The effects of human trampling on the microbiological properties of soil and vegetation in mediterranean mountain areas

Increased tourist activity and recreational use of wilderness and other protected areas has endangered zones of high environmental value. The aim of this work was to evaluate the effects of trampling intensity (low, high use trails and untrampled trails) and distance from the trails (on the trails, at 10 and 20 m from the trails) on the vegetation, chemical, physical and microbiological properties of a soil in Mediterranean mountain areas. Trail type and distance from the trail significantly influenced several parameters. High use trails showed lower values of plant cover and diversity of vegetation species, as well as soil respiration and some enzyme activities (phosphatase, β‐glucosidase and dehydrogenase) than low use trails. In addition, the effects of trampling spatially extended further from these high use trails than from low use trails. Statistical analysis showed that some microbiological (basal respiration, dehydrogenase activity and β‐glucosidase activity) and vegetal parameters (plant cover and diversity) may be established as a set of indicators for the evaluation of soil quality on these areas subjected to human trampling. We concluded that trampling significantly impacts on soil microbial processes and vegetal communities, and visitor should be restricted from entering ecologically sensitive areas due to the effects of trampling. Copyright © 2010 John Wiley & Sons, Ltd.     

长期施有机肥与缺素施肥对潮土微生物活性的影响

利用中国科学院封丘农业生态国家实验站潮士农田生态系统养分平衡长期定位试验地,研究长期施有机肥或缺索施肥对农田土壤呼吸强度及酶活性的影响.结果发现,与不施肥对照(CK)相比.施肥处理均不同程度地提高了土壤的呼吸强度及转化酶、脲酶与磷酸酶活性;从N、P、K平衡施肥角度比较,施有机肥[OM)与有机无机配施(1/20M+1/2NPK)的效果均显著高于施无机肥(p<0.05);从缺素施肥角度分析,缺P显著低于NPK处理(p<0.05),缺N次之,缺K影响较小.结果表明,长期配施有机肥更有利于提高潮土的微生物活性,长期缺施P肥最不利于保育潮土的微生物学质量.     

黄土旱塬长期秸秆还田对土壤养分、酶活性及玉米产量的影响

研究黄土旱塬区玉米生产中长期秸秆还田对土壤性质及玉米产量的影响,可为农田土壤可持续利用及质量提升提供科学依据。本研究基于连续24年(1992—2016年)秸秆还田长期定位试验,设置秸秆过腹还田、秸秆直接还田、秸秆覆盖还田以及不还田处理,研究长期不同秸秆还田方式对土壤化学性质、酶活性以及玉米产量的影响。研究表明,秸秆不还田处理累积玉米产量为1.695×105 kg·hm?2,覆盖还田、直接还田和过腹还田处理累积玉米产量分别为1.885×105 kg·hm?2、1.854×105 kg·hm?2、2.001×105 kg·hm?2,其增产率分别为10.1%、8.6%、15.3%。3种秸秆还田均可以显著提高0～20 cm土层土壤有机碳含量6%～14%,对20～40 cm土层土壤有机碳含量无显著影响。与秸秆不还田相比,长期过腹还田可显著增加土壤全氮、全磷、全钾、有效氮、有效磷和有效钾含量,秸秆直接还田可显著增加土壤全氮、全钾、有效氮和有效钾含量,长期覆盖还田仅提高土壤有效氮和有效钾含量。土壤蔗糖酶活性表现为过腹还田最高,直接还田和覆盖还田次之,不还田处理最低。秸秆直接还田0～20 cm纤维素酶活性最高,是不还田处理的2.2倍。过腹还田使土壤脲酶活性和碱性磷酸酶活性分别显著提高13.0%和20.5%,直接还田和秸秆覆盖对脲酶和碱性磷酸酶活性无显著影响。玉米生产中长期连续秸秆过腹还田和直接还田对土壤养分含量及酶活性产生了深远的影响,尤其是土壤蔗糖酶活性的提高与玉米产量稳定和提升有非常紧密联系。     

Effects of sulfuric,nitric, and mixed acid rain on litter decomposition,soil microbial biomass,and enzyme activities in subtropical forests of China

