Methods to Estimate Aggregate Protected Soil Organic Carbon, 2: Does the Grinding of the Plant Residues Affect the Estimations of the Aggregate Protected Soil Organic Carbon?

A method to estimate the amount of soil organic carbon (SOC) physically protected within macroaggregates (>200 μm) consists of crushing soil samples and measuring the following SOC mineralization increase. This study investigated the effect of grinding the plant residues during soil crushing on the calculated amount of the protected SOC on two tropical soils (Arenosol and Ferralsol). Incubations of crushed and uncrushed soil samples amended with ground or unground plant residues were conducted. Our results showed that soil crushing increased SOC mineralization and that the presence of plant residues enhanced soil respiration also. The plant residues of the two soils had different decomposition rates, but grinding plant residues did not increase the amounts of cumulative carbon (C) mineralized after the 28 days of the experiment. We propose that the extra C mineralized after soil crushing is due to the breakdown of the soil structure and not to the grinding of plant residues.     

Nitrogen Mineralization Potential as Influenced by Microbial Biomass,Cotton Residues and Temperature

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha^?1 in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.) residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO₂) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.     

Nitrogen and carbon mineralization of surface-applied and incorporated winter wheat and peanut residues

Laboratory incubation experiments were conducted to study the C and N mineralization dynamics of crop residues (fine roots and straw) of the two main crops (winter wheat and peanut) in the Chinese Loess Plateau under different ways of incorporation. The C mineralization patterns of the soil amended with winter wheat residues differed greatly, and the highest C mineralization was observed in the treatment with winter wheat straw incorporated (39% of the total added C mineralized). The way of straw placement had only a minor effect on the pattern of C mineralization for peanut. Generally, winter wheat residues showed a stronger immobilization than peanut residues during the incubation period, without any net N release. Winter wheat straw incorporated showed the strongest N immobilization with 35 mg kg⁻¹ (equivalent to 27% of added N) immobilized at the eighth week. This study indicated that retaining crop residues at the soil surface in the dry land soils of the Chinese Loess Plateau is beneficial for C sequestration. It also showed that N immobilization occurs only during a limited period of time, sufficient to prevent part of the mineral N pool from leaching, and that net N mineralization can be expected during the subsequent cropping season, thus enhancing synchronization of N supply and demand.     

Sulfur mineralization in two soils amended with organic manures,crop residues,and green manures

The mineralization of sulfur (S) was investigated in a Vertisol and an Inceptisol amended with organic manures, green manures, and crop residues. Field‐moist soils amended with 10 g kg^—1 of organic materials were mixed with glass beads, placed in pyrex leaching tubes, leached with 0.01 M CaCl₂ to remove the mineral S and incubated at 30 °C. The leachates were collected every fortnight for 16 weeks and analyzed for SO₄‐S. The amount of S mineralized in control and in manure‐amended soils was highest in the first week and decreased steadily thereafter. The total S mineralized in amended soils varied considerably depending on the type of organic materials incorporated and soil used. The cumulative amounts of S mineralized in amended soils ranged from 6.98 mg S (kg soil)^—1 in Inceptisol amended with wheat straw to 34.38 mg S (kg soil)^—1 in Vertisol amended with farmyard manure (FYM). Expressed as a percentage of the S added to soils, the S mineralized was higher in FYM treated soils (63.5 to 67.3 %) as compared to poultry manure amended soils (60.5 to 62.3 %). Similarly the percentage of S mineralization from subabul (Leucaena leucocephala) loppings was higher (53.6 to 55.5 %) than that from gliricidia (Gliricidia sepium) loppings (50.3 to 51.1 %). Regression analysis clearly indicated the dependence of S mineralization on the C : S ratio of the organic materials added to soil. The addition of organic amendments resulted in net immobilization of S when the C : S ratio was above 290:1 in Vertisol and 349:1 in Inceptisol. The mineralizable S pool (S_o) and first‐order rate constant (k) varied considerably among the different types of organic materials added and soil. The S_o values of FYM treated soils were higher than in subabul, gliricidia, and poultry manure treated soils.     

