Effects of rainfall pattern on carbon and nitrogen dynamics in soil amended with biogas slurry and composted cattle manure

Soil moisture affects the degradation of organic fertilizers in soils considerably, but less is known about the importance of rainfall pattern on the turnover of C and N. The objective of this study was to determine the effects of different rainfall patterns on C and N dynamics in soil amended with either biogas slurry (BS) or composted cattle manure (CM). Undisturbed soil cores without (control) or with BS or CM, which were incorporated at a rate of 100 kg N ha^–1, were incubated for 140 d at 13.5°C. Irrigation treatments were (1) continuous irrigation (cont_irr; 3 mm d^–1); (2) partial drying and stronger irrigation (part_dry; no irrigation for 3 weeks, 1 week with 13.5 mm d^–1), and (3) periodic heavy rainfall (hvy_rain; 24 mm d^–1 every 3 weeks for 1 d and 2 mm d^–1 for the other days). The average irrigation was 3 mm d^–1 in each treatment. Cumulative emissions of CO₂ and N₂O from soils amended with BS were 92.8 g CO₂‐C m^–2 and 162.4 mg N₂O‐N m^–2, respectively, whereas emissions from soils amended with CM were 87.8 g CO₂‐C m^–2 and only 38.9 mg N₂O‐N m^–2. While both organic fertilizers significantly increased CO₂ production compared to the control, N₂O emissions were only significantly increased in the BS‐amended soil. Under the conditions of the experiment, the rainfall pattern affected the temporal production of CO₂ and N₂O, but not the cumulative emissions. Cumulative NO leaching was highest in the BS‐amended soils (9.2 g NO ‐N m^–2) followed by the CM‐amended soil (6.1 g NO ‐N m^–2) and lowest in the control (4.7 g NO ‐N m^–2). Nitrate leaching was also independent of the rainfall pattern. Our study shows that rainfall pattern may not affect CO₂ and N₂O emissions and NO leaching markedly provided that the soil does not completely dry out.     

Injection of pig slurry and its effects on dynamics of nitrogen and carbon in a loamy soil unter laboratory conditions

Dynamics of nitrogen (N) and carbon (C) were investigated in a loamy soil amended or injected with pig slurry. Treatments were with or without acetylene C₂H₂ (which is assumed to inhibit reduction of nitrous oxide (N₂O) to dinitrogen (N₂), and soil cores were conditioned for 15 days at 25°C while pH, production of CO₂ and N₂O, ammonia (NH₃) emission and (nitrate) (NO₃ ^–) and (ammonium) (NH₄ ⁺) concentrations were monitored. There was no significant difference in CO₂ production between the injected and surface applied pig slurry treatments, and within 15 days ca. 5% of the C applied had been mineralized, if no priming effect was assumed. Neither the production of N₂O nor the total gaseous production of the denitrification process (N₂O plus N₂) were affected by the way the pig slurry was added to the soil. NH₃ volatilization, however, decreased by 90% when pig slurry was injected. The addition of C₂H₂ significantly increased the CO₂ production and the concentration of NH₄ ⁺, but significantly decreased the concentration of NO₃ ^–. It was concluded that the injection of pig slurry to a dry soil was an acceptable alternative to its application to the soil surface, as not only was NH₃ volatilization reduced, but the production of N₂O and N₂ through denitrification was not stimulated. It is also suggested that the composition of the organic C fraction in the pig slurry, most likely the concentration of fatty acids, had an important effect on the dynamics of N and C in the soil. Received: 12 May 1997     

Microbial carbon dynamics in nitrogen amended Arctic tundra soil: Measurement and model testing