Acid rain pollution is changing gradually from sulfuric acid rain (SAR) to mixed acid rain (MAR) and then to nitric acid rain (NAR) with the rapidly growing number of motor vehicles. The influences of changed acid rain types on ecosystem functions, particularly on litter decomposition, remain unclear. Two dominant litter types from a coniferous forest and a broad-leaved forest were incubated in microcosms with original forest soils and treated by five types of acid rain with different SO₄²⁻ to NO₃⁻ ratios (1:0, 5:1, 1:1, 1:5, and 0:1). During a six-month incubation period, litter mass losses, soil microbial biomass, and enzyme activities were investigated. Results showed that various acid treatments inhibited litter decomposition, soil microbial biomass, and most enzyme activities, and the inhibitory effects of NAR were more significant than those of SAR and MAR. The resistance to external acid of microbial communities in broad-leaved forest was higher than that in coniferous forest. NAR and MAR treatments slowed down soil carbon (C), nitrogen (N), and phosphorus (P) mineralization by attenuating the correlations between litter mass losses and the enzymes involved in C, N, and P cycling. Results reveal that the ratio of SO₄²⁻ to NO₃⁻ in acid rain is an important factor which profoundly influences litter decomposition process. In the future, a decreasing ratio of SO₄²⁻ to NO₃⁻ in acid rain will be observed in subtropical forests. Thus, soil C would accumulate as a consequence of future acid precipitation, and this may seriously affect the balance of ecosystem C, N flux.     

长期施肥对红壤旱地土壤活性有机碳和酶活性的影响

以江西进贤长期肥料定位试验为平台,研究了红壤旱地不同施肥措施对土壤微生物生物量、活性有机C、C库管理指数以及土壤酶活性的影响。研究结果表明:与不施肥和单施化肥土壤相比,施有机肥处理土壤的pH、CEC、有机C、全N、全P、无机N、速效P、速效K及土壤微生物生物量均显著增加,土壤活性有机C和C库管理指数也较试前土壤和其他处理土壤明显提高,此外,土壤的转化酶、脱氢酶、脲酶和酸性磷酸酶活性也较其他处理显著增加。土壤微生物生物量、活性有机C以及4种土壤酶活性之间的相关关系显著,且它们均与土壤有机C、全N、全P、无机N、速效P等土壤养分呈显著正相关。因此,红壤旱地通过长期施用有机肥或与无机肥配施,不仅能显著提高土壤有机质的数量和质量,而且能增加土壤微生物生物量和酶活性,从而显著提高土壤肥力和土壤持续生产力。     

Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico

 The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however, the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation was not due to pollutants nor did microbial biomass:TOC ratios and qCO₂ values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected, however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase in mobility due to higher mineralization rates. Received: 28 April 1999     

The impact of a low humus level in arable soils on microbial properties, soil organic matter quality and crop yield

 In arable soils in Schleswig-Holstein (Northwest Germany) nearly 30% of the total organic C (TOC) stored in former times in the soil has been mineralized in the last 20 years. Microbial biomass, enzyme activities and the soil organic matter (SOM) composition were investigated in order to elucidate if a low TOC level affects microbial parameters, SOM quality and crop yield. Microbial biomass C (C_mic) and enzyme activities decreased in soils with a low TOC level compared to soils with a typical TOC level. The decrease in the C_mic/TOC ratio suggested low-level, steady-state microbial activity. The SOM quality changed with respect to an enrichment of initial litter compounds in the top soil layers with a low TOC level. Recent management of the soils had not maintained a desirable level of humic compounds. However, we found no significant decrease in crop yield. We suggest that microbial biomass and dehydrogenase and alkaline phosphatase activities are not necessarily indicators of soil fertility in soils with a high fertilization level without forage production and manure application. Received: 12 December 1997     

