Microbial biomass and activity at various soil depths in a Brazilian oxisol after two decades of no-tillage and conventional tillage

The advantages of no-tillage (NT) over conventional tillage (CT) systems in improving soil quality are generally accepted, resulting from benefits in soil physical, chemical and biological properties. However, most evaluations have only considered surface soil layers (maximum 0-30 cm depth), and values have not been corrected to account for changes in soil bulk density. The objective of this study was to estimate a more realistic contribution of the NT to soil fertility, by evaluating C- and N-related soil parameters at the 0-60 cm depth in a 20-year experiment established on an oxisol in southern Brazil, with a soybean (summer)/wheat (winter) crop succession under NT and CT. At full flowering of the soybean crop, soil samples were collected at depths of 0-5, 5-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm. For the overall 0-60 cm layer, correcting the values for soil bulk density, NT significantly increased the stocks of C (18%) and N (16%) and microbial biomass C (35%) and N (23%) (MB-C and -N) in comparison to CT. Microbial basal respiration and microbial quotient (qMic) were also significantly increased under NT. When compared with CT, NT resulted in gains of 0.8 Mg C ha⁻¹ yr⁻¹ (67% of which was in the 0-30 cm layer) and 70 kg N ha⁻¹ yr⁻¹ (73% in the 0-30 cm layer). In the 0-5-cm layer, MB-C was 82% higher with NT than with CT; in addition, the 0-30 cm layer accumulated 70% of the MB-C with NT, and 58% with CT. In comparison to CT, the NT system resulted in total inputs of microbial C and N estimated at 38 kg C ha⁻¹ yr⁻¹ and 1.5 kg N ha⁻¹ yr⁻¹, respectively. Apparently, N was the key nutrient limiting C and N stocks, and since adoption of NT resulted in a significant increase of N in soils which were deficient in N, efforts should be focused on increasing N inputs on NT systems.     

Biochemical analysis of soil organic matter and microbial biomass composition—a pilot study

Biochemical composition of both intracellular (biomass) and extracellular soil organic matter was determined after extraction with 0.5 M K₂SO₄. Extractable carbon, hexoses, pentoses, total reducing sugars, ninhydrin-reactive nitrogen (NRN), proteins and DNA content were colorimetrically determined. The objective of the pilot study was to examine the information potential included in newly measured biochemical characteristics, their environmental variance and the relationships with main soil properties. Correlation analysis and PCA showed independence between biochemical parameters and physico-chemical properties of the soil. Thus, the parameters characterising biochemical composition of the soil biomass and extracellular matter seem to bring new information about the soils beyond the physico-chemical parameters. They also seem to reveal a more detailed view on microbial biomass or extracellular organic matter pool than C_bio or C_ext alone, respectively. The variance, which occurred in biochemical characteristics, also displayed a high discrimination potential between the defined soil categories. Three types of indices were newly proposed: index I (“substrate quantity index”)—the biomass-specific amount of the extracellular organic compounds, index II (“immobilisation ratio”)—the portion of the organic compound immobilised in microbial biomass, and index III (“substrate quality index”)—the extracellular organic compound content related to extracellular organic carbon. The indices displayed a higher potential than both soil biotic and abiotic parameters to discriminate soil characters and soil types.     

Determination of soil microbial biomass phosphorus in acid red soils from southern China

A CHCl₃ fumigation and 0.03 M NH₄F-0.025 M HCl extraction procedure was used to measure microbial biomass P (P_mic) in 11 acid red soils (pH <6.0) from southern China and the results compared to those obtained by the commonly-used CHCl₃ fumigation and 0.5 M NaHCO₃ extraction method. Extraction with NH₄F-HCl was found to be more effective and accurate than NaHCO₃ extraction for detecting the increase of P from microbial biomass P following chloroform fumigation due to its higher efficiency in extracting both native labile phosphate and added phosphate (³²P) in the soils. This was confirmed by the recovery of ³²P from in situ ³²P-labeled soil microbial biomass following fumigation and extraction by the NH₄F-HCl solution. Soil microbial biomass P, measured by the NH₄F-HCl extraction method, was more comparable with soil microbial biomass C (with a more narrow C:P ratio range of 4.3 to 22.3 and a mean of 15.6 in the microbial biomass), than that obtained by NaHCO₃ solution (with a mean C:P ratio of 30.7 and a wide range of 14.9 to 48.9). K_p, the fraction of soil microbial biomass P extracted after CHCl₃ fumigation, by the NH₄F-HCl solution was 0.34. The amount of microbial biomass P determined (using K_p =0.34) was 3–400% (mean 131%) higher than that obtained by the NaHCO₃ extraction (using K_p =0.40) for the 11 red soils studied. The results suggest that the CHCl₃ fumigation and NH₄F-HCl extraction method is more reliable for measuring microbial biomass P than the NaHCO₃ extraction method in acid red soils.     

