温度对不同粘粒含量稻田土壤有机碳矿化的影响

模拟了亚热带地区3种不同粘粒含量的水稻土(砂壤土、壤粘土、粉粘土)在5种温度(10、15、20、25和30℃)下的有机碳(SOC)矿化特征,分析SOC矿化对温度变化的响应.结果表明:在160d的培养期内,温度对3种水稻土SOC矿化量的影响有一定差异,30℃时砂壤土、壤粘土和粉粘土SOC矿化量分别是10℃时的3.5、5.2和4.7倍.在较低温度(≤20℃)下,SOC矿化速度较低且相对稳定;在较高温度(≥25℃)下,前期SOC矿化速度较高,随着培养时间的延长逐渐降低,并趋于稳定.3种水稻土SOC矿化的温度系数(Q10)随培养时间出现波动,砂壤土的Q10平均值最低,为1.92,壤粘土和粉粘土的Q10平均值较接近,分别为2.37和2.32;3种土壤矿化速率常数(k)与温度呈极显著的指数相关(P<0.01).3种水稻土有机碳矿化对温度变化的响应敏感度依次为壤粘土>粉粘土>砂壤土.     

Mineral control of organic carbon mineralization in a range of temperate conifer forest soils

Coupled climate–ecosystem models predict significant alteration of temperate forest biome distribution in response to climate warming. Temperate forest biomes contain approximately 10% of global soil carbon (C) stocks and therefore any change in their distribution may have significant impacts on terrestrial C budgets. Using the Sierra Nevada as a model system for temperate forest soils, we examined the effects of temperature and soil mineralogy on soil C mineralization. We incubated soils from three conifer biomes dominated by ponderosa pine (PP), white fir (WF), and red fir (RF) tree species, on granite (GR), basalt (BS), and andesite (AN) parent materials, at three temperatures (12.5°C, 7.5°C, 5.0°C). AN soils were dominated by noncrystalline materials (allophane, Al‐humus complexes), GR soils by crystalline minerals (kaolinite, vermiculite), and BS soils by a mix of crystalline and noncrystalline materials. Soil C mineralization (ranging from 1.9 to 34.6 [mg C (g soil C)^?1] or 0.1 to 2.3 [mg C (g soil)^?1]) differed significantly between parent materials in all biomes with a general pattern of ANδ¹³C values of respired CO₂ suggest greater decomposition of recalcitrant soil C compounds with increasing temperature, indicating a shift in primary C source utilization with temperature. Our results demonstrate that soil mineralogy moderates soil C mineralization and that soil C response to temperature includes shifts in decomposition rates, mineralizable pool size, and primary C source utilization.     

Interactions between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils

We used long-term laboratory incubations and chemical fractionation to characterize the mineralization dynamics of organic soils from tussock, shrub, and wet meadow tundra communities, to determine the relationship between soil organic matter (SOM) decomposition and chemistry, and to quantify the relative proportions of carbon (C) and nitrogen (N) in tundra SOM that are biologically available for decomposition. In all soils but shrub, we found little decline in respiration rates over 1 year, although soils respired approximately a tenth to a third of total soil C. The lack of decline in respiration rates despite large C losses indicates that the quantity of organic matter available was not controlling respiration and thus suggests that something else was limiting microbial activity. To determine the nature of the respired C, we analyzed soil chemistry before and after the incubation using a peat fractionation scheme. Despite the large losses of soil C, SOM chemistry was relatively unchanged after the incubation. The decomposition dynamics we observed suggest that tundra SOM, which is largely plant detritus, fits within existing concepts of the litter decay continuum. The lack of changes in organic matter chemistry indicates that this material had already decomposed to the point where the breakdown of labile constituents was tied to lignin decomposition. N mineralization was correlated with C mineralization in our study, but shrub soil mineralized more and tussock soil less N than would have been predicted by this correlation. Our results suggest that a large proportion of tundra SOM is potentially mineralizable, despite the fact that decomposition was dependent on lignin breakdown, and that the historical accumulation of organic matter in tundra soils is the result of field conditions unfavorable to decomposition and not the result of fundamental chemical limitations to decomposition. Our study also suggests that the anticipated increases in shrub dominance may substantially alter the dynamics of SOM decomposition in the tundra. Received 31 January 2002; accepted 16 July 2002.     