Tillage effects on soil organic matter in density fractions of a Cerrado Oxisol

Reclamation of Brazilian cerrados (savannas) has been intensified in the last decades, with implications for soil quality and soil organic matter (SOM) dynamics. Studying the impact of different tillage systems is essential to define better strategies for land use in Cerrado, which may favor C sequestration and improve soil quality. We used density fractionation and ¹³C natural abundance to assess changes in SOM in an Oxisol previously under a cerrado sensu-stricto following 30 years of cultivation. The objectives of the study were to: (i) evaluate the long-term impact of tillage systems on SOM stocks in a Dark Red Latosol (Oxisol) from the Cerrado Biome, and (ii) better understand the dynamics of SOM in different density fractions of this soil. Cultivation led to compaction, which significantly increased soil bulk density. This resulted in the systematic overestimation of C and N stocks in cultivated areas when compared to the natural cerrado. Conversion of the cerrado into cropland using plow tillage (PT) or no-tillage (NT) system did not alter the total C (100 Mg ha⁻¹) and N (7 Mg ha⁻¹) stocks in the first 45 cm depth at the end of 30 years of cultivation. However, about 22% of the total C was replaced by C from maize. The relative replacement of C decreased following the order: free light fraction (F-LF)>heavy fraction (HF)>occluded light fraction (O-LF). The low substitution in the O-LF was attributed to a possible presence of charcoal. Converting cerrado into cropland significantly decreased F-LF quantity. The proportions of C replacement in this fraction were higher in PT than NT, suggesting a faster turnover in PT. Nevertheless, because most C (95%) was held in the HF, C dynamics in the whole soil were controlled by the behavior of this fraction. The maintenance of C levels even at the end of 30 years of cultivation and the lack of differentiation between NT and PT were attributed to the high clay contents and Fe+Al oxi-hydroxides concentrations of the studied soil as well as to a sufficient C supply by the maize crop.     

长期施肥对黄壤有机碳平衡及玉米产量的影响

基于长期定位试验,以黔中典型黄壤为研究对象,采用单因素方差分析、可持续性指数、稳定性指数等方法对长期定位试验获取的数据进行分析和比较,以探讨长期不同施肥处理对黄壤有机碳含量、有机碳平衡量、玉米产量稳定性、可持续性及其相互关系的影响。结果表明:(1)与施化肥和对照处理相比,施有机肥处理土壤有机碳含量明显升高,按大小排序依次为:MMNPK1/2M+1/2NPK1/4M+3/4NPK;(2)施有机肥处理黄壤有机碳平衡量为正值,且随有机肥施用量增加而增加,相反,施化肥和对照处理均为负值,大小依次为:MNPK、M1/2M+1/2NPK1/4M+3/4NPKNPKNKNPN、CKPK,各处理差异显著;(3)有机肥与化肥配施、有机肥单施及氮磷钾化肥协调施用更有利于提高玉米产量,排序为:MNPK1/4M+3/4NPK、1/2M+1/2NPKNPK、MNPNK、PK、NCK;(4)适量有机肥与化肥配施可提高玉米产量稳定性和可持续性(可持续性指数0.6,变异系数0.3),其中,1/4M+3/4NPK处理玉米产量稳定性和持续性最好;(5)玉米年产量与黄壤有机碳平衡量相关度较高,而玉米可持续性、稳定性则主要受有机碳含量影响。综上,有机肥与化肥配施有利于黄壤有机碳含量提升、玉米维持高产稳产。按适量"减肥"原则,以25%有机肥配施75%氮磷钾化肥效果最佳。     

林分密度对马尾松林下土壤养分及酶活性的影响

以退化马尾松林下土壤为对象,通过调查我国红壤丘陵区典型林分密度的马尾松人工林,研究林分密度对土壤养分和土壤酶活性的影响。3种林分密度中,1 560株/hm2 左右中等林分密度的马尾松土壤有机质、全氮、全钾、速效钾、全磷、交换性钙和交换性镁等较高,但土壤酸化也较严重;同时,1 560株/hm2 左右马尾松林的土壤转化酶活性、脲酶活性和多酚氧化酶活性均较高,但过氧化氢酶活性表现最低;林分密度对马尾松土壤酸性磷酸酶活性影响不明显。因此,适宜林分密度的马尾松人工林一定程度上可改善该区林下土壤肥力及生化强度。     