Effects of Temperature,Moisture, and Chemical Composition of Organic Substrates on C Mineralization in Soils

Laboratory experiments were conducted to (i) study the influence of chemical composition of organic substrates (green manure, rice straw, wheat straw, and farmyard manure) and temperature on carbon (C) mineralization under flooded and nonflooded moisture conditions, (ii) study the relationship between C mineralization and chemical composition of organic materials, and (iii) model C mineralization kinetics under different temperature and moisture conditions. The proportion of added C mineralized under nonflooded conditions ranged between 45 and 66% at 35 °C compared to 18 to 42% at 15 °C. Flooding the soil reduced the proportion of added C mineralized, which ranged between 25 to 47% at 35 °C and 6 to 20% at 15 °C. Water-soluble components, cellulose, lignin, and nitrogen content of the organic source significantly influenced C mineralization. Temperature sensitivity of decomposition depended on the quality of the organic substrate with relatively less decomposable farmyard manure (FYM) being more sensitive (Q₁₀ ?3.0) than the easily decomposable green manure (Q₁₀ ?2.5). A first-order monocomponent model that is based on relative rate of mineralization and includes a parameter for speed of aging best described C mineralization under both the temperature and moisture conditions. It was concluded that FYM with preponderance of recalcitrant components and low decomposability provides greater C sequestration potential than green manure and crop residues.     

Carbon mineralization in soils of different textures as affected by water-soluble organic carbon extracted from composted dairy manure

The water-soluble organic C in composted manure contains a portion of labile C which can stimulate soil microbial activity. The objective of this experiment was to evaluate the effects of water-soluble organic C extracted from composted dairy manure on C mineralization in soil with different textures. Three soils with textures varying from 3 to 54% clay were amended with 0 to 80 mg water-soluble organic C kg^–1 soil extracted from a composted dairy manure and incubated for 16 weeks at 23°C. The total amount of C mineralized was greater than the amount of C added in the three soils. Differences in mineralizable C with and without added water-soluble organic C were approximately 13–16 times, 4.8–8 times, and 7.5–8 times greater than the amount of C added to clay, loam, and sand soils, respectively. The results of this experiment suggest that immediately following composted manure applications, C mineralization rates increase, and that most of the C mineralized comes mainly from the indigenous soil organic C pool.CLBRR contribution No. 94-71     

Management of N mineralization from crop residues of high N content using amendment materials of varying quality

Abstract. A potential technique for reducing overwinter leaching from high N containing crop residues is to immobilize the N released during decomposition by co-incorporating materials of a wider C : N ratio. This article describes the use of laboratory incubation experiments to investigate the effects of a wide range of such amendment materials on the mineralization of N from sugar beet and brassica leaf residues in a sandy loam and a silt loam. These materials were of varying quality, with C : N ratio ranging from 15 : 1 to 520 : 1, and cellulose content from 0 to 34%. Amendments were added at a fixed rate of 3.5 mg C g⁻¹ of dry soil, equivalent to around 10 t ha⁻¹ C (to 20 cm depth). The soils were then incubated at 15°C, and net mineral N derived from the leaves was measured at regular intervals over 168 days. Net mineralization of residue N was greatest with molasses (C : N ratio of 18 : 1), whereas paper waste (C : N ratio of 520 : 1) reduced N mineralized by up to 90% compared with a soil-only control. As the concentration of cellulose and lignin in the amendment materials increased, so the amounts of N mineralized decreased, with 62 and 54% of variance in N mineralized explained by cellulose and lignin content, respectively. Reduced levels of mineral N were associated with higher levels of biomass-N. The levels of N₂O-N lost from sugar beet residues on day 14 were significantly reduced from 66 to 5 g ha⁻¹ where compactor (cardboard) waste had been mixed into sandy loam, but this effect was not observed in the silt loam. These techniques could lead to greater efficiency of N use in rotations through reduction in N losses, and provide alternative routes for disposal of wastes when the EC Landfill Directive is implemented.     

Organic carbon dynamics in soils with pyrogenic organic matter that received plant residue additions over seven years

