施用聚合果属废弃物与生物炭后砂质石灰性土壤二氧化碳排放及生物化学性质的动态

Biochar is a carbon-rich product obtained by biomass pyrolysis and considered a mean of carbon sequestration. In this research, a sandy calcareous soil from the Farm of the College of Food & Agriculture Sciences, King Saud University, Saudi Arabia, was amended with either woody waste of Conocarpus erectus L.(CW) or the biochar(BC) produced from CW at rates of 0(control), 10, 30 and 50 g kg-1. The effects of the amendments on soil p H, dissolved organic carbon(DOC), microbial biomass carbon(MBC), CO2 emission and metabolic quotient(q CO2) of the sandy calcareous soil were studied in a 60-d incubation experiment. The results showed that the addition of CW led to a significant decrease in soil p H compared to the control and the addition of BC. The CO2-C emission rate was higher in the first few days of incubation than when the incubation time progressed. The cumulative CO2-C emission from the soil amended with CW, especially at higher rates, was higher(approximately 3- to 6-fold) than that from the control and the soil amended with BC. The BC-amended soil showed significant increases in CO2-C emission rate during the first days of incubation as compared to the non-amended soil, but the increase in cumulative CO2-C emission was not significant after 60 d of incubation. On the other hand, CW applications resulted in considerably higher cumulative CO2-C emission, MBC and DOC than the control and BC applications. With the exception of 0 day(after 1 h of incubation), both CW and BC applications led to lower values of q CO2 as compared to the control. The power function kinetic model satisfactorily described the cumulative CO2-C emission. Generally, the lowest values of CO2 emission were observed in the soil with BC, suggesting that the contribution of BC to CO2 emission was very small as compared to that of CW.     

酸雨对土壤有机碳氮潜在矿化的影响

Acid rain is a serious environmental problem worldwide. In this study, a pot experiment using forest soils planted with the seedlings of four woody species was performed with weekly treatments of pH 4.40, 4.00, 3.52, and 3.05 simulated acid rain （SAR） for 42 months compared to a control ofpH 5.00 lake water. The cumulative amounts of C and N mineralization in the five treated soils were determined after incubation at 25 ℃ for 65 d to examine the effects of SAR treatments. For all five treatments, cumulative CO2-C production ranged from 20.24 to 27.81 mg kg^-1 dry soil, net production of available N from 17.37 to 48.95 mg kg^-1 dry soil, and net production of NO3-N from 9.09 to 46.23 mg kg^-1 dry soil. SAR treatments generally enhanced the emission of CO2-C from the soils; however, SAR with pH 3.05 inhibited the emission. SAR treatments decreased the net production of available N and NO3-N. The cumulative CH4 and N2O productions from the soils increased with increasing amount of simulated acid rain. The cumulative CO2-C production and the net production of available N of the soil under Acmena acuminatissima were significantly higher （P 〈 0.05） than those under Schima superba and Cryptocarya concinna. The mineralization of soil organic C was related to the contents of soil organic C and N, but was not related to soil pH. However, the overall effect of acid rain on the storage of soil organic matter and the cycling of important nutrients depended on the amount of acid deposition and the types of forests.     

生物碳可以防止土壤活性有机质矿化吗？

Biochar could help to stabilize soil organic(SOM) matter, thus sequestering carbon(C) into the soil. The aim of this work was to determine an easy method i) to estimate the effects of the addition of biochar and nutrients on the organic matter(SOM)mineralization in an artificial soil, proposed by the Organization for Economic Co-operation and Development(OECD), amended with glucose and ii) to measure the amount of labile organic matter(glucose) that can be sorbed and thus be partially protected in the same soil, amended or not amended with biochar. A factorial experiment was designed to check the effects of three single factors(biochar, nutrients, and glucose) and their interactions on whole SOM mineralization. Soil samples were inoculated with a microbial inoculum and preincubated to ensure that their biological activities were not limited by a small amount of microbial biomass, and then they were incubated in the dark at 21℃ for 619 d. Periodical measurements of C mineralized to carbon dioxide(CO_2) were carried out throughout the 619-d incubation to allow the mineralization of both active and slow organic matter pools. The amount of sorbed glucose was calculated as the difference between the total and remaining amounts of glucose added in a soil extract. Two different models, the Freundlich and Langmuir models, were selected to assess the equilibrium isotherms of glucose sorption. The CO_2-C release strongly depended on the presence of nutrients only when no biochar was added to the soil. The mineralization of organic matter in the soil amended with both biochar and glucose was equal to the sum of the mineralization of the two C sources separately. Furthermore, a significant amount of glucose can be sorbed on the biochar-amended soil, suggesting the involvement of physico-chemical mechanisms in labile organic matter protection.     