长期施肥对红壤性水稻土团聚体稳定性及固碳特征的影响

施用有机肥是提高土壤有机碳(SOC)含量、促进土壤团聚体形成和改善土壤结构的重要措施。本研究旨在探讨长期作物残留和投入有机物料对水稻土团聚体分布及稳定性的影响,分析不同粒级团聚体的固碳特征及其与团聚体形成的相关性,以及土壤和不同粒级团聚体对累积碳投入的响应。长期定位施肥试验始于1986年,设不施肥(CK)、单施化肥(CF)、秸秆化肥混施(RS)、低量粪肥配施化肥(M1)和高量粪肥配施化肥(M2)5个处理。2009年采集0~10 cm土壤样品,测定总土以及大团聚体(LM,2 mm)、较大团聚体(SM,0.25~2 mm)、微团聚体(MA,0.25~0.053 mm)和黏粉粒(SC,0.053 mm)的质量比例及其SOC浓度,并分析闭蓄于SM内部的颗粒有机物(POM)、微团聚体(MA-SM)和黏粉粒(SC-SM)的质量含量和SOC浓度。结果表明,与CK和CF比较,有机肥混施化肥处理(RS、M1和M2)均显著提高了LM和SM的质量比例和平均当量直径(MWD),降低了SC质量含量;两个粪肥配施化肥处理(M1和M2)的效果优于秸秆化肥混施(RS),但是M1和M2间差异不显著;单施化肥则降低了稳定性团聚体的比例。团聚体的SOC浓度没有随粒级增大而增加,各处理均为LM和SM结合的SOC浓度最高,其次为SC,最小为MA。与CK比较,有机肥混施化肥处理均显著提高了各粒级团聚体的SOC浓度。总土SOC的增加主要取决于SM的SOC含量,而MA-SM组分决定了SM固持SOC的能力。总土、LM和SM的SOC含量以及从SM分离出的POM、MA-SM和SC-SM的SOC含量均与累积碳投入量呈显著正相关,但总土分离出的MA和SC的SOC含量对累积碳投入量反应不敏感,表现出碳饱和迹象。因此,尽管长期大量施用有机物料促进了红壤性水稻土大团聚体的形成和团聚体稳定性,增加了其SOC的固持,但有机质可能不是该土壤水稳性团聚体形成的最主要黏结剂。     

Model of apparent and real priming effects: Linking microbial activity with soil organic matter decomposition

The most frequently used models simulating soil organic matter (SOM) dynamics are based on first-order kinetics. These models fail to describe and predict such interactions as priming effects (PEs), which are short-term changes in SOM decomposition induced by easily available C or N sources. We hypothesized that if decomposition rate depends not only on size of the SOM pool, but also on microbial biomass and its activity, then PE can be simulated. A simple model that included these interactions and that consisted of three C pools - SOM, microbial biomass, and easily available C - was developed. The model was parameterized and evaluated using results of ¹²C-CO₂ and ¹⁴C-CO₂ efflux after adding ¹⁴C-labeled glucose to a loamy Haplic Luvisol. Experimentally measured PE, i.e., changes in SOM decomposition induced by glucose, was compared with simulated PE. The best agreement between measured and simulated CO₂ efflux was achieved by considering both the total amount of microbial biomass and its activity. Because it separately described microbial turnover and SOM decomposition, the model successfully simulated apparent and real PE.The proposed PE model was compared with three alternative approaches with similar complexity but lacking interactions between the pools and neglecting the activity of microbial biomass. The comparison showed that proposed new model best described typical PE dynamics in which the first peak of apparent PE lasted for 1 day and the subsequent real PE gradually increased during 60 days. This sequential decomposition scheme of the new model, with immediate microbial consumption only of soluble substrate, was superior to the parallel decomposition scheme with simultaneous microbial consumption of two substrates with different decomposability. Incorporating microbial activity function in the model improved the fit of simulation results with experimental data, by providing the flexibility necessary to properly describe PE dynamics. We conclude that microbial biomass should be considered in models of C and N dynamics in soil not only as a pool but also as an active driver of C and N turnover.     

长期冬种绿肥对红壤性水稻土微生物特性及酶活性的影响

以农业部衡阳红壤环境重点野外科学观测基地长期冬种绿肥稻田为平台,研究了双季稻种植区长期冬种绿肥下红壤性水稻土微生物特性及酶活性与土壤质量的关系,阐明了长期冬种绿肥翻压下土壤健康的微生物指标功能。研究分析了26年冬种不同绿肥的红壤性水稻土微生物学参数之间的差异及其提升土壤肥力的作用,结果表明,与冬季休闲处理相比,长期冬种绿肥翻压处理的微生物种群数量、微生物生物量碳(SMBC)、微生物生物量氮(SMBN)、土壤呼吸、脲酶、转化酶和脱氢酶活性都有所提高,代谢熵(qCO2)降低,以长期冬种紫云英翻压处理效果最明显。微生物种群数量、SMBC、脲酶、脱氢酶与土壤总有机碳(TOC)、全氮(TN)、速效氮(AN)、缓效钾(SLK)和速效钾(AK)呈显著或极显著相关;TOC,TN,AN,SLK,AK,微生物种群数量,脲酶、转化酶、脱氢酶活性与水稻产量呈显著正相关关系。长期冬种绿肥翻压能明显地改善红壤性水稻土的微生物特性与酶活性,提高土壤肥力。     

