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1.
Soils that are forming on volcanic parent materials have unique physical and chemical properties and in most cases, on wet and humid climates, are classified as Andisols. The main purpose of this study is to examine if the soils that are forming on volcanic materials under a dry Mediterranean climate, in Nisyros Island (Greece), meet the requirements to be classified as Andisols. Soils from seven sites were sampled and examined for their main physico-chemical properties and selective dissolution analysis. Dithionite–citrate–bicarbonate (DCB) extractable Al and Fe (Áld, Fed), acid ammonium oxalate extractable Al, Fe, and Si (Álo, Feo and Sio), and sodium pyrophosphate extractable Al and Fe (Alp, Fep) were measured. In addition, Al and Si were determined after reaction with hot 0.5 M NaOH, (AlNaOH and SiNaOH) and with Tiron-(C6H4Na2O8S2), (AlT and SiT). P-retention was also measured. The soils are characterised by coarse texture, low organic matter content, low values of cation exchange capacity (CEC), and high pH values. Values of Sio, Alo and Feo are less than 0.022%, 0.09% and 0.35% respectively, highlighting the lack of noncrystalline components. The ratio (Fed–Feo)100/Fed is quite high expressing the degree of crystallisation of free iron oxides. For all samples tested, values of the Alo + 1/2Feo index are extremely low (< 0.24%). High SiNaOH and SiT (arising 2.76% and 2.18% respectively) indicate the presence of silica in amorphous forms. P-retention values are very low (< 12.6%). The results indicated the absence of noncrystalline minerals except for amorphous silica, and do not exhibit andic or vitric soil characteristics to be classified as Andisols. 相似文献
2.
Soil organic P (Po) mineralization plays an important role in soil P cycling. Quantitative information on the release of available inorganic P (Pi) by this process is difficult to obtain because any mineralized Pi gets rapidly sorbed. We applied a new approach to quantify basal soil Po mineralization, based on 33PO4 isotopic dilution during 10 days of incubation, in soils differing in microbiological activity. The soils originated from a 20 years old field experiment, including a conventional system receiving exclusively mineral fertilizers (MIN), a bio-organic (ORG) and bio-dynamic (DYN) system. Indicators of soil microbiological activity, such as size and activity of the soil microbial biomass and phosphatase activity, were highest in DYN and lowest in MIN. In order to assess Po hydrolysis driven by phosphatase in sterile soils, a set of soil samples was γ-irradiated. Basal Po mineralization rates in non-irradiated samples were between 1.4 and 2.5 mg P kg−1 day−1 and decreased in the order DYN>ORG≥MIN. This is an amount lower, approximately equivalent to, or higher than water soluble Pi of MIN, ORG and DYN soils, respectively, but in every soil was less than 10% of the amount of P isotopically exchangeable during one day. This shows that physico-chemical processes are more important than basal mineralization in releasing plant available Pi. Organic P mineralization rates were higher, and differences between soils were more pronounced in γ-irradiated than in non-irradiated soils, with mineralization rates ranging from 2.2 to 4.6 mg P kg−1 day−1. These rates of hydrolysis, however, cannot be compared to those in non-sterile soils as they are affected by the release of cellular compounds, e.g. easily mineralizable Po, derived from microbial cells killed by γ-irradiation. 相似文献
3.
The annual carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) dynamics were measured with static chambers on two organic agricultural soils with different soil characteristics. Site 1 had a peat layer of 30 cm, with an organic matter (OM) content of 74% in the top 20 cm. Site 2 had a peat layer of 70 cm but an OM content of only 40% in the top 20 cm. On both sites there were plots under barley and grass and also plots where the vegetation was removed. All soils were net sources of CO2 and N2O, but they consumed atmospheric CH4. Soils under barley had higher net CO2 emissions (830 g CO2-C m−2 yr−1) and N2O emissions (848 mg N2O-N m−2 yr−1) than those under grass (395 g CO2-C m−3 yr−1 and 275 mg N2O-N m−2 yr−1). Bare soils had the highest N2O emissions, mean 2350 mg N2O-N m−2 yr−1. The mean CH4 uptake rate from vegetated soils was 100 mg CH4-C m−3 yr−1 and from bare soils 55 mg CH4-C m−2 yr−1. The net CO2 emissions were higher from Site 2, which had a high peat bulk density and a low OM content derived from the addition of mineral soil to the peat during the cultivation history of that site. Despite the differences in soil characteristics, the mean N2O emissions were similar from vegetated peat soils from both sites. However, bare soils from Site 2 with mineral soil addition had N2O emissions of 2-9 times greater than those from Site 1. Site 1 consumed atmospheric CH4 at a higher rate than Site 2 with additional mineral soil. N2O emissions during winter were an important component of the N2O budget even though they varied greatly, ranging from 2 to 99% (mean 26%) of the annual emission. 相似文献
4.
