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1.
Labile fractions of soil organic C (SOC) can respond rapidly to changes in C supply and are considered to be important indicators of soil quality. An attempt is made in this paper to investigate into the dynamics of total organic C (C tot), oxidisable organic C (C oc), very labile C (C frac 1), labile C (C frac 2), less labile C (C frac 3), non-labile C (C frac 4), microbial biomass C (C mic), mineralizable C (C min) and particulate organic C (C p) in relation to the system productivity of a 20-year-old rice (Oryza sativa L)–berseem (Trifolium alexandrium L) cropping system with different management strategies [no fertilization, only NPK and NPK + FYM (farmyard manure) applied in different seasons] in the hot humid, subtropics of India. Cultivation over the years caused a net decrease, while balanced fertilization with NPK maintained the SOC. About 62% of the C applied as FYM was stabilized into SOC. The passive pool (C frac 3 + C frac 4) constituted about 55% of the C tot. A larger proportion (63%) of applied C was stabilized in the passive pool of SOC. Of the analysed pools, C frac 1, C mic, C p and C min were influenced most by the treatments imposed and explained higher per cent variability in the yield of the crops.  相似文献   

2.
Understanding carbon dynamics in soil is the key to managing soil organic matter. Our objective was to quantify the carbon dynamics in microcosm experiments with soils from long-term rye and maize monocultures using natural 13C abundance. Microcosms with undisturbed soil columns from the surface soil (0-25 cm) and subsoil (25-50 cm) of plots cultivated with rye (C3-plant) since 1878 and maize (C4-plant) since 1961 with and without NPK fertilization from the long-term experiment ‘Ewiger Roggen’ in Halle, Germany, were incubated for 230 days at 8 °C and irrigated with 2 mm 10−2 M CaCl2 per day. Younger, C4-derived and older, C3-derived percentages of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass (Cmic) and CO2 from heterothropic respiration were determined by natural 13C abundance. The percentage of maize-derived carbon was highest in CO2 (42-79%), followed by Cmic (23-46%), DOC (5-30%) and SOC (5-14%) in the surface soils and subsoils of the maize plots. The percentage of maize-derived C was higher for the NPK plot than for the unfertilized plot and higher for the surface soils than for the subsoils. Specific production rates of DOC, CO2-C and Cmic from the maize-derived SOC were 0.06-0.08% for DOC, 1.6-2.6% for CO2-C and 1.9-2.7% for Cmic, respectively, and specific production rates from rye-derived SOC of the continuous maize plot were 0.03-0.05% for DOC, 0.1-0.2% for CO2-C and 0.3-0.5% for Cmic. NPK fertilization did not affect the specific production rates. Strong correlations were found between C4-derived Cmic and C4-derived SOC, DOC and CO2-C (r≥0.90), whereas the relationship between C3-derived Cmic and C3-derived SOC, DOC and CO2-C was not as pronounced (r≤0.67). The results stress the different importance of former (older than 40 years) and recent (younger than 40 years) litter C inputs for the formation of different C pools in the soil.  相似文献   

3.
ABSTRACT

Management of grassland may affect the dynamics of soil organic carbon (SOC). Objectives were to analyze the effect of different harvesting frequencies and nitrogen fertilization regimes on SOC and total N stocks in a field trial on a sandy loam to loamy sand soil of a grassland site near Kiel (Germany). Additionally, effects on microbial biomass C (Cmic) and ergosterol (as proxy for fungi) contents, water-stable aggregate size-classes and density fractions were studied. In the surface soil (0–10 cm), SOC and total N stocks, amounts of large water-stable macroaggregates (> 2000 µm) and contents of Cmic and ergosterol were significantly higher under a five cut regime. Cmic (rSpearman = 0.61) and ergosterol contents (rSpearman = 0.67) were correlated with amounts of large water-stable macroaggregates suggesting that fungi and microbial biomass play an important role in binding of small macroaggregates into large macroaggregates. The free light fraction of SOM showed significantly higher C concentrations under three cut compared to five cut at 30–60 cm, presumably related to the C/N ratio and the decomposability of root litter. This study indicates the importance of cutting frequency on SOC and total N stocks, amounts of large macroaggregates and contents of Cmic and ergosterol.  相似文献   