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.     

添加表面活性剂土壤中蒽的去除以及矿质态氮动态研究

Surfactants, such as non-ionic Surfynol 485 （ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol）, have been applied to accelerate removal of polycyclic aromatic hydrocarbons from soil. This study investigated the dissipation of anthracene, and carbon （C） and nitrogen （N） mineralization in soil amended with non-ionic Surfynol 485 at different rates. Soil samples of a Typic Fragiudept taken from Otumba, Mexico were spiked with anthracene at a final concentration of 520 mg kg^-1 dry soil using acetone as solvent, amended with 0.0, 24.9, 49.8 or 124.4 g kg^-1 soil of the surfactant and incubated in the laboratory. The soil not amended with anthracene, acetone and the surfactant was used as a control. Dynamics of C and N and the concentration of anthracene were monitored for 56 d. After 56 d of incubation, 38% of the anthracene was removed from the unamended soil, and 47%, 55% and 66% of the anthracene were removed when 24.9, 49.8 and 124.4 g kg^-1 of the surfactant were applied, respectively. Application of acetone, anthracene or surfactant increased the emission of CO2, but decreased the mineral N compared to the unamended control. Applying the surfactant to the acetone or anthracene-amended soil reduced emission of CO2, but increased the mineral N at the lower application rates of the surfactant. It was found that the application of the non-ionic surfactant increased the bioavailability of anthracene and thus its removal from soil, increased C mineralization, but decreased N miaeralization. Consequently, the application of non-ionic surfactant could be easily used to accelerate the removal of pollutants from hydrocarbon-contaminated soils, but mineral N in the soil would decrease, which might inhibit plant growth.     

不同碳源添加对钙质土高累积硝态氮向土壤有机氮库转化的研究

Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizers or manures used in combination with low carbon inputs. We investigated the potential of different carbon substrates added to transform soil nitrate into soil organic N (SON). A 56-d laboratory incubation experiment using the 15 N tracer (K15 NO3 ) technique was carried out to elucidate the proportion of SON derived from accumulated soil nitrate following amendment with glucose or maize straw at controlled soil temperature and moisture. The dynamics and isotopic abundance of mineral N (NO3 and NH+4 ) and SON and greenhouse gas (N2O and CO2 ) emissions during the incubation were investigated. Although carbon amendments markedly stimulated transformation of nitrate to newly formed SON, this was only a substitution effect of the newly formed SON with native SON because SON at the end of the incubation period was not significantly different (P > 0.05) from that in control soil without added C. At the end of the incubation period, amendment with glucose, a readily available C source, increased nitrate immobilization by 2.65 times and total N2O-N emission by 33.7 times, as compared with maize straw amendment. Moreover, the differences in SON and total N2O-N emission between the treatments with glucose and maize straw were significant (P < 0.05). However, the total N2O-N emission in the straw treatment was not significantly (P > 0.05) greater than that in the control. Straw amendment may be a potential option in agricultural practice for transformation of nitrate N to SON and minimization of N2O emitted as well as restriction of NO3-N leaching.     