We examined the responses of grazers (protozoa and nematodes) and their main food sources to low levels of nitrogen (N) fertilisation and applied carbon (C) flux models to our data. Replicate plots of tundra soil adjacent to the Kongsfjorden (Svalbard 78°N) were amended with ammonium and nitrate at concentrations of 1 and 5 kg N ha⁻¹ to assess the impact of anthropogenic N deposition over three summers. Bacterial abundance as determined using the fluorochrome SYBR Green and epifluorescence microscopy ranged between 9.73×10⁸ and 102.49×10⁸ cells/g dry wt of soil, with a significant response to N addition occurring only during the second sampling in 2001. Despite little change in bacterial biomass, bacterial production (measured by the incorporation of ³H thymidine into DNA) during the second sampling in 2002, increased in NH₄ enriched plots compared to control and NO₃ amended plots, indicating that NH₄ was the preferred source of inorganic N. The main bacterial predators were heterotrophic flagellates (HNAN) and naked amoebae, which showed no significant response to the N addition. HNAN showed a correlation with bacterial abundance suggesting a dependence on bacteria as a food source. The inability of a microbial C flux model to fit our data (RWSS/data=18.6, r²=0.088) was at least partly due to insufficient bacterial production to meet the C demands of predator taxa, and high variability in the data over time. This is reflected in the performance statistics for model variants where select microbial taxa and data were removed. The optimal model in terms of predictive utility was a model with data from 2002 only, minus naked amoebae (RWSS/data=2.45, r²=0.806).     

Carbon and nitrogen dynamics in a forest soil amended with purified tannins from different plant species

Tannins are purported to be an important factor controlling nitrogen cycling in forest ecosystems, and the ability of tannins to bind proteins in protein-tannin complexes is thought to be the primary mechanism responsible for these effects. In this study, we examined the influence of well-characterized tannins purified from five different plant species on C and N dynamics of a forest soil A horizon. Tannic acid, a commonly used and commercially available hydrolyzable tannin (HT), and cellulose were also included for comparison. With the exception of tannins from huckleberry (Vaccinium ovatum), the amendments increased respiration 1.4-4.0 fold, indicating that they were acting as a microbial C source. Tannic acid was significantly more labile than the five purified tannins examined in this study. All treatments decreased net N mineralization substantially, through greater N immobilization and decreased mineralization. The six tannins inhibited gross ammonification rates significantly more than cellulose. This suggests that added tannins had effects in addition to serving as an alternative C source. Tannins purified from Bishop pine (Pinus muricata) were the only tannins that significantly inhibited potential gross nitrification rates, however, rates were low even in the control soil making it difficult to detect any inhibition. Differences in tannin structure such as condensed versus HTs and the hydroxylation pattern of the condensed tannin B-ring likely explain differences observed among the tannin treatments. Contrary to other studies, we did not find that condensed tannins were more labile and less inhibitory than HTs, nor that shorter chained tannins were more labile than longer chained tannins. In addition to supporting the hypothesis that reduced N availability in the presence of tannins is caused by complexation reactions, our data suggests tannins act as a labile C source leading to increased N immobilization.     

Wheat yield and leachability of phosphorus and mineral nitrogen in pig slurry amended Soils

Abstract

An outdoor pot experiment was conducted using wheat plants (Triticum aestivum L. cv. Lotti). Each pot was filled with the upper layer of either a Cambic arenosol (soil A) or a Dystric cambisol (soil B) removed from the correspondent lysimeter where a two‐year wheat experiment (1993–1995) had been carried out with an equivalent experimental design as in the present study. The main objectives of this research were (1) to study the effects of increasing applications (5, 15, and 25 t ha^‐1) of solid phase from pig slurry (SP) on wheat yield and tissue elemental composition and (2) to investigate the risk of contamination of drainage water by leaching of phosphorus (P) and mineral nitrogen (N_min) as a result of those applications to the soil. The control consisted of a basic dressing of NPK fertilizer. Results from the study showed that grain production was lower in the 5 and 15 t ha^‐1 SP treatments compared to the control in soil A probably due to a potassium (K) deficiency. Increasing application rates of SP significantly enhanced P and N_min leaching losses in both soils. Finally on soil A high rates of SP amendments led to the contamination of water with P.     