The significance of microbial biomass sulphur in soil

The soil microbial biomass S fraction of total organic S in soil is considered to be relatively labile and the most active S pool for S turnover in soil. Its significance has been demonstrated in studies of S deficiency in agronomic situations and in those of S pollution from high atmospheric inputs. The utility of the CHCl₃ fumigation-extraction technique for the measurement of microbial S has been proved for a range of soils and conditions. The various methodologies currently available are discussed, including the need for determination of the conversion (K _s) factor. Microbial S values, summarized from the available literature, ranged from 3 to 300 g S g^-1 dry weight soil. They were generally greater in grassland than in arable systems, though the greatest values were obtained in the few examples from forest and peatland soil systems. Microbial S values showed direct relationships with both microbial C and with total soil organic S. Again, there were significant differences between arable and grassland systems. The effect of factors such as organic and inorganic inputs as well as soil physical conditions on microbial S are described. Microbial S turnover rates were estimated from seasonal, ³⁵S-labelling and modelling studies. These rates varied between an approximately annual turnover rate in undisturbed soils up to 80 year^-1 following the addition of readily available substrates. Prospective future research areas are also outlined.     

Size and activity of the soil microbial biomass under grass and arable management

 The effects of 5 years of continuous grass/clover (Cont grass/clover) or grass (Cont grass) pasture or 5 years of annual grass under conventional (Ann grass CT) or zero tillage (Ann grass ZT) were compared with that of 5 years of continuous barley (LT arable) on a site which had previously been under arable crops for 11 years. For added comparison, a long-term grass/clover pasture site (LT past) nearby was also sampled. Soil organic C (C_org) content followed the order LT arable=Ann grass CT<Ann grass ZT<Cont grass=Cont grass/clover<LTpast. Trends with treatment for microbial biomass C (C_mic), basal respiration, flourescein diacetate (FDA) hydrolytic activity, arginine ammonification rate and the activities of dehydrogenase, protease, histidase, acid phosphatase and arylsulphatase enzymes were broadly similar to those for C_org. For C_mic, FDA hydrolysis, arginine ammonification and the activities of histidase, acid phosphatase and arylsulphatase, the percentage increase caused by 5 years of continuous pasture (in comparison with LT arable) was 100–180%, which was considerably greater than that for organic C (i.e. 60%). The microbial metabolic quotient (qCO₂) was higher for the two treatments which were mouldboard ploughed annually (LT arable and Ann grass CT) than for the undisturbed sites. At the undisturbed sites, C_org declined markedly with depth (0–15 cm) and there was a similar stratification in the size and activity of C_mic and enzyme activity. The microbial quotient (C_mic/C_org) declined with depth whilst qCO₂ tended to increase, reflecting a decrease in the proportion of readily available substrate with depth. Received: 7 July 1998     

不同农田生态系统土壤微生物生物量碳的变化研究

试验研究不同农田生态系统土壤微生物生物量碳的变化结果表明,长期单施N、P肥处理对土壤有机碳和微生物生物量碳的影响不明显,施有机肥处理土壤微生物生物量碳及微生物生物量碳/有机碳值均高于其他施肥处理,轮作中引入豆科作物或豆科连作均对土壤微生物生物量碳的积累有显著作用。     

