去除有机质对城市浅水湖泊氮磷释放特征的影响

[目的] 分析南昌市浅水湖泊象湖表层沉积物的释放特征及有机质对氮、磷释放的影响,为城市内浅水湖泊治理中富营养化控制提供理论依据。[方法] 通过释放动力学试验以及释放潜能试验研究了城市浅水湖泊氨氮（NH₄⁺-N）和溶解性活性磷（SRP）的释放特征,以及与通过H₂O₂去除有机质后的释放特征进行了对比。[结果] 去除前后的氮磷的释放速率都是先由一个较快的过程逐渐变慢最后趋于稳定达到最大释放量（Q_max）。去除有机质后NH₄⁺-N的释放平衡时间缩短,SRP则几乎不变。去除有机质后,NH₄⁺-N的最大释放量（Q_max）与有机质含量呈显著正相关,而SRP与有机质无显著相关性。[结论] 影响沉积物氮磷释放的因素多样,其中高等水生植物丰富的区域对磷的释放有明显的抑制作用。沉积物有机质的含量越高沉积物氮的最大释放量（Q_max）也越高,磷的的最大释放量（Q_max）则受有机质含量、活性、组成成分、吸附与结合的铁铝磷含量等因素共同影响。     

上海郊区河流沉积物N、P释放的初步研究

A laboratory study was conducted to observe the release of nitrogen and phosphorus from the sedimentsunder both anaerobic and aerobic conditions. The samples used were five creek sediments and a fish-pondsediment (as a comparison) obtained from suburban Shanghai. High loads of nitrogen and phosphoruswere found in the creek sediments. Total nitrogen of the sediments ranged from 1.17 to 5.95 g kg^-1; totalphosphorus from 608.63 to 2 033.95 mg kg^-1. Making up more than 90% of the total nitrogen, organicnitrogen was the dominant nitrogen fraction in the sediments; where as inorganic phosphorus was the dominant phosphorus fraction, which made up more than 85 percent of the total phosphorus. Cabound phosphorus fraction dominated inorganic phosphorus, which occupied more than 50% of the total. A large amount of ammonium was released from the sediments under both aerobic and anaerobic conditions, and the anaerobic releases were slightly greater than the aerobic. In addition, ammonium contents in the aerobic waters decreased sharply after reaching the peaks because of strong nitrification, compared with the relatively maintained ammonium peaks in the anaerobic waters. Anaerobic phosphate releases were much greater than the aerobic and the released ortho-phosphate was mainly from Fe-bound phosphorus. Ammonium and ortho-phosphate releases from the sample of the dredged creek were the lowest, showing that creek dredging could effectively remove contaminants from the surface of sediments and weaken the release potentials of nitrogen and phosphorus. Ammonium and ortho-phosphate releases from the fish-pond sediment were greater than those from the creek sediments though its total nitrogen and phosphorus were not the highest, which was probably due to the larger amount of biologically degraded organic matter in the fish-pond sediment.     

疏浚底泥的养分特征及污染化学性质研究

本文以运河 (杭州段 )待疏浚底泥为材料 ,分析了疏浚底泥的养分特征及其污染化学性质。结果发现 ,疏浚底泥中含有较高的养分 ,其中有机质、P、K含量较高而N偏低 ;施入土壤后 ,有机质矿化很快 ,P的供应较为持久。疏浚底泥重金属含量较一般城市污泥低 ,基本低于污泥农用中污染物控制标准 ,可考虑直接使用以节约处置费用 ;重金属的有效态含量不高 ,相对活性顺序为Cd Cu Pb Zn,直接大量施用会对种子发芽产生一定的毒害。供试作物种子对疏浚底泥毒害作用的反应不同 ,抗性顺序为青菜 羊茅草 三叶草。直接利用疏浚底泥比城市污泥具有更大的安全性 ,只要物种选取合适、用量恰当 ,是一种很好的肥源和复垦用土。     