Microbial dynamics in an anaerobic soil slurry amended with glucose, and their dependence on geochemical processes

Under anoxic conditions, microbial activities interact closely with geochemical reactions and consequently affect soils, underlying aquifers, and the atmosphere. Recent studies have noted the relationships between microbial biodiversity and environmental conditions, but the dynamics of numerous coexisting microbial groups in connection with soil biogeochemical processes has never been investigated. In this work, we investigated the dynamics of anaerobic microbial populations using a new method combining PCR-SSCP and epifluorescent direct counts, and analysed these results in the light of biogeochemical changes. Batch incubations were performed over an 8-day period on a calcic cambisol (WRB) incubated anaerobically, either without amendment (treatment C) or after adding glucose (treatment +G). In treatment +G, the predominant microbial processes included (i) NO₃⁻ and NO₂⁻ reduction during the first 12 and 24 h of incubation respectively, (ii) fermentations during the first 6 days with non-symbiotic N₂ fixation between days 1 and 6, enabling bacterial growth during this period, and probably (iii) reduction of FeIII by H₂ oxidation throughout the incubation period. In treatment C, microbiological and geochemical measurements revealed no prominent microbial activities, and the PCR-SSCP method led to complex bacterial density profiles without prominent peaks. In treatment +G, 78 microbial groups were distinguished; these were divided into seven sets (A to G) according to their dynamics. Bacteria belonging to sets A, E and F grew during the period of intense fermentation and were probably able to fix N₂, as is the case with Clostridium butyricum (set A). Bacteria belonging to sets B, D, and G were probably able to reduce FeIII to FeII with concomitant oxidation of H₂ into H₃O⁺, but unable to fix N₂. Two microbial groups in these sets were closely related to Clostridium favosporum (set B) and the genus Bacillus (set B). Bacteria belonging to class C were probably only able to reduce N oxide(s). Lastly, we obtained two similar estimates of the gross increase in microbial biomass by taking into account either (i) the sum of gross increases for the 78 microbial groups, or (ii) the energy yield of catabolic reactions minus the energy requirement for N₂ fixation.     

黑土有机氮肥替代率演变及其对土壤有机碳的响应

【目的】 探索长期有机培肥下黑土有机肥替代率与土壤肥力的量化关系,为农田土壤培肥和有机替代提供理论依据。 【方法】 本研究依托公主岭黑土肥力长期试验的32年定位观测数据,选取其中的4个处理即不施肥 (CK)、单施化学氮磷钾肥 (NPK)、单施常量有机肥[30 t/(hm2·a),M1]和单施高量有机肥[60 t/(hm2·a),M2],试验用化肥为尿素、过磷酸钙和硫酸钾,年施用N 150 kg/hm2、P₂O₅ 75 kg/hm2、K₂O 75 kg/hm2。分别测定作物产量、植株含氮量以及土壤全氮、碱解氮、全磷、有效磷、全钾、速效钾、有机碳含量。基于作物氮素养分吸收量,探讨长期高产条件下施用不同量有机肥其替代率的变化特征,在分析高产条件下有机肥替代率与土壤肥力的基础上,进一步探讨两者之间的数量化关系。 【结果】 基于作物氮素养分吸收量,长期高产条件下高量有机肥处理 (M2) 的有机肥替代率高于常量有机肥处理 (M1),且高产条件下有机肥替代率与施肥年限呈极显著线性正相关 (P < 0.01);通径分析和多元逐步回归分析结果表明,土壤有机碳含量对高产条件下有机肥替代率有显著正效应,是决定高产条件下有机肥替代率差异的主要土壤肥力要素,决定了高产条件下有机肥替代率70%的变异。长期施用常量和高量有机肥处理 (M1和M2),黑土土壤有机碳含量显著增加 ( P < 0.01);土壤有机碳含量与高产条件下有机肥替代率非线性相关,并达到了极显著水平 ( P < 0.01)。 【结论】 化肥氮的有机氮替代率70%取决于土壤有机碳含量的高低。长期施用有机肥能显著提高土壤有机碳含量,在提升土壤肥力的同时,提升了有机氮对玉米吸收的贡献,减少了对化肥氮的依赖。黑土土壤有机碳含量达到24.89 g/kg时,有机肥对化肥的替代率趋近95%,达到最大值。      