Denitrification assays in soils spiked with zinc salt have shown inhibition of the N2O reduction resulting in increased soil N2O fluxes with increasing soil Zn concentration. It is unclear if the same is true for environmentally contaminated soils. Net production of N2O and N2 was monitored during anaerobic incubations (25 °C, He atmosphere) of soils freshly spiked with ZnCl2 and of corresponding soils that were gradually enriched with metals (mainly Zn) in the field by previous sludge amendments or by corrosion of galvanized structures. Total denitrification activity (i.e. the sum of N2O+N2 production rate) was not inhibited by freshly added Zn salts up to 1600 mg Zn kg−1, whereas N2O reduction decreased by 50% (EC50) at total Zn concentrations of 231 mg Zn kg−1 (ZEV soil) and 368 mg Zn kg−1 (TM soil). In contrast, N2O reduction was not reduced by soil Zn in any of the field contaminated soils, even at total soil Zn or soil solution Zn concentrations exceeding more than 5 times corresponding EC50's of the freshly spiked soil. The absence of adverse effects in the field contaminated soils was unrelated to soil NO3 or organic matter concentration. Ageing (2-8 weeks) and soil leaching after spiking reduced the toxicity of Zn on N2O reduction, either expressed as total Zn or soil solution Zn, suggesting adaptation reactions. However, no full recovery after spiking was identified at the largest incubation period in one soil. In addition, the denitrification assay performed with sewage sludge showed elevated N2O release in Zn contaminated sludges (>6000 mg Zn kg−1 dry matter) whereas this was not observed in low Zn sludge (<1000 mg Zn kg−1 dry matter) suggesting limits to adaptation reactions in the sludge particles. It is concluded that the use of soils spiked with Zn salts overestimates effects on N2O reduction. Field data on N2O fluxes in sludge amended soils are required to identify if metals indeed promote N2O emissions in sludge amended soils. 相似文献
5.
Rice (Oryza sativa) was grown in sunlit, semi-closed growth chambers (4×3×2 m, L×W×H) at 650 μl l−1 CO2 (elevated CO2) to determine: (1) rice root-derived carbon (C) input into the soil under elevated CO2 in one growing season, and (2) the effect of the newly input C on decomposition of the more recalcitrant native soil organic C. The initial δ13C value of the experimental soil was −25.8‰, which was 6‰ less depleted in 13C than the plants grown under elevated CO2. Significant changes in δ13C of the soil organic C were detected after one growing season. The amount of new soil C input was estimated to be 0.9 t ha−1 (or 2.1%) at 30 kg N ha−1 and 1.8 t ha−1 (4.1%) at 90 kg N ha−1. Changes in soil δ13C suggested that the surface 5 cm of soil received more C input from plants than soils below. Laboratory incubation (25 °C) of soils from different horizons indicated that increased availability of the labile plant-derived C in the soil reduced decomposition of the native soil organic C. Provided the retardant effect of the new C on old soil organic C holds in the field in the longer-term, paddy soils will likely sequester more C from the atmosphere if more plant C enters the soil under elevated atmospheric CO2. 相似文献
6.
《Soil biology & biochemistry》2004,36(6):917-925
We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak (Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO2, CH4 and N2O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH4 uptake rates (<1 kg C ha−1 yr−1) and, coinciding with WFPS values >70%, episodes of CH4 emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH4 (4.7 kg C ha−1 yr−1). The N2O releases at the cropland and pasture sites (2.7 and 4.8 kg N2O-N ha−1 yr−1) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N2O-N ha−1 yr−1). The highest N2O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH4 and N2O. On the contrary, afforestation resulted in increases in SOM content and CH4 uptake, as well as decreases in N2O emissions. 相似文献
7.