4.
Soil samples from the upper 10-cm-thick layer of the humus horizon (without forest litter) were taken in Podol’sk and Serpukhov districts (1130 and 1080 km2, respectively) of Moscow oblast. At each sampling site, ecosystem (forest, plowland, or fallow), soil (soddy-podzolic, soddy-gley, bog-podzolic, meadow alluvial, gray forest, and anthropogenically transformed soils of lawns and industrial zones), predominant vegetation, and topography (floodplain and low, medium, and upper parts of watersheds) were determined. The carbon content of the microbial biomass (Cmic) was determined by the method of substrate-induced respiration; we also determined the rate of basal (microbial) respiration (BR) and the organic carbon content, pH, and particle-size distribution. Overall, 237 samples from Serpukhov district and 45 samples from Podol’sk district were analyzed. The BR/Cmic ratios (respiration quotient qCO2) and Cmic/Corg ratios were calculated. The Cmic content in the soils ranged from 43 to 1394 μg C/kg; the BR varied from 0.06 to 25 μg CO2-C/g per h, qCO2, from 0.34 to 6.52 μg CO2-C/mg Cmic per h; and the Cmic/Corg ratio, from 0.19 to 10.65%. It was found that the most significant factors affecting the variability of the Cmic and BR are the parameters of ecosystem (50% and 80%, respectively) and soil (30% and 9%, respectively). The most significant variability of these indices was found in forest soils; it was mainly controlled by the soil texture (33 and 23%) and the Corg content (19 and 24%). The Cmic parameter made it possible to differentiate the soils of the territory for the purposes of their evaluation, monitoring, and biological assessment more clearly than the BR value and the soil chemical characteristics.  相似文献   

5.
In the mineral horizons of the soils under different southern taiga forests (oak, archangel spruce, and aspen in the Kaluzhskie Zaseki Reserve of Kaluga region and the green moss spruce and spruce-broadleaved forests of the Zvenigorod Biological Station of Moscow State University in Moscow region), the carbon content in the microbial biomass (Cmic), the rate of the basal respiration (BR), and the specific microbial respiration (qCO2= BR/Cmic) were determined. The Cmic content was measured using the method of substrate-induced respiration (SIR). In the upper humus horizons of the soils, the Cmic content amounted to 762–2545 μg/g and the BR ranged from 1.59 to 7.55 μg CO2-C/g per h. The values of these parameters essentially decreased down the soil profiles. The portion of Cmic in the organic carbon of the humus horizons of the forest soils was 4.4 to 13.2%. The qCO2values increased with the depth in the soils of the Biological Station and did not change in the soils of the Reserve. The pool of Cmic and Corg and the microbial production of CO2 (BR) within the forest soil profiles are presented.  相似文献   

6.
Urban soils (constructozems) were studied in Moscow and several cities (Dubna, Pushchino, and Serebryanye Prudy) of Moscow oblast. The soil sampling from the upper 10-cm-thick layer was performed in the industrial, residential, and recreational functional zones of these cities. The biological (the carbon of the microbial biomass carbon, Cmic and the microbial (basal) respiration, BR) and chemical (pHwater and the contents of Corg, heavy metals, and NPK) indices were determined in the samples. The ratios of BR to Cmic (the microbial respiration quotient, qCO2) and of Cmic to Corg were calculated. The Cmic varied from 120 to 738 μg C/g soil; the BR, from 0.39 to 1.94 μg CO2-C/g soil per hour; the Corg, from 2.52 to 5.67%; the qCO2, from 1.24 to 5.28 μg CO2-C/mg Cmic/g soil per h; and the Cmic/Corg, from 0.40 to 1.55%. Reliable positive correlations were found between the Cmic and BR, the Cmic and Cmic/Corg, and the Cmic and Corg values (r = 0.75, 0.95, and 0.61, respectively), as well as between the BR and Cmic/Corg values (r = 0.68). The correlation between the Cmic/Corg and qCO2 values was negative (r = −0.70). The values of Cmic, BR, Corg, and Cmic/Corg were found to correlate with the ammonium nitrogen content. No correlative relationships were revealed between the determined indices and the climatic characteristics. The principal component analysis described 86% of the variances for all the experimental data and clearly subdivided the locations of the studied soil objects. The ANOVA showed that the variances of Cmic, Corg, and BR are controlled by the site location factor by 66, 63, and 35%, respectively. The specificity of the functioning of the anthropogenic soils as compared with their natural analogues was clearly demonstrated. As shown in this study, measurable biological indices might be applied to characterize the ecological, environmental-regulating, and productive functions of soils, including urban soils.  相似文献   

