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1.

Purpose  

The study of phosphorus (P) transfer from soils to rivers is a subject of interest as there is a clear relation between land use and water quality. P transfer in the soil/sediment system was evaluated by comparing the concentrations of total (PT) and bioavailable P (PA).  相似文献   

2.

Purpose

The aim of this study was to evaluate the role of phosphine in the mobilization of phosphorus in the rhizosphere soil of rice seedlings and to determine the relative efficiency of phosphine in plant P acquisition.

Materials and methods

An indoor simulation experiment was conducted and the matrix-bound phosphine (MBP), phosphorus fractions, and phosphatase activity in the rhizosphere soil samples from rice cultivation, biomass, the plant P, and the root system activity were measured under different phosphine concentrations (0, 1.4, 4.2, and 7.0 mg m?3) for a period of 30 days.

Results and discussion

The results indicated that phosphine treatments enhanced MBP, inorganic P (resin–Pi, NaHCO3–Pi, and NaOH–Pi), and phosphatase activity, as well as the root system activity, and the content of P in the rice seedlings was stimulated with increasing phosphine concentrations. However, organic P (NaHCO3–Po and NaOH–Po) accumulation occurred in the rhizosphere of the rice seedlings. In addition, the content of organic P in the soil samples decreased with increased phosphine concentration.

Conclusions

Therefore, relatively high concentrations of phosphine in paddy field could have a positive impact on the effectiveness of phosphorus in rice plants via influencing the rhizosphere properties.
  相似文献   

3.

Purpose  

Soil strength and thus stability concerning wind erosion are controlled by the soil water content. The concept of soil critical water content (Θcrit.) for deflation was extended to include matric potential (Ψcrit.) as well. The focus of this paper is to quantify the Θcrit. and Ψcrit. as the upper boundary for wind erosion or as the lower boundary for soil strength, to model the Ψcrit. at the immediate soil surface (0–0.2 cm) and to evaluate the effect of soil moisture upon erosion as a function of time and sampling height.  相似文献   

4.

Purpose  

Vegetable production is one of the most intensive agricultural systems with high rates of nitrogen (N) fertilizer use and irrigation, conditions conducive for nitrate (NO3) leaching, and nitrous oxide (N2O) emissions. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3 leaching and N2O emissions in vegetable production systems.  相似文献   

5.

Purpose  

Volcanoes are a natural source of Hg, whose deposition can occur in neighbouring soils. This study examines the role of soil compounds in the geochemical behaviour of total Hg (Hg T ) in volcanic soils. An estimation of Hg from lithological origin is also assessed to ascertain the relevance of other sources in Hg T accumulated in volcanic soils.  相似文献   

6.

Purpose  

Acetylene (C2H2) is employed for the quantification of important biological processes such as nitrogen fixation, nitrous oxide reduction, ammonium and methane oxidation, and methanogenesis. Although acetylene is not a natural product, the ability of bacteria to grow on C2H2 is a phenomenon common to soils and sediments. Our experiment was designed to study the modification of CO2 production, O2 uptake and microbial biomass (Cmic) in soil in response to the consumption of added acetylene.  相似文献   

7.

Purpose  

The effects of the addition of an acidic fertilizer solution and/or slaked lime (5.5 g Ca(OH)2 kg−1) on a slightly acidic shooting range soil (pH 6.1, % organic carbon 5.4) with moderate metal (e.g., 620 mg kg−1 Pb) and metalloid (17 mg kg−1 Sb) concentrations on metal and Sb solubility and plant accumulation were investigated.  相似文献   

8.

Background

Labile carbon (Clabile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating Clabile additions use laboratory incubations. We need to field-apply Clabile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.

Aims

Here, we evaluated the impact of adding an in situ pulse of an inexpensive and 13C-depleted source of Clabile—crude glycerol carbon (Cglyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.

Methods

We broadcast-applied Cglyc at three rates (0, 216, and 866 kg C ha−1) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured Cglyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO3–N) and potential net N mineralization to examine short-term effects on N cycling.

Results

Cglyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total Cglyc added). The δ13C values of the other measured C pools were too variable to accurately track the Clabile fate. NO3–N was decreased by 13%–57% with the 216 and 866 kg C ha−1 rates, respectively, and was strongly related to greater microbial uptake of Cglyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.

Conclusions

Overall, glycerol is an inexpensive and effective way to measure in situ, Clabile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO3–N.  相似文献   

9.

