Yi Yang, Bin Peng, Kaiyu Guan, Ming Pan, Trenton. E. Franz, Michael H. Cosh, Carl J. Bernacchi
Understanding soil moisture variability and estimating high‐resolution soil moisture at subfield to field scales is critical for agricultural research and applications. However, systematic investigation of subfield scale soil moisture variability over cropland is still lacking from both measurement and satellite remote sensing. In this study, we aim to investigate (1) the characteristics of within‐field soil moisture distribution over typical cropland in the US Midwest and (2) the capabilities of satellite remote sensing in capturing the spatiotemporal variabilities of soil moisture at subfield scale. Specifically, we conducted soil moisture field experiments in three typical commercial agricultural fields (∼85 acres per field) in central Illinois, representing typical commercial farmlands in the US Midwest, and compared the soil moisture measurements with satellite remote sensing data from optical and active microwave sensors. In each field, dense soil moisture samples (spaced at 50–60 m) were obtained for two dry down events in May and July 2021, and multiple long‐term soil moisture stations were installed. We found prominent time‐invariant spatial structures of soil moisture at within‐field scales both during the dry down period and over longer time scales, and the stability is minimally affected by plant water use during the growing season. Comparing the field campaign measurements with satellite remote sensing data, we found that surface reflectance of shortwave infrared bands, such as SWIR1 (1610 nm) from Sentinel‐2, can capture relative surface soil moisture patterns at within‐field scales, but their relationships with soil moisture are field specific. These findings and the improved understanding of within‐field soil moisture dynamics could potentially help future research on high‐resolution soil moisture estimation with multi‐source remote sensing data.
{"title":"Within‐field soil moisture variability and time‐invariant spatial structures of agricultural fields in the US Midwest","authors":"Yi Yang, Bin Peng, Kaiyu Guan, Ming Pan, Trenton. E. Franz, Michael H. Cosh, Carl J. Bernacchi","doi":"10.1002/vzj2.20337","DOIUrl":"https://doi.org/10.1002/vzj2.20337","url":null,"abstract":"Understanding soil moisture variability and estimating high‐resolution soil moisture at subfield to field scales is critical for agricultural research and applications. However, systematic investigation of subfield scale soil moisture variability over cropland is still lacking from both measurement and satellite remote sensing. In this study, we aim to investigate (1) the characteristics of within‐field soil moisture distribution over typical cropland in the US Midwest and (2) the capabilities of satellite remote sensing in capturing the spatiotemporal variabilities of soil moisture at subfield scale. Specifically, we conducted soil moisture field experiments in three typical commercial agricultural fields (∼85 acres per field) in central Illinois, representing typical commercial farmlands in the US Midwest, and compared the soil moisture measurements with satellite remote sensing data from optical and active microwave sensors. In each field, dense soil moisture samples (spaced at 50–60 m) were obtained for two dry down events in May and July 2021, and multiple long‐term soil moisture stations were installed. We found prominent time‐invariant spatial structures of soil moisture at within‐field scales both during the dry down period and over longer time scales, and the stability is minimally affected by plant water use during the growing season. Comparing the field campaign measurements with satellite remote sensing data, we found that surface reflectance of shortwave infrared bands, such as SWIR1 (1610 nm) from Sentinel‐2, can capture relative surface soil moisture patterns at within‐field scales, but their relationships with soil moisture are field specific. These findings and the improved understanding of within‐field soil moisture dynamics could potentially help future research on high‐resolution soil moisture estimation with multi‐source remote sensing data.