7.
The contributions of root and microbial respiration to the total emission of CO2 from the surface of gray forest and soddy-podzolic soils were compared under laboratory and field conditions for the purpose of optimizing the field version of the substrate-induced respiration method. The magnification coefficients of respiration upon the addition of saccharose (k mic) were first determined under conditions maximally similar to the natural conditions. For this purpose, soil cleared from roots was put into nylon nets with a mesh size of 40 μm to prevent the penetration of roots into the nets. The nets with soil were left in the field for 7–10 days for the compaction of soil and the stabilization of microbial activity under natural conditions. Then, the values of k mic were determined in the root-free soil under field conditions or in the laboratory at the same temperature and water content. The contribution of root respiration as determined by the laboratory version of the substrate-induced respiration method (7–36%) was lower compared to two field versions of the method (27–60%). Root respiration varied in the range of 24–60% of the total CO2 emission from the soil surface in meadow ecosystems and in the range of 7–56% in forest ecosystems depending on the method and soil type.  相似文献   

8.
Knowledge about soil organic carbon (SOC) stock and its allocation into different pools is important for global food and environmental security. Accordingly, an attempt is made in the present study to investigate into the dynamics of SOC pools i.e. total soil organic carbon (TOC), oxidisable organic carbon (OC) and its different fractions viz. very labile (CVL), labile (CL), less labile (CLL) and non-labile (CNL) in soils under a 26 years old long-term experiment with rice (Oryza sativa L) – wheat (Triticum aestivum L) cropping system on Inceptisols under humid agro-climatic region of India with different soil management practices (control, 100% recommended dose of NPK, and 50% recommended dose of NPK + 50% N through farmyard manure (FYM). Of the several pools analyzed, a higher proportion of C was found in labile pool followed by very labile, non-labile, and less labile ones constituting about 46, 26.5, 20 and 7.3% of the total organic C at surface soil. The NPK+FYM treatment was found to have higher SOC pools, lability index (LI), recalcitrance indices and stratification ratio as compared to others. Results indicated that balanced fertilization with inorganic and organics is important for maintaining overall sustainability of the rice-wheat system.  相似文献   

9.
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.  相似文献   

10.
Little work has been done to quantify annual soil CO2 effluxes in the High Arctic region because of the difficulty in taking winter measurements. Since the effects of climate change are expected to be higher in Arctic than in temperate ecosystems, it is important that summer measurements are extended to cover the entire year. This study evaluates the quantity and quality of soil organic C (SOC) and seasonal controls of soil CO2 effluxes in three soils under three dominating types of vegetation (Dryas, Cassiope, and Salix) at Svalbard. Measurements included soil CO2 effluxes in the field and the laboratory, temperature, water content, and snow thickness. About 90% of the variation in soil respiration throughout 1 year was due to near-surface soil temperatures which ranged from −12 to +12 °C. Total annual soil CO2 effluxes varied from 103 g C m−2 at soils under Cassiope, 152 g C m−2 under Dryas sites, and 176 g C m−2 under Salix, with 20%, 14%, and 30%, respectively, being released during a 6-month winter period. The sensitivity of soil respiration with respect to soil temperature was the same year round and differences in winter CO2 effluxes at the three vegetation types were mainly related to subsurface soil temperatures controlled by snow depth. The quantity and quality of soil organic matter varied under the different vegetation types. Soils under Salix had the largest and most labile pool of SOC and were characterized by a long period of snow cover. In contrast, soils under Cassiope were more nutrient-poor, more acidic and held the smallest amount of total and labile SOC, whereas soils under Dryas remained snow-free most of the winter and therefore had the coldest winter conditions. Thus, winter soil respiration rates under Dryas and Cassiope were significantly lower than those under Salix; under Dryas this was mainly due to snow depth, under Cassiope this was a combination of snow depth and poor litter quality. It is concluded that winter respiration is highly variable across Arctic landscapes and depends on the spatial distribution of snow, which acts as a direct control on soil temperatures and indirect on vegetation types and thereby, the amount and quality of soil organic matter, which serve as additional important drivers of soil respiration.  相似文献   