秸秆促腐还田土壤养分及微生物量的动态变化

采用盆钵培养法,通过模拟旱作覆膜条件下秸秆还田,研究了添加不同腐解剂(多个好氧性菌种复合培养而成的F1、富含分解纤维素、半纤维素、木质素和其他生物有机物质的微生物菌群F2、由芽孢杆菌、丝状真菌、放线苗和酵母菌组成的F3)后,小麦秸秆、玉米秸秆在120 d的腐解过程中,土壤养分及土壤微生物量的动态变化特征。结果表明:小麦、玉米秸秆经过120 d的腐解,各处理土壤有机质、碱解氮、全氮的增加速率一致表现为先增加后减小,土壤磷素、钾素的增加速率总体则呈现增-减-增-减的趋势;整个试验阶段小麦秸秆各处理土壤微生物量碳(SMBC)含量表现为先增后减。玉米秸秆土壤SMBC的变化与小麦秸秆差异较大,呈现波浪式变化;玉米秸秆土壤微生物量氮(SMBN)变化在100 d后则与小麦截然不同。秸秆添加腐解剂还田土壤养分增加速率和土壤微生物量碳氮含量均大于秸秆直接还田(对照),培肥土壤效果明显,能够有效增加土壤微生物量碳氮含量。小麦、玉米秸秆添加腐解剂F3的处理各养分含量高于其他处理,即内含具特殊功能的芽孢杆菌、丝状真菌、放线菌和酵母菌的秸秆腐解剂F3增加土壤养分的效果最好;相同腐解剂下不同种类秸秆处理的土壤养分含量表现为:F1,小麦玉米;F2,小麦≥玉米;F3,小麦玉米,即F1对小麦秸秆促腐优势最大,F3对玉米秸秆的促腐作用优于F1和F2,F2对小麦、玉米秸秆的促腐效果基本相似。不同腐解剂下,小麦秸秆处理SMBC、SMBN含量表现为F2F3F1;玉米秸秆处理SMBC含量F2F3≈F1,SMBN为F3F2≈F1。玉米秸秆各处理的SMBC均大于小麦秸秆,SMBN则均小于后者,与秸秆C/N的趋势一致,即C/N越大,SMBC值越大,SMBN值越小。     

Microbial biomass and activity in urban soils contaminated with Zn and Pb

Summary The effects of heavy metals on microbial biomass and activity were investigated in 30 urban soils, contaminated mainly with Zn and Pb to different extents, in terms of the physicochemical and biological characteristics of the soils. Evaluated by simple and multiple regression analyses, the microbial biomass was not affected significantly by easily soluble Zn + Pb (extractable with 0.1 NHCI). The biomass was accounted for as a function of cation exchange capacity (CEC), total organic C and the numbers of fungal colonies present (R ² = 0.692). Carbon dioxide evolution from soils, which reflected microbial activity, was studied on soils incubated with microbial-promoting substrates (glucose and ammonium sulfate) or without. Carbon dioxide evolution was negatively related to Zn+Pb, and this inhibitory effect of the metals was greater in the soils incubated with substrates. Carbon dioxide evolution in soils with substrates was closely related to Zn+Pb, bacterial numbers and the numbers of fungal colonies (R ² = 0.718). Carbon dioxide evolution in soils without substrates was accounted for as a function of Zn + Pb, biomass and the C/N ratio (R ² = 0.511). Using these relationships, the effects of heavy metals on soil microorganisms are discussed in terms of metabolically activated and dormant populations.     

The contribution of biogas residues to soil organic matter formation and CO2 emissions in an arable soil

The biogas production process generates as side-products biogas residues containing microbial biomass which could contribute to soil organic matter formation or induce CO₂ emissions when applied to arable soil as fertilizer. Using an isotope labelling approach, we labelled the microbial biomass in biogas residues, mainly G⁺ bacteria and methanogenic archaea via KH¹³CO₃, and traced the fate of microbial biomass carbon in soil with an incubation experiment lasting 378 days. Within the first seven days, 40% of the carbon was rapidly mineralized and after that point mineralization continued, reaching 65% by the end of the experiment. Carbon mineralization data with 93% recovery could be fitted to a two-pool degradation model which estimated proportions and degradation rate constants of readily and slowly degrading pools. About 49% of the carbon was in the slowly degrading pool with a half-life of 1.9 years, suggesting mid-term contribution to living and non-living soil organic matter formation. Biogas residues caused a priming effect at the beginning, thus their intensive application should be avoided.     

Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico

 The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however, the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation was not due to pollutants nor did microbial biomass:TOC ratios and qCO₂ values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected, however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase in mobility due to higher mineralization rates. Received: 28 April 1999     

Characteristics of microbial biomass and soil organic matter in newly reclaimed wetland rice soils

Microbial biomass C, N, total organic C, N and mineralizable N were measured in newly reclaimed wetland sandy loam rice soil with a very low nutrient status. Microbial biomass C increased 5.4–10.4 times due to application of barnyard manure, but decreased drastically to 24–27% during rice cultivation. Organic C and N contents also decreased during cultivation, but to a lesser extent to 59–76%. At the tillering stage of the rice plant, microbial biomass N was highly correlated with mineralizable N (r=0.986).     

不同碳氮比有机肥对有机农业土壤微生物生物量的影响

有机肥能提高土壤微生物活性, 改善土壤品质。碳氮比是影响有机肥肥效的重要因素。本试验以无肥处理为对照(CK), 设置4个有机肥碳氮比处理(20︰1、15︰1、10︰1、5︰1), 在温室中进行茄子盆栽试验, 定期采集土壤样品, 用熏蒸提取法测定土壤微生物生物量碳(SMBC)、氮(SMBN), 研究等氮条件下不同碳氮比有机肥料对土壤生物活性的影响。试验结果表明, 不同碳氮比的有机肥均能提高土壤的SMBC和SMBN含量, 具体表现为SMBC: 20︰1>10︰1≈15︰1>5︰1>CK, SMBN: 15︰1>10︰1>20︰1>5︰1>CK。SMBC/SMBN的比率反映土壤氮素生物活性, 其值越低, 生物活性越大, 氮素损失越少, 本试验SMBC/SMBN表现为: 15︰1<10︰1<20︰1≈5︰1相似文献   

Impact of agricultural practices on the size and activity of the microbial biomass in a long-term field experiment

The Dehérain long-term field experiment was initiated in 1875 to study the impact of fertilization on a wheat-sugarbeet rotation. In 1987, the rotation was stopped to be replaced by continuous maize. Crop residues were soil-incorporated and the mineral fertilization was doubled in some plots. The impact of those changes on the microbial biomass and activity are presented. In spring 1987, the soil was still in a steady-state condition corresponding to the rotation. The microbial biomass was correlated with total organic C and decreased in the order farmyard manure>mineral NPK>unfertilized control. Microbial specific respiratory activity was higher in the unfertilized treatments. The soil biomass was closely related to soil N plant uptake. In 1989, after 2 years of maize and crop residue incorporation, the steady-state condition corresponding to the previous agricultural practices disappeared. So did the relationship between the biomass and total organic C, and the soil N plant uptake. Biomass specific respiratory activity increased because of low efficiency in the use of maize residues by microbes under N stress.     

Determination of ecophysiological maintenance carbon requirements of soil microorganisms in a dormant state

Summary An experimental approach was attempted for determining the maintenance carbon requirements of the dormant microbial biomass of two agricultural soils (I, II) and one, forest soil (III). The amount of carbon needed for preventing microbial-C loss during incubation expressed as coefficient m (mg glucose-C·mg^-1 biomass-C·h^-1) was 0.00031, 0.00017 and 0.00017 h^-1 at 28°C and 0.000043, 0.000034 and 0.000016 h^-1 at 15°C for soils I, II and III, respectively. Depending on the temperature, the determined m values of the dormant population were two to three orders of magnitude below known values from pure cultures or m values of metabolically activated biomasses under in situ conditions. Corresponding microbial-C loss quotients were comparable to the observed maintenance coefficients but were always above m.The metabolic quotient q for CO₂ (mg CO₂-C·mg^-1 biomass-C·h^-1) of the dormant populations in the three soils tested was at q = 0.0018 h^-1 (22°C) one order of magnitude below metabolically activated cells but did not correspond to the low maintenance values determined, which implies that in addition to possible utilization of native soil organic matter dormant biomasses must largely have an endogenously derived respiratory activity.     

