不同浸提剂处理森林土壤溶解性有机碳含量比较

为了解亚热带森林土壤溶解性有机碳(DOC)的特征规律,采用培养离心的方法获取土壤溶液测得DOC含量,对比传统水溶性有机碳(WSOC)提取法间的差异。选取湖南大山冲森林公园保存完好的3种亚热带典型次生林地,按10cm一层采集剖面土壤,采用不同方法提取测定土壤DOC和WSOC含量,分析与土壤理化指标的相关性及方法间的显著性关系。结果表明:①典型森林土壤DOC或WSOC含量随土壤剖面深度的增加,呈显著下降趋势。培养离心提取测得的土壤DOC含量明显较低,仅0.82～9.52 mg/kg,超纯水浸提的风干土WSOC含量达10.56～249.19 mg/kg,而0.5 mol/L K_2SO_4提取的鲜土WSOC含量达155.70～576.94 mg/kg,0.5mol/L K_2SO_4浸提的干土WSOC含量最高,达158.94～797.56 mg/kg,含量表现为:DOC干土超纯水浸提WSOC鲜土K_2SO_4浸提WSOC干土K_2SO_4浸提WSOC;②3种次生林土壤DOC或WSOC含量存在显著差异,不同方法测定的含量均表现为针叶林常绿阔叶林落叶林;③培养离心法测得土壤DOC含量与其他测定方法间存在极显著正相关(P0.01),并且土壤DOC和WSOC均与土壤pH、总有机碳、胡敏酸、富啡酸、全氮、全磷、速效态氮以及微生物生物量碳氮达到极显著相关(P0.01),与土壤含水率和容重显著相关(P0.05)。培养离心法测得土壤DOC含量远低于水溶液提取WSOC含量,该方法下的测得值更接近于原位土壤溶解性有机碳实际值。     

Carbon limitations to nitrous oxide emissions in a humid tropical forest of the Brazilian Amazon

The availability of labile organic C for microbial metabolic processes could be an important factor regulating N₂O emissions from tropical soils. We explored the effects of labile C on the emissions of N₂O from a forest soil in the State of Rondônia in the southwestern quadrant of the Brazilian Amazon. We measured emissions of N₂O from a forest soil after amendments with solutions containing glucose, water only or NO₃^–. Addition of glucose to the forest soil resulted in very large increases in N₂O emissions whereas the water only and NO₃^– additions did not. These results suggest a strong C limitation on N₂O production in this forest soil in the southwestern Amazon.     

碳酸钙与石膏对土壤磷及溶解有机碳淋溶的影响

研究碳酸钙与石膏对南澳大利亚典型土壤P和溶解有机碳淋溶的影响结果表明,碳酸钙可同时降低土壤P和溶解有机碳的淋溶,而石膏可降低土壤P淋溶和增加溶解有机碳的淋溶。     

Porous tubing for use in monitoring soil CO2 concentrations

The composition of the soil atmosphere is an indicator of biological processes, and soil CO₂ gradients have been used to estimate CO₂ efflux from the surface. Soil atmosphere samplers, constructed with gas-permeable materials, have been used to quantify soil CO₂ concentrations. The type of material used can influence the perceived real-time concentrations of CO₂ in the soil. Previous works have not directly compared different types of materials under the same conditions. The objective of this study was to determine the diffusion coefficient (D) and time of 95% equilibrium (t_eq) of CO₂ through several materials, and to evaluate the effect of long-term soil burial (183 days) on diffusion characteristics. Materials tested included silicone, expanded Teflon (ePTFE), and ultra high molecular weight polyethylene (PE) tubing. The D of each material was determined using a closed-loop system consisting of a CO₂-enriched (7800 ppm) chamber, a CO₂ analyzer and an inner tube (experimental tubing) placed inside the chamber. Air was re-circulated through the inner tube, and as CO₂ diffused from the chamber into the tubing, the analyzer recorded the increase in concentration. The silicone tubes had values of D ranging from 8.64 to 5.80×10⁻⁶ cm² s⁻¹ with corresponding t_eq between 3.9 and 9.7 h. Diffusion coefficients of the ePTFE (1.25×10⁻⁴ cm² s⁻¹) and PE (7.70×10⁻⁴ cm² s⁻¹) materials were 2 orders of magnitude greater, with t_eq<6 min. Exposure to the soil environment for 183 days did not visibly deteriorate the materials or significantly affect the D or t_eq values. Use of the ePTFE or PE materials, over the silicone materials, may allow for better characterization of dynamic CO₂ concentrations in the soil based on the greater D and lesser t_eq values of these materials.     