Global warming potential (GWP) of sandy paddy soils may be reduced by trade-offs between N2O, CH4 and CO2 emissions. Laboratory experiments using either rice straw (1% or 0.5%) or together with urea-N (25 or 50 mg N kg−1 soil) at various levels of soil water were carried out for 30 days each, to test this assumption. Waterlogging combined with urea-N increased total N2O emissions, with greater release upon rewaterlogging (7.4 mg N kg−1 soil) than experienced by removing waterlogging only. Rice straw±urea-N either emitted small amounts of N2O or resulted in negative values at all water levels, including saturated and aerobic. Total CH4 fluxes declined with the decreased water levels and amount of rice straw (<193 mg C kg−1 soil), and also for CO2 with the latter (<1340 mg C kg−1 soil), and rewaterlogging had little influence on both. N2O under rewaterlogged and waterlogged±urea-N, CH4 under waterlogged with rice straw, and CO2 for the remainder were the major contributors to GWP. Results show that waterlogging following aerobic decomposition of rice straw (1%) with urea-N, applied either at the beginning or at the end of the aerobic conditions, could decrease GWP by 56-64% and 32-42% over the sole addition of rice straw (1% and 0.5%) under waterlogged and saturated conditions, respectively. 相似文献
8.
Phosphorus losses by surface runoff from agricultural lands have been of public concern due to increasing P contamination to surface waters. Five representative commercial citrus groves (C1-C5) located in South Florida were studied to evaluate the relationships between P fractions in soils, surface runoff P, and soil phosphatase activity. A modified Hedley P sequential fractionation procedure was employed to fractionate soil P. Soil P consisted of mainly organically- and Ca/Mg-bound P fractions. The organically-bound P (biological P, sum of organic P in the water, NaHCO3 and NaOH extracts) was dominant in the acidic sandy soils from the C2 and C3 sites (18% and 24% of total soil P), whereas the Ca/Mg-bound P (HCl-extractable P) accounted for 45-60% of soil total P in the neutral and alkaline soils (C1, C4 and C5 soils). Plant-available P (sum of water and NaHCO3 extractable P fractions) ranged from 27 to 61 mg P kg−1 and decreased in the order of C3>C4>C1>C2>C5. The mean total P concentrations (TP) in surface runoff water samples ranged from 0.51 to 2.64 mg L−1. Total P, total dissolved P (TDP), and PO43−-P in surface runoff were significantly correlated with soil biological P and plant-available P forms (p<0.01), suggesting that surface runoff P was directly derived from soil available P pools, including H2O- and NaHCO3- extractable inorganic P, water-soluble organic P, and NaHCO3- and NaOH-extractable organic P fractions, which are readily mineralized by soil microorganisms and/or enzyme mediated processes. Soil neutral (55-190 mg phenol kg−1 3 h−1) and natural (measured at soil pH) phosphatase activities (77-295 mg phenol kg−1 3 h−1) were related to TP, TDP, and PO43−-P in surface runoff, and plant-available P and biological P forms in soils. These results indicate that there is a potential relationship between soil P availability and phosphatase activities, relating to P loss by surface runoff. Therefore, the neutral and natural phosphatase activities, especially the natural phosphatase activity, may serve as an index of surface runoff P loss potential and soil P availability. 相似文献
9.
