Influence of pore size distribution and soil water content on nitrous oxide emissions

Soil Research ◽  
2012 ◽  
Vol 50 (2) ◽  
pp. 125 ◽  
Author(s):  
Tony J. van der Weerden ◽  
Francis M. Kelliher ◽  
Cecile A. M. de Klein
Keyword(s):  
Nitrous Oxide ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Soil Water ◽  
Gas Diffusion ◽  
Field Conditions ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions

Nitrous oxide (N2O) emissions from agricultural soils have been estimated to comprise about two-thirds of the biosphere’s contribution of this potent greenhouse gas. In pasture systems grazed by farmed animals, where substrate is generally available, spatial variation in emissions, in addition to that cause by the patchiness of urine deposition, has been attributed to soil aeration, as governed by gas diffusion. However, this parameter is not readily measured, and the soil’s water-filled pore space (WFPS) has often been used as a proxy, despite gas diffusion in soils depending on the volumetric fractions of water and air. With changing water content, these fractions will reflect the soil’s pore size distribution. The aims of this study were: (i) to determine if the pore size distribution of two pastoral soils explains previously observed differences in N2O emissions under field conditions, and (ii) to assess the most appropriate soil water/gas diffusion metric for estimating N2O emissions. The N2O emissions were measured from intact cores of two soils (one classified as well drained and one as poorly drained) that had been sampled to a depth of 50 mm beneath grazed pasture. Nitrogen (N, 500 kg N/ha) was applied to soil cores as aqueous nitrate solution, and the cores were drained under controlled conditions at a constant temperature. The poorly drained soil had a larger proportion of macropores (23.5 v. 18.7% in the well-drained soil), resulting in more rapid drainage and increased pore continuity, thereby reducing the duration of anaerobicity, and leading to lower N2O emissions. Emissions were related to three soil water proxies including WFPS, volumetric water content (VWC), and matric potential (MP), and to relative diffusion (RD). All parameters showed highly significant relationships with N2O emissions (P < 0.001), with RD, WFPS, VWC, and MP accounting for 59, 72, 88, and 93% of the variability, respectively. As VWC is more readily determined than MP, the former is potentially more suitable for estimating N2O emission from different soils across a range of time and space scales under field conditions.

Effect of variability in soil properties plus model complexity on predicting topsoil water content and nitrous oxide emissions

Soil Research ◽  
2018 ◽  
Vol 56 (8) ◽  
pp. 810 ◽  
Author(s):  
Iris Vogeler ◽  
Rogerio Cichota
Keyword(s):  
Nitrous Oxide ◽  
Soil Properties ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Soil Profile ◽  
Nitrous Oxide Emissions ◽  
Soil Types ◽  
N2o Emissions ◽  
Silt Loam

Despite the importance of soil physical properties on water infiltration and redistribution, little is known about the effect of variability in soil properties and its consequent effect on contaminant loss pathways. To investigate the effects of uncertainty and heterogeneity in measured soil physical parameters on the simulated movement of water and the prediction of nitrous oxide (N2O) emissions, we set up the Agricultural Production Systems sIMulator (APSIM) for different soil types in three different regions of New Zealand: the Te Kowhai silt loam and the Horotiu silt loam in the Waikato region, and the Templeton silt loam in the Canterbury region, and the Otokia silt loam and the Wingatui silt loam in the Otago region. For each of the soil types, various measured soil profile descriptions, as well as those from a national soils database (S-map) were used when available. In addition, three different soil water models in APSIM with different complexities (SWIM2, SWIM3, and SoilWat) were evaluated. Model outputs were compared with temporal soil water content measurements within the top 75mm at the various experimental sites. Results show that the profile description, as well as the soil water model used affected the prediction accuracy of soil water content. The smallest difference between soil profile descriptions was found for the Templeton soil series, where the model efficiency (NSE) was positive for all soil profile descriptions, and the RMSE ranged from 0.055 to 0.069m3/m3. The greatest difference was found for the Te Kowhai soil, where only one of the descriptions showed a positive NSE, and the other two profile descriptions overestimated measured topsoil water contents. Furthermore, it was shown that the soil profile description highly affects N2O emissions from urinary N deposited during animal grazing. However, the relative difference between the emissions was not always related to the accuracy of the measured soil water content, with soil organic carbon content also affecting emissions.

scholarly journals Study on the Mechanical Criterion of Ice Lens Formation Based on Pore Size Distribution

2020 ◽  
Vol 10 (24) ◽  
pp. 8981
Author(s):  
Yuhang Liu ◽  
Dongqing Li ◽  
Lei Chen ◽  
Feng Ming
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Initial Water Content ◽  
Mean Stress ◽  
Initial Water ◽  
Unfrozen Water Content ◽  
The Mean ◽  
Lens Formation