Losses of nitrogen,phosphorus and potassium from agricultural watersheds of minor rivers in the Oka Valley

The losses of nitrogen (NH₄, NO₃, N_org), phosphorus (P_ortho, P_poly, P_org) and potassium (K⁺) from watershed areas of minor rivers, draining regions of different agricultural land use in the Oka Valley, U.S.S.R., were investigated. No N, P, and K pollution was shown in these watersheds, even though the rate of losses was found to be highly correlated with the amounts of mineral fertilizers and FYM applied. The losses were also determined by the natural soil fertility, erosion processes and soil texture under the similar level of fertilization.     

土壤有机矿质复合体研究Ⅳ.有机矿质复合体中有机磷的分布

本文研究湖沼母质发育的青紫泥水稻土和第四纪红土母质上发育的黄筋泥水稻土的有机矿质复合体中有机磷的分布。结果表明:各组复合体中有机磷的含量(μg/g)是G₂>G₁>G₀C/P₀和N/P₀比例是G₂高于G₀和G₁,说明有机磷在复合体G₂中的富集低于有机碳和氮。复合体中可溶性有机磷化合物总量较全土高。可溶性有机磷化合物中,肌醇磷占有机磷12.1-32.3%,核酸磷占1.9-5.8%,磷酸磷占0.7-3.1%。复合体中肌醇磷、核酸磷和磷脂磷的含量(μg/g)G₂明显高于G₀和G₁。复合体中有机磷的活性分级为:活性磷占10%左右,中等活性磷占50%左右,中等稳定性磷和高度稳定性磷各占20%左右。G₀组的活性磷比例较全土高,但G₁和G₂组中则明显降低。不同土壤有机矿质复合体中活性磷和中等活性磷的分布,与有机磷化合物中的核酸磷和肌醇磷的含量有关。     

Effect of Lake Management Efforts on the Trophic State of a Subtropical Shallow Lake in Lakeland, Florida, USA

For more than a decade, Lakeland, FL, has invested in restoring its urban Lake Hollingsworth from a hypereutrophic state to its natural eutrophic state. The lake bottom was dredged of nearly 2 million m³ of accumulated organic sediments, and treatment wetlands, storm water curb inlet strainers, and a storm water baffle box were installed within the lake’s catchment area to reduce the loading of dirt, leaves, and trash to the lake. After dredging ceased, the lake was dosed one time with alum to improve water clarity and reduce phosphorus recycling from its sediments. Water quality surrogates for algal biomass— Secchi disk transparency and water column total nitrogen, total phosphorus, and chlorophyll-α concentrations— were reviewed to assess Lakeland’s progress towards its goal. In the years since dredging has stopped, algal biomass concentration in Lake Hollingsworth has significantly declined. Even with these improvements, however, the lake still remains hypereutrophic.     

Pore‐system characteristics of pavement seam materials of urban sites

The original light‐brown sandy seam filling of pavements in urban areas turns dark and changes its properties by the time due to various inputs of urban dust. Deposited C_org inputs do mostly not have natural characteristics but are man‐made, e.g., diesel dust. Thus, properties of the seam material are not predictable from experiences with forest or agricultural soils. Semiperviously sealed urban areas are sites of contaminant deposition as well as groundwater recharge. For an assessment of the resulting groundwater‐contamination risk in these areas, the properties of the seam material, which influences transport processes, must be known. The aim of this study was to investigate the pore‐system build‐up, which includes size distribution and fractal character in the seam material of urban sites. The investigated samples were taken from pavements adjacent to roads in Berlin and Warsaw. The micropore parameters (nanometer range) were characterized using water‐vapor desorption isotherms, mesopore parameters (micrometer range) were estimated from mercury‐intrusion porosimetry and macropore parameters (millimeter range) from water‐retention curves. Particle density, dry bulk density, and particle‐size distribution were measured using standard methods. Volumes of micro‐ and mesopores as well as particle densities and dry bulk densities correlated with C_tot contents. However, no such relation was found for macropore volumes. Compared to the original sandy seam filling, the altered seam material shows significantly higher C_org contents and higher amounts of micro‐ and mesopores. Therefore, the available water capacity increases by 0.05–0.11 m³ m^–3, as compared to the original sandy seam filling. Compared to natural sandy soils having similar C_org contents, the seam material shows similar macropore volumes, but the volume of mesopores and micropores is a few times smaller. That is mainly because of the particulate character of the organic matter.     

