Soil Water Retention Curve
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Author(s):  
André De Moura Andrade ◽  
Rui Da Silva Andrade ◽  
Erich Collicchio

Brazilian soybean has undergone considerable economic growth. Its production depends on the demand for some inputs. One of these inputs is the soil water supply, which can be made artificially or obtained by natural rainfall. Knowledge of available water capacity (AWC), which depends on total water availability (TWA), is poorly accessible and difficult to measure in the field. This study aimed to map the AWC of the state of Tocantins, based on pedotransfer functions (PTFs), to evaluate the water availability of the soils of the microregions of that state. We used the Arya and Paris model, aided by a computer program, Qualisolo, made by Embrapa Instrumentação. One hundred fifty-seven tropical soil samples were extracted from the Embrapa Solos portal. Preliminarily, the soil water retention curve (SWRC) was obtained and, subsequently, the TWA and AWC for this oilseed were estimated. Multiple linear regressions show the correlation between TWA and clay (CL), Silt (ST) and total sand (TS) contents. The correlation established was TWA = 3.2993 – 0.0028TS – 0.0034CL. This main conclusion reflects a fruitful AWC for decision-making by the soybean agribusiness and exposes the regional weaknesses for this crop under a rainfed regime in some regions of Tocantins. We could observe that, in terms of water availability, agribusiness is a potential threat to the environment protection area (APA) of the Ilha do Bananal/Cantão, Formoso River microregion.


Author(s):  
Jiangu Qian ◽  
Zhiqiang Lin ◽  
Zhenhao Shi

This paper presents a soil-water retention curve (SWRC) model for fine-grained soils. Compared with existing studies, the proposed model accounts for the distinct roles of the volume change of soils on capillarity and adsorption mechanisms. The capillary water is described by a relation that includes the characteristics of the pore-size distributions as parameters, while the absorbed water is modeled by a novel proposition that both considers the phenomenon of capillary condensation and allows for the decoupling between the degree of capillary and adsorptive saturation. Based on this feature, the void ratio effects are considered in a way in which they only affect capillary water, i.e., consistent with how volume change influences soil microstructures. The relative contributions of void ratio effects and hydraulic hysteresis on the path- and history-dependence of SWRC in Sr-s-e space for deformable unsaturated soils are examined. The significance of discriminating the effects of volume change on capillary and adsorptive water is illustrated by applying the SWRC model to computing the shear strength of unsaturated soils with different void ratios. The model performance is assessed by comparing against test data reported for four types of fine-grained soils and that tested for natural loess in this work.


2021 ◽  
Vol 69 (2) ◽  
pp. 220-231
Author(s):  
Antonín Nikodem ◽  
Radka Kodešová ◽  
Miroslav Fér ◽  
Aleš Klement

Abstract Soil hydraulic conductivities of topsoils were studied at 5 points of the hillslope transects delineated at 4 geomorphologically diverse areas, where the original soil types (Chernozem, Luvisol and two Cambisols) were due to erosion transformed into different soil unites. Hydraulic conductivities of saturated soils and for a pressure head of –2 cm were measured directly in the field using a Guelph permeameter (K s,GP ) and mini disk tension infiltrometer (K h=– 2 ,MDI ), and in the laboratory using a multistep outflow method (K s,MSO , K h= – 2 ,MSO ). While K s,GP ≈ K s,MSO in the Chernozem and Cambisol (sandy loam) regions, and K s,GP < K s,MSO in the Luvisol and Cambisol (loam) regions. The K s values obtained using different methods showed different trends along the hillslope transects. The K h= – 2 values obtained using different methods showed similar trends along the transects in the Chernozem and Luvisol regions. These trends could be explained by the position within the transects (i.e., different stages of erosion/accumulation processes). No relationships were found between the K h=– 2 values in the Cambisol regions. The pressure head at an inflection point of the a soil-water retention curve was the main parameter, which appeared to associate (negative correlation) with K h=– 2 and K s,MSO in the Chernozem and Luvisol regions.