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140810143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Recipients of 2023 SSSA Editor's Citation for Excellence named","authors":"","doi":"10.1002/vzj2.20342","DOIUrl":"https://doi.org/10.1002/vzj2.20342","url":null,"abstract":"","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140654106","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Timothy B. Wilson, John Kochendorfer, Howard J. Diamond, Tilden P. Meyers, Mark Hall, Temple R. Lee, Rick D. Saylor, Praveena Krishnan, Ronald D. Leeper, Michael A. Palecki
Soil bulk electrical conductivity (BEC) was evaluated alongside soil volumetric water content (VWC) and soil temperature measurements using the HydraProbe (model HydraProbe, Stevens Water Monitoring Systems, Inc.) (hereafter called HP) with accuracy range of BEC ≤ 0.3 S m−1, and the time domain reflectometry (TDR)‐315L Probe (model TDR‐315L, Acclima, Inc.) (hereafter called AP) suitable for BEC up to 0.6 S m−1, at 23 stations of the U.S. Climate Reference Network. Previous evaluations revealed inconsistent performance of both sensors in some clay soils using manufacturer‐recommended calibrations in converting dielectric permittivity measurements to VWC. Here, we found that hourly values of BEC reached 0.6 S m−1 in high clay content soils and exceeded 2 S m−1 in high saline soils, and these high values of BEC were associated with poor performance and failures of both HP and AP sensors. Large values of BEC occurred in predominantly saturated soils where VWC values reached about 0.5 m3 m−3 for saline soils and about 0.7 m3 m−3 for clay soils, while low magnitudes of BEC were associated with low soil water content and seldomly saturated soils. Low hourly BEC values of less than 0.1 S m−1 were observed in wide variety of soil types, where sensor performance was typically excellent. The most influential factor on BEC was high soil water content conditions. Although dielectric permittivity measurements in estimating the soil water content were sensitive to BEC as some high clay content and high salinity soils increased BEC, the impact of large BEC on dielectric permittivity measurements was smaller in the well‐drained top soil layers than in deep soil layers that remained near saturation. Soil temperature had only a small impact on BEC. With high clay content and high salinity, the specific area of clay minerals was also associated with the magnitude of BEC.
使用 HydraProbe（型号 HydraProbe，Stevens Water Monitoring Systems, Inc.以下简称 HP）和时域反射仪 (TDR)-315L 探头（型号 TDR-315L，Acclima，Inc.）（以下简称 AP）进行了评估，前者的精度范围为 BEC ≤ 0.3 S m-1，后者的精度范围为 BEC ≤ 0.6 S m-1。之前的评估显示，在将介电常数测量值转换为 VWC 时，使用制造商推荐的校准方法，这两种传感器在某些粘土中的性能并不一致。在这里，我们发现在粘土含量较高的土壤中，每小时的 BEC 值达到 0.6 S m-1，而在高盐度土壤中则超过 2 S m-1，这些高 BEC 值与 HP 和 AP 传感器的性能不佳和故障有关。较大的 BEC 值出现在主要饱和的土壤中，盐碱土的 VWC 值达到约 0.5 立方米/立方米，粘土的 VWC 值达到约 0.7 立方米/立方米，而较低的 BEC 值则与土壤含水量低和很少饱和有关。在各种类型的土壤中都能观察到每小时小于 0.1 S m-1 的较低 BEC 值，在这些土壤中，传感器的性能通常非常出色。对 BEC 影响最大的因素是土壤含水量高。虽然在估算土壤含水量时介电常数测量对 BEC 很敏感，因为一些高粘土含量和高盐度土壤会增加 BEC，但在排水良好的表层土壤中，大 BEC 对介电常数测量的影响要小于接近饱和的深层土壤。土壤温度对介电常数的影响很小。在粘土含量高和盐度高的情况下，粘土矿物的比面积也与 BEC 的大小有关。
{"title":"Evaluation of soil water content and bulk electrical conductivity across the U.S. Climate Reference Network using two electromagnetic sensors","authors":"Timothy B. Wilson, John Kochendorfer, Howard J. Diamond, Tilden P. Meyers, Mark Hall, Temple R. Lee, Rick D. Saylor, Praveena Krishnan, Ronald D. Leeper, Michael A. Palecki","doi":"10.1002/vzj2.20336","DOIUrl":"https://doi.org/10.1002/vzj2.20336","url":null,"abstract":"Soil bulk electrical conductivity (BEC) was evaluated alongside soil volumetric water content (VWC) and soil temperature measurements using the HydraProbe (model HydraProbe, Stevens Water Monitoring Systems, Inc.) (hereafter called HP) with accuracy range of BEC ≤ 0.3 S m<jats:sup>−1</jats:sup>, and the time domain reflectometry (TDR)‐315L Probe (model TDR‐315L, Acclima, Inc.) (hereafter called AP) suitable for