11.
Tree species differ in their effect on soil development and nutrient cycling. Conversion of beech coppice to pine plantations can alter soil physical and chemical properties, which in turn may have significant impacts on soil microbial biomass C and N (Cmic, Nmic). The major objective of this study was to evaluate soil quality changes associated with the forest conversion in humid NW Turkey. Results from this study showed that levels of soil organic carbon (Corg), total nitrogen (Nt), moisture, Cmic and Nmic under beech coppice were consistently higher but levels of pH, CaCO3 and EC were lower compared to pine plantation. Differences between the forest stands in Cmic and Nmic were mainly related to the size of the Corg stores in soil and to tree species. In addition, high level of CaCO3 is likely to reduce pools of soil organic C and possibly even microbial biomass C and N in pine forests. The average Cmic:Nmic ratios were higher in soils under beech coppice than pine plantation, while Cmic:Corg and Nmic:Nt percentages were similar in both forest types. These results revealed the differences in microbial community structure associated with different tree species and the complex interrelationships between microbial biomass, soil characteristics, litter quantity and quality. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

12.
In 11 rain‐fed arable soils of the Potohar plateau, Pakistan, the amounts of microbial‐biomass C (Cmic), biomass N (Nmic), and biomass P (Pmic) were analyzed in relation to the element‐specific total storage compartment, i.e., soil Corg, Nt, and Pt. The effects of climatic conditions and soil physico‐chemical properties on these relationships were highlighted with special respect to crop yield levels. Average contents of soil Corg, Nt, and Pt were 3.9, 0.32, and 0.61 mg (g soil)–1, respectively. Less than 1% of Pt was extractable with 0.5 M NaHCO3. Mean contents of Cmic, Nmic, and Pmic were 118.4, 12.0, and 3.9 µg (g soil)–1. Values of Cmic, Nmic, Pmic, soil Corg, and Nt were all highly significantly interrelated. The mean crop yield level was closely connected with all soil organic matter– and microbial biomass–related properties, but showed also some influence by the amount of precipitation from September to June. Also the fraction of NaHCO3‐extractable P was closely related to soil organic matter, soil microbial biomass, and crop yield level. This reveals the overwhelming importance of biological processes for P turnover in alkaline soils.  相似文献   

13.
Hedley labile phosphorus(P)pools in soil tend to be several times larger than annual forest requirements,even in highly weathered soils characterized by P limitation.The discrepancy between plant and soil P status could be partly attributable to the frequently adopted air-drying pretreatment that tends to increase soil P solubility.In this study,the effects of air-drying on the distribution of Hedley P fractions were examined using soils collected under 4 forest types at Gongga Mountain,southwestern China.The results showed that the microbial biomass P(Pmic)in the organic horizon decreased markedly after air-drying.The concentrations of Hedley labile P in the air-dried samples were 31%–73%more than those in the field-moist samples.Consequently,the air-drying-induced increments of Hedley labile P pools in the surface soil horizons were 0.8–3.8 times the annual plant P requirements.The organic horizon was more susceptible to the air-drying-induced increases in Hedley labile P than the mineral horizon,probably because of the stronger release of Pmicand disruption of soil organic matter.The quality of P,indexed by the ratio of Hedley labile P to slowly cycling P,shifted in favor of the Hedley labile fractions after air-drying,further revealing that air-drying changed the distribution of Hedley P pools in forest soils.These indicated that the effects of air-drying could not be ignored when interpreting the discrepancy between the P status of plants and the Hedley labile P pools in forest soils.To more efficiently evaluate the P status in forest soils via the Hedley fractionation procedure,the use of field-moist soils is recommended.  相似文献   

14.
Soil organic carbon (SOC) consists of various classes of organic substances that can be pooled as labile and non-labile fractions. Previous studies have suggested that plant invasion increases SOC content, but whether invasion consistently alters SOC fractions remains unclear. Consequently, the present study was conducted to observe the effects of Praxelis clematidea invasion on SOC fractions in a tropical savanna of southern China. Soil samples were collected in two surface soil layers (0–10 and 10–20 cm) from non-, slightly and severely invaded plots to analyse the total SOC, readily oxidizable SOC (ROC), and non-readily oxidizable SOC (NROC) content. The results showed that severe P. clematidea invasion significantly increased the SOC content by 47% in the surface soil (p < 0.001). The increase in SOC content largely originated from the accumulation of NROC (the non-labile fraction), rather than ROC which typically is regarded as the labile OC fraction. This change may be beneficial to long-term soil C stabilization because chemical recalcitrance is an important pathway to prevent SOC from decomposition. Although the mechanisms for NROC accumulation have not been thoroughly elucidated to date, our results suggest that P. clematidea invasion may facilitate soil C sequestration in this tropical savanna.  相似文献   