Ice lens is the key factor which determines the frost heave in engineering construction in cold regions. At present, several theories have been proposed to describe the formation of ice lens. However, most of these theories analyzed the ice lens formation from a macroscopic view and ignored the influence of microscopic pore sizes and structures. Meanwhile, these theories lacked the support of measured data. To solve this problem, the microscopic crystallization stress was converted into the macro mean stress through the principle of statistics with the consideration of pore size distribution. The mean stress was treated as the driving force of the formation of ice lens and induced into the criterion of ice lens formation. The influence of pore structure and unfrozen water content on the mean stress was analyzed. The results indicate that the microcosmic crystallization pressure can be converted into the macro mean stress through the principle of statistics. Larger mean stress means the ice lens will be formed easier in the soil. The mean stress is positively correlated with initial water content. At the same temperature, an increase to both the initial water content and the number of pores can result in a larger mean stress. Under the same initial water content, mean stress increases with decreasing temperature. The result provides a theoretical basis for studying ice lens formation from the crystallization theory.

FRACTAL ANALYSIS OF SURFACE ROUGHNESS EFFECTS ON GAS DIFFUSION IN POROUS NANOFIBERS

Fractals ◽  
2020 ◽  
Vol 28 (07) ◽  
pp. 2050125
Author(s):  
QIAN ZHENG ◽  
HUILI WANG ◽  
JIAN JIANG ◽  
CHAO XU
Keyword(s):  
Surface Roughness ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Scaling Laws ◽  
Current Model ◽  
Fractal Model ◽  
Gas Diffusion ◽  
Fibrous Materials ◽  
Microstructural Parameters

Fractal model of gas diffusion in porous nanofibers with rough surfaces is derived, in which the porous structure is assumed to be composed of a bundle of tortuous capillaries whose pore size distribution and surface roughness follow the fractal scaling laws. The analytical expression for gas relative diffusion coefficient is a function of the relative roughness and the other microstructural parameters (porosity, the fractal dimension for pore size distribution and tortuosity, the maximum and minimum pore diameter and the characteristic length). The proposed fractal model is validated by comparison with available experimental data and correlations. At the same time, the effect of microstructural parameters of porous fibrous materials on gas diffusion has been studied in detail. It is believed that the current model may be extended to porous materials other than fibrous materials.

Compaction behaviour of lime-treated metakaolin

2020 ◽  
Author(s):  
Mozhen Hu ◽  
Yu-Jun Cui ◽  
Yunzhi Tan
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Uniform Structure ◽  
Dry Density ◽  
Soil Stiffness ◽  
Effect Of Water ◽  
Compaction Curve ◽  
Lime Addition

Metakaolin has been widely used as pozzolanic additive to improve the pozzolanic activity of lime-based products. In this study, normal standard Proctor compaction test was performed on metakaolin with (5% lime) and without (0% lime) lime addition. The changes in stiffness, suction and microstructure with remoulding water content were investigated on statically compacted samples. Results show that lime-treated metakaolin exhibits one and half-peak compaction curve, while untreated metakaolin exhibits common one-peak compaction curve. The uncommon shape of the compaction curve of the treated metakaolin can be explained by the non-fully developed soil suction when water is not continuous. Treated and untreated samples compacted at both dry and wet of optimum show uni-modal pore size distribution characteristics, indicating the absence of aggregates. This is related to the specific thermal treatment, forming separate metakaolin platelets and leading to a modified uniform structure with diffuse platelets. The soil stiffness is rather dominated by the number of particle contacts or soil dry density, the effect of suction being insignificant. For the suction changes, on the dry side, the effect of pore size distribution prevails facing the effect of water content, while on wet side it is the effect of water content that becomes prevailing.

Equations for the soil-water characteristic curve

1994 ◽  
Vol 31 (4) ◽  
pp. 521-532 ◽  
Author(s):  
D.G. Fredlund ◽  
Anqing Xing
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Soil Water ◽  
Characteristic Curve ◽  
Nonlinear Least Squares ◽  
Soil Water Characteristic Curve ◽  
Nonlinear Curve Fitting ◽  
Soil Behaviour ◽  
Nonlinear Curve

The soil-water characteristic curve can be used to estimate various parameters used to describe unsaturated soil behaviour. A general equation for the soil-water characteristic curve is proposed. A nonlinear, least-squares computer program is used to determine the best-fit parameters for experimental data presented in the literature. The equation is based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution of the soil (i.e., the desaturation is a function of the pore-size distribution). The equation has the form of an integrated frequency distribution curve. The equation provides a good fit for sand, silt, and clay soils over the entire suction range from 0 to 106 kPa. Key words : soil-water characteristic curve, pore-size distribution, nonlinear curve fitting, soil suction, water content.

