/hm2增加到130.7 kg/hm2。但过量施氮未显著增加土壤的有机碳含量,却显著增加了土壤有机氮含量,过量施氮0—20、20—40 cm土层土壤有机碳分别为9.24和5.39 g/kg,有机氮分别为1.05和0.71 g/kg,较对照增加52.2%和54.3%。同样,过量施氮未显著影响0—20、20—40 cm土层土壤微生物量碳含量,其平均含量分别为253和205 mg/kg,却显著提高了0—20、20—40 cm土层土壤微生物量氮含量,由对照的24.1和7.5 mg/kg提高到43.6和16.1 mg/kg。【结论】过量施氮可以显著增加旱地土壤剖面中的硝态氮累积量、夏闲期氮素矿化量、小麦播前土壤氮素供应量和土壤微生物量氮含量,但对土壤有机碳和微生物量碳没有显著性影响,同时过量施氮增加了土壤硝态氮淋溶风险,故在有机质含量低的黄土高原南部旱地冬小麦种植中不宜施用高量氮肥,以减少土壤氮素残留和农业投入,达到保护环境和培肥土壤的目的。