The effect of repeated application of plant residues on mineralization of different organic carbon (OC) pools in a pyrogenic organic matter (PyOM) amended soil was determined using an incubation study conducted over 7.1 years. At five occasions during this period, sugarcane residues (C₄) were mixed with the soil (C₄) with or without PyOM (C₃) amendments. Organic C mineralized during the incubation period or remaining in different physical soil fractions after 7.1 years was partitioned into PyOM carbon (PyOM-C) and native soil organic matter C (nSOM-C) or sugarcane C plus nSOM-C (SC-C + nSOM-C). When compared to the control, total cumulative OC (comprising both nSOM-C and PyOM-C) mineralized in the presence of PyOM was 40% higher after the first 2.5 years, but equal by 6.2 years and 3% lower by the end of the incubation period. The cumulative nSOM mineralization after 7.1 years was 2.57 mg CO₂–C g⁻¹ soil with PyOM compared to 3.16 mg CO₂–C g⁻¹ soil without PyOM addition (p = 0.13; n = 3). More than 60% of the added PyOM-C was present in the free-light fraction by the end of the 7.1 years. In total, 93% of the added PyOM-C remained in soil compared to 25–28% of SC-C + nSOM-C. Sugarcane residues increased the remaining PyOM-C in the occluded-light fraction by 3% (p < 0.05) and in the organo-mineral fraction by 4% (p < 0.1), suggesting a possible preferential use of SC-C or accumulation of metabolites of decomposed PyOM. However, the addition of sugarcane had no significant effect on overall mineralization of PyOM. The presence of PyOM accelerated the mineralization of SC-C + nSOM-C by 9% (p < 0.001). This is probably due to enhanced mineralization of sugarcane residues rather than native SOM. Although PyOM was likely to accelerate mineralization of added plant residues throughout a 7-year period, PyOM did not increase cumulative nSOM mineralization when plant residues were absent (p > 0.05), so PyOM may reduce nSOM mineralization in the long term.     

Effect of organic manures,crop residues and green manure (Sesbania aculeata) on nitrogen and phosphorus transformations in a sandy loam at field capacity and under waterlogged conditions

Summary The influence of the water regime on mineralization and immobilization of N and P was investigated in a calcareous sandy loam incubated with cattle, poultry and green manure (Sesbania aculeata), and wheat and rice straw in a pot experiment. At field capacity, N released from poultry and green manure during the first 4 weeks of incubation was 45% and 59%, respectively. During the next 12 weeks, only around 40% more organic N was mineralized from both sources. In contrast, addition of cattle manure resulted in a period of net N immobilization lasting up to 4 weeks. By the end of 16 weeks of incubation only about 19010 of the added N was mineralized. High rates of N immobilization were observed during the first 4 weeks of incubation of rice or wheat straw with C/N ratios of 78 and 85, respectively. The N mineralization kinetics of poultry and green manure and of untreated soil showed an initial fast reaction followed by a slow release of inorganic N and could be described by two simultaneous first-order reactions. Under waterlogged conditions mineralized N was lost simultaneously in significant amounts possibly through nitrification — denitrification reactions. At field capacity, the largest amount of Olsen P was accumulated in the soil amended with poultry manure, followed by cattle manure. Results from other treatments did not differ much from those of the untreated soil. About 15% of P from poultry manure was mineralized during the 1st week of incubation. In contrast to the field-capacity moisture regime, marked increases in Olsen P in the soils amended with green manure and crop residues were observed under water-logged conditions.     

Mineralization and changes in microbial biomass in water-saturated soil amended with some tropical plant residues

An incubation experiment was conducted in the laboratory at 25 and 35°C during 56 d to analyze the mineralization patterns and the changes in microbial biomass in water-saturated soils amended with 6 types of organic materials (O.M.) including residues from 4 tropical plants. C and N mineralization in amended and non-amended soils was influenced by the temperature, A significantly positive correlation was observed between C mineralization and the amount of hexoses of the amended O.M. regardless of the period of incubation. A negative relationship between the N mineralized from amended O.M. and C/N ratios and the amounts of cellulose plus hemicellulose of the added O.M. was observed during the period of maximum mineralization on the 49th day at 25°C. The critical C/N ratio value for N mineralization and immobilization was observed in dhaincha (15.7) and cowpea (22.0).

The pattern of changes in microbial biomass C and N was almost similar at both 25 and 35°C. The amount of biomass C and N gradually increased up to a period of 28 to 42 d and thereafter decreased gradually. A significant increase in the amount of biomass C and N was observed in O.M. amended soils over the control. The contribution of rice straw and cowpea to biomass C formation was significantly larger than that of other O.M. at the end of incubation (56 d). In the case of biomass N, the contribution of rice straw was significantly larger than that of other O.M. except for azolla at 25°C and cowpea at 35°C. The significant contribution of rice straw and cowpea to biomass formation suggests that microbial biomass remaining in soil on the 56th day had been influenced by the combination of a larger amount of cellulose plus hemicellulose and higher C/N ratio in plant residues.     