The importance of subsoil denitrification on the fate of agriculturally derived nitrate (NO3) leached to groundwater is crucial for budgeting N in an ecosystem and for identifying areas where the risk of excess NO3 is reduced. However, the high atmospheric background of di-nitrogen (N2) causes difficulties in assessing denitrification enzyme activity (DEA) and denitrification potential (DP) in soils directly. Here, we apply Membrane Inlet Mass Spectrometry (MIMS) technique to investigate indirectly DEA and DP in soils by measuring N2/Ar ratio changes in headspace water over soil. Soils were collected from 0-10, 15-25 and 60-70 cm depths of a grazed ryegrass and grass-clover. The samples were amended with helium-flushed deionized water containing ranges of NO3 and carbon (glucose-C) and were incubated for six hours in the dark at 21 °C. The peaks for N2/Ar ratio, declined with increasing soil depth, indicating a reduced substrate requirements to initiate DEA en-masse (15-30 mg NO3-N alone or with 60-120 mg glucose-C, kg−1 soil). The dissolved N2O concentrations were very small (0.004-0.269 μg N kg−1 soil) but responded well to the added N and C, showing a reduction in DEA with soil depth. In three separate studies, only subsoils were incubated for 3 days at 12 °C with 20-30 mg NO3-N ± 40-60 mg glucose-C, kg−1 soil. Denitrification capacity (DC, NO3 only treatment) was not statistically different to the control (no amendment) within a land use (0.03-0.05 vs. 0.07-0.22 mg N kg−1 soil d−1), the highest being in ryegrass subsoils receiving groundwater. The DP was significantly (P < 0.0001) higher in subsoils under ryegrass than under grass-clover (0.50-0.71 vs. 1.15 mg N kg−1 soil d−1). The rates of DP (NO3 + glucose-C) increased significantly (P < 0.0001) in unsaturated and saturated subsoils (0.92 and 2.19 mg N kg−1 soil d−1, respectively) of grass-clover, due to the higher reductive state resulting from the 10 day pre-incubation. Available C accelerated denitrification in soils and superseded the temporary elevation in oxidative state due to NO3 addition. The substrates load differences between the land uses regulated the degree of denitrification rates. Results suggest that both dissolved N2O measured by gas chromatography and N2/Ar ratio measured by MIMS to indirectly determine DEA, and the latter to quantify total DC/DP in soils can be used. However, interference of oxygen in the MIMS system should be considered if available C is added or is naturally elevated in soil or groundwater. 相似文献
10.
Ogasawara Islands are important ecosystems sustaining many indigenous spices. To clarify the indigenous soil environments of Ogasawara Islands, we studied the chemistry of the soils. Many surface soils were low in bio-available P (0 to 0.55 g P2O5 kg−1, average: 0.04 g P2O5 kg−1 as Bray II P, n = 22), but several soils were found to contain extremely large amounts of bio-available P (1.36 to 6.98 g P2O5 kg−1, average: 2.93 g P2O5 kg−1, n = 5). From soil profile analyses, the authors concluded that the extremely large amount of bio-available P could not be explained by the effects of parent materials with high P contents nor the effect of fertilizations by human activity, but the effects of natural seabird activities in the past could be the cause. The soil profiles with large amounts of bio-available P indicate deep migration of soil materials from A horizons, which could be a result of intensive mixing of upper horizons by seabird activities. The intensive mixing was supported by the low mechanical impedance of the horizons for the P-accumulating soils (8.17 ± 2.54 kg cm−2, n = 8) than those for the non-P-accumulating soils (17.46 ± 3.52 kg cm−2, n = 36). It is likely that in the past seabirds, such as shearwaters, made burrows in the soils for nesting and propagating and inadvertently transported a large amount of P from the sea to the soils, resulting in the extremely large amounts of bio-available P in the present soils. 相似文献
11.
Phuy-Chhoy Vong Séverine Piutti Sophie Slezack-Deschaumes Emile Benizri Armand Guckert 《Geoderma》2008,148(1):79-84
In this study we examined the effects of glucose-C on the activities of fungi and bacteria determined by the method of substrate-induced respiration (SIR) in combination with the selective inhibition technique, the immobilized-S and the arylsulphatase (ARS) activity in two calcareous arable and fallow soils. The amounts of glucose-C were added at six doses: 0, 125, 250, 500, 750 and 1000 mg kg− 1 soil to the soils and then incubated for one week with a Na235SO4 solution (518.9 kBq kg− 1 dry soil and 20 mg S kg− 1 dry soil) prior to analysis. At the highest dose of 1000 mg kg− 1 soil, fungal activity increased by 59.1% (of the dose 0) versus 45.5% for bacterial activity in the arable soil, while in the fallow soil the increases were more marked and corresponded to 69.9% and 71.1%, respectively. Largest increase in immobilized-S was observed in the arable soil (300.7%) compared with the fallow soil (153.1%). In contrast, the ARS activity increased by 16.4% in the arable soil versus 32.1% in the fallow soil. These results indicate that glucose proportionately affected more the intensities of immobilized-S than those of ARS. Strong positive correlation coefficients were found between fungal activities and immobilized-S in the arable soil (r = 0.96, P < 0.01) and in the fallow soil (r = 0.98, P < 0.001). However, non-significant correlations were observed between fungal activities and ARS in both studied soils. As to bacterial activities, positive significant correlation coefficients were found with immobilized-S in the arable soil (r = 0.95, P < 0.01) and in the fallow soil (r = 0.90, P < 0.05) as well as with ARS activities in the arable soil (r = 0.83, P < 0.05) and in the fallow soil (r = 0.97, P < 0.01). Overall, we also found positive and significant correlation coefficients of immobilized-S with ARS activities in the arable soil (r = 0.86, P < 0.05) and in the fallow soil (r = 0.83, P < 0.05). Accordingly, the results showed a presence of extracellular arylsulphatase activity of 38.7 mg p-nitrophenol kg− 1 soil h− 1 in the arable soil and of 63.5 mg p-nitrophenol kg− 1 soil h− 1 in the fallow soil. It was concluded that fallowing maintained larger activities of fungi, bacteria and arylsulphatase compared with the arable soil. 相似文献
12.