长期施用化肥和有机肥对太湖地区水稻土有机碳特征的影响

A long-term experiment set up in 1980 compared the effects of applying manures and chemical fertilizers on a paddy soil in the Taihu Lake region,China.Of the fourteen randomly distributed treatments consisting of different combinations of organic manure,inorganic nitrogen (N),phosphorus (P),and potassium (K),and rice straw,eight were selected for the present study in 2007.Application of organic manure plus straw significantly increased soil organic carbon (SOC) content of the topsoil (0-10 cm) compared to that of chemical fertilizers alone.The content of SOC was relatively stable in the 10-30 cm layer in the chemical fertilizer treatments and in the 20-40 cm layer in the manure treatments.The stable carbon isotope ratio (δ 13 C) ranged from 24‰ to 28‰ and increased gradually with depth.The content of SOC was significantly (P < 0.05) negatively correlated with δ 13 C.In the 0-20 cm layer,the δ 13 C value significantly decreased in the treatments of manure alone (M),manure and chemical N and P fertilizers (MNP),manure and chemical N,P,and K fertilizers (MNPK),manure,rice straw,and chemical N fertilizer (MRN),and chemical N fertilizer and rice straw (CNR),as compared with the no-fertilizer control.In the 30-50 cm layer,however,the ratio significantly increased in all the treatments except Treatment CNR.Mineralization of organic C peaked in the first 2-4 d of incubation and gradually leveled off thereafter over the first 3 weeks,being faster in the manure treatments than the chemical fertilizer treatments.The average rate of mineralization varied from 55.36 to 75.46 mL CO 2 kg-1 d-1 and that of stable mineralization from 10 to 20 mL CO 2 kg-1 d-1.In eight weeks of incubation,cumulative mineralization was always higher in the manure treatments than the chemical fertilizer treatments,being the highest in Treatment MRN.Combined humus in the soil was mainly (over 50%) composed of tightly combined fraction.The loosely combined humus and its ratio of humic acid (HA) to fulvic acid (FA) significantly increased with long-term application of organic manure and chemical fertilizers.It could be concluded that the cycle of organic C in the paddy soil ecosystem studied was stable over the long-term application of fertilizers and continued cultivation.     

中国亚热带稻田土壤碳氮含量及矿化动态

Dynamics of soil organic matter in a cultivation chronosequence of paddy fields were studied in subtropical China. Mineralization of soil organic matter was determined by measuring CO2 evolution from soil during 20 days of laboratory incubation. In the first 30 years of cultivation, soil organic C and N contents increased rapidly. After 30 years, 0-10 cm soil contained 19.6 g kg^-1 organic C and 1.62 g kg^-1 total N, with the corresponding values of 18.1 g kg^-1 and 1.50 g kg^-1 for 10-20 cm, and then remained stable even after 80 years of rice cultivation. During 20 days incubation the mineralization rates of organic C and N in surface soil （0-10 cm） ranged from 2.2% to 3.3% and from 2.8% to 6.7%, respectively, of organic C and total N contents. Biologically active C size generally increased with increasing soil organic C and N contents. Soil dissolved organic C decreased after cultivation of wasteland to 10 years paddy field and then increased. Soil microbial biomass C increased with number of years under cultivation, while soil microbial biomass N increased during the first 30 years of cultivation and then stabilized. After 30 years of cultivation surface soil （0-10 cm） contained 332.8 mg kg^-1 of microbial biomass C and 23.85 mg kg^-1 of microbial biomass N, which were 111% and 47% higher than those in soil cultivated for 3 years. It was suggested that surface soil with 30 years of rice cultivation in subtropical China would have attained a steady state of organic C content, being about 19 g kg^-1.     

腐殖质功能团酸解的常数: Ⅰ. 风化煤和暗黄土的富里酸和胡敏酸的电位数据的亲和光谱模型分析

In order to study the influence of difference in C2H2 concentration on the production of CO2,N2O,NH4-N and volatile fatty acids(VFA).soil slurries with a gradient in C2H2 concentration were anaerobically incubated at 25℃ for 2 weeks.Acetate,butyrate and CO2 production and NH4-N accumulation were inhibited in the slurres in the presence of C2H2;and the inhibition effect increased with increasing C2H2 from 0 to 20 kPa in the headspace gas of the incubation bottle.However,N2O,isobutyrate and propionate production was not obviously different among the slurres amended with C2H2 from 2.5 to 20 kPa.Therefore,the results implied that the C2H2 did not promote the inhibition but only increased the side effect on other microbial processes.The C2H2 of 2.5 kPa was suggested to be the optimum choice for the present denitrification study.     