Plant canopy effects on litter accumulation and soil microbial biomass in two temperate forests

The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha⁻¹) compared to oak stands (15.7t ha⁻¹). Canopy leaf area was also significantly larger in mixed stands (1.96m² m⁻²) than in oak stands (1.73m² m⁻²). Soil organic carbon (C _org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C _mic), nitrogen (N _mic), and total soil nitrogen (N _tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C _org/N _tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C _mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.     

Influence of soil tillage systems on aggregate stability and the distribution of C and N in different aggregate fractions

Soil aggregation is influenced by the tillage system used, which in turn affects the amount of C and N in the different aggregate fractions. This study assessed the impact of different tillage systems on soil aggregates by measuring the aggregate stability, the organic carbon (C_org) and the total nitrogen (N_tot) contents within different aggregate fractions, and their release of dissolved organic carbon (DOC). Soil samples were collected from the top 0 to 10 cm of a long-term tillage experiment at Fuchsenbigl (Marchfeld, Austria) where conventional tillage (CT), reduced tillage (RT), and minimum tillage (MT) treatments were applied to a Chernozem fine sandy loam. The stable aggregates (1000–2000 μm) were subject to dispersion by the soil aggregate stability (SAS or wet sieving) method after Kemper and Rosenau (1986), and the ultrasonic method of Mayer et al. (2002). Chemical analysis of the soil was obtained for the aggregate fractions 630–1000, 250–630 and 63–250 μm gathered from the ultrasonic method. Using the SAS method, CT and RT had the least amounts of stable aggregates (18.2% and 18.9%, respectively), whereas MT had twice as much stable aggregates (37.6%). Using the ultrasonic method, MT also had the highest amount of water stable aggregates in all three fractions (1.5%, 3.7%, and 35%, respectively), followed by RT (1%, 2.3%, 32.3%), and CT (0.8%, 1.7%, 29.1%). For comparison, a reference soil, EUROSOIL 7 (ES-7) was also analysed (40%, 6.7%, and 12.1%). The highest amounts of C_org and N_tot were measured under MT in all three fractions, with 8.9%, 3.8%, and 1.3% for C_org, and 0.4%, 0.3%, and 0.1% for N_tot. Apart from the fraction 630–1000 μm, the aggregates of RT and CT contained <50% of the C_org and N_tot values of MT. The C/N ratio was least favourable for CT (42.6) in the aggregate fraction 630–1000 μm. The DOC release from stable aggregates after 10 min of ultrasonic dispersion was highest from MT soil (86.7 mg l⁻¹). The values for RT and CT were 21% and 25% below this value. The results demonstrate that tillage type influences both aggregate stability and aggregate chemical composition. This research confirms that CT interferes more with the natural soil properties than RT and MT. Furthermore, MT has the highest potential to sequester C and N in this agriculturally used soil.     