BEC up to 0.6 S m<jats:sup>−1</jats:sup>, at 23 stations of the U.S. Climate Reference Network. Previous evaluations revealed inconsistent performance of both sensors in some clay soils using manufacturer‐recommended calibrations in converting dielectric permittivity measurements to VWC. Here, we found that hourly values of BEC reached 0.6 S m<jats:sup>−1</jats:sup> in high clay content soils and exceeded 2 S m<jats:sup>−1</jats:sup> in high saline soils, and these high values of BEC were associated with poor performance and failures of both HP and AP sensors. Large values of BEC occurred in predominantly saturated soils where VWC values reached about 0.5 m<jats:sup>3</jats:sup> m<jats:sup>−3</jats:sup> for saline soils and about 0.7 m<jats:sup>3</jats:sup> m<jats:sup>−3</jats:sup> for clay soils, while low magnitudes of BEC were associated with low soil water content and seldomly saturated soils. Low hourly BEC values of less than 0.1 S m<jats:sup>−1</jats:sup> were observed in wide variety of soil types, where sensor performance was typically excellent. The most influential factor on BEC was high soil water content conditions. Although dielectric permittivity measurements in estimating the soil water content were sensitive to BEC as some high clay content and high salinity soils increased BEC, the impact of large BEC on dielectric permittivity measurements was smaller in the well‐drained top soil layers than in deep soil layers that remained near saturation. Soil temperature had only a small impact on BEC. With high clay content and high salinity, the specific area of clay minerals was also associated with the magnitude of BEC.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140634492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kritika Malhotra, Jasmeet Lamba, Thomas R. Way, Colleen Williams, K. G. Karthikeyan, Suman Budhathoki, Rishi Prasad, Puneet Srivastava, Jingyi Zheng
Repeated broiler litter application on agricultural lands can cause nutrient enrichment of subsurface effluent, especially with the existence of preferential flow through soil macropores. Previous studies quantifying soil macropores have not attempted to establish a connection of soil macropore characteristics with the subsurface nutrient (nitrogen [N] and phosphorus [P]) losses, across different topographical locations in the field. This study investigated the effect of broiler litter application and preferential flow on subsurface nutrient transport (N and P) at different topographical positions (upslope, midslope, and downslope) in a no‐till pasture field located in Alabama, USA. Twelve intact soil columns (150 mm id and 500 mm length) were used, and the nutrient leaching measurements from laboratory experiments were linked to soil macropore characteristics quantified using X‐ray computed tomography image analysis and solute transport modeling. Treatments included surface broadcast broiler litter (5 Mg ha−1, on dry basis) and unamended control. Leachates were analyzed for dissolved reactive P (DRP), total P (TP), and nitrate + nitrite‐N (NO3− + NO2−–N). The bromide breakthrough curves provided evidence of preferential flow in all columns. Litter application significantly increased leachate P concentrations, and average TP and DRP concentrations were significantly higher in the leachate from upslope columns compared to those at downslope location. The NO3−–N concentrations in leachate exceeded the US EPA drinking water standard of 10 mg L−1 in all the treatment columns. The highest flow‐weighted mean concentrations of TP and DRP, at 2.7 and 2.5 mg L−1, respectively, were recorded in the upslope columns. Soil physicochemical properties and nutrient leaching losses varied substantially across topographical positions, indicating a need for variable litter application rates to reduce P build‐up and subsequent leaching in vulnerable locations within the field. The relevance of the effect of topographic position on nutrient leaching found in this study should be further tested by investigating a wider range of slopes and soil types in pastures.