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 ...     

Interactions of NaCl and Na2SO4 on soil organic C mineralization after addition of maize straws

NaCl and Na₂SO₄ often dominate salt compositions in saline soils. While either salt alone affects soil organic matter mineralization, their interactions on soil organic matter dynamics are unknown. This study aimed to investigate interactive effects of the two salts on organic C mineralization and microbial biomass C of the saline soils after addition of maize straws. Both NaCl and Na₂SO₄ were applied at 0, 40 and 80 mmol Na kg⁻¹ soil and the incubation was undertaken at soil water content of 15% and 20% (w/w) in dark at 28.5 °C for 70 days. The study found significant interactions of NaCl and Na₂SO₄ on CO₂-C evolution during the early incubation periods—a suppressing effect at days 1-2 but a stimulating effect at days 6-8 and 17-20, and thereafter the salt interactions were influenced by water content. The interactions of water content with NaCl or Na₂SO₄ on CO₂-C evolution were observed through the incubation periods except days 1-2, showing that the salt effects were dependent on water content. Total CO₂ evolution over the 70-day-long incubation decreased with increasing NaCl but increased with increasing Na₂SO₄ compared to the nil-salted treatment. Salt interactions on soil microbial biomass C were observed at days 7, 21, but not at day 49. Microbial biomass C increased at day 7 in the soils treated with either NaCl or Na₂SO₄ but decreased where the two salts were combined. At day 21, microbial biomass C increased with NaCl but decreased with Na₂SO₄ regardless whether the counterpart salt was added. The results suggest that soil organic C mineralization can be affected by the interactions of NaCl and Na₂SO₄, possibly through the salt-induced changes in microbial biomass community structure.     

Kinetics of native and added carbon mineralization on incubating at different soil and moisture conditions in Typic Ustochrepts and Typic Halustalf

The carbon dynamics in soils is of great importance due to its links to the global carbon cycle. The prediction of the behavior of native soil organic carbon (SOC) and organic amendments via incubation studies and mathematical modeling may bridge the knowledge gap in understanding complex soil ecosystems. Three alkaline Typic Ustochrepts and one Typic Halustalf with sandy, loamy sand, and clay loam texture, varying in percent SOC of 0.2; S₁, 0.42; S₂, 0.67; S₃ and 0.82; S₄ soils, were amended with wheat straw (WS), WS + P, sesbania green manure (GM), and poultry manure (PM) on 0.5% C rate at field capacity (FC) and ponding (P) moisture levels and incubated at 35 °C for 1, 15, 30 and 45 d. Carbon mineralization was determined via the alkali titration method after 1, 5, 7 14, 21, and 28 d. The SOC and inorganic carbon contents were determined from dried up (50 °C) soil samples after 1, 15, 30, and 45 d of incubation. Carbon from residue mineralization was determined by subtracting the amount of CO₂-C evolved from control soils. The kinetic models; monocomponent first order, two-component first order, and modified Gompertz equations were fitted to the carbon mineralization data from native and added carbon. The SOC decomposition was dependent upon soil properties, and moisture, however, added C was relatively independent. The carbon from PM was immobilized in S₄. All the models fitted to the data predicted carbon mineralization in a similar range with few exceptions. The residues lead to the OC build-up in fine-textured soils having relatively high OC and cation exchange capacities. Whereas, fast degradation of applied OC in coarse-textured soils leads to faster mineralization and lower build-up from residues. The decline in CaCO₃ after incubation was higher at FC than in the P moisture regime.     

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO₃-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N₂O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO₃-N decreased. When ¹⁵NO₃-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg^?1 only 1.1 ± 0.4 mg kg^?1 NO₃-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N₂O-N emissions were at levels of only micrograms kg^?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N₂O.     