scholarly journals Prediction of soil water retention properties using pore-size distribution and porosity

2013 ◽  
Vol 50 (4) ◽  
pp. 435-450 ◽  
Author(s):  
Christopher T.S. Beckett ◽  
Charles E. Augarde
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Soil Water ◽  
Water Retention ◽  
Adsorbed Water ◽  
Retention Data ◽  
Soil Water Retention ◽  
Pore Size Distributions ◽  
Water Retention Properties

Several models have been suggested to link a soil's pore-size distribution to its retention properties. This paper presents a method that builds on previous techniques by incorporating porosity and particles of different sizes, shapes, and separation distances to predict soil water retention properties. Mechanisms are suggested for the determination of both the main drying and wetting paths, which incorporate an adsorbed water phase and retention hysteresis. Predicted results are then compared with measured retention data to validate the model and to provide a foundation for discussing the validity and limitations of using pore-size distributions to predict retention properties.

scholarly journals Nitrous oxide emissions from soil of an African rain forest in Ghana

2012 ◽  
Vol 9 (11) ◽  
pp. 16565-16588 ◽  
Author(s):  
S. Castaldi ◽  
T. Bertolini ◽  
A. Valente ◽  
T. Chiti ◽  
R. Valentini
Keyword(s):  
Soil Respiration ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Rain Forest ◽  
Nitrous Oxide Emissions ◽  
Clear Correlation ◽  
N2o Emissions ◽  
African Continent ◽  
N2o Fluxes

Abstract. Most recently atmospheric studies have evidenced the imprint of large N2O sources in tropical/subtropical lands. This source might be attributed to agricultural areas as well as to natural humid ecosystems. The uncertainty related to both sources is very high, due to the paucity of data and small frequency of sampling in tropical studies. This is particularly relevant for the African continent. The principal objective of this work was to quantify the annual budget of N2O emissions in an African tropical rain forest. Soil N2O emissions were measured over 19 months in Ghana, National Park of Ankasa, in upland and lowland areas, for a total of 119 days of observation. The calculated annual average emission was 2.33 ± 0.20 kg N-N2O ha−1yr−1, taking into account the proportion of upland vs. lowland, as the two areas showed significantly different fluxes, the lowland being characterized by lower N2O emissions. N2O fluxes peaked between June and August and were significantly correlated with soil respiration on a daily and monthly basis. No clear correlation was found in the upland areas between N2O fluxes and soil water content or rain whereas in the lowland soil water content concurred with soil respiration in determining N2O flux variability. The N2O source strength calculated in this study, very close to those reported for the other two available studies in African rain forests and to the estimated mean derived from worldwide studies in humid tropical forests (2.96 ± 2.0 kg N-N2O ha−1 yr−1), supports the concept that tropical humid forests represent the strongest natural source of N2O emissions, most probably the strongest source of N2O in the African continent.

scholarly journals The impacts of freeze–thaw cycles on saturated hydraulic conductivity and microstructure of saline–alkali soils

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Wenshuo Xu ◽  
Kesheng Li ◽  
Longxiao Chen ◽  
Weihang Kong ◽  
Chuanxiao Liu
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Saturated Hydraulic Conductivity ◽  
High Water Content ◽  
Soil Permeability ◽  
Freeze Thaw ◽  
Alkali Soil

AbstractStudy on the microscopic structure of saline–alkali soil can reveal the change of its permeability more deeply. In this paper, the relationship between permeability and microstructure of saline–alkali soil with different dry densities and water content in the floodplain of southwestern Shandong Province was studied through freeze–thaw cycles. A comprehensive analysis of soil samples was conducted using particle-size distribution, X-ray diffraction, freeze–thaw cycles test, saturated hydraulic conductivity test and mercury intrusion porosimetry. The poor microstructure of soil is the main factor that leads to the category of micro-permeable soil. The porosity of the local soil was only 6.19–11.51%, and ultra-micropores (< 0.05 μm) and micropores (0.05–2 μm) dominated the pore size distribution. Soil saturated water conductivity was closely related to its microscopic pore size distribution. As the F–T cycles progressed, soil permeability became stronger, with the reason the pore size distribution curve began to shift to the small pores (2–10 μm) and mesopores (10–20 μm), and this effect was the most severe when the freeze–thaw cycle was 15 times. High water content could promote the effects of freeze–thaw cycles on soil permeability and pore size distribution, while the increase of dry density could inhibit these effects. The results of this study provide a theoretical basis for the remediation of saline–alkali soil in the flooded area of Southwest Shandong.

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