Carbon sequestration potential of soils in southeast Germany derived from stable soil organic carbon saturation

Sequestration of atmospheric carbon (C) in soils through improved management of forest and agricultural land is considered to have high potential for global CO₂ mitigation. However, the potential of soils to sequester soil organic carbon (SOC) in a stable form, which is limited by the stabilization of SOC against microbial mineralization, is largely unknown. In this study, we estimated the C sequestration potential of soils in southeast Germany by calculating the potential SOC saturation of silt and clay particles according to Hassink [Plant and Soil 191 (1997) 77] on the basis of 516 soil profiles. The determination of the current SOC content of silt and clay fractions for major soil units and land uses allowed an estimation of the C saturation deficit corresponding to the long‐term C sequestration potential. The results showed that cropland soils have a low level of C saturation of around 50% and could store considerable amounts of additional SOC. A relatively high C sequestration potential was also determined for grassland soils. In contrast, forest soils had a low C sequestration potential as they were almost C saturated. A high proportion of sites with a high degree of apparent oversaturation revealed that in acidic, coarse‐textured soils the relation to silt and clay is not suitable to estimate the stable C saturation. A strong correlation of the C saturation deficit with temperature and precipitation allowed a spatial estimation of the C sequestration potential for Bavaria. In total, about 395 Mt CO₂‐equivalents could theoretically be stored in A horizons of cultivated soils – four times the annual emission of greenhouse gases in Bavaria. Although achieving the entire estimated C storage capacity is unrealistic, improved management of cultivated land could contribute significantly to CO₂ mitigation. Moreover, increasing SOC stocks have additional benefits with respect to enhanced soil fertility and agricultural productivity.     

Impact of Atmospheric Nitrogen Deposition on Carbon Dynamics in Two Scots Pine Forest Soils of Northern Germany

The impact of atmospheric N deposition on the dynamics of various carbon fractions was investigated in two Scots pine forest soils (cambisol, podzol) of Northern Germany in microcosm experiments. Total organic carbon (TOC), CO₂ emission, microbial carbon (C_mic) as well as organic hot- and coldwater extractable carbon fractions (C_hwe, C_cwe) were analyzed before, during, and after soil incubation in microcosms, run in three treatments: 0, +45, and +90 kg N ha⁻¹a⁻¹. On both sites, the N treatment showed no response to total organic carbon (TOC) contents in most of the investigated soil layers. Microbial carbon (C_mic) was significantly increased in the organic layer of both soil types by the N application. Subsequent to the N application, the CO₂ emission increased in all mineral soil layers of the cambisol but remained almost unaffected in the podzol. After the N application, a remarkable increase of hotwater extractable C (C_hwe) was detected for the organic layer of the cambisol but not for the podzol, whereas coldwater extractable C (C_cwe) concentrations decreased at both sites. The N application did not have a significant impact on the leachate concentrations of total organic carbon (TOC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in the podzol, whereas the concentrations of these C fractions were decreased in the organic layer and the 35–70~cm mineral soil layer of the cambisol. The N treatment changed the contents of most of the investigated C fractions in both soil types and resulted in a considerable C~mobilization. But the processes of the C~mobilization between the cambisol and the podzol were completely different. According to the presented data, the cambisol obtaining moderate atmospheric N loads is much more sensitive to additional N inputs than the podzol that already received high amounts of atmospheric N.     