Carbon and nitrogen mineralization in acidic, limed and calcareous agricultural soils: Apparent and actual effects

Soil pH and calcium carbonate contents are often hypothesized to be important factors controlling organic matter turnover in agricultural soils. The aim of this study was to differentiate the effects of soil pH from those related to carbonate equilibrium on C and N dynamics. The relative contributions of organic and inorganic carbon in the CO₂ produced during laboratory incubations were assessed. Five agricultural soils were compared: calcareous (74% CaCO₃), loess (0.2% CaCO₃) and an acidic soil which had received different rates of lime 20 years ago (0, 18 or 50 t ha⁻¹). Soil aggregates were incubated with or without rape residues under aerobic conditions for 91 days at 15 °C. The C and N mineralized, soil pH, O₂ consumption and respiratory quotient (RQ=ΔCO₂/ΔO₂) were monitored, as well as the δ¹³C composition of the evolved CO₂ to determine its origin (mineral or organic). Results showed that in non-amended soils, the cumulative CO₂ produced was significantly greater in the limed soil with a pH>7 than in the same soil with less or no lime added, whereas there was no difference in N mineralization or in O₂ consumption kinetics. We found an exponential relationship between RQ values and soil pH, suggesting an excess production of CO₂ in alkaline soils. This CO₂ excess was not related to changes in substrate utilization by the microbial biomass but rather to carbonates equilibrium. The δ¹³C signatures confirmed that the CO₂ produced in soils with pH>7 originated from both organic and mineral sources. The contribution of soil carbonates to CO₂ production led to an overestimation of organic C mineralization (up to 35%), the extent of which depended on the nature of soil carbonates but not on the amount. The actual C mineralization (derived from organic C) was similar in limed and unlimed soil. The amount of C mineralized in the residue-amended soils was ten times greater than in the basal soil, thus masking the soil carbonate contribution. Residue decomposition resulted in a significant increase in soil pH in all soils. This increase is attributed to the alkalinity and/or decarboxylation of organic anions in the plant residue and/or to the immobilization of nitrate by the microbial biomass and the corresponding release of hydroxyl ions. A theoretical composition (C, O, H, N) of residue and soil organic matter is proposed to explain the RQ measured. It emphasizes the need to take microbial biomass metabolism, O₂ consumption due to nitrification and carbon assimilation yield into account when interpreting RQ data.     

Carbon‐mineralization kinetics in an organically managed Cambic Arenosol amended with organic fertilizers

The dynamics of C mineralization in an organically managed Cambic Arenosol amended with hen manure, a stabilized compost (compost), and three different combinations of both fertilizers (varying from a 1:100 to a 1:10 ratio) were studied during an incubation experiment to estimate the potential of such combinations to preserve/restore soil C content relative to single applications. A strong increase of the CO₂‐C emissions relative to the unamended soil (control) was observed after soil application of all five organic‐fertilizer treatments. A significantly higher amount of applied C was lost in hen‐manure treatment (648 mg CO₂‐C [g C applied]^–1) when compared to compost (159 mg CO₂‐C [g C applied]^–1) or to the three combined treatments (176–195 mg CO₂‐C [g C applied]^–1). The first‐order exponential model and the double exponential model were used to fit the C‐mineralization data in the treatments considered. Results showed that mixing “small” amounts of hen manure with compost did not affect the total amount of potentially mineralizable C, but significantly increased the mineralization rate constant. Clearly, combinations of both fertilizers promoted an initial faster mineralization of the organic matter, and consequently a faster release of nutrients, without affecting the total amount of C sequestered in soil.     

玉米秸秆应用和腐化对钙质苏打土改良的影响: 实验室试验研究

A laboratory lysimeter experiment was conducted to investigate the effects of forage corn (Zea mays L.) stalk application on the CO₂ concentration in soil air and calcareous sodic soil reclamation. The experimental treatments tested were soil exchangeable sodium percentage (ESP) levels of 1, 11, and 19, added corn stalk contents of 0 to 36 g kg^-1, and incubation durations of 30 and 60 days. The experimental results indicated that corn stalk application and incubation significantly increased CO₂ partial pressure in soil profile and lowered pH value in soil solution, subsequently increased native CaCO₃ mineral dissolution and electrolyte concentration of soil solution, and finally significantly contributed to reduction on soil sodicity level. The reclamation effciency of calcareous sodic soils increased with the added corn stalk. When corn stalks were added at the rates of 22 and 34 g kg^-1 into the soil with initial ESP of 19, its ESP value was decreased by 56% and 78%, respectively, after incubation of 60 days and the leaching of 6.5 pore volumes (about 48 L of percolation water) with distilled water. Therefore, crop stalk application and incubation could be used as a choice to reclaim moderate calcareous sodic soils or as a supplement of phytoremediation to improve reclamation effciency.     