In previous studies, Al extracted by acid ammonium acetate (Ala) or Na-pyrophosphate (Alp), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Ala is a comparable method (as much as CuCl2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Ala, Alp, oxalate (Alo, Sio and Feo), cold NaOH (Aln) and un-buffered salts, CuCl2 (AlCu), LaCl3 (AlLa) and KCl (Alk). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Ala had a good correspondence with Alp (R2 = 0.76) in the top soil with Ala/Alp ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R2 > 0.62). Acid ammonium acetate was as effective as AlCu to determine the Al-OM in allophanic soils. It is cheaper than AlCu and Alp and 0.5 h shaking is required compared to 2 h of AlCu and 16 h of Alp. The efficiency of the extraction was: Aln ≥ Alo > Alp > AlCu ≥ Ala > AlLa > Alk. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R2 = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R2 > 0.60) the largest proportion of variation of soil OC across studied soils. 相似文献
13.
Cyanobacterial inoculation of heated soils: effect on microorganisms of C and N cycles and on chemical composition in soil surface 总被引：2，自引：0，他引：2
Physiological groups of soil microorganisms, total C and N and available nutrients were investigated in four heated (350 °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g−1 soil or 3.0 μg chlorophyll a g−1 soil) with four cyanobacterial strains of the genus Oscillatoria, Nostoc or Scytonema and a mixture of them.Cyanobacterial inoculation promoted the formation of microbiotic crusts which contained a relatively high number of NH4+-producers (7.4×109 g−1 crust), starch-mineralizing microbes (1.7×108 g−1 crust), cellulose-mineralizing microbes (1.4×106 g−1 crust) and NO2− and NO3− producers (6.9×104 and 7.3×103 g−1 crust, respectively). These crusts showed a wide range of C and N contents with an average of 293 g C kg−1 crust and 50 g N kg−1 crust, respectively. In general, Ca was the most abundant available nutrient (804 mg kg−1 crust), followed by Mg (269 mg kg−1 crust), K (173 mg kg−1 crust), Na (164 mg kg−1 crust) and P (129 mg kg−1 crust). There were close positive correlations among all the biotic and abiotic components of the crusts.Biofertilization with cyanobacteria induced great microbial proliferation as well as high increases in organic matter and nutrients in the surface of the heated soils. In general, cellulolytics were increased by four logarithmic units, amylolytics and ammonifiers by three logarithmic units and nitrifiers by more than two logarithmic units. C and N contents rose an average of 275 g C kg−1 soil and 50 g N kg−1 soil while the C:N ratio decreased up to 7 units. Among the available nutrients the highest increase was for Ca (315 mg kg−1 soil) followed by Mg (189 mg kg−1 soil), K (111 mg kg−1 soil), Na (109 mg kg−1 soil) and P (89 mg kg−1 soil). Fluctuations of the microbial groups as well as those of organic matter and nutrients were positively correlated.The efficacy of inoculation depended on both the type of soil and the class of inoculum. The best treatment was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone. In the medium term there were not significant differences between the two inocula amounts tested.These results showed that inoculation of burned soils with alien N2-fixing cyanobacteria may be a biotechnological means of promoting microbiotic crust formation, enhancing C and N cycling microorganisms and increasing organic matter and nutrient contents in heated soils. 相似文献
14.