Effect of forest and soil type on microbial biomass carbon and respiration

The aim of study was to evaluate the variation of soil microbial biomass carbon (C_mic) and microbial respiration (M_R) in three types soil (Chromic Cambisols, Chromic Luvisols and Eutric Leptosols) of mixed beech forest (Beech- Hornbeam and Beech- Maple). Soil was randomly sampled from 0–10 cm layer (plant litter removed), 90 soil samples were taken. C_mic determined by the fumigation-extraction method and M_R by closed bottle method. Soil C_org, N_tot and pH were measured. There are significant differences between the soil types concerning the C_mic content and M_R. These parameters were highest in Chromic Cambisols following Chromic Luvisols, while the lowest were in Eutric Leptosols. A similar trend of C_org and N_tot was observed in studied soils. Two-way ANOVA indicated that soil type and forest type have significantly effect on the most soil characteristics. Chromic Cambisols shows a productive soil due to have the maximum C_mic, M_R, C_org and N_tot. In Cambisols under Beech- Maple forest the C_mic value and soil C/N ratio were higher compared to Beech-Hornbeam (19.5 and 4.1 mg C g^–1, and 16.3 and 3.3, respectively). This fact might be indicated that Maple litter had more easy decomposable organic compounds than Hornbeam. According to regression analysis, 89 and 68 percentage of C_mic variability could explain by soil C_org and N_tot respectively.     

Effect of crop residues on the organic matter composition of a leached chernozem in the Western Siberian forest-steppe

In leached chernozems used in crop rotations with different amounts of plant residues for nine years, the following parameters have been determined: the changes in the contents of the total carbon and carbon and nitrogen from the readily hydrolyzable components of the soil organic matter: the labile humus, detritus, and mortmass. No significant differences in the content of C_org in the soil among the crop rotations have been found. The different inputs of plant residues have significantly affected the contents of carbon and nitrogen in the readily mineralizable soil organic matter. The decrease in the mean annual input of the aboveground plant residues to the soil from 1.5 to 0.2 t C/ha resulted in the reduction of the carbon and nitrogen contents in the soil by 19–25% for the labile humus, 24–28% for the detritus, and 33–36% for the mortmass. The labile humus formed the largest fraction (3890 mg of C/kg soil or 10.3% of C_org on the average for the crop rotations); the fractions of the detritus (1546 mg C/kg soil or 10.3%) and mortmass (627 mg C/kg soil or 1.7% of C_org) were the next.     

Selected Nutrients and Iron in Interstitial Waters of the Estuary of Southern Baltic (Gulf of Gdañsk and the Pomeranian Bay) in Relation to Redox Potential

The following parameters were determined in the interstitial waters of the Gulf of Gdańsk and the Pomeranian Bay: nutrients (ammonia and phosphates), sulphates, total iron and iron(II) concentrations. Redox potential (Eh), pH, humidity and organic matter content measured as a loss on ignition were determined in bottom sediments from these regions. Interstitial waters of both regions were found to have reducing character (Eh < 250 mV). Reduction processes were more advanced in the Gulf of Gdańsk, rich in organic matter, as evidenced by lower values of the redox potential, lower Fe(III)/Fe_tot ratio, and incidents of sulphates exhaustion.     

东祁连山不同高寒草地型牧草返青期土壤碳分布特征

以东祁连山高寒草地为样点,对土壤有机质、K2SO4浸提碳和微生物量碳(氯仿熏蒸浸提法)等进行了研究.结果表明:该区土壤有机质介于82.3～207.2 g·kg-1,植被类型影响土壤有机质含量.土壤K2SO4浸提碳介于23.61～138.81 mg·kg-1,分别占土壤有机质和土壤微生物量碳的0.03%～0.06%和9.97%～18.46%;灌丛草地中,高山柳草地显著低于杜鹃草地(P<0.05);草本草地中,珠芽蓼草地、沼泽草地和嵩草草地显著高于禾草草地(P<0.05).土壤微生物量碳介于156.19～1 182.84mg·kg-1,上层显著高于下层(P<0.05),除2005年沼泽草地外草本草地与灌丛草地间差异显著(P<0.05);微生物量碳对土壤有机质的贡献率介于0.19%～0.48%,禾草草地最低(0.19%),金露梅灌丛草地最高(0.48%),除珠芽蓼草地和沼泽草地外均为上层高于下层;且除禾草草地和嵩草草地外微生物量碳与土壤有机质、全氮和速效磷间呈显著(P<0.05)或极显著正相关(P<0.01),与土壤K2SO4浸提碳在灌丛草地呈显著正相关(P<0.05),在草本草地呈极显著正相关(P<0.01),与微生物量氮、磷间呈极显著正相关(P<0.01).该结果表明微生物量碳及其对土壤有机质的贡献率在草地型闻和土层间差异明显,且与土壤有机质、K2SO4浸提碳、全氮和速效磷关系密切.     