猪粪厌氧、有氧发酵物氮源对甘蓝生长及土壤养分的影响

探讨了在等氮量供应下,猪粪厌氧发酵物(沼液)及有氧发酵物(堆肥)氮源对甘蓝生长及土壤养分的影响,结果表明:在等氮量供应的情况下,施用猪粪沼液不仅可以替代化肥为作物提供生长所必需的氮素,而且提高了养分的利用效率,对甘蓝的增产效果显著;而施用猪粪堆肥处理的甘蓝产量较低,但是施用猪粪堆肥可以提高土壤有机质和土壤p H值,减少施用化肥带来的土壤酸化危害;在等氮量供应的情况下,单施猪粪堆肥处理的土壤有效磷、速效钾含量最高。     

Enhanced sorption of polycyclic aromatic hydrocarbons by soil amended with biochar

Purpose  

Polycyclic aromatic hydrocarbon (PAHs) are ubiquitous pollutants in agricultural soils in China. Biochar is the charred product of biomass pyrolysis, which is widely applied to soils to sequestrate atmospheric carbon dioxide and guarantees a long-term benefit for soil fertility. Knowledge about the impacts of various biochars on soil sorption affinity remains obscure. In this study, we evaluated the effects of various biochars on PAHs sorption to biochar-amended agricultural soil.     

Heterogeneity of O2 dynamics in soil amended with animal manure and implications for greenhouse gas emissions

Soil oxygen (O₂) availability influences nitrification and denitrification, the major biological processes responsible for nitrous oxide (N₂O) production and emissions from soil. In this study O₂-specific planar optodes were used to visualise O₂ distribution with high spatial and temporal resolution in soils in which the same amount of solid fraction of pig manure had been distributed in three different ways (mixed, layered, single patch) and which were maintained at a water potential of −5 kPa (corresponding to 91% of water-filled pore space). In parallel, the greenhouse gas emissions (N₂O, CO₂ and CH₄) from soil at high temporal resolution were monitored. At the end of the incubations, vertical profiles of mineral nitrogen (ammonium and nitrate) in the soil matrix were quantified. The optode results revealed that anoxia rapidly developed in zones with manure addition and gradually expanded to the entire soil during the 66-h experimental period. The anoxia in the soil developed more quickly as the heterogeneity of manure distribution decreased (from single patch to layered to mixed). The single patch distribution of manure solids delayed peak emission rates of both N₂O and CO₂, but stimulated the cumulative N₂O emissions and reduced the cumulative CO₂ fluxes. The faster the anoxia developed, the less the nitrification process appeared to contribute to N₂O emissions. No treatment effects on CH₄ emissions were observed. Combined high resolution imaging of O₂ dynamics and measurements of N₂O emission rates are essential to get a detailed understanding of how O₂ availability regulates the distribution and coupling of denitrification and nitrification activity in soil. Such unique information on soil O₂ dynamics could be used for further modelling and quantification of processes producing greenhouse gases from soil ecosystems.     

Carbon and nitrogen mineralization dynamics in different soils of the tropics amended with legume residues and contrasting soil moisture contents

Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect, C and N mineralization dynamics in three tropical soils (Af, An₁, and An₂) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g⁻¹ dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days. The legume residues markedly enhanced the net cumulative CO₂–C flux and its rate throughout the incubation period. The cumulative CO₂–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO₂–C. In one of the three soils (An₁), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH₄⁺–N and NO₃⁻–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally in both NH₄⁺–N and NO₃⁻–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period.     

Impact of cattle slurry acidification on carbon and nitrogen dynamics during storage and after soil incorporation

Acidification of animal slurry is recommended in order to reduce NH₃ emissions, but relatively little is known about the effect of such treatment on C and N dynamics during acidification, storage, and after soil application. A laboratory study was performed, and the CO₂ emissions from a high–dry matter slurry (HDM), a low–dry matter slurry (LDM), and the same respective acidified slurries (AHDM and ALDM) were followed during a storage period and after soil incorporation. The N‐mineralization and nitrification processes, as well as microbial‐biomass activity were also estimated in soil receiving both the acidified and nonacidified materials. We observed a strong CO₂ emission during the acidification process, and acidification led to a small increase in CO₂ emissions (≈ 11%) during storage of AHDM relative to HDM. No effect of LDM acidification on CO₂ emissions during storage was observed. About 30% of C released during storage of AHDM was inorganic C, and for ALDM the C release was exclusively inorganic. Soil application of AHDM and ALDM led to a decrease in soil respiration, nitrification, and microbial‐biomass‐C values, relative to soil application of HDM and LDM, respectively. Furthermore, it was shown that this effect was more pronounced in ALDM‐ than AHDM‐treated soil. Considering both steps (storage and soil application), acidification led to a significant decrease of C losses and lower C losses were observed from LDM slurries than from HDM slurries.     