Influence of fertilization and organic amendments on organic‐carbon fractions in Heilu soil on the loess plateau of China

The influence of fertilization on organic‐carbon fractions separated by density and particle size in Heilu soil (Calcic Kastanozems, FAO) was investigated in a 20‐year (1979–1999) long‐term experiment on the Loess Plateau of China. Compared to an unfertilized treatment, N application alone did not increase total organic carbon (TOC) and its fractions of density and particle size. However, the treatment of N + P fertilization significantly increased salty‐solution–soluble organic carbon (SSOC), microbial biomass C (MB‐C), and organic C associated with fine silt. When manure was applied alone and in combination with N and P fertilizer, the light fraction of organic C (LFOC), SSOC, and MB‐C were increased significantly, and the TOC was as high as that of a native Heilu soil. Organic C associated with different particle‐size fractions was also increased significantly, and the allocation of C among the fractions was altered: the proportions of C in sand (>50 μm), coarse‐silt (20–50 μm), and fine‐clay (<0.2 μm) fractions were increased whereas fine‐silt (2–20 μm) and coarse‐clay (0.2–2 μm) fractions were decreased. It is concluded that N fertilizer alone is not capable of restoring organic‐matter content in the Heilu soils of the Loess Plateau and that C‐containing material like manure and straw is necessary to produce significant increase in soil organic carbon in these soils.     

Radiocesium transfer from Andosols to brown rice in the northern and northwest areas of Tochigi Prefecture,in the first 3 years following the 2011 Fukushima Daiichi nuclear power plant accident

ABSTRACT

Following the Fukushima Daiichi Nuclear Power Plant accident of 2011, the potential for radiocesium transfer from contaminated soils, such as Andosols, to agricultural crops became a significant concern. Andosols account for up to 70％ of paddy soils in the northern and northwest areas of Tochigi Prefecture, where the radiocesium concentration is 1000 Bq kg^?1 or greater in the soil of some fields. The present study was carried out in order to determine the phytoavailability of radiocesium in Andosols by comparing it with that of gray lowland soils in the first 3 years following the accident. The transfer factor (TF) tended to be higher in Andosols than in gray lowland soils, leading to higher radiocesium concentrations in brown rice grown in Andosols. The exchangeable potassium (Ex-K₂O) in Andosols was highly and negatively correlated with TF, followed by clay. The Ex-K₂O value was positively correlated with the clay/total carbon (T-C) value, suggesting that a high T–C ratio could weaken K₂O adsorption on clay mineral sites; hence, the low clay/T-C values can partially explain the relatively large TF values of Andosols. Samples with Ex-K₂O contents less than 200 mg kg^?1 and with low clay/T-C values showed striking decreases in TF values from 2011 to 2012. However, the decrease from 2012 to 2013 was quite small; radiocesium in these samples was potentially available for rice uptake for a long time, likely due to the reversible adsorption and fixation characteristics of allophane. Most gray lowland soil samples showed very low TF values over the 3 years of the study, except for those with TF values greater than 0.1 due to low Ex-K₂O and clay contents; the geometric mean (GM) value of TF was below 0.01 in 2012. The extraction of exchangeable radiocesium (Ex-Cs) with a 1 mol L^?1 ammonium acetate solution may not be an appropriate method for explaining the variability in radiocesium TF in Andosols. This is because the Ex-Cs value was significantly correlated with Ex-K₂O in Andosols, but not in gray lowland soils, indicating that Ex-K₂O explained this variability in relation to Ex-Cs.     