Emissions of N2O were measured following addition of 15N-labelled (2.6-4.7 atom% excess 15N) agroforestry residues (Sesbania sesban, mixed Sesbania/Macroptilium atropurpureum, Crotalaria grahamiana and Calliandra calothyrsus) to a Kenyan oxisol at a rate of 100 mg N kg soil−1 under controlled environment conditions. Emissions were increased following addition of residues, with 22.6 mg N m−2 (124.4 mg N m−2 kg biomass−1; 1.1 mg 15N m−2; 1.03% of 15N applied) emitted as N2O over 29 d after addition of both Sesbania and Macroptilium residues in the mixed treatment. Fluxes of N2O were positively correlated with CO2 fluxes, and N2O emissions and available soil N were negatively correlated with residue lignin content (r=−0.49;P<0.05), polyphenol content (r=−0.94;P<0.05), protein binding capacity (r=−0.92;P<0.05) and with (lignin+polyphenol)-to-N ratio (r=−0.55;P<0.05). Lower emission (13.6 mg N m−2 over 29 d; 94.5 mg N m−2 kg biomass−1; 0.6 mg 15N m−2; 0.29% of 15N applied) after addition of Calliandra residue was attributed to the high polyphenol content (7.4%) and high polyphenol protein binding capacity (383 μg BSA mg plant−1) of this residue binding to plant protein and reducing its availability for microbial attack, despite the residue having a N content of 2.9%. Our results indicate that residue chemical composition, or quality, needs to be considered when proposing mitigation strategies to reduce N2O emissions from systems relying on incorporation of plant biomass, e.g. improved-fallow agroforestry systems, and that this consideration should extend beyond the C-to-N ratio of the residue to include polyphenol content and their protein binding capacity. 相似文献
15.
Impact of land-use types on soil nitrogen net mineralization in the sandstorm and water source area of Beijing,China 总被引：1，自引：0，他引：1
Changes of land-use type (LUT) can affect soil nutrient pools and cycling processes that relate long-term sustainability of ecosystem, and can also affect atmospheric CO2 concentrations and global warming through soil respiration. We conducted a comparative study to determine NH4+ and NO3− concentrations in soil profiles (0–200 cm) and examined the net nitrogen (N) mineralization and net nitrification in soil surface (0–20 cm) of adjacent naturally regenerated secondary forests (NSF), man-made forests (MMF), grasslands and cropland soils from the windy arid and semi-arid Hebei plateau, the sandstorm and water source area of Beijing, China. Cropland and grassland soils showed significantly higher inorganic N concentrations than forest soils. NO3−-N accounted for 50–90% of inorganic N in cropland and grassland soils, while NH4+-N was the main form of inorganic N in NSF and MMF soils. Average net N-mineralization rates (mg kg−1 d−1) were much higher in native ecosystems (1.51 for NSF soils and 1.24 for grassland soils) than in human disturbed LUT (0.15 for cropland soils and 0.85 for MMF soils). Net ammonification was low in all the LUT while net nitrification was the major process of net N mineralization. For more insight in urea transformation, the increase in NH4+ and, NO3− concentrations as well as C mineralization after urea addition was analyzed on whole soils. Urea application stimulated the net soil C mineralization and urea transformation pattern was consistent with net soil N mineralization, except that the rate was slightly slower. Land-use conversion from NSF to MMF, or from grassland to cropland decreased soil net N mineralization, but increased net nitrification after 40 years or 70 years, respectively. The observed higher rates of net nitrification suggested that land-use conversions in the Hebei plateau might lead to N losses in the form of nitrate. 相似文献
16.