Purpose  

In this study, a process-oriented biogeochemistry model, denitrification–decomposition (DNDC), was employed and adapted to interpret and integrate the field observations that the tested ecosystem was a weak sink of atmospheric carbon dioxide (CO2) in 2004 but a strong source in 2005 during the growing seasons. Then we applied the model to predict long-term impacts of climate change on carbon (C) dynamics in the semiarid grassland.  相似文献   

10.

Background

Organic farmers frequently report sufficient yield levels despite low or even very low soil phosphorous (P) contents questioning the applicability of widely used laboratory methods for soil P testing for organic farming.

Aims

The aim of this study was to compare the validity of a broad range of different soil extraction methods on soils under organic management from South West Germany and to test the correlation of the measured soil P concentration with plant offtake.

Methods

Twenty-two soil samples of eight different organic farms were extracted with different solutions: (1) water, (2) CAL, (3) Olsen, (4) Mehlich 3, (5) Bray P1, (6) Bray P2, (7) NaOH+Na2EDTA, and (8) total P. The results were then correlated with above ground plant P.

Results

Spearman's rank correlation coefficient (rs) of correlations between above ground plant P and extractable soil P (Water-P, CAL-P, and Olsen-P [+active charcoal {+AC}]) determined with ICP-OES were strong (0.94, 0.90, and 0.93, respectively). Among the tested methods, above ground plant P showed a strong correlation with CAL-P as detected by ICP-OES (rs = 0.90) and colorimetry (rs = 0.91). The comparison of CAL-P data provided by farmers and CAL-P analyzed during this research showed discrepancies between the results.

Conclusions

The results of this study indicate that the CAL method can be used in organic farming despite a low extraction of organic P (Porg). Furthermore, it is recommended for farmers to take soil samples for analyses regularly and interpret changes in P in the long-term instead of interpreting individual samples.  相似文献   

11.

Purpose  

The oxidation of ammonium (NH4+) to nitrate (NO3) in the soil is an important biogeochemical process, which has major environmental implications as it can contribute to NO3 leaching and nitrous oxide (N2O) emissions. Nitrification inhibitors have been used to slow down this process to reduce NO3 leaching and N2O emissions from agricultural land. The objective of this study was to determine the effectiveness of a liquid formulation of 3,4-Dimethylpyrazole phosphate (DMPP) compared with a dicyandiamide (DCD) solution in inhibiting the growth of ammonium-oxidizing bacteria (AOB) and ammonium oxidizing archaea (AOA) and slowing down the rate of NH4+ oxidation in soil.  相似文献   

12.

Purpose  

Methanotrophs are an important group of methane (CH4)-oxidizing bacteria in the soil, which act as a major sink for the greenhouse gas, CH4. In grazed grassland, one of the ecologically most sensitive areas is the animal urine patch soil, which is a major source of both nitrate (NO3 ) leaching and nitrous oxide (N2O) emissions. Nitrification inhibitors, such as dicyandiamide (DCD), have been used to mitigate NO3 leaching and N2O emissions in grazed pastures. However, it is not clear if the high nitrogen loading rate in the animal urine patch soil and the use of nitrification inhibitors would have an impact on the abundance of methanotrophs in grazed grassland soils. The purpose of this study was to determine the effect of animal urine and DCD on methanotroph abundance in grazed grassland soils.  相似文献   

13.

Purpose

Colloid-facilitated migration of phosphorus (P) is a widely accepted phenomenon in surface and subsurface environment. Release and migration of colloidal P (Pcoll) in agricultural fields are closely related to P fertilization regimes. In this study, a site-specific experiment with rice/oilseed rape rotation was conducted to determine the export potential of Pcoll from the field and literatures reporting the impact of P fertilization regimes on release and migration of Pcoll in other agricultural fields were compared.

Materials and methods

In this 2-year field experiment, four P fertilization regimes (no fertilizer control, inorganic P fertilizer of low and high rates, and swine manure treatment) with three replicates were conducted. Floodwater and runoff samples were collected in flooding season and the 100-cm-depth soil samples were collected after both crops’ harvest seasons. Colloidal particles were separated by microfiltration and ultracentrifugation processes and determined gravimetrically. The Pcoll value was calculated as the difference between the concentration of total P in non-ultracentrifuged and ultracentrifuged samples. The same method was applied for the colloidal mineral elements (Fe and Al) and organic carbon.