Soil respiration is not limited by reductions in microbial biomass during long-term soil incubations

Declining rates of soil respiration are reliably observed during long-term laboratory incubations. However, the cause of this decline is uncertain. We explored different controls on soil respiration to elucidate the drivers of respiration rate declines during long-term soil incubations. Following a long-term (707 day) incubation (30 °C) of soils from two sites (a cultivated and a forested plot at Kellogg Biological Station, Hickory Corners, MI, USA), soils were significantly depleted of both soil carbon and microbial biomass. To test the ability of these carbon- and biomass-depleted (“incubation-depleted”) soils to respire labile organic matter, we exposed soils to a second, 42 day incubation (30 °C) with and without an addition of plant residues. We controlled for soil carbon and microbial biomass depletion by incubating field fresh (“fresh”) soils with and without an amendment of wheat and corn residues. Although respiration was consistently higher in the fresh versus incubation-depleted soil (2 and 1.2 times higher in the fresh cultivated and fresh forested soil, respectively), the ability to respire substrate did not differ between the fresh and incubation-depleted soils. Further, at the completion of the 42 day incubation, levels of microbial biomass in the incubation-depleted soils remained unchanged, while levels of microbial biomass in the field-fresh soil declined to levels similar to that of the incubation-depleted soils. Extra-cellular enzyme pools in the incubation-depleted soils were sometimes slightly reduced and did not respond to addition of labile substrate and did not limit soil respiration. Our results support the idea that available soil organic matter, rather than a lack microbial biomass and extracellular enzymes, limits soil respiration over the course of long-term incubations. That decomposition of both wheat and corn straw residues did not change after major changes in the soil biomass during extended incubation supports the omission of biomass values from biogeochemical models.     

Effects of pasture improvement and intensive cultivation on microbial biomass,enzyme activities,and composition and size of earthworm populations

We investigated the quantity and distribution of organic C, microbial biomass C, protease, arylsulphatase and arylphosphatase activity, and earthworm numbers and biomass in the soil from a 37-year-old grazed pasture supplied with superphosphate at rates of 0, 188, and 376 kg ha^-1 annually. The results were compared with a non-irrigated wilderness site which had not been used for agriculture and an arable site that had been intensively cultivated for 11 consecutive years. In the 0- to 5-cm layer, organic C followed the trend arableAporrectodea caliginosa (77–89% of total numbers) although Lumbricus rubellus made an increasing contribution to the population with increasing superphosphate rates. In the unirrigated wilderness site the population consisted of 56% A. caliginosa and 44% L. rubellus. While Octolasion cyaneum and A. rosea made up a small proportion of the population in the improved pasture sites, they were not present in the wilderness or arable sites. A. caliginosa was the only species present in the arable site. The mean fresh weight of individuals followed the order arable相似文献   

Responses of soil organic matter and greenhouse gas fluxes to soil management and land use changes in a humid temperate region of southern Europe

We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO₂, CH₄ and N₂O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH₄ uptake rates (<1 kg C ha⁻¹ yr⁻¹) and, coinciding with WFPS values >70%, episodes of CH₄ emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH₄ (4.7 kg C ha⁻¹ yr⁻¹). The N₂O releases at the cropland and pasture sites (2.7 and 4.8 kg N₂O-N ha⁻¹ yr⁻¹) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N₂O-N ha⁻¹ yr⁻¹). The highest N₂O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH₄ and N₂O. On the contrary, afforestation resulted in increases in SOM content and CH₄ uptake, as well as decreases in N₂O emissions.     