Long‐term effects of liming on microbial biomass and activity and soil organic matter quality (13C CPMAS NMR) in organic horizons of Norway spruce forests in Southern Germany

Long‐term effects of liming on microbial biomass and activity and soil organic matter (SOM) were investigated in samples from organic horizons (Of/Oh) in spruce forests at Adenau, Höglwald, Idar‐Oberstein, and Schluchsee (Southern Germany) where plots have been manually treated 7 to 13 years ago with dolomitic limestone. At all sites, pH values were markedly increased after liming. The contents of C and N in the organic horizons of the limed plots appeared to be lower with the greatest decrease at Höglwald (Dystric Luvisol) where liming has affected the soil properties for the longest time of all sites. Catalase activity was promoted after liming at Adenau (Cambic Podzol). This was also the case for the Dystric Luvisol where liming resulted also in higher basal respiration. Biomass‐C was higher in samples from the limed plot at Idar‐Oberstein (Dystric Cambisol). The ¹³C CPMAS NMR spectra of organic horizons from the control plots indicate no differences in the gross carbon composition of SOM. Furthermore, spectra from the limed Cambic Podzol, Dystric Cambisol, and Haplic Podzol (Schluchsee) were remarkably similar. However, for the Dystric Luvisol, the lime‐induced promotion of microbial activity resulted in lower O‐alkyl‐C intensity. The observed patterns of microbial biomass and activity were site‐dependent rather than a result of liming. Obviously liming had only small long‐term effects on the humus quality in the organic horizons, as far as detectable by CPMAS NMR spectroscopy. More sensitive techniques like pyrolysis‐GC/MS should be applied to analyze differences in C composition.     

Tillage and no-tillage effects on physical and chemical properties of an Argiaquoll soil under long-term crop rotation in Buenos Aires,Argentina

No-tillage systems are able to reduce the negative effects of agricultural intensification on soil properties. However, knowledge of long-term impacts of no-tillage systems on soil properties is insufficient. It is essential to know which soil quality indicators are the most sensitive to management practices in each particular environment. Therefore, the objective of this work is to determine which soil quality properties are more sensitive to the impact of two tillage systems in a vertic Argiaquoll soil from Buenos Aires, Argentina. This work started in 2006 and included crop rotation and tillage systems, including both tillage and no-tillage. Physical and chemical properties were measured in three consecutive years (2013–2015) at two depths (0–10 cm and 10–20 cm). The tillage system modified soil physical and chemical properties, mainly in the surface layer. No-tillage showed significantly higher bulk density (2013–2015 p < 0.05), gravimetric moisture (2013; 2014 p < 0.05), organic carbon (2013–2015 p < 0.05), and aggregates stability in the face of a heavy rain (2013; 2015 p < 0.05), than soil under tillage. Soil saturation (or total porosity) was significantly greater under tillage. The tillage system did not affect hydraulic conductivity, total nitrogen and extractable phosphorus from the surface, nor physical and chemical properties from the second depth. No-tillage alleviates, but is not enough to mitigate, the loss of soil organic carbon and aggregate stability caused by continuous cropping in this vertic Argiaquall. Bulk density, organic carbon, aggregates stability and saturation are indicators for future studies performed in environments with similar soil and climate conditions.     

Remnant tree effects on soil microbial carbon and nitrogen in tropical seasonal pasture in western Mexico

Selection of plant species for agro-silvo-pastoral or ecological reclamation programs must be based on a deeper knowledge of the existing relationships between plant species and soil nutrient dynamics in each ecosystem. We evaluated the seasonal pattern of soil microbial carbon (C) and nitrogen (N) under two remnant tree species (Caesalpinia eriostachys and Cordia elaeagnoides) in a tropical seasonal pasture dominated by Panicum maximum in western Mexico. Soil samples were taken from under two arboreal species and P. maximum in rainy and dry seasons. The soil C:N ratio was higher under P. maximum [17] than under both tree species [15]. The soil microbial C (Cm) was higher under C. elaeagnoides than under C. eriostachys and P. maximum. Magnitude and direction of effect of the two remnant tree species on soil biogeochemistry changed with seasonal rainfall. The interaction of plant species and seasonal rainfall did have an effect on soil microbial N (Nm). Soil samples from April and July had the lowest microbial N concentrations under the three plant species, increasing four fold in September under C. elaeagnoides and P. maximum. At the end of the wet season, C. elaeagnoides clearly had the highest Nm values (130 μg N g⁻¹), suggesting that this tree species has a higher capacity to protect soil N within microbial biomass than C. eriostachys, because under C. elaeagnoides the soil had more organic matter due a higher input of litter and root chemical quality. Therefore, C. elaeagnoides would be the best plant species to implement in agro-silvo-pastoral programs or ecological reclamation of TDF pastures.     