Results and discussion

Total P concentration in paddy floodwater significantly increased after fertilization but decreased quickly in the following days, maintaining at 6.0 mg m?2. In soil extracts, concentration of Pcoll was low but stable, which ranged from 6 to 22 % of total P after oilseed rape season and from 7 to 18 % after rice season. In runoff samples, there were positive correlations between Pcoll, colloidal Fe (Fecoll), colloidal Al (Alcoll), and colloidal TOC (TOCcoll); the majority of P forms was molybdate reactive P. In both crops’ seasons, the amount of colloids increased with soil depth. Content of soil Pcoll was low and occupied 0.1–2 % of total P. The literature review showed that Pcoll in soil solution, runoff, and leachate ranged from 1.4 to 94 % of total P.

Conclusions

These results suggested that although the concentrations of Pcoll were not high, they widely distributed in paddy floodwater, runoff, and soil profile. Fertilization regimes and planting systems had a significant influence on the contents of Pcoll. Moreover, the Pcoll binding with Fe/Al minerals and organic carbon might be an alternative route of P loss in paddy field.
  相似文献   

14.

Purpose

Soil-plant transfer models are needed to predict levels of mercury (Hg) in vegetables when evaluating food chain risks of Hg contamination in agricultural soils.

Materials and methods

A total of 21 soils covering a wide range of soil properties were spiked with HgCl2 to investigate the transfer characteristics of Hg from soil to carrot in a greenhouse experiment. The major controlling factors and prediction models were identified and developed using path analysis and stepwise multiple linear regression analysis.

Results and discussion

Carrot Hg concentration was positively correlated with soil total Hg concentration (R 2?=?0.54, P?<?0.001), and the log-transformation greatly improved the correlation (R 2?=?0.76, P?<?0.001). Acidic soil exhibited the highest bioconcentration factor (BCF) (ratio of Hg concentration in carrot to that in soil), while calcareous soil showed the lowest BCF among the 21 soil types. The significant direct effects of soil total Hg (Hgsoil), pH, and free Al oxide (AlOX) on the carrot Hg concentration (Hgcarrot) as revealed by path analysis were consistent with the result from stepwise multiple linear regression that yielded a three-term regression model: log [Hgcarrot]?=?0.52log [Hgsoil]???0.06pH???0.64log [AlOX]???1.05 (R 2?=?0.81, P?<?0.001).

Conclusions

Soil Hg concentration, pH, and AlOX content were the three most important variables associated with carrot Hg concentration. The extended Freundlich-type function could well describe Hg transfer from soil to carrot.  相似文献   

15.

Background

Evidence of trivalent manganese (Mn3+) in the aqueous phase of soils is unknown so far although this strong oxidant has large environmental implications.

Aims

We aimed to modify a spectrophotometric protocol (porphyrin method) and to discriminate between Mn2+ and Mn3+ in the aqueous phase of forest soils based on kinetic modeling.

Methods

We investigated manganese speciation in 12 forest floor solutions and 41 soil solutions from an acidic forest site by adjusting pH and correcting for absorbance.

Results

The solutions showed broad ranges in pH (3.4−6.3), dissolved organic carbon (DOC, 1.78−77.1 mg C L−1), and total Mn (MnT, 23.9−908 µg L−1). For acidic solutions, a pH-buffer was added to increase the pH of the solutions to 7.5−8.0, and background absorption was corrected for colored solutions, that is, solutions high in DOC. This was done to accelerate the reaction kinetics and avoid overestimation of MnT concentrations. After the pH and color adjustments, the comparison of MnT concentrations between the porphyrin method and optical emission spectrometry showed good agreement. Trivalent Mn, which is stabilized by organic ligands, constitutes significant proportions in both forest floor solutions (10−87%) and soil solutions (0.5−74%).

Conclusions

The dissolved Mn3+ is present in acidic forest soils. Thus, we revise the paradigm that this species is not stable and encourage to apply the revised method to other soils.  相似文献   

16.

Purpose  

Up to date, most studies about the plant photosynthetic acclimation responses to elevated carbon dioxide (CO2) concentration have been performed in temperate areas, which are often N limited under natural conditions and with low ambient N deposition. It is unclear whether photosynthetic downregulation is alleviated with increased N availability, for example, from increased N deposition due to fossil fuel combustion in the tropics and subtropics. Awareness of plant photosynthetic responses to elevated CO2 concentration will contribute to the better understanding and prediction of future forest productivity under global change.  相似文献   

17.

Purpose

Re-establishment of soil nitrogen (N) capital is a priority in mine rehabilitation. We aimed to evaluate the effects of biochar addition on improving mine spoil N pools and the influence of elevated CO2 concentration on mine rehabilitation.