Distribution of transformed organic matter in structural units of loamy sandy soddy-podzolic soil

The effect of land use types and fertilizing systems on the structural and aggregate composition of loamy sandy soddy-podzolic soil and the quantitative parameters of soil organic matter has been studied. The contribution of soil aggregates 2–1 mm in size to the total C_org reserve in the humus horizon is higher than the contributions of other aggregates by 1.3–4.2 times. Reliable correlations have been revealed between the contents of total (C_org), labile (C_lab), and active (C₀) organic matter in the soil. The proportion of C₀ is 44–70% of C_lab extractable by neutral sodium pyrophosphate solution. The contributions of each of the 2–1, 0.5–0.25, and <0.25 mm fractions to the total C₀ reserve are 14–21%; the contributions of each of the other fractions are 4–12%. The chemically labile and biologically active components of humic substances reflect the quality changes of soil organic matter under agrogenic impacts. A conceptual scheme has been proposed for the subdivision of soil organic matter into the active, slow (intermediate), and passive pools. In the humus horizon of loamy sandy soddy-podzolic soil, the active, slow, and passive pools contain 6–11, 34–65, and 26–94% of the total C_org, respectively.     

Earthworms change the distribution and availability of phosphorous in organic substrates

In laboratory controlled soil microcosms, the distribution and availability of phosphorous (P) were determined in the surface-casts and the burrows-linings of the anecic earthworm L. terrestris and were compared with non-ingested soil. To simulate more realistic earthworm community conditions, a combination of L. terrestris plus the endogeic A. caliginosa was tested. For a 2-month period, the earthworms were given two organic food substrates: rye-grass littered onto the soil surface and sewage sludge mixed with soil. The following treatments were designed: (i) soil alone (S), (ii) soil and sewage sludge (SS), soil and rye-grass litter (SL), and (iv) soil, litter and sludge (SSL). Analyses were performed for P contents (total, available and organic), organic matter content (organic carbon, C_org and total nitrogen, N_tot) and the two acid and alkaline phosphatase activities (AcPA and AkPA). Earthworms enhanced AcPA and were also responsible for additional AkPA in soil. The two AcPA and AkPA increased not only in surface-casts but also in burrows-linings that paralleled with the decrease of organic P in SL and SSL treatments. The stimulation of AcPA began quickly and declined rapidly in casts (from 19 to 8 μmol phenol g⁻¹ dry wt h⁻¹, respectively at week 2 and 8 in the SL treatment) but it was initiated later and maintained at a high level for longer in burrows (more than 10 μmol phenol g⁻¹ dry wt h⁻¹ at week 8 in the SL treatment). Significant positive correlations were found between the AkPA activities and N_tot contents (r=0.95, p=0.001) and to a lesser extend with C_org contents (r=0.76, p=0.05) in casts from the SL treatment, while AcPA significantly correlated with N_tot (r=0.91, p=0.004) but not with C_org (r=0.72, p=0.06). P availability was always highest in casts. However, the available P contents decreased sharply over time in casts and were still low in burrow-linings, suggesting that a large part of inorganic P produced was rapidly immobilized for the microbial growth. Total P content was unchanged except in the SL treatment in which it increased in casts and burrows (ca. 725 μg g⁻¹, at week 4). Organic P was first the highest in casts and then decreased over time (from 168 at week 1 to 140 μg g⁻¹ at week 8 in the SL treatment). This study illustrates that earthworms facilitate P transfer downward increasing a P patchy distribution in the soil, and significantly change the biogeochemical status of P (availability, organic phosphorous pool, AcPA activities) in certain hot spots such as casts and burrow-linings.     