{"title":"Preferential flow of phosphorus and nitrogen under steady‐state saturated conditions","authors":"Kritika Malhotra, Jasmeet Lamba, Thomas R. Way, Colleen Williams, K. G. Karthikeyan, Suman Budhathoki, Rishi Prasad, Puneet Srivastava, Jingyi Zheng","doi":"10.1002/vzj2.20331","DOIUrl":"https://doi.org/10.1002/vzj2.20331","url":null,"abstract":"Repeated broiler litter application on agricultural lands can cause nutrient enrichment of subsurface effluent, especially with the existence of preferential flow through soil macropores. Previous studies quantifying soil macropores have not attempted to establish a connection of soil macropore characteristics with the subsurface nutrient (nitrogen [N] and phosphorus [P]) losses, across different topographical locations in the field. This study investigated the effect of broiler litter application and preferential flow on subsurface nutrient transport (N and P) at different topographical positions (upslope, midslope, and downslope) in a no‐till pasture field located in Alabama, USA. Twelve intact soil columns (150 mm id and 500 mm length) were used, and the nutrient leaching measurements from laboratory experiments were linked to soil macropore characteristics quantified using X‐ray computed tomography image analysis and solute transport modeling. Treatments included surface broadcast broiler litter (5 Mg ha<jats:sup>−1</jats:sup>, on dry basis) and unamended control. Leachates were analyzed for dissolved reactive P (DRP), total P (TP), and nitrate + nitrite‐N (NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> + NO<jats:sub>2</jats:sub><jats:sup>−</jats:sup>–N). The bromide breakthrough curves provided evidence of preferential flow in all columns. Litter application significantly increased leachate P concentrations, and average TP and DRP concentrations were significantly higher in the leachate from upslope columns compared to those at downslope location. The NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>–N concentrations in leachate exceeded the US EPA drinking water standard of 10 mg L<jats:sup>−1</jats:sup> in all the treatment columns. The highest flow‐weighted mean concentrations of TP and DRP, at 2.7 and 2.5 mg L<jats:sup>−1</jats:sup>, respectively, were recorded in the upslope columns. Soil physicochemical properties and nutrient leaching losses varied substantially across topographical positions, indicating a need for variable litter application rates to reduce P build‐up and subsequent leaching in vulnerable locations within the field. The relevance of the effect of topographic position on nutrient leaching found in this study should be further tested by investigating a wider range of slopes and soil types in pastures.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140634493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marcia S. Batalha, Camila R. Bezerra‐Coelho, Elizabeth M. Pontedeiro, Martinus Th van Genuchten, Jian Su
This comment concerns evaluation of the Mualem–van Genuchten (MvG) unsaturated soil hydraulic functions at very low (negative) pressure heads as described recently in an important study by Heinen. He showed that below some critical pressure head, the unsaturated hydraulic conductivity should be approximated by a power function, even when evaluated using double precision computations. We show that a more precise approximation is possible when the approximation is formulated in terms of effective fluid saturation (Se) rather than the pressure head, h. More general constraints are also provided when the approximated hydraulic conductivity equation should be used. The alternative formulation and constraints were implemented earlier in the SOHYP and RETC software packages.
{"title":"Comment on “Modified expression for unsaturated hydraulic conductivity according to Mualem–van Genuchten to allow proper computations at low pressure heads” by M. Heinen","authors":"Marcia S. Batalha, Camila R. Bezerra‐Coelho, Elizabeth M. Pontedeiro, Martinus Th van Genuchten, Jian Su","doi":"10.1002/vzj2.20332","DOIUrl":"https://doi.org/10.1002/vzj2.20332","url":null,"abstract":"This comment concerns evaluation of the Mualem–van Genuchten (MvG) unsaturated soil hydraulic functions at very low (negative) pressure heads as described recently in an important study by Heinen. He showed that below some critical pressure head, the unsaturated hydraulic conductivity should be approximated by a power function, even when evaluated using double precision computations. We show that a more precise approximation is possible when the approximation is formulated in terms of effective fluid saturation (<jats:italic>S<jats:sub>e</jats:sub></jats:italic>) rather than the pressure head, <jats:italic>h</jats:italic>. More general constraints are also provided when the approximated hydraulic conductivity equation should be used. The alternative formulation and constraints were implemented earlier in the SOHYP and RETC software packages.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
David Mulla, Jake Galzki, Aaron Hanson, Jirka Simunek