Potential diffusion of doramectin into a soil amended with female pig manure. A field experiment

Doramectin is a veterinary drug used as an antihelminthic and is excreted mainly in the feces as the nonmetabolized drug. This study investigated the time profile of doramectin excretion in pig feces and the potential transfer and persistence of doramectin in the soil when the pig manure is used as an organic amendment to the soil. The concentration of doramectin in feces peaked at 143.0 ng/g in the dry feces 4 days after treatment. On day 62, the drug was still detected in the pig feces. After the land application of pig manure, the maximum concentration of doramectin in soil (ppb level) was detected 6 days after treatment. Seven months after the manure application, traces of doramectin were detected in the soil from the surface to a depth of 90 cm. Successive applications of manure from pigs treated with doramectin in a specific area could produce an accumulation of this drug in the soil.     

联合施用不同植物物质和鸡粪对土壤碳氮含量和蔬菜产量的影响

The use of plant materials as soil amendments is an uncommon practice amongst major farming communities in Ghana, although it is necessary for soil fertility improvement. An examination of the effects of soil amendments is necessary to encourage the use of under-utilized organic resources in Ghana. Thus, a field experiment was conducted using 8 different tropical plant materials mixed with chicken manure as soil amendments for growth of tomato as a test crop. The plant materials included Leucaena leucocephala, Centrosema pubescens, Sesbania sesban, Gliricidia sepium, Mucuna pruriens, Pueraria phaseoloides, Azadirachta indica, and Theobroma cacao. There were two other treatments: one with equivalent amounts of chemical fertilizers and the other with no-fertilizer input (control). Plant materials were mixed with chicken manure to obtain a uniform carbon-to-nitrogen (C:N) ratio of 5:1. Except the no-fertilizer control, all treatments received the same amount of nitrogen (N). To clarify the decomposition pattern of the plant materials in soil, an incubation experiment was conducted using only the plant materials before the field experiment. The Gliricidia treatment released significantly more mineral N than the other plant materials in the incubation experiment. However, the tomato fruit yield was not enhanced in the Gliricidia treatment in the field experiment. The known quality parameters of the tested plant materials, such as total N, total carbon (C), C:N ratio, and total polyphenols, had minimal effects on their mineralization dynamics. Azadirachta showed the best synergistic effect with chicken manure through significantly increasing soil microbial biomass and fruit yield of tomato. This result provides insights into the possible adoption of Azadirachta in combination with chicken manure as a soil amendment in small-scale agricultural holdings.     

Nitrogen dynamics in soils amended with slurry treated by acid or DMPP addition

The objective of the present study was to evaluate the impact of the treatment of slurry liquid fraction (LF) acidified to pH 5.5 (ALF) on nitrification and denitrification processes after soil application. The impact of such treatment was compared with that of untreated LF, LF treated with a nitrification inhibitor (3,4-Dimethylpyrazole phosphate (DMPP)) (LF + DMPP). An incubation was conducted using the denitrification incubation system (DENIS/gas-flow-core technique) at a constant temperature of 20 °C and lasted for 32 days in order to follow nitrogen dynamics and gaseous emissions (N₂O, NO, CO₂) from soil. Inhibition of ammonium nitrification and nitrate accumulation was evident in both LF + DMPP and ALF at the top soil (0–3.75 cm) and those effects were stronger in the LF + DMPP. Denitrification was the main source of N₂O emissions from soils amended with treated and untreated LF. Compared to the untreated LF, the ALF significantly reduced the total N lost as N₂O from 0.10% to 0.05% of the applied N whereas the DMPP reduced the total N lost as N₂O from 0.10% to 0.07%. Relative to the untreated LF, the ALF reduced the total N lost as NO emissions from 0.03% to 0.02% of the applied N whereas DMPP addition led to a stronger decrease from 0.03% to 0.01%. Both, ALF and LF + DMPP had no impact on CO₂ emissions relative to the untreated LF. The ALF reduced CO₂ emissions by 19% relative to the LF + DMPP. Our results demonstrate that slurry acidification affect not only nitrification but also the denitrification process. This suggests that slurry acidification is a valid technique to minimize N emissions.     