Indications for soil organic matter quality in soils under different management

Changes in management practice are reflected by soil carbon and nitrogen status, in particular by the proportion of soil organic matter (SOM) being easily transformed (active SOM). We describe SOM quality for three management practices, Organic Farming system (OF), Integrated Crop Production (ICP) and pasture sites (G), which intend to achieve sustainable management practice. The experimental sites were conventionally farmed until 1992. SOM quality was examined by describing active SOM pools, such as the decomposed ‘young soil organic matter’ (YSOM), ratio of microbial biomass carbon (C_mic) to organic carbon (C_org), ecophysiological status of the microbial biomass (qCO₂), and the ratio of light particulate organic matter (POM-LF) to C_org. Ratios of soil microbial biomass (C_mic/C_org) and POM-LF (POM-LF/C_org) and the amount of decomposed YSOM were relatively similar to each other, despite differences in management practice and soil texture. Soil microbial parameters (C_mic, C_mic/C_org and qCO₂) were significantly (p<0.05) affected by the amount of decomposed YSOM and the silt content in the OF. In the ICP, soil microbial parameters depended only on the amount of decomposed YSOM, which was considered to be a consequence of the more heterogeneous texture at the OF-sites. Management effects were detectable for no-tillage in the ICP leading to an accumulation of active SOM in the surface soil (0–10 cm). The ratio POM-LF/C_org showed no difference between G and OF despite markedly higher C_org-contents at the G-sites. Conclusively, all methods used indicate comparable SOM qualities for the three management systems, despite differences in soil texture and soil management during 7 years. Management practices seem to be well adapted to the site conditions.     

Interactive effects of substrates and ectomycorrhizal colonization on growth of a poplar clone

A balsam poplar clone (Populus trichocarpa cv. Weser 6) was inoculated by two ectomycorrhizal strains (Laccaria bicolor MW 158 and Paxillus involutus 1444) in Kick‐Brauckmann‐pots. The substrates were two arable sandy soils (Cambisols) with different organic matter content and nutrient supply. One soil (WIL) was rich in organic matter (C_org = 1.6%) and total nitrogen (N_t = 0.14%), whereas the other soil (RIE) had low contents of C_org (0.8%) and N_t (0.08%). Leaf nutrient concentrations, shoot lengths, root and shoot biomass production and nitrogen accumulation in the biomass were determined to discover possible inoculation effects. Mycorrhization indices (% colonized fine roots) of 36% with Laccaria bicolor and 40% with Paxillus involutus were observed on the C_org rich soil (WIL) in contrast to 16% and 14% on the C_org poor soil (RIE), respectively. Inoculation of poplar on the soil WIL increased shoot length, biomass production, shoot:root ratio and total N uptake of the cuttings, whereas on the soil RIE only the shoot:root ratio increased and the N nutrition was improved. We conclude that interactions between soil and fungus should be tested when choosing ectomycorrhizal strains for inoculation.     

Reconstruction of Late Glacial and Holocene landscape-climatic changes in the central Selenga Middle Mountains based on the isotopic composition of organic matter

The results of investigation into the composition of stable carbon and nitrogen isotopes of organic matter in the soils developed within soil–sedimentary sequences in the central part of the Selenga Middle Mountains in the Late Glacial and Holocene are presented. In the past 15000 years, the organic matter of the investigated soils has only been formed from the biomass of C3 plants (without the participation of C4 plants). This is confirmed by the of δ¹³С values from–27.00 to–23.35‰. A combined analysis of the parameters of the organic matter (С_org, N_total, C/N, δ¹³С, and δ¹⁵N) of soils formed in different periods makes it possible to assume that the isotopic composition of carbon and nitrogen reflects changes in the climate humidity during the Late Glacial and Holocene periods. The specified intervals of soil formation correspond to the climate humidification and stabilization of the surface owing to the development of dense vegetation. Aridization periods were characterized by the accumulation of sediments that buried soil horizons. The most pronounced stages of climate aridization occurred at the transition from the Late Glacial to the Holocene, from the Boreal to the Atlantic, and from the Atlantic to the Subboreal periods. The optimum soil-forming conditions existed in the periods of 11700–11000, 8800–6900, and 4700–1000 years ago, which is confirmed by the published data on the landscape-climatic changes in the adjacent areas in the past 15000 years.     