Carbon and nitrogen turnover in adjacent grassland and cropland ecosystems

The effects of cultivation and soil texture on net and gross N mineralization, CO₂ evolution and C and N turnover were investigated using paired grassland and cropped sites on soils of three textures. Gross N mineralization and immobilization were measured using¹⁵N-isotope dilution. Grassland soils had high CO₂ evolution and gross N mineralization rates, and low net N mineralization rates. Cropland soils had low CO₂ evolution rates but had high net and gross N mineralization rates. Grassland soils thus had high immobilization rates and cropland soils had low immobilization rates. Cultivation increased N turnover but reduced C turnover. The data suggest that the microflora in grassland soils are N limited, while those of cropland soils are limited by C availability. Increasing clay content reduced N turnover. C turnover was less clearly related to texture. Differences in the immobilization potential of substrates help explain why agricultural soils have higher N losses than do grassland soils.     

Effects of Soil Texture on Belowground Carbon and Nutrient Storage in a Lowland Amazonian Forest Ecosystem

Soil texture plays a key role in belowground C storage in forest ecosystems and strongly influences nutrient availability and retention, particularly in highly weathered soils. We used field data and the Century ecosystem model to explore the role of soil texture in belowground C storage, nutrient pool sizes, and N fluxes in highly weathered soils in an Amazonian forest ecosystem. Our field results showed that sandy soils stored approximately 113 Mg C ha^-1 to a 1-m depth versus 101 Mg C ha^-1 in clay soils. Coarse root C represented a large and significant ecosystem C pool, amounting to 62% and 48% of the surface soil C pool on sands and clays, respectively, and 34% and 22% of the soil C pool on sands and clays to 1-m depth. The quantity of labile soil P, the soil C:N ratio, and live and dead fine root biomass in the 0–10-cm soil depth decreased along a gradient from sands to clays, whereas the opposite trend was observed for total P, mineral N, potential N mineralization, and denitrification enzyme activity. The Century model was able to predict the observed trends in surface soil C and N in loams and sands but underestimated C and N pools in the sands by approximately 45%. The model predicted that total belowground C (0–20 cm depth) in sands would be approximately half that of the clays, in contrast to the 89% we measured. This discrepancy is likely to be due to an underestimation of the role of belowground C allocation with low litter quality in sands, as well as an overestimation of the role of physical C protection by clays in this ecosystem. Changes in P and water availability had little effect on model outputs, whereas adding N greatly increased soil organic matter pools and productivity, illustrating the need for further integration of model structure and tropical forest biogeochemical cycling. Received 3 March 1999; accepted 27 August 1999.     

喀斯特森林植被自然恢复过程中土壤可矿化碳库特征

2011年9月,采用空间代替时间方法,研究了茂兰自然保护区喀斯特森林自然恢复过程中土壤可矿化碳库的特征.结果表明: 研究期间,喀斯特森林自然恢复过程中不同深度土壤的总有机碳含量、可矿化碳含量和矿化速率随土层加深而减少,随恢复的进程而增加;累积矿化排放量及其速率随恢复的进程增加,其速率随培养时间延长而减小;矿化率随恢复的进程增加,而随土层加深的变化不明显;qCO₂值随恢复的进程和土层加深而递减;土壤可矿化碳与凋落物现存量及其分解质量损失率分别呈负相关(r=-0.796)和正相关(r=0.924);土壤生境由早期干扰强烈转向中后期日趋稳定,土壤的固碳能力由早期差、潜力大转向中后期强、潜力小.     

Soil fertility status under shifting cultivation in East Kalimantan with special reference to mineralization patterns of labile organic matter

We investigated soil fertility status under shifting cultivation in East Kalimantan with special reference to mineralization patterns of labile soil organic matter (SOM). The soils in this region were generally strongly acidic with high Al, low bases and low pH values. A 133-day incubation experiment using fresh soils revealed that NH₄ ⁺ often accumulated during the course of N mineralization, indicating a delay of nitrification relative to N mineralization in these soils. Principal component analysis followed by stepwise multiple linear regression showed the contribution of soil physicochemical properties to mineralization patterns of SOM. Those results indicated that the overall SOM level positively contributed to the amount of readily mineralizable C and N, NH₄ at day 133, and NO₃ at day 133. The results also showed that the factors relating to soil acidity and P and K depletion, as well as accumulation of readily mineralizable C, contributed to suppress nitrification and accelerate NH₄ ⁺ accumulation and possibly subsequent N immobilization. Our results suggest that it will be difficult to establish a cropping system without a long period of fallow unless very high amounts of fertilizer as well as liming are applied in these regions.     