Effluxed CO2-C from sterilized and unsterilized treatments of a calcareous soil

Soil inorganic carbon (C) represents a substantial C pool in arid ecosystems, yet little data exist on the contribution of this pool to ecosystem C fluxes. A closed jar incubation study was carried out to test the hypothesis that CO₂-¹³C production and response to sterilization would differ in a calcareous (Mojave Desert) soil and a non-calcareous (Oklahoma Prairie) soil due to contributions of carbonate-derived CO₂. In addition to non-sterilized controls, soils were subjected to sterilization treatments (unbuffered HgCl₂ addition for Oklahoma soil and unbuffered HgCl₂ addition, buffered HgCl₂ addition, and autoclaving for Mojave Desert soil) to decrease biotic respiration and more readily measure abiotic CO₂ flux. Temperature and moisture treatments were also included with sterilization treatments in a factorial design.The rate of CO₂ production in both soils was significantly decreased (36-87%) by sterilization, but sterilization treatments differed in effectiveness. Sterilization had no significant effect on effluxed CO₂-¹³C values in the non-calcareous Oklahoma Prairie soil and autoclaved Mojave Desert soil as compared to their respective non-sterilized controls. However, sterilization significantly altered CO₂-¹³C values in Mojave Desert soil HgCl₂ sterilization treatments (both buffered and non-buffered). Plots of 1/CO₂ versus CO₂-δ¹³C (similar to Keeling plots) indicated that the source CO₂-δ¹³C value of the Oklahoma Prairie soil treatments was similar to the δ¹³C value of soil organic matter [(SOM); −17.76‰ VPDB] whereas the source for the (acidic) unbuffered-HgCl₂ sterilized Mojave Desert soil was similar to the δ¹³C value of carbonates (−0.93‰ VPDB). The source CO₂-δ¹³C value of non-sterilized and autoclaved (−18.4‰ VPDB) Mojave Desert soil treatments was intermediate between SOM (−21.43‰ VPDB) and carbonates and indicates up to 13% of total C efflux may be from abiotic sources in calcareous soils.     

Temperature, water content and wet-dry cycle effects on DOC production and carbon mineralization in agricultural peat soils

Agricultural peat soils in the Sacramento-San Joaquin Delta, California have been identified as an important source of dissolved organic carbon (DOC) and trihalomethane precursors in waters exported for drinking. The objectives of this study were to examine the primary sources of DOC from soil profiles (surface vs. subsurface), factors (temperature, soil water content and wet-dry cycles) controlling DOC production, and the relationship between C mineralization and DOC concentration in cultivated peat soils. Surface and subsurface peat soils were incubated for 60 d under a range of temperature (10, 20, and 30 °C) and soil water contents (0.3-10.0 g-water g-soil⁻¹). Both CO₂-C and DOC were monitored during the incubation period. Results showed that significant amount of DOC was produced only in the surface soil under constantly flooded conditions or flooding/non-flooding cycles. The DOC production was independent of temperature and soil water content under non-flooded condition, although CO₂ evolution was highly correlated with these parameters. Aromatic carbon and hydrophobic acid contents in surface DOC were increased with wetter incubation treatments. In addition, positive linear correlations (r²=0.87) between CO₂-C mineralization rate and DOC concentration were observed in the surface soil, but negative linear correlations (r²=0.70) were observed in the subsurface soil. Results imply that mineralization of soil organic carbon by microbes prevailed in the subsurface soil. A conceptual model using a kinetic approach is proposed to describe the relationships between CO₂-C mineralization rate and DOC concentration in these soils.