Interaction effects of nitrogen and phosphorus fertilizer on nitrogen mineralization of wheat residues in a calcareous soil

Abstract

Because of the high pH of the soil in semiarid regions, phosphorus adsorption is unfavorable. So, considerable amounts of phosphorus fertilizers are used annually, where this fertilizer may affect the plant residues' decomposition. To examine the interaction effects of nitrogen and phosphorus on nitrogen mineralization in calcareous soil, a factorial experiment was performed in a completely randomized design with three replications. The first factor consisted of various C:N ratios (20, 40, and 60 or three levels of nitrogen N₁:0, N₂:11, and N₃:43?kg N ha^?1, respectively) and the second factor consisted of various C:P ratios (87, 174, and 260 or three levels of phosphorus P₁:0, P₂:12, and P₃:45?kg P ha^?1, respectively), under incubation conditions. The results indicated that the cumulative mineral nitrogen content in all treatments, except for N1P2 and N1P3 treatments, started from a positive amount and remained positive until the end of the incubation period. The highest amount of cumulative mineral nitrogen among treatments was related to N3P1 treatment, while the lowest was associated with N2P3 treatment. Mineralization of nitrogen during 60?d of incubation was the dominant phenomenon, except for the N1P2 and N1P3 treatments which remained in the organic phase. The effect of phosphorus on the cumulative mineralization of nitrogen was significant. With increasing the amount of phosphorus, the total inorganic nitrogen diminished. Nitrogen release begins earlier with lower C:N ratios, and therefore the available nitrogen can be released more quickly to the plant. It is generally concluded that, in calcareous soil, the use of nitrogen fertilizer to adjust C:N ratio and to improve the mineralization of wheat residues will be a suitable option.     

Soil microbial biomass and activity: the effect of site characteristics in humid temperate forest ecosystems

Microbial biomass, respiratory activity, and in‐situ substrate decomposition were studied in soils from humid temperate forest ecosystems in SW Germany. The sites cover a wide range of abiotic soil and climatic properties. Microbial biomass and respiration were related to both soil dry mass in individual horizons and to the soil volume in the top 25 cm. Soil microbial properties covered the following ranges: soil microbial biomass: 20 µg C g^–1–8.3 mg C g^–1 and 14–249 g C m^–2, respectively; microbial C–to–total organic C ratio: 0.1%–3.6%; soil respiration: 109–963 mg CO₂‐C m^–2 h^–1; metabolic quotient (qCO₂): 1.4–14.7 mg C (g C_mic)^–1 h^–1; daily in‐situ substrate decomposition rate: 0.17%–2.3%. The main abiotic properties affecting concentrations of microbial biomass differed between forest‐floor/organic horizons and mineral horizons. Whereas microbial biomass decreased with increasing soil moisture and altitude in the forest‐floor/organic horizons, it increased with increasing N_tot content and pH value in the mineral horizons. Quantities of microbial biomass in forest soils appear to be mainly controlled by the quality of the soil organic matter (SOM), i.e., by its C : N ratio, the quantity of N_tot, the soil pH, and also showed an optimum relationship with increasing soil moisture conditions. The ratio of C_mic to C_org was a good indicator of SOM quality. The quality of the SOM (C : N ratio) and soil pH appear to be crucial for the incorporation of C into microbial tissue. The data and functional relations between microbial and abiotic variables from this study provide the basis for a valuation scheme for the function of soils to serve as a habitat for microorganisms.