Water-extractable soil carbon in relation to the belowground carbon cycle

We investigated the role of water-extractable carbon (C-extr) as potential substrate for forest soil microorganisms by comparing belowground C fluxes at a plot with the forest floor removed (no-litter) and at a control plot. One-third lower soil respiration rates at the no-litter plot gave evidence that the forest floor was the source of considerable amounts of microbially degradable C. Laboratory incubation of C-extr, fractionated into neutral and acid moieties, showed that part of the C-extr was degraded rapidly, and that the high-molecular-weight acid fraction was much less degradable than the neutral C. To the extent that the degradable portion of the water-extractable C can be regenerated quickly, it may supply much of the substrate for heterotrophic soil respiration. Received: 11 December 1995     

Agricultural and ecological aspects of a sandy soil as affected by the application of municipal solid waste composts

We present the results of a plot experiment in which the changes in physical, chemical and physico-chemical properties of a sandy soil were examined after amending the soil with two different composts produced from municipal solid wastes. Triticale (X Triticosecale), cultivated in a 3-y monoculture, was used as a test plant. Both composts differed in their concentrations of heavy metals. Composts were applied non-recurrently in the spring before sowing, at the rates of 18, 36, and 72 t dry matter ha⁻¹. The plots without fertilization, and those fertilized annually with mineral nitrogen (N), phosphorous (P), and potassium (K) were used as controls. Soil samples were collected 1 month after compost application, as well as each year after harvesting. Application of both composts improved soil physical properties, associated with increasing content of organic carbon (OC). Statistically significant increases of total porosity, field water capacity and amounts of plant-available water were found only in the short time after compost application. Despite the fact that soil OC content decreased with time, a C:N ratio clearly increased in the third year after compost application, which was explained by a depletion of N reserve. Both composts caused a large increase of plant-available P, K, and magnesium (Mg), which was observed during the entire period of the experiment. Beneficial changes were also observed in soil humic substances composition. These were confirmed by increased humic acids content and humic/fulvic acid ratios. Soil cation exchange capacity and base saturation increased in all plots amended with composts. This effect was still observed 1 year after compost application, while in the third year it remained significant only at the highest compost rates. Compost originating from industrial areas, even if applied in low amounts, caused a significant increase in total concentration of soil heavy metals. This fact did not result, however, in any substantial changes in soil quality with regard to heavy metals content.     

Longterm influence of liquid sewage sludge on the organic carbon and nitrogen content of a furrow-irrigated desert soil

Summary In this study we evaluated the impact of five annual liquid sewage-sludge applications on the organic C and N content of a furrow-irrigated desert soil. Mineralization rates showed that sludge organic matter is mineralized rapidly (65% per year). Resistant residual sludge organic matter accumulation resulted in a theoretical increase in total soil organic C of 0.013% for the single sludge rate or 0.038% for three annual applications. These small additions were not detected in sludged soils at any depth to 270 cm. Similarly, increases in total soil N were not detected at any depth. However, soluble forms of organic C and N did increase in sludged soils relative to the non-sludged soils. In addition, soluble C:N ratios decreased significantly in the sludged soils. Soluble C and N also increased with depth due to leaching. This study therefore shows that applications of liquid sludge onto desert soils could affect the status of underground aquifers with respect to nitrate pollution.     

膨润土改善鸡粪厌氧消化产酸产甲烷特性

为探究膨润土对鸡粪厌氧消化过程中产甲烷特性和可溶性有机酸代谢特性的影响,采用L8(23)正交试验设计,以鸡粪添加量(有机负荷率)、膨润土添加量和接种量为三因素,每个因素设置2个水平,研究了中温条件下(35±1)℃膨润土添加对鸡粪厌氧消化过程中产酸和产甲烷特性的影响。结果表明:与对照组相比,低有机负荷条件下,膨润土添加能显著(P0.05)提高鸡粪挥发性固体(volatile solid,VS)产甲烷量,添加量为3.0%和1.5%时VS产甲烷量分别提升了22.72%、27.72%(膨润土添加量不同的组差异不显著(P0.05));高有机负荷条件下,膨润土添加能极显著(P0.01)提高鸡粪VS产甲烷量,添加量为3.0%和1.5%时VS产甲烷量分别提升了78.68%和55.41%(膨润土添加量不同的组差异显著(P0.05))。当鸡粪添加量为19.91 g挥发性固体,膨润土添加量为3.0%(占干基比)和接种量为80 m L(体积分数20%)时,单位挥发性固体产甲烷量最高为301.92 m L/g,比对照组高87.8%,此时可变成本也最低为2.43元/m~3,比两对照组分别低1.29和1.68元/m~3。方差分析表明:膨润土添加可提高鸡粪厌氧消化过程中挥发性脂肪酸,pH值,可溶性有机碳和可溶性无机碳的稳定性。膨润土可加强鸡粪厌氧消化系统的稳定性,降低产甲烷的可变成本,为膨润土强化鸡粪厌氧处理提供了试验验证据。