华南典型人工林土壤有机碳库及其稳定性特征研究

研究了华南地区4种25年林龄的典型人工林土壤有机碳库及其稳定性特征。测定了林内0～10 cm和10～20 cm层土壤的有机碳(Total organic carbon,TOC)含量、易分解碳库/稳定性碳库大小以及土壤微生物生物量碳。结果表明,4种林型土壤TOC含量为:马占相思林大叶相思林湿地松林荷木林,其中豆科人工林(马占相思和大叶相思林)的TOC含量显著高于非豆科人工林(湿地松和荷木林)。在表土层(0～10 cm),荷木林易分解碳库最大(7.80 mg g-1),易分解性碳潜在周转时间最短(49 d),马占相思林易分解碳库最小(2.14 mg g-1),占总碳量也最小(8.63%),说明马占相思林土壤有机碳库比其它人工林具有更好的稳定性。4种人工林表土层土壤微生物量碳含量为马占相思林湿地松林大叶相思林荷木林,马占相思林显著高于其它3种人工林,表土层微生物量碳含量格局与土壤有机碳含量相似,较高的微生物量有利于更多的枯枝落叶转化为土壤有机碳。在亚表土层(10～20 cm),大叶相思林土壤微生物量碳最大,马占相思林最小,与表土层的格局相反,但亚表土层微生物碳总含量并不高。因而,人工林土壤有机碳积累水平与土壤有机碳的稳定性及表层土壤微生物量有关。     

Carbon mineralization characteristics of compost made from pruning material

To investigate carbon (C) mineralization characteristics of compost made from pruning material (PM), C mineralization parameters were evaluated, including mineralizable C (C₀), apparent activation energy (E_a), and the rate constant of mineralization (k). These properties were also examined in conventional composts made from dung (D), fallen leaves (L), and bark (B). No significant differences among the plant composts (L, B and PM) were observed for E_a. Notably, the values of the respective indicators were significantly greater in PM, L and B than in D. The C₀ of PM was significantly greater than that of the other composts. Conversely, the k-value for PM was significantly smaller than that for the other composts. These results indicate that PM supplies a substantial amount of mineralizable C that persists for a long time after the PM has been mixed with soil.

     

Incubation experiments on nitrogen mineralization in loess and sandy soils

Summary In aerobic incubation experiments, nitrogen mineralization was investigated in agricultural loess and sandy soils. Fresh, fieldmoist samples were used for incubation. Using an optimization procedure the N-mineralization was split into two nitrogen fractions: A resistant, slowly decomposable organic N-fraction (index rpm) and a fast decomposable N-fraction (index dpm).Loess- and sandy soils showed similar mean reaction coefficients for N-mineralization. The results also indicated that the amount of mineralizable nitrogen in the resistant N-fraction depended directly on clay content.Soil sampling at different times during crop growing period gave different mineralization amounts and courses.Effect of added plant residues on N-mineralization, was also studied by incubation. Variation of type and quantity of added residues changed the net N-mineralization in a characteristic way: Sugar beet leaves, added in minced form, caused an increase in mineralization; while straw caused a temporary immobilization, followed by remineralization.Incubation experiments on undisturbed soil columns showed nearly linear mineralization with time.This paper was presented in part at the 1983 Congress of the German Soil Science Society held at Trier.     