Ground-mounted photovoltaic sites are often treated as impervious surfaces in stormwater permits. This ignores the pervious soils beneath and between solar arrays and leads to an overestimation of runoff. Our objective was to improve solar farm stormwater hydrology models by explicitly considering the disconnected impervious nature of solar design and site characteristics. Experimental sites established on utility scale solar farms in Colorado, Georgia, Minnesota, New York, and Oregon had perennial vegetative plantings with mean precipitation ranging from 40.6 to 124.5 cm, and soil texture ranging from loamy sand to clay. Soil moisture measurements were collected beneath arrays, under drip edges, and in the vegetated area between arrays at each site. Hydrus-3D models for soil moisture and stormwater hydrology were developed that accounted for precipitation falling on solar panels, drip edge redistribution of rainfall, infiltration, and runoff in the pervious areas between solar arrays and beneath panels. Drip edge runoff averaged 3- to 10-times incident precipitation at the New York and Minnesota sites, respectively. Root mean square error values between measured sub-hourly soil moisture and predicted moisture for large measured single storm events averaged 0.029 across all five sites. Predicted runoff depths were strongly affected by precipitation depth, soil texture, soil profile depth, and soil bulk density. Runoff depths across the five experimental sites averaged 13%, 25%, and 45% of the 2-, 10-, and 100-year design storm depths, clearly showing that these solar farms do not behave like impervious surfaces, but rather as disconnected impervious surfaces with substantial infiltration of runoff in the vegetated areas between and beneath solar arrays.
{"title":"Measuring and modeling soil moisture and runoff at solar farms using a disconnected impervious surface approach","authors":"David Mulla, Jake Galzki, Aaron Hanson, Jirka Simunek","doi":"10.1002/vzj2.20335","DOIUrl":"https://doi.org/10.1002/vzj2.20335","url":null,"abstract":"Ground-mounted photovoltaic sites are often treated as impervious surfaces in stormwater permits. This ignores the pervious soils beneath and between solar arrays and leads to an overestimation of runoff. Our objective was to improve solar farm stormwater hydrology models by explicitly considering the disconnected impervious nature of solar design and site characteristics. Experimental sites established on utility scale solar farms in Colorado, Georgia, Minnesota, New York, and Oregon had perennial vegetative plantings with mean precipitation ranging from 40.6 to 124.5 cm, and soil texture ranging from loamy sand to clay. Soil moisture measurements were collected beneath arrays, under drip edges, and in the vegetated area between arrays at each site. Hydrus-3D models for soil moisture and stormwater hydrology were developed that accounted for precipitation falling on solar panels, drip edge redistribution of rainfall, infiltration, and runoff in the pervious areas between solar arrays and beneath panels. Drip edge runoff averaged 3- to 10-times incident precipitation at the New York and Minnesota sites, respectively. Root mean square error values between measured sub-hourly soil moisture and predicted moisture for large measured single storm events averaged 0.029 across all five sites. Predicted runoff depths were strongly affected by precipitation depth, soil texture, soil profile depth, and soil bulk density. Runoff depths across the five experimental sites averaged 13%, 25%, and 45% of the 2-, 10-, and 100-year design storm depths, clearly showing that these solar farms do not behave like impervious surfaces, but rather as disconnected impervious surfaces with substantial infiltration of runoff in the vegetated areas between and beneath solar arrays.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140578529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mariel F. Davies, Ottfried Dietrich, Horst H. Gerke, Christoph Merz
Degraded peatlands release large amounts of greenhouse gases. The development of effective mitigation and management measures requires an understanding of relevant site‐specific biogeochemical and hydraulic processes. However, the simulation of water fluxes and vadose zone state variables of degrading peatlands relies on proper process description, parameterization of hydraulic functions, and representation of the boundary conditions. The objective of this study was to analyze the effects of unimodal versus bimodal soil hydraulic functions and pressure head versus flux‐type lower boundary conditions (LBCs) on the calculated hydraulic characteristics of a degraded peat profile. HYDRUS‐1D was used to study the hydraulic flow dynamics parameterized with data from a weighable groundwater lysimeter for the period from May 1 to December 31, 2019. Simulations comparing uni‐ and bimodal hydraulic functions showed only minor differences. Simulations of soil water pressure at a depth of 30 cm using a flux‐type LBC (RMSE: 27 cm, where RMSE is root mean square error) performed better than simulations using a pressure head LBC (RMSE: 48 cm). The pressure head LBC performed better at simulating volumetric water contents in 30‐cm depth than the flux LBC variant (RMSE: 0.05 vs. 0.09 cm3 cm−3). For specific site conditions with a shallow, fluctuating groundwater table and temporary air entrapment, the choice of LBC was important for a more accurate simulation of soil water fluxes and volumetric water content.