15.
Management intensity modifies soil properties, e.g., organic carbon (Corg) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (Pmic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling Pmic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on Pmic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (Cmic), Pmic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, Pmic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil Corg is the profound driver of plant diversity effects on Pmic in grasslands. For both forest and grassland, we found regional differences in Pmic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on Pmic due to a lack of effects on controlling variables (e.g., Corg). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling Pmic or Cmic in soil differ in part and that regional differences in controlling variables are more important for Pmic in soil than those induced by management.  相似文献   

16.

Purpose

The aim of this study was to understand the effect of nitrogen fertilization on soil respiration and native soil organic carbon (SOC) decomposition and to identify the key factor affecting soil respiration in a cultivated black soil.

Materials and methods

A field experiment was conducted at the Harbin State Key Agroecological Experimental Station, China. The study consisted of four treatments: unplanted and N-unfertilized soil (U0), unplanted soil treated with 225?kg?N?ha?1 (UN), maize planted and N-unfertilized soil (P0), and planted soil fertilized with 225?kg?N?ha?1 (PN). Soil CO2 and N2O fluxes were measured using the static closed chamber method.

Results and discussion

Cumulative CO2 emissions during the maize growing season with the U0, UN, P0, and PN treatments were 1.29, 1.04, 2.30 and 2.27?Mg?C?ha?1, respectively, indicating that N fertilization significantly reduced the decomposition of native SOC. However, no marked effect on soil respiration in planted soil was observed because the increase of rhizosphere respiration caused by N addition was counteracted by the reduction of native SOC decomposition. Soil CO2 fluxes were significantly affected by soil temperature but not by soil moisture. The temperature sensitivity (Q 10) of soil respiration was 2.16?C2.47 for unplanted soil but increased to 3.16?C3.44 in planted soil. N addition reduced the Q 10 of native SOC decomposition possibly due to low labile organic C but increased the Q 10 of soil respiration due to the stimulation of maize growth. The estimated annual CO2 emission in N-fertilized soil was 1.28?Mg?C?ha?1 and was replenished by the residual stubble, roots, and exudates. In contrast, the lost C (1.53?Mg?C?ha?1) in N-unfertilized soil was not completely supplemented by maize residues, resulting in a reduction of SOC. Although N fertilization significantly increased N2O emissions, the global warming potential of N2O and CO2 emissions in N-fertilized soil was significantly lower than in N-unfertilized soil.

Conclusions

The stimulatory or inhibitory effect of N fertilization on soil respiration and basal respiration may depend on labile organic C concentration in soil. The inhibitory effect of N fertilization on native SOC decomposition was mainly associated with low labile organic C in tested black soil. N application could reduce the global warming potential of CO2 and N2O emissions in black soil.  相似文献   

17.
The effects of timber harvesting and the resultant soil disturbances (compaction and forest floor removal) on relative soil water content, microbial biomass C and N contents (Cmic and Nmic), microbial biomass C:N ratio (Cmic-to-Nmic), microbial respiration, metabolic quotient (qCO2), and available N content in the forest floor and the uppermost mineral soil (0-3 cm) were assessed in a long-term soil productivity (LTSP) site and adjacent mature forest stands in northeastern British Columbia (Canada). A combination of principal component analysis and redundancy analysis was used to test the effects of stem-only harvest, whole tree harvest plus forest floor removal, and soil compaction on the studied variables. Those properties in the forest floor were not affected by timber harvesting or soil compaction. In the mineral soil, compaction increased soil total C and N contents, relative water content, and Nmic by 45%, 40%, 34% and 72%, respectively, and decreased Cmic-to-Nmic ratio by 29%. However, these parameters were not affected by stem only harvesting or whole tree harvesting plus forest floor removal, contrasting the reduction of white spruce and aspen growth following forest floor removal and soil compaction reported in an earlier study. Those results suggest that at the study site the short-term effects of timber harvesting, forest floor removal, and soil compaction are rather complex and that microbial populations might not be affected by the perturbations in the same way as trees, at least not in the short term.  相似文献   