2021 ◽  
Vol 69 (2) ◽  
pp. 121-139
Author(s):  
Mirko Castellini ◽  
Simone Di Prima ◽  
David Moret-Fernández ◽  
Laurent Lassabatere

Abstract The determination of soil hydraulic properties is important in several environmental sciences but may be expensive and time consuming. Therefore, during the last decades, a great effort has been made in soil sciences to develop relatively easy, robust, and inexpensive methods for soil hydraulic characterization. In this manuscript, we reviewed and discussed different infiltrometer techniques in light of the available experimental applications. More specifically, we considered the simplified falling head (SFH) infiltrometer technique and the single-ring infiltration experiment of the Beerkan type. Concerning this latter method, we considered different algorithms for data analysis: two simplified methods based on the analysis of transient (TSBI) and steady (SSBI) Beerkan infiltration data, and the Beerkan Estimation of Soil pedoTransfer parameters algorithm (BEST), that allows to estimate the soil characteristics curves, i.e., the soil water retention curve and hydraulic conductivity functions. For a given method, after dealing briefly theory and practice, available literature references were reported to account for specific applications in order to provide findings on method validation and application. With the aim to provide practical information on available tools for a simpler application of the reviewed methods, several video tutorials were reported to show i) how to conduct correctly field experiments and ii) how to calculate saturated hydraulic conductivity or soil hydraulic functions using user-friendly tools for data analysis. Finally, details on a new automated single-ring infiltrometer for Beerkan infiltration experiments (i.e., construction, assembly and field use) were presented.


Author(s):  
Yu Su ◽  
Yu-Jun Cui ◽  
Jean-Claude Dupla ◽  
Jean Canou

An interlayer soil identified in the French conventional rail track corresponded to a mixture of fine soil and coarse grains. To investigate the role of fines in the soil-water retention property of such mixture, different coarse grain contents fv and dry densities of fine soil ρd-f were considered. The filter paper method was applied to measure the matrix suction. Mercury intrusion porosimetry tests were performed for the microstructure observation of fine soil. In terms of gravimetric water content of fine soil wf with matrix suction Ψ, the soil-water retention curve (SWRC) was significantly affected by ρd-f for Ψ < 715 kPa, while independent of ρd-f for Ψ > 715 kPa. Interestingly, this threshold Ψ corresponded to a delimiting pore diameter of bi-modal microstructure of fine soil, which separated micro-pores from macro-pores. In terms of degree of saturation Sr with Ψ, the SWRC was significantly affected by ρd-f in the full suction range, while independent of fv. These findings help better understand the results on samples with the dry density of mixture ρd kept constant: an increase of fv resulted in a decrease of ρd-f and the suction changed accordingly. In that case, both fv and Ψ affected the mechanical behavior.


2021 ◽  
Author(s):  
Hong Zhao ◽  
Yijian Zeng ◽  
Xujun Han ◽  
Bob Su

&lt;p&gt;Basic soil physical properties (i.e., soil texture and organic matter) and associated soil hydraulic properties (i.e., soil water retention curve and hydraulic conductivity) play an essential role in land surface models (LSMs) for estimating soil moisture. With the physical link between soil properties, LSMs and Radiative Transfer Models (RTMs), the soil physical properties can be retrieved, using a LSM coupled with a microwave L-band emission observation model in a data assimilation framework. To this purpose, this paper couples an enhanced physically-based discrete scattering-emission model with the Community Land Model 4.5 (CLM), to retreive soil physical properties using the Local Ensemble Transform Kalman Filter (LETKF) algorithm, assimilating Soil Moisture Active and Passive (SMAP) Level-1C (L1C) brightness temperature at H and V polarization ( and ) separately, assisted with in situ measurements at the Maqu site on the eastern Tibetan Plateau. Results show the improved estimate of soil properties at the topmost layer via assimilating SMAP ( H, V), as well as at profile using the retrieved top-layer soil properties and a prior depth ratio. The use of &amp;#160;and &amp;#160;shows varied sensitivities to retrievals of different soil compositions (i.e., sand, clay, silt) and soil moisture estimates. However, analyses show that the retrieved soil properties with fine accuracy are not sensitive factors affecting soil moisture estimates. Instead, uncertainties of CLM model structures shall be considered, such as the fixed PTFs (pedotransfer functions), the hydraulic function describing soil water retention curve and the water stress function determining root water update.&lt;/p&gt;


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