好氧发酵猪粪部分替代化肥提高夏玉米氮素利用率和土壤肥力

  【目的】  化肥及畜禽粪便的不合理施用不仅影响作物增产,还严重威胁土壤健康和环境安全。探究不同发酵方式猪粪有机肥及有机肥替代化肥的比例对夏玉米氮素吸收及土壤碳、氮含量的影响,为规模化养猪场粪便快速处理,及制定其与化肥的适宜配比提供理论依据。  【方法】  以‘先玉335’为供试材料,在中国农业大学丰宁动物试验基地进行田间试验。设置5个处理:不施肥 (CK),100%化肥氮 (CF),100%自然堆肥猪粪氮 (PM),100%好氧发酵猪粪氮 (PC),50%好氧发酵猪粪氮 + 50%化肥氮 (FM)。分析猪粪不同发酵方式及有机氮替代比例对夏玉米氮素吸收及土壤碳氮的影响。  【结果】  在等氮条件下,与CF处理相比,FM处理产量、穗粒数、千粒重均以FM处理最高,其中FM处理显著增产13.2%,PC、PM处理与CF处理差异均不显著。FM处理玉米氮素积累量最高,两年平均为304.6 kg/hm2,较CF处理氮素累积量显著提高15.5%;PC、PM处理与CF处理氮素积累量差异不显著。与CF 处理相比,FM处理的氮素当季回收率、氮素农学利用率和偏生产力两年平均分别显著提高85.9%、59.5%和13.2% (P < 0.05),PC、PM处理与CF 处理之间无显著差异。在玉米拔节期和抽穗期,FM处理0—40 cm土壤无机氮含量均最高,与 CF 无显著差异;在成熟期,FM处理土壤无机氮含量较CF处理显著增加41.8%,而PC和PM处理与CF处理无显著差异。此外,施用有机肥可不同程度地增加土壤有机碳和全氮含量,与CF处理相比,PC和FM处理使有机碳含量分别显著提高13.3%和9.8%;FM处理土壤全氮含量显著提高33.4%。  【结论】  在等氮条件下与单施化肥相比,50%好氧发酵猪粪氮 + 50%化肥氮配施不仅显著提高了夏玉米产量和氮素累积吸收量,还提升了土壤全氮和有机碳含量以及0—40 cm土层土壤无机氮含量。单独施用自然堆肥、好氧发酵猪粪及化肥在产量和氮素积累方面没有显著差异,但可增加土壤全氮和有机碳含量,有利于土壤培肥,而施用好氧发酵猪粪的效果又优于施用自然堆肥。     

Effects of compost,biochar and manure on carbon mineralization of biogas residues applied to soil

Biogas residues contain microbial biomass, which contributes to the formation of soil organic matter. Whether the potential of biogas residues to increase soil organic matter can be enhanced by co‐application with compost, biochar or manure is unknown, however. The aim of this paper is to evaluate the effects of co‐amendment on the mineralization of biogas residues, carbon dioxide emissions and the carbon flow within the microbial food web. We determined the fate of ¹³C‐labelled microbial biomass present in biogas residues applied together with compost, biochar and manure to soil, by analysing CO₂ and biomarker phospholipid fatty acids. Although the rate of mineralization constant of the slowly degrading carbon pool was not affected by co‐amendments, co‐amendment with manure resulted in a larger rate of mineralization constant of the readily degrading carbon pool of biogas residues. The incorporation of carbon was mainly to Gram‐negative biomass and was the smallest with manure co‐amendment, which indicated differences in bioavailability of the carbon source.     