不同退化沙地土壤碳的矿化潜力

通过实验室土壤培养试验 ,研究了科尔沁退化沙质草地不同生境 (流动沙地 ,半固定沙地 ,固定沙地和丘间低地 )下土壤碳的矿化潜力及不同凋落物在沙地土壤中的分解。经 33d的室内培养 ,不同生境土壤 CO2 - C的释放有极显著的差异 ,与生境植被盖度 ,凋落物积累 ,土壤沙化程度 ,土壤有机碳和全氮含量的分布有显著相关。流动沙地土壤有极低的土壤有机碳和氮的含量及其微弱的土壤微生物呼吸 ,表明土地沙漠化不仅导致土壤有机碳库衰竭 ,也使土壤微生物活性丧失。在有机质含量很低的流动沙地和半固定沙地土壤中 ,含氮量高的小叶锦鸡儿 (Caragana microphylla)凋落物比含氮量低、C/N比高的差巴嘎蒿(Artemisia halodendron)和 1年生植物凋落物有较快的分解。在沙漠化的演变中 ,土壤的粗粒化 ,有机物质和养分及微生物活性的丧失制约着凋落物在土壤中的矿化潜力。灌木的存在使更多的有机物质和养分积聚在灌丛下 ,形成灌丛肥岛 ,因而显著贡献于碳的固存。     

The retention of organic matter in soils

The turnover of C in soils is controlled mainly by water regimes and temperature, but is modified by factors such as size and physicochemical properties of C additions in litter or root systems, distribution of C throughout the soil as root systems, or addition as litter, distribution of C within the soil matrix and its interaction with clay surfaces.Soil factors which retard mineralization of C in soils are identified from correlations of C contents of soils with other properties such as clay content and base status. The rate and extent of C mineralization depends on the chemistry of the added organic matter and interaction with clays of the microbial biomass and metabolites.The organomineral interactions are shown to depend on cation bridges involving mainly Ca in neutral to alkaline soils, Al in acid soils and adsorption of organic materials on iron oxide surfaces. The various organomineral interactions lead to aggregations of clay particles and organic materials, which stabilizes both soil structure and the carbon compounds within the aggregates.     

20th Century Carbon Budget of Forest Soils in the Alps

Dendrochronological studies and forest inventory surveys have reported increased growth and biospheric carbon (C) sequestration for European forests in the recent past. The potential of concomitant changes in forest soil C stocks are not accounted for in the IPCC guidelines for national greenhouse gas inventories. We developed a model-based approach to address this problem and assess the role of soils in forest C balance in the European Alps. The decomposition model FORCLIM-D was driven by long-term (that is, 1900–1985 AD) litter input scenarios constructed from forest inventory data, region-specific dendrochronological basal area indices, and time series of anthropogenic litter removal. The effect of spatial climate variability on organic matter decomposition across the case study region (Switzerland) was explicitly accounted for by constant long-term annual means of actual evapotranspiration and temperature. Uncertainties in forest development, litter removal, fine root litter input, and dynamics of forest soil C were studied by an explorative factorial sensitivity analysis. We found that forest soils contribute substantially to the biospheric C sequestration for Switzerland: Our “best estimate” yielded an increase of 0.35 Mt C/y or 0.33 t C/(ha y) in forest soils for 1985, that is, 27% of the C sequestered by forest trees (BUWAL 1994). Uncertainties regarding C accumulation in forest soils were substantial (0.11–0.58 Mt C/y) but could be reduced by estimating forest soil C stocks in the future. Whereas soils can be important for the C balance in naturally regrowing forests, their C sequestration is negligible (less than 5%) relative to anthropogenic CO₂ emissions in Western Europe at present. Received 25 August 1998; accepted 17 March 1999.     