金沙江干涸峡谷中6种固氮绿篱品种剪枝中氮的矿化研究

A litterbag experiment of 12 weeks was conducted to study nitrogen mineralization process of prunings of six nitrogen-fixing hedgerow species in a dry valley of the Jinsha River. Prunings were incorporated into soil or used as mulch. The results indicated that pruning N of the six hedgerow species was mineralized fast in the first week and then decreased slowly in the rest of the study period. When prunings were incorporated into soil, the amount of nitrogen mineralized by the end of the first week accounted for 69.9%, 58.2%, 54.5%, 43.0%, 29.6% and 20.6% of the total N in prunings of Desmodium rensonii, Tephrosia candida, Leucaena leucocephala, Albizia yunnanensis, Acacia dealbata, and Acacia mearnsii, respectively. When prunings of L. leucocephala were used as mulch materials, the amount of nitrogen mineralized in the first week was 16.2% less than that of prunings incorporated into soil. The mineralization pattern of pruning N could be simulated by an exponent model N_t% = N₀₁% (1 -exp(-k₁t)) + N₀₂% (1-exp (-k₂t)) where N_t% is cumulative mineralized N in time t, N₀₁% and N₀₂% are readily and less readily mineralizable N in prunings, respectively, and k₁ and k₂ are rate constants. A half-life period of pruning nitrogen mineralization could also be determined by this model. The nitrogen content in the pruning residues decreased quickly in the first week but fluctuated thereafter. The initial C/N ratio was negatively related to the mineralization rate of prunings.     

养分化学计量比对稻田土壤葡萄糖矿化及其激发效应的影响

选择13C-葡萄糖作为稻田土壤典型易利用态外源有机碳,通过室内培养试验,研究不同C/N/P/S计量比条件下,葡萄糖分解矿化的动态规律及其激发效应。结果表明,稻田土壤中葡萄糖-碳(C)快速矿化,60 d培养实验后,有65.5%~74.6%的葡萄糖-C矿化。养分元素的添加使土壤中葡萄糖-C快速转化碳库的比例逐渐由58%增加至65%,从而使葡萄糖-C矿化率提高了3.9%~12.5%,养分元素的添加量与葡萄糖-C快速转化碳库的比例和矿化率均表现出显著的正相关关系(R2=0.63,p0.05;R2=0.83,p0.05)。葡萄糖-C矿化过程中,导致稻田土壤碳的累积负激发效应为-370~-570 mg kg-1,养分元素添加比例越大,其负激发效应越强,二者呈显著的负相关性(R2=0.66,p0.05)。研究表明,稻田土壤中易利用态碳的矿化受C/N/P/S元素计量比的影响,高比例养分元素的添加,促进土壤中易利用态碳的矿化,抑制土壤原有有机质的分解,增强负激发效应。本研究可为深入了解稻田生态系统碳循环、实现农田土壤肥力提升和温室气体减排提供理论依据。     

Fate of nitrogen from crop residues as affected by biochemical quality and the microbial biomass

Net mineralization of N from a range of shoot and root materials was determined over a period of 6 months following incorporation into a sandy-loam soil under controlled environment conditions. Biochemical “quality” components of the materials showed better correlation with net N mineralization than did gross measures of the respiration and N content of the soil microbial community during decomposition. The quality components controlling net N mineralization changed during decomposition, with water-soluble phenolic content significantly correlated with net N mineralization at early stages, and water-soluble N, followed by cellulose at later stages. C-to-N and total N were correlated with net N mineralization towards the end of the incubation only. Cumulative microbial respiration during the early stages of decomposition was correlated with net N mineralization measured after 2 months, at which time maximum net N mineralization was recorded for most residues. However, there was no relationship between microbial-N and net N mineralization. Biochemical quality factors controlling the C and N content of the residue remaining at the end of the incubation as light fraction organic matter (LFOM) were also investigated. Both C and N content of LFOM derived from the residues were correlated with residue cellulose content, and the chemical characteristics of LFOM were highly correlated with those of the original plant material. Incorporation of low cellulose, high water-soluble N-containing shoot residues resulted in more N becoming mineralized than had been added in the residues, demonstrating that net mineralization of native soil organic matter had occurred. Large amounts of N were lost from the mineral-N pool during the incubation, which could not be accounted for by microbial immobilization.     