We evaluated the spatial structures of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) fluxes in an Acacia mangium plantation stand in Sumatra, Indonesia, in drier (August) and wetter (March) seasons. A 60 × 100-m plot was established in an A. mangium plantation that included different topographical elements of the upper plateau, lower plateau, upper slope and foot slope. The plot was divided into 10 × 10-m grids and gas fluxes and soil properties were measured at 77 grid points at 10-m intervals within the plot. Spatial structures of the gas fluxes and soil properties were identified using geostatistical analyses. Averaged N2O and CO2 fluxes in the wetter season (1.85 mg N m−2 d−1 and 4.29 g C m−2 d−1, respectively) were significantly higher than those in the drier season (0.55 mg N m−2 d−1 and 2.73 g C m−2 d−1, respectively) and averaged CH4 uptake rates in the drier season (−0.62 mg C m−2 d−1) were higher than those in the wetter season (−0.24 mg C m−2 d−1). These values of N2O fluxes in A. mangium soils were higher than those reported for natural forest soils in Sumatra, while CO2 and CH4 fluxes were in the range of fluxes reported for natural forest soils. Seasonal differences in these gas fluxes appears to be controlled by soil water content and substrate availability due to differing precipitation and mineralization of litter between seasons. N2O fluxes had strong spatial dependence with a range of about 18 m in both the drier and wetter seasons. Topography was associated with the N2O fluxes in the wetter season with higher and lower fluxes on the foot slope and on the upper plateau, respectively, via controlling the anaerobic-aerobic conditions in the soils. In the drier season, however, we could not find obvious topographic influences on the spatial patterns of N2O fluxes and they may have depended on litter amount distribution. CO2 fluxes had no spatial dependence in both seasons, but the topographic influence was significant in the drier season with lowest fluxes on the foot slope, while there was no significant difference between topographic positions in the wetter season. The distributions of litter amount and soil organic matter were possibly associated with CO2 fluxes through their effects on microbial activities and fine root distribution in this A. mangium plantation. 相似文献
17.
We investigated the relationship between soil organic matter (SOM) content and N dynamics in three grassland soils (0-10 and 10-20 cm depth) of different age (6, 14 and 50 y-old) with sandy loam textures. To study the distribution of the total C and N content the SOM was fractionated into light, intermediate and heavy density fractions of particulate macro-organic matter (150-2000 μm) and the 50-150 μm and <50 μm size fractions. The potential gross N transformation rates (mineralisation, nitrification, NH4+ and NO3− immobilization) were determined by means of short-term, fully mirrored 15N isotope dilution experiments (7-d incubations). The long-term potential net N mineralisation and gross N immobilization rates were measured in 70-d incubations. The total C and N contents mainly tended to increase in the 0-10 cm layer with increasing age of the grassland soils. Significant differences in total SOM storage were detected for the long-term (50 y-old) conversion from arable land to permanent grassland. The largest relative increase in C and N contents had occurred in the heavy density fraction of the macro-organic matter, followed by the 50-150 and <50 μm fractions. Our results suggest that the heavy density fraction of the macro-organic matter could serve as a good indicator of early SOM accumulation, induced by converting arable land to permanent grassland. Gross N mineralisation, nitrification, and (long-term) gross N immobilization rates tended to increase with increasing age of the grasslands, and showed strong, positive correlations with the total C and N contents. The calculated gross N mineralisation rates (7-d incubations) and net N mineralisation rates (70-d incubations) corresponded with a gross N mineralisation of 643, 982 and 1876 kg N ha−1 y−1, and a net N mineralisation of 195, 208 and 274 kg N ha−1 y−1 in the upper 20 cm of the 6, 14 and 50 y-old grassland soils, respectively. Linear regression analysis showed that 93% of the variability of the gross N mineralisation rates could be explained by variation in the total N contents, whereas total N contents together with the C-to-N ratios of the <50 μm fraction explained 84% of the variability of the net N mineralisation rates. The relationship between long-term net N mineralisation rates and gross N mineralisation rates could be fitted by means of a logarithmic equation (net m=0.24Ln(gross m)+0.23, R2=0.69, P<0.05), which reflects that the ratio of gross N immobilization-to-gross N mineralisation tended to increase with increasing SOM contents. Microbial demand for N tended to increase with increasing SOM content in the grassland soils, indicating that potential N retention in soils through microbial N immobilization tends to be limited by C availability. 相似文献
18.