Dissolved Organic Carbon in Terrestrial Ecosystems: Synthesis and a Model

The movement of dissolved organic carbon (DOC) through soils is an important process for the transport of carbon within ecosystems and the formation of soil organic matter. In some cases, DOC fluxes may also contribute to the carbon balance of terrestrial ecosystems; in most ecosystems, they are an important source of energy, carbon, and nutrient transfers from terrestrial to aquatic ecosystems. Despite their importance for terrestrial and aquatic biogeochemistry, these fluxes are rarely represented in conceptual or numerical models of terrestrial biogeochemistry. In part, this is due to the lack of a comprehensive understanding of the suite of processes that control DOC dynamics in soils. In this article, we synthesize information on the geochemical and biological factors that control DOC fluxes through soils. We focus on conceptual issues and quantitative evaluations of key process rates to present a general numerical model of DOC dynamics. We then test the sensitivity of the model to variation in the controlling parameters to highlight both the significance of DOC fluxes to terrestrial carbon processes and the key uncertainties that require additional experiments and data. Simulation model results indicate the importance of representing both root carbon inputs and soluble carbon fluxes to predict the quantity and distribution of soil carbon in soil layers. For a test case in a temperate forest, DOC contributed 25% of the total soil profile carbon, whereas roots provided the remainder. The analysis also shows that physical factors—most notably, sorption dynamics and hydrology—play the dominant role in regulating DOC losses from terrestrial ecosystems but that interactions between hydrology and microbial–DOC relationships are important in regulating the fluxes of DOC in the litter and surface soil horizons. The model also indicates that DOC fluxes to deeper soil layers can support a large fraction (up to 30%) of microbial activity below 40 cm. Received 14 January 2000; accepted 6 September 2000     

Increase in pH stimulates mineralization of ‘native’ organic carbon and nitrogen in naturally salt-affected sandy soils

Large amounts of terrestrial organic C and N reserves lie in salt-affected environments, and their dynamics are not well understood. This study was conducted to investigate how the contents and dynamics of ‘native’ organic C and N in sandy soils under different plant species found in a salt-affected ecosystem were related to salinity and pH. Increasing soil pH was associated with significant decreases in total soil organic C and C/N ratio; particulate (0.05–2 mm) organic C, N and C/N; and the C/N ratio in mineral-associated (<0.05 mm) fraction. In addition, mineral-associated organic C and N significantly increased with an increase in clay content of sandy soils. During 90-day incubation, total CO₂-C production per unit of soil organic C was dependent on pH [CO₂-C production (g kg⁻¹ organic C) = 22.5 pH – 119, R ² = 0.79]. Similarly, increased pH was associated with increased release of mineral N from soils during 10-day incubation. Soil microbial biomass C and N were also positively related to pH. Metabolic quotient increased with an increase in soil pH, suggesting that increasing alkalinity in the salt-affected soil favoured the survival of a bacterial-dominated microbial community with low assimilation efficiency of organic C. As a result, increased CO₂-C and mineral N were produced in alkaline saline soils (pH up to 10.0). This pH-stimulated mineralization of organic C and N mainly occurred in particulate but not in mineral-associated organic matter fractions. Our findings imply that, in addition to decreased plant productivity and the litter input, pH-stimulated mineralization of organic matter would also be responsible for a decreased amount of organic matter in alkaline salt-affected sandy soils.     

Importance of Environmental Black Carbon to Dissolved Petroleum Hydrocarbons Sorption on Soil

Importance of environmental black carbon (BC) to sorption of dissolved petroleum hydrocarbons (DPH) on two soils with high BC:TOC ratios (33% and 11%, respectively) was evaluated at a relatively high concentrations (mg/L ～ μ g/L range). Sorption isotherms of DPH were determined for the two original soils and soils combusted at 375°C (only BC). The sorption isotherms of the original soils were linear, whereas the isotherms of the combusted soils were highly nonlinear (n _F = 0.45, 0.60). It is indicated that intrinsic BC-water sorption coefficient is not possible to be used to estimate total sorption to the original soil, even in our relatively high concentrations. From the sorption isotherms, Freundlich coefficient of environmental BC sorption, K _F,BC ^env of 10 ^{2.55 ± 0.21} was calculated and could be used as a generic starting point for environmental modeling purposes. From the data, it could be deduced that BC was responsible for 50% of the total sorption at concentrations of 45 and 4 μ g/L (μ g/L range), which were significantly higher than literature concentrations (ng/L range). These results demonstrate that in soil with high BC:TOC ratio BC is the most important geosorbent constituent with respect to sorption of DPH at relatively high concentrations ranged in μ g/L.     