Predictors of gross N mineralization and immobilization during decomposition of stabilized organic matter in agricultural soil

Long-term additions of different types of organic amendments affect the amount of soil organic matter. Less is known about how this in turn affects carbon (C) and nitrogen (N) mineralization from the pool of stabilized soil organic matter, or the extent to which gross N immobilization influences the net amount of N mineralized. Soils, differing in the quantity and quality of organic matter inputs they had received since 1956, were sampled approximately 6 or 18 months after the most recent applications of organic amendments. Two laboratory experiments were carried out to: (i) evaluate if, and how, the organic amendments had affected C mineralization, gross and net N mineralization; (ii) examine the relation between gross N immobilized and free-light fraction of organic matter; and (iii) assess predictors for gross N mineralization and immobilization rates in soils. The amount of soil organic C and N were major determinants of C and gross N mineralization, but not of net N mineralization. Carbon mineralization was related to gross N mineralization, but the ratio between the two was not constant. Gross N immobilization was related to the amount of free-light fraction material in the soil with 90% variation explained. For most common organic amendments applied in autumn, our results support the use of total soil organic N and C mineralization as predictors of gross N mineralization from stabilized soil organic matter. In addition, we propose that the amount of free-light fraction material present in the soil in spring is adequate as a predictor of the immobilization potential of the soil, without a need to consider the C-to-N ratio of this material.     

Respiration pattern and microbial use of field-grown transgenic Bt-maize residues

A 49-day incubation experiment was carried out with the addition of field-grown maize stem and leaf residues to soil at three different temperatures (5, 15, and 25 °C). The aim was to study the effects of two transgenic Bt-maize varieties in comparison to their two parental non-Bt varieties on the mineralization of the residues, on their incorporation into the microbial biomass and on changes in the microbial community structure. The stem and leaf residues of Novelis-Bt contained 3.9 μg g⁻¹ dry weight of the Bt toxin Cry1Ab and those of Valmont-Bt only 0.8 μg g⁻¹. The residues of the two parental non-Bt varieties Nobilis and Prelude contained higher concentrations of ergosterol (+220%) and glucosamine (+190%) and had a larger fungal C-to-bacterial C ratio (+240%) than the two Bt varieties. After adding the Bt residues, an initial peak in respiration of an extra 700 μg CO₂-C g⁻¹ soil or 4% of the added amount was observed in comparison to the two non-Bt varieties at all three temperatures. On average of the four varieties, 19-38% of the maize C added was mineralized during the 49-day incubation at the three different temperatures. The overall mean increase in total maize-derived CO₂ evolution corresponded to a Q₁₀ value of 1.4 for both temperature steps, i.e. from 5 to 15 °C and from 15 to 25 °C. The addition of maize residues led to a strong increase in all microbial properties analyzed. The highest contents were always measured at 5 °C and the lowest at 25 °C. The variety-specific contents of microbial biomass C, biomass N, ATP and adenylates increased in the order Novelis-Bt ? Prelude<Valmont-Bt ? Nobilis. The mineralization of Novelis-Bt residues with the highest Bt concentration and lowest N concentration and their incorporation into the microbial biomass was significantly reduced compared to the parental non-Bt variety Nobilis. These negative effects increased considerably from 5 to 25 °C. The transgenic Bt variety Valmont did not show further significant effects except for the initial peak in respiration at any temperature.     

Decomposition of 14C- and 15N-labelled microbial cells in soil

To obtain detailed information on the quantities and characteristics of nitrogen derived from mineralizing dead microbial biomass in soil, ¹⁴C- and ¹⁵N-labelled microorganisms, i.e. three eukaryotic (fungal) species, two prokaryotic species or their mixture (eukaryotic to prokaryotic cells = 8:2), were grown in vitro, dried, ground and added to parabrown earth and chernozem soils, respectively. The mean percent of ¹⁴C decomposition of labelled microorganisms obtained after 10 days was 43 ± 6.3% for parabrown earth and 34 ± 4.0% for chernozem soil. About 50% of the C in the dead microorganisms was mineralized during the first 28 days of incubation. About 76% of the flush of soil organic N mineralization within 28 days, which was caused by the drying-rewetting treatment, was derived from dead microbial biomass in soil. About 33% of the added dead microbial-¹⁵N was mineralized in parabrown earth soil during 28 days of incubation and about 37% of newly immobilized ¹⁵N during the decomposition of added microorganisms was mineralized during the 28 days following a dryingrewetting treatment.     