Biochemical characterization of urban soil profiles from Stuttgart, Germany

The knowledge of biochemical properties of urban soils can help to understand nutrient cycling in urban areas and provide a database for urban soil management. Soil samples were taken from 10 soil profiles in the city of Stuttgart, Germany, differing in land use—from an essentially undisturbed garden area to highly disturbed high-density and railway areas. A variety of soil biotic (microbial biomass, enzyme activities) and abiotic properties (total organic C, elemental C, total N) were measured up to 1.9 m depth. Soil organic matter was frequently enriched in the subsoil. Microbial biomass in the top horizons ranged from 0.17 to 1.64 g C kg⁻¹, and from 0.01 to 0.30 g N kg⁻¹, respectively. The deepest soil horizon at 170-190 cm, however, contained 0.12 g C kg⁻¹ and 0.05 kg N kg⁻¹ in the microbial biomass. In general, arylsulphatase and urease activity decreased with depth but in three profiles potentially mineralizable N in the deepest horizons was higher than in soil layers directly overlying. In deeply modified urban soils, subsoil beside topsoil properties have to be included in the evaluation of soil quality. This knowledge is essential because consumption of natural soils for housing and traffic has to be reduced by promoting inner city densification.     

4种熏蒸剂处理对土壤可溶性有机氮和微生物量碳氮的影响

采用室内恒温通气培养法,以北京大棚蔬菜地土壤为研究对象,以未使用熏蒸剂土壤为对照,研究4种熏蒸剂[氯化苦(Pic)、1,3-二氯丙烯(1,3-D)、二甲基二硫(DMDS)和威百亩(MS)]对土壤可溶性氮素和微生物量碳、氮的影响。结果表明,4种熏蒸剂处理均能增加土壤中可溶性有机氮的含量,熏蒸处理后敞气0 d时,Pic、MS、DMDS和1,3-D处理的土壤可溶性有机氮累积量分别为47.55 mg·kg-1、42.15 mg·kg-1、40.34 mg·kg-1和32.02 mg·kg-1,较对照(29.97 mg·kg-1)分别增加58.67%、40.65%、34.61%和6.87%。敞气后14~84 d,Pic、DMDS和MS处理DON含量仍持续上升,1,3-D和对照变化不大,各处理之间DON含量差异显著。4种熏蒸剂处理后短时间内,土壤中可溶性氨基酸(DAA)与对照相比大幅上升,在熏蒸后7 d达到最大值,其中Pic处理的上升幅度最大,为12.87 mg·kg-1,对照DAA含量最低,为5.74 mg·kg-1。4种熏蒸剂处理之后,土壤中微生物量碳和氮均呈现急剧下降的趋势,其中Pic处理对微生物的杀灭作用最强,敞气后0 d,Pic处理的微生物量碳和微生物量氮含量分别比对照下降69.39%和70.95%,MS和DMDS次之,1,3-D的杀灭作用最弱。     

长期不同施氮处理玉米根茬的田间分解特性

以7年氮肥定位试验地玉米根茬为研究对象,通过把玉米根茬按2%比例与15 cm和45 cm土层深度的土壤混合后田间埋袋的方法,研究长期不同施氮量处理[分别为0 kg(N)?hm?2、120 kg(N)?hm?2和240 kg(N)?hm?2]的玉米根茬(分别用R0、R120、R240表示),在陕西省长武黑垆土中埋藏分解1 a后对土壤碳、氮组分的影响及根茬有机碳的分解特性。与未添加玉米根茬的对照土壤相比,玉米根茬加入能够显著增加各层土壤的微生物量碳、可溶性有机碳和矿质态氮含量,3种施氮量处理间差异不显著。随着分解时间延长,土壤可溶性有机物中结构相对复杂的芳香类化合物比例逐渐增加。分解1 a后,R0、R120和R240根茬的有机碳残留率在15 cm土层中分别为44.4%、35.3%和34.9%,在45 cm土层中分别为53.3%、44.3%和42.5%。R0根茬的碳残留率显著高于R120和R240;玉米根茬在15 cm土层的碳分解率和分解速率常数显著高于45 cm土层。采用一级动力学方程拟合玉米根茬碳残留率变化结果显示,R0、R120和R240根茬有机碳分解95%所需要的时间在45 cm土层比15cm土层分别长3.2 a、2.3 a和1.9 a。氮肥施用量影响玉米根茬在土壤中的分解特性,在评价农田氮肥施用与土壤固碳时,应考虑不同氮肥用量下残茬养分组成及其在土壤中分解的差异。