Microbial characteristics of soils on a latitudinal transect in Siberia

Soil microbial properties were studied from localities on a transect along the Yenisei River, Central Siberia. The 1000 km‐long transect, from 56°N to 68°N, passed through tundra, taiga and pine forest characteristic of Northern Russia. Soil microbial properties were characterized by dehydrogenase activity, microbial biomass, composition of microbial community (PLFAs), respiration rates, denitrification and N mineralization rates. Relationships between vegetation, latitude, soil quality (pH, texture), soil organic carbon (SOC) and the microbial properties were examined using multivariate analysis. In addition, the temperature responses of microbial growth (net growth rate) and activity (soil respiration rate) were tested by laboratory experiments. The major conclusions of the study are as follows: 1. Multivariate analysis of the data revealed significant differences in microbial activity. SOC clay content was positively related to clay content. Soil texture and SOC exhibited the dominant effect on soil microbial parameters, while the vegetation and climatic effects (expressed as a function of latitude) were weaker but still significant. The effect of vegetation cover is linked to SOC quality, which can control soil microbial activity. 2. When compared to fine‐textured soils, coarse‐textured soils have (i) proportionally more SOC bound in microbial biomass, which might result in higher susceptibility of SOC transformation to fluctuation of environmental factors, and (ii) low mineralization potential, but with a substantial part of the consumed C being transformed to microbial products. 3. The soil microbial community from the northernmost study region located within the permafrost zone appears to be adapted to cold conditions. As a result, microbial net growth rate became negative when temperature rose above 5 °C and C mineralization then exceeded C accumulation.     

Long-term effects of continuous direct seeding mulch-based cropping systems on soil nitrogen supply in the Cerrado region of Brazil

In the Cerrado region of Brazil conventional soybean monoculture is since the 1980s being replaced by direct seeding mulch-based cropping (DMC) with two crops per year and absence of tillage practices. The objective of this study was to assess the long-term impact of DMC on soil organic matter accumulation and nitrogen (N) mineralization. Measurements of soil organic carbon (C) content, soil total N content and soil N mineralization, both under laboratory conditions using disturbed soil samples and under field conditions using intact soil cores were conducted on a chronosequence of 2-, 6-, 9- and 14-year-old DMC fields (DMC-2, DMC-6, DMC-9 and DMC-14, respectively). The average increase of organic C in the 0–30 cm topsoil layer under DMC was 1.91 Mg C ha⁻¹ year⁻¹. Soil total N increased with 103 kg N ha⁻¹ year⁻¹ (0–30 cm). The potential N mineralization rate under laboratory conditions (28°C, 75% of soil moisture at field capacity) was 0.27, 0.28, 0.39 and 0.36 mg N kg soil⁻¹ day⁻¹ for, respectively, the DMC-2, DMC-6, DMC-9 and DMC-14 soils. The corresponding specific N mineralization rates were 0.16, 0.15, 0.22 and 0.17 mg N g N⁻¹ day⁻¹. There was no obvious explanation for the higher specific N mineralization rate of soils under DMC-9, given the similar soil conditions and land-use history before DMC was introduced. Results from the in situ N incubation experiments were in good agreement with those from the laboratory incubations. We estimated that soil N mineralization increases with about 2.0 kg N ha⁻¹ year⁻¹ under DMC. The increase was mainly attributed to the larger soil total N content. These results indicate that even in the medium term (10 years), continuous DMC cropping has limited implications for N fertilization recommendations, since the extra soil N supply represents less than 20% of the common N fertilization dose for maize in the region.