A long-term field experiment was established to determine the influence of mineral fertilizer (NPK) or organic manure (composed of wheat straw, oil cake and cottonseed cake) on soil fertility. A tract of calcareous fluvo-aquic soil (aquic inceptisol) in the Fengqiu State Key Experimental Station for Ecological Agriculture (Fengqiu county, Henan province, China) was fertilized beginning in September 1989 and N2O emissions were examined during the maize and wheat growth seasons of 2002-2003. The study involved seven treatments: organic manure (OM), half-organic manure plus half-fertilizer N (1/2 OMN), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), fertilizer PK (PK) and control (CK). Manured soils had higher organic C and N contents, but lower pH and bulk densities than soils receiving the various mineralized fertilizers especially those lacking P, indicating that long-term application of manures could efficiently prevent the leaching of applied N from and increase N content in the plowed layer. The application of manures and fertilizers at a rate of 300 kg N ha−1 year−1 significantly increased N2O emissions from 150 g N2O-N ha−1 year−1 in the CK treatment soil to 856 g N2O-N ha−1 year−1 in the OM treatment soil; however, there was no significant difference between the effect of fertilizer and manure on N2O emission. More N2O was released during the 102-day maize growth season than during the 236-day wheat growth season in the N-fertilized soils but not in N-unfertilized soils. N2O emission was significantly affected by soil moisture during the maize growth season and by soil temperature during the wheat growth season. In sum, this study showed that manure added to a soil tested did not result in greater N2O emission than treatment with a N-containing fertilizer, but did confer greater benefits for soil fertility and the environment. 相似文献
19.
Emission of N2O and CH4 oxidation rates were measured from soils of contrasting (30-75%) water-filled pore space (WFPS). Oxidation rates of 13C-CH4 were determined after application of 10 μl 13C-CH4 l−1 (10 at. % excess 13C) to soil headspace and comparisons made with estimates from changes in net CH4 emission in these treatments and under ambient CH4 where no 13C-CH4 had been applied. We found a significant effect of soil WFPS on 13C-CH4 oxidation rates and evidence for oxidation of 2.2 μg 13C-CH4 d−1 occurring in the 75% WFPS soil, which may have been either aerobic oxidation occurring in aerobic microsites in this soil or anaerobic CH4 oxidation. The lowest 13C-CH4 oxidation rate was measured in the 30% WFPS soil and was attributed to inhibition of methanotroph activity in this dry soil. However, oxidation was lowest in the wetter soils when estimated from changes in concentration of 12+13C-CH4. Thus, both methanogenesis and CH4 oxidation may have been occurring simultaneously in these wet soils, indicating the advantage of using a stable isotope approach to determine oxidation rates. Application of 13C-CH4 at 10 μl 13C-CH4 l−1 resulted in more rapid oxidation than under ambient CH4 conditions, suggesting CH4 oxidation in this soil was substrate limited, particularly in the wetter soils. Application of and (80 mg N kg soil−1; 9.9 at.% excess 15N) to different replicates enabled determination of the respective contributions of nitrification and denitrification to N2O emissions. The highest N2O emission (119 μg 14+15N-N2O kg soil−1 over 72 h) was measured from the 75% WFPS soil and was mostly produced during denitrification (18.1 μg 15N-N2O kg soil−1; 90% of 15N-N2O from this treatment). Strong negative correlations between 14+15N-N2O emissions, denitrified 15N-N2O emissions and 13C-CH4 concentrations (r=−0.93 to −0.95, N2O; r=−0.87 to −0.95, denitrified 15N-N2O; P<0.05) suggest a close relationship between CH4 oxidation and denitrification in our soil, the nature of which requires further investigation. 相似文献
20.
A laboratory investigation was performed to compare the fluxes of dinitrogen (N2), N2O and carbon dioxide (CO2) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0-10 cm) were incubated for 2 weeks at 25 °C at either 75% or 60% water-filled pore space (WFPS) with 15N-labeled fertilizers (100 mg N kg−1 soil). Gas and soil samples were collected at 1-4 day intervals during the incubation period. The N2O and CO2 fluxes were measured by a gas chromatography (GC) system while total N2 and N2O losses and their 15N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N2 and N2O were significantly affected by tillage, N source and soil moisture. We observed higher (P<0.05) fluxes of N2+N2O, N2O and CO2 from the NT soils than from the CT soils. Compared with the addition of nitrate (NO3−), the addition of ammonium (NH4+) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH4+ on the N2 and/or N2O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N2O emission under the lower moisture condition. Total and fertilizer-induced emissions of N2 and/or N2O were higher (P<0.05) at 75% WFPS than with 60% WFPS, while CO2 fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N2O loss from NT soils than CT soils. Avoiding wet soil conditions (>60% WFPS) and applying a NO3− form of N fertilizer would reduce potential N2O emissions from arable soils. 相似文献