化肥与有机肥配施对设施土壤团聚体稳定性及其有机碳、全氮含量的影响

为探究设施栽培条件下化肥与有机肥配施对0～20 cm土层土壤团聚体稳定性及其有机碳、全氮含量的影响。以设施栽培连续7年定位施肥田间试验为依托,选择4个施用化肥处理(N₀PK、N₁PK、N₂PK和N₃PK)和4个化肥与有机肥配施处理(N₀PKM、N₁PKM、N₂PKM和N₃PKM),其中,N₀、N₁、N₂和N₃氮用量分别为0、187.5、375.0和562.5 kg·hm^-2,磷(P₂O₅)和钾(K₂O)用量分别为225.0和450.0 kg·hm^-2,有机肥(M)为75000kg·hm^-2,研究单施化肥及化肥与有机肥配施土壤团聚体稳定性及其有机碳、全氮含量。结果显示,与单施化肥相比,化肥与有机肥配...     

Differentiating the mineralization dynamics of the originally present and newly synthesized amino acids in soil amended with available carbon and nitrogen substrates

Newly synthesized amino acids are the principle compounds created after inorganic nitrogen (N) is rapidly immobilized into microbial tissues. However, little is known about the mineralization kinetics of these newly synthesized amino acids compared to the amino acids originally present in the soil, and how substrate availability controls their mineralization. With ¹⁵N isotope tracing, the newly synthesized (¹⁵N-labeled) amino acids can be differentiated from the amino acids originally present (unlabeled) in soil, making it possible to evaluate the mineralization of the newly synthesized amino acids in tandem with the original amino acids. As amino acids can serve as both N and carbon (C) sources for microorganisms, the mineralization dynamics of amino acids may be manipulated by the availability of extraneous C and N. In this study, an aerobic 30-week intermittent leaching experiment was conducted, using glucose as C source and (¹⁴NH₄)₂SO₄ as N source, following separate additions to soil. The newly synthesized amino acids were determined by an isotope-based high performance liquid chromatography/mass spectrometry (HPLC/MS). The newly synthesized soil amino acids mineralized faster than the original ones, which indicated more rapid cycling of N in the newly synthesized soil amino acids pool. Glucose addition significantly decreased the mineralization of both the newly synthesized and the original amino acids. However, when inorganic N was abundant, the newly synthesized amino acids decomposed rapidly, and preferentially as a C source and energy, while N addition inhibited the mineralization of the original amino acids in the soil. We conclude that the presence of readily degradable C (e.g. glucose) and inorganic N controls the mineralization of newly synthesized and original amino acid pools in soil differently, which is a crucial mechanism in adjusting the N supply and sequestration processes in soil ecosystems.     

Modelling water, carbon and nitrogen dynamics in soil covered with decomposing mulch

A decomposing mulch of residues on the soil affects strongly the water, carbon and nitrogen cycling in the soil. The mulch generates complex and interacting effects that remain difficult to quantify and model. An original mulch module was developed and implemented in the PASTIS model to account for the main biological and physical effects of decomposing mulch. In the extended model, PASTIS_mulch, the formalism splits the mulch into a decomposable layer in contact with the soil and an overlying not decomposable layer that ‘feeds’ the former. The model was calibrated on laboratory data derived from mulched soil columns experiments. Two types of residues were tested: rape residues made of large elemental particles (length, 10 mm; width, 3–10 mm; thickness, 0.1–8 mm) with a C:N ratio of 29, and rye residues consisting of smaller particles (length, 10 mm; width, 2 mm; thickness, 0.1 mm) with a smaller C:N ratio of 16. Calibration showed that mulch parameters were dependent on the type of residue. The model run with calibrated parameters provided good simulations of the water, carbon and nitrogen dynamics, with global efficiencies greater than 0.8. The sensitivity analysis carried out on seven key parameters showed that the total mulch dry mass and the proportion of this dry mass in contact with the soil are decisive parameters. PASTIS_mulch highlighted that mulch decomposition was not a continuous process but occurred in the form of successive pulses that correspond to favourable hydric conditions.