Effects of ecological restoration on microbial activity,microbial functional diversity,and soil organic matter in mixed-oak forests of southern Ohio,USA

As a result of many decades of fire suppression and atmospheric deposition the deciduous forests of eastern North America have changed significantly in stem density, basal area, tree size-frequency distribution, and community structure. Consequently, soil organic matter quality and quantity, nutrient availability, and microbial activity have likely been altered. This study evaluated the effects of four alternative forest ecosystem restoration strategies on soil microbial activity, microbial functional diversity, soil organic C, and soil N status in two mixed-oak (Quercus spp.) forests in southern Ohio, USA. The soils of these forests were sampled during the fourth growing season after application of (1) prescribed fire, (2) thinning of the understory and midstory to pre-settlement characteristics, (3) the combination of fire and thinning, and (4) an untreated control. Prescribed fire, with or without thinning, resulted in increased bacterial but not fungal activity when assessed using Biolog^®. In contrast, assays of acid phosphatase and phenol oxidase activity indicated greater microbial activity in the thinning treatment than in the other three treatments. Functional diversity of both bacteria and fungi was affected by restoration treatment, with the bacterial and fungal assemblages present in the thin + burn sites and the fungal assemblage present in the thinned sites differing significantly from those of the control and burned sites. Treatments did not result in significant differences in soil organic C content among experimental sites; however, the soil C:N ratio was significantly greater in thinned sites than in sites given the other three treatments. Similarly, there were no significant differences in dissolve inorganic N, dissolved organic N, or microbial biomass N among treatments. Bacterial and fungal functional diversity was altered significantly. Based on Biolog^® utilization treatments the bacterial assemblage in the thin-only treatment appeared to be relatively N-limited and the fungal assemblage relatively C-limited, whereas in the thin + burn treatment this was reversed. Although effects of restoration treatments on soil organic matter and overall microbial activity may not persist through the fourth post-treatment year, effects on microbial functional diversity are persistent.     

Biological, chemical and thermal indices of soil organic matter stability in four grassland soils

The various ecosystem functions of soil organic matter (SOM) depend on both its quantity and stability. Numerous fractionation techniques have been developed to characterize SOM stability, and thermal analysis techniques have shown promising results to describe the complete continuum of SOM in whole soil samples. However, the potential link between SOM thermal stability and biological or chemical stability has not yet been adequately explored. The objective of this study was to compare conventional chemical and biological methods used to characterize SOM stability with results obtained by thermal analysis techniques. Surface soil samples were collected from four North American grassland sites along a continental mean annual temperature gradient, each with a native and cultivated land use. Soil organic C concentrations ranged from 6.8 to 33 g C kg⁻¹ soil. Soils were incubated for 588 days at 35 °C, and C mineralization rates were determined periodically throughout the incubation by measuring CO₂ concentration using an infrared gas analyzer (IRGA) to calculate biological indices of SOM stability. Hot-water extractable organic C (HWEOC) contents were determined before and after incubation as chemical indices. Finally, samples from before and after incubation were analyzed by simultaneous thermal analysis (i.e., thermogravimetry (TG) and differential scanning calorimetry (DSC)) to determine thermal indices of SOM stability. Long-term incubation resulted in the mineralization of up to 33% of initial soil C. The number of days required to respire 5% of initial soil organic carbon (SOC), ranged from 27 to 115 days, and is proposed as a standardized biological index of SOM stability. The number of days was greater for cultivated soils compared to soils under native vegetation, and generally decreased with increasing site mean annual temperature. HWEOC (as % of initial SOC) did not show consistent responses to land use, but was significantly lower after long-term incubation. Energy density (J mg⁻¹ OM) was greater for soils under native vegetation compared to cultivated soils, and long-term incubation also decreased energy density. The temperatures at which half of the mass loss or energy release occurred typically showed larger responses to land use change than to incubation. Strong correlations demonstrated a link between the thermal and biogeochemical stability of SOM, but the interpretation of the thermal behavior of SOM in bulk soil samples remains equivocal because of the role the mineral component and organo-mineral interactions.     