18.
Twenty plots (20 m2 each) were selected in coniferous and mixed forests of the industrial Vologda district and the Vytegra district without developed industries in Vologda region. In March, snow cores corresponding to the snow cover depth were taken on these plots. In August, soil samples from the 0- to 20-cm layer of litter-free soddy-podzolic soil (Albic Retisol (Ochric)) were taken on the same plots in August. The content of mineral nitrogen (Nmin), including its ammonium (NH+4) and nitrate (NO-3) forms, was determined in the snow (meltwater) and soil. The contents of total organic carbon, total nitrogen, and elements (Al, Ca); pH; particle size distribution; and microbiological parameters―carbon of microbial biomass (Cmic) and microbial respiration (MR)―were determined in the soil. The ratio MR/Cmic = qCO2 (specific respiration of microbial biomass, or soil microbial metabolic quotient) was calculated. The content of Nmic in meltwater of two districts was 1.7 mg/L on the average (1.5 and 0.3 mg/L for the NH+4 and NO–3 forms, respectively). The annual atmospheric deposition was 0.6–8.9 kg Nmin/ha, the value of which in the Vologda district was higher than in the Vytegra district by 40%. Reliable correlations were found between atmospheric NH+4 depositions and Cmic (–0.45), between NH+4 and qCO2 (0.56), between atmospheric NO-3 depositions and the soil NO-3 (–0.45), and between NO-3 and qCO2 (–0.58). The content of atmospheric Nmin depositions correlated with the ratios C/N (–0.46) and Al/Ca (–0.52) in the soil. In forests with the high input of atmospheric nitrogen (>2.0 kg NH+4/(ha yr) and >6.4 kg Nmin/(ha yr)), a tendency of decreasing Cmic, C/N, and Al/Ca, as well as increasing qCO2, was revealed, which could be indicative of deterioration in the functioning of microbial community and the chemical properties of the soil.  相似文献   

19.
Fifteen citrus varieties (four varieties of limes/lemons, three varieties of mandarins, and eight varieties of sweet oranges) were tested in a row-to-row multireplicate field experiment on Typic Rhodustalf. Pre-bearing growth behavior of different citrus varieties showed a significant difference (P ≤ 0.05) with respect to canopy volume (1.221 m3 with Bearss lemon and 0.220 m3 with Cara Cara Navel) governed by changes in different rhizospheric properties (soil-available nutrients, soil microbial population, and soil microbial biomass nutrients). Response in canopy volume was more governed by soil microbial biomass nutrients [carbon (Cmic), nitrogen (Nmic), and phosphorus (Pmic)] followed soil microbial population and soil available nutrients in decreasing order. Indices developed through diagnosis and recommendation integrated system further helped in partitioning interrhizosphere nutrient deficiencies. These studies suggested that (i) biological properties of rhizosphere soils of limes and lemons were of much superior quality and (ii) rhizospheric biological properties are transformed according to plant species and variety.  相似文献   

20.
The occurrence of substantial quantities of black carbon (BC) in urban soil due to local dispersal following incomplete combustion of fossil fuel complicates the determination of labile soil organic carbon (SOC). Estimates of SOC content were made from loss on ignition (LOI) analyses undertaken on samples (0–15 cm depth) from comprehensive soil geochemical surveys of three UK urban areas. We randomly selected 10 samples from each decile of the LOI distribution for each of the surveys of Coventry (n = 808), Stoke‐on‐Trent (n = 737) and Glasgow (n = 1382) to investigate the proportions of labile SOC and BC. We determined their total organic carbon (TOC) and BC contents, and by difference the labile SOC content, and investigated the linear relationship of the latter with SOC estimates based on LOI analyses. There was no evidence for a difference in the slope of the regression for the three urban areas. We then used a linear regression of labile SOC based on LOI analyses (r2 = 0.81) to predict labile SOC for all survey samples from the three urban areas. We attribute the significantly higher median BC concentrations in Glasgow (1.77%, compared with 0.46 and 0.59% in Coventry and Stoke‐on‐Trent) to greater dispersal of coal ash across the former. An analysis of the 30 samples showed that LOI at 450 °C accounts for a consistent proportion of BC in each sample (r2 = 0.97). Differences between TOC (combustion at 1050 °C after removal of inorganic carbon) and an LOI estimate of SOC may be a cost‐effective method for estimation of BC. Previous approaches to estimation of urban SOC contents based on half the mean SOC content of the equivalent associations under pasture, underestimate the empirical mean value.  相似文献   

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