Materials and methods

We assessed the effects of pinewood biochar, produced at three temperatures (650, 750 and 850 °C, referred as B650, B750 and B850, respectively), on mine spoil total N concentrations with five different plant species, including a tree species (Eucalyptus crebra), N-fixing shrubs (Acacia floribunda and Allocasuarina littoralis) and C3 and C4 grasses (Austrodanthonia tenuior and Themeda australis) incubated at ambient (400 μL L?1) and elevated (700 μL L?1) atmospheric CO2 concentrations, as well as the effects of elevated CO2 on mine rehabilitation.

Results and discussion

Soil total N significantly improved following biochar incorporation under all plant species (P < 0.05) except for T. Australis. E. crebra had the highest soil total N (0.197%, 0.198% and 0.212% for B650, B750 and B850, respectively). Different from the negligible influence of elevated CO2 on soil properties under the grasses and the N-fixing shrubs, elevated CO2 significantly increased soil water and hot water extractable organic C (WEOC and HWEOC, respectively) and decreased total C under E. crebra, indicating that the nutrient demands were not met.

Conclusions

Biochar addition showed the potential in mine rehabilitation in terms of improving soil N pool, especially with E. crebra. However, it would be more difficulty to rehabilitate mine spoils in future with the rising atmospheric CO2 concentration.
  相似文献   

18.
19.
The development of soil structure units with defined forms and dimensions (e.g. platy by soil compaction or prismatic up to subangular-blocky by swelling–shrinkage processes) can lead to direction-dependent behaviour of mechanical and hydraulic properties. However, little research has investigated direction-dependent behaviour directly. Undisturbed samples were collected at different horizons and orientations (vertical and horizontal) of Stagnic Luvisols derived from glacial till (Weichselian moraine region in Northern Germany). A direct shear test determined the cohesion (c) and the angle of internal friction (φ). The water retention curve (WRC), the saturated hydraulic conductivity (ks) and the air permeability (ka) were also measured. The air-filled porosity (a) was determined and pore continuity indices (N) and blocked porosities (b) were derived from the relationship between ka and a.Although the pore volume as a scalar is isotrop, the saturated hydraulic conductivity and air permeability can be anisotropic. In the seedbed (SB) and plough pan (PP) of conventionally managed soils the effective porosity is non-direction-dependent, however, differences in ks as a function of sampling direction can reach one order of magnitude in PP (ksh > ksv). The shear strength parameters do not present a significant anisotropy, although, a pronounced spatial orientation of soil aggregates (e.g. induced by soil compaction in a plough pan) lead to direction-dependent shear strength (by σn: 10 kPa, σtv: 12 kPa and σth: 19 kPa). This behaviour was especially observed in pore continuity indices (e.g. vertical and horizontal oriented aggregates observed in Bvg and PP presented bv < bh and bv > bh, respectively) showing that the identification of soil structure can be used as the first parameter to estimate if hydraulic properties present a direction-dependent behaviour at the scale of the soil horizon, which is relevant in modelling transport processes.  相似文献   

20.

Background

Riparian buffers are primarily implemented for their water quality functions in agroecosystems. Their location in the agricultural landscape allows them to intercept and process pollutants from immediately adjacent agricultural land. Vegetated riparian buffers recycle soil organic matter, which elevates soil carbon (C), which upon processing, processes and releases carbon dioxide (CO2). The elevated soil C and seasonally anoxic environments associated with riparian buffers promote denitrification and fermentation, further increasing soil CO2 production.

Aim

Against this context, a replicated plot-scale experiment was established at North Wyke, UK, to measure the extent of soil CO2 emissions in permanent pasture served by grass, willow, and woodland riparian buffers, as well as a no-buffer control.

Methods

Soil CO2 was measured using the static chamber technique in conjunction with soil and environmental variables between June 2018 and February 2019.

Results

Cumulative soil CO2 fluxes were in the descending order: woodland riparian buffer; 11,927.8 ± 1987.9 kg CO2 ha–1 > no-buffer control; 11,101.3 ± 3700.4 kg CO2 ha–1 > grass riparian buffer; 10,826.4 ± 2551.8 kg CO2 ha–1 > upslope pasture; 10,554.6 ± 879.5 kg CO2 ha–1 > willow riparian buffer; 9294.9 ± 1549.2 5 kg CO2 ha–1. There was, however, no evidence of significant differences among all treatments of the current study.

Conclusions

Despite the lack of significant differences, the results from our short-term study show that the woodland riparian buffer had relatively larger soil CO2 emissions than the remainder of the other riparian buffers and the upslope pasture it serves. Our short-term findings may be useful in developing soil CO2 mitigation strategies through careful selection of riparian buffer vegetation and may be useful in calibrating mechanistic models for simulating such emissions from similar agro systems.  相似文献   

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