不同种植模式对雷州半岛玄武岩母质砖红壤氮磷钾养分状况的影响

  目的  探究化肥配施不同类型有机物料连续施用对热带砖红壤性质、氮素转化过程速率及相关土壤酶活性的影响,以期为提高砖红壤生产力及发展农田氮素管理高效模式提供理论依据。  方法  基于田间原位试验,采集了连续种植6年不同施肥管理的砖红壤土样,测定单施化肥（N）、化肥配施秸秆（N + straw）和化肥配施羊粪（N + manure）处理的土壤理化性质、氮素转化速率和相关酶活性。  结果  化肥配施有机物料较单施化肥处理增加了土壤有机碳、土壤全氮及pH值,增幅范围分别为7.43% ~ 40.28%,28.57% ~ 42.86%和1.60% ~ 52.05%;降低了土壤C/N值,降幅范围为1.44% ~ 15.35%,其中化肥配施羊粪影响较大。有机物料连续施用土壤氮素矿化速率、氨氧化潜力、净硝化速率和反硝化潜力分别增加了3.00倍,11.48倍,0.28倍和4.07倍。化肥配施有机物料显著增加了土壤脲酶、硝酸还原酶、亚硝酸还原酶和β-1,4-葡萄糖苷酶,但显著降低了土壤亚硝酸氧化酶和多酚氧化酶活性,其中化肥配施羊粪较化肥配施秸秆作用更强。氮素转化速率（除净硝化速率）与土壤有机碳、全氮和pH呈显著正相关,与脲酶、亚硝酸还原酶、硝酸还原酶活性均呈显著正相关,而与多酚氧化酶活性呈显著负相关。  结论  化肥配施有机物料能够改善砖红壤性状,加速土壤氮素周转,其中化肥配施羊粪较化肥配施秸秆效果更加明显,因此化肥配施羊粪是改善热带砖红壤性状和提升氮素可利用性的有效措施。     

Effect of organic and inorganic sources of nutrients on soil microbial activity and soil organic carbon build-up under rice in west coast of India

The effect of medium-term (5 years) application of organic and inorganic sources of nutrients (as mineral or inorganic fertilizers) on soil organic carbon (SOC), SOC stock, carbon (C) build-up rate, microbial and enzyme activities in flooded rice soils was tested in west coast of India. Compared to the application of vermicompost, glyricidia (Glyricidia maculate) (fresh) and eupatorium (Chromolaena adenophorum) (fresh) and dhaincha (Sesbania rostrata) (fresh), the application of farmyard manure (FYM) and combined application of paddy straw (dry) and water hyacinth (PsWh) (fresh) improved the SOC content significantly (p < 0.05). The lowest (p < 0.05) SOC content (0.81%) was observed in untreated control. The highest (p < 0.05) SOC stock (23.7 Mg C ha^?1) was observed in FYM-treated plots followed by recommended dose of mineral fertilizer (RDF) (23.2 Mg C ha^?1) and it was lowest (16.5 Mg C ha^?1) in untreated control. Soil microbial biomass carbon (C_mb) (246 µg g^?1 soil) and C_mb/SOC (1.92%) were highest (p < 0.05) in FYM-treated plot. The highest (p < 0.05) value of metabolic quotient (qCO₂) was recorded under RDF (19.7 µg CO₂-C g^?1 C_mb h^?1) and untreated control (19.6 µg CO₂-C g^?1 C_mb h^?1). Application of organic and inorganic sources of nutrients impacted soil enzyme activities significantly (p < 0.05) with FYM causing highest dehydrogenase (20.5 µg TPF g^?1 day^?1), phosphatase (659 µg PNP g^?1 h^?1) and urease (0.29 µg urea g^?1 h^?1) activities. Application of organic source of nutrients especially FYM improved the microbial and enzyme activities in flooded and transplanted rice soils. Although the grain yield was higher with the application of RDF, but the use of FYM as an organic agricultural practice is more useful when efforts are intended to conserve more SOC and improved microbial activity.