Microbial utilization and mineralization of [14C]glucose added in six orders of concentration to soil

The substrate availability for microbial biomass (MB) in soil is crucial for microbial biomass activity. Due to the fast microbial decomposition and the permanent production of easily available substrates in the rooted top soil mainly by plants during photosynthesis, easily available substrates make a very important contribution to many soil processes including soil organic matter turnover, microbial growth and maintenance, aggregate stabilization, CO₂ efflux, etc. Naturally occurring concentrations of easily available substances are low, ranging from 0.1 μM in soils free of roots and plant residues to 80 mM in root cells. We investigated the effect of adding ¹⁴C-labelled glucose at concentrations spanning the 6 orders of magnitude naturally occurring concentrations on glucose uptake and mineralization by microbial biomass. A positive correlation between the amount of added glucose and its portion mineralized to CO₂ was observed: After 22 days, from 26% to 44% of the added 0.0009 to 257 μg glucose C g^?1 soil was mineralized. The dependence of glucose mineralization on its amount can be described with two functions. Up to 2.6 μg glucose C g^?1 soil (corresponds to 0.78% of initial microbial biomass C), glucose mineralization increased with the slope of 1.8% more mineralized glucose C per 1 μg C added, accompanied by an increasing incorporation of glucose C into MB. An increased spatial contact between micro-organisms and glucose molecules with increasing concentration may be responsible for this fast increase in mineralization rates (at glucose additions <2.6 μg C g^?1). At glucose additions higher than 2.6 μg C g^?1 soil, however, the increase of the glucose mineralization per 1 μg added glucose was much smaller as at additions below 2.6 μg C g^?1 soil and was accompanied by decreasing portions of glucose ¹⁴C incorporated into microbial biomass. This supports the hypothesis of decreasing efficiency of glucose utilization by MB in response to increased substrate availability in the range 2.6–257 μg C g^?1 (=0.78–78% of microbial biomass C). At low glucose amounts, it was mainly stored in a chloroform-labile microbial pool, but not readily mineralized to CO₂. The addition of 257 μg glucose C g^?1 soil (0.78 μg C glucose μg^?1 C micro-organisms) caused a lag phase in mineralization of 19 h, indicating that glucose mineralization was not limited by the substrate availability but by the amount of MB which is typical for 2nd order kinetics.     

土壤水分和植物残体对紫色水稻土有机碳矿化的影响

采用为期62.d的实验室恒温(281)℃培养方法,研究了土壤水分和植物残体对紫色水稻土有机碳矿化的影响。结果表明,紫色水稻土有机碳矿化速率在培养30.d后基本达到稳定,好气条件下土壤有机碳累积矿化量高于淹水条件,且差异达到极显著水平。用一级动力学方程对植物残体的矿化速率进行拟合表明,好气条件下,植物残体的分解速率常数(k值)大小顺序为蚕豆秸秆玉米秸秆水稻秸秆,而淹水条件则为水稻秸秆蚕豆秸秆玉米秸秆。水分状况和植物残体化学组分的差异影响紫色水稻土中有机碳的动态变化,最终导致碳累积矿化量差异。     

Effect of lignite amendment on carbon and nitrogen mineralization from raw and composted manure during incubation with soil

The application of animal manure as a source of plant nutrients requires the determination of the amount and pattern of nutrient mineralization from manure.A laboratory incubation study was conducted to investigate the influence of lignite amendment and lignite type on carbon(C) and nitrogen(N)mineralization in raw(feedstock) and composted cattle manure following application to soil at 30 and 60 t ha^-1.The mineralization of C and N was determined by measuring changes in CO2 evolution ...     

Mineralization rate of C-labelled dissolved organic matter from leaf litter in soils of a weathering chronosequence

During the processes of primary succession and soil development, large stocks of organic C with very long residence times accumulate in many soils. Soluble organic C adsorbed by soils may contribute to the stock of organic C accumulating during soil development. We determined whether the mineralization rate of water-soluble organic C and the insoluble residue from ¹⁴C-labelled leaf litter added to soils from a weathering chronosequence decrease as soil age and adsorption capacity increase. The soils were formed on mudflows of andesitic material deposited about 75, 255, 616 y ago, and another older but undetermined time before this study. The percentage of the DOC adsorbed by the soils increased with age. After 1 year of incubation there were no significant differences in the mineralization rates of DOC added to soils of different ages. The DOC appeared to be comprised of two fractions, one that comprises about 32% of the total that mineralized with a half decay time of 0.02 y (7 d) and a second fraction comprising 68% with a half decay time of about 1.6 y. Consequently, the slowly mineralized fraction of the soluble C contributed to the accumulation of slowly mineralized C in the soil. Both the slowly and rapidly mineralized fractions of the insoluble residue decomposed more slowly than the corresponding fractions in DOC. We found no support for the idea that increased adsorption capacity due to weathering resulted in protection of soluble organic C from microbial mineralization.