{"title":"Modeling water flow and volumetric water content in a degraded peat comparing unimodal with bimodal porosity and flux with pressure head boundary condition","authors":"Mariel F. Davies, Ottfried Dietrich, Horst H. Gerke, Christoph Merz","doi":"10.1002/vzj2.20328","DOIUrl":"https://doi.org/10.1002/vzj2.20328","url":null,"abstract":"Degraded peatlands release large amounts of greenhouse gases. The development of effective mitigation and management measures requires an understanding of relevant site‐specific biogeochemical and hydraulic processes. However, the simulation of water fluxes and vadose zone state variables of degrading peatlands relies on proper process description, parameterization of hydraulic functions, and representation of the boundary conditions. The objective of this study was to analyze the effects of unimodal versus bimodal soil hydraulic functions and pressure head versus flux‐type lower boundary conditions (LBCs) on the calculated hydraulic characteristics of a degraded peat profile. HYDRUS‐1D was used to study the hydraulic flow dynamics parameterized with data from a weighable groundwater lysimeter for the period from May 1 to December 31, 2019. Simulations comparing uni‐ and bimodal hydraulic functions showed only minor differences. Simulations of soil water pressure at a depth of 30 cm using a flux‐type LBC (RMSE: 27 cm, where RMSE is root mean square error) performed better than simulations using a pressure head LBC (RMSE: 48 cm). The pressure head LBC performed better at simulating volumetric water contents in 30‐cm depth than the flux LBC variant (RMSE: 0.05 vs. 0.09 cm<jats:sup>3</jats:sup> cm<jats:sup>−3</jats:sup>). For specific site conditions with a shallow, fluctuating groundwater table and temporary air entrapment, the choice of LBC was important for a more accurate simulation of soil water fluxes and volumetric water content.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140578527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Luwen Zhuang, Hao Chen, Ping Yan, Xingmei Liang, Wenceslau G. Teixera, Martinus Th. van Genuchten, Kairong Lin
Many anthropogenic soils, often referred to as red bed or purple soils, are distributed in various areas of southern China. Purple soils typically are highly weathered and often lead to natural and engineering hazards because of their relatively poor water retention properties. Knowledge of the unsaturated soil hydraulic properties of purple soils is crucial for their optimal management and various assessment studies. In this work, the hydraulic properties of purple soils from southern China were measured in the laboratory over the full moisture range using a combination of evaporation (HYPROP) and psychrometer (WP4C) approaches. Measured data were analyzed in terms of four different unimodal and bimodal soil hydraulic models. The measurements and analyses showed that bimodality was not overly significant for most samples. The good fit of the Peters–Durner–Iden models furthermore suggested that corner and film flows were important under relative dry conditions. Existing soil pedotransfer functions were found to provide a fairly close match for the slope of water retention curves with the exception of near saturated water contents and the saturated conductivity. To the best of our knowledge, this is the first time that unsaturated hydraulic data of purple soils are provided over the full moisture range.
{"title":"Unsaturated hydraulic property measurements of subtropical anthropogenic (purple) soils in China","authors":"Luwen Zhuang, Hao Chen, Ping Yan, Xingmei Liang, Wenceslau G. Teixera, Martinus Th. van Genuchten, Kairong Lin","doi":"10.1002/vzj2.20334","DOIUrl":"https://doi.org/10.1002/vzj2.20334","url":null,"abstract":"Many anthropogenic soils, often referred to as red bed or purple soils, are distributed in various areas of southern China. Purple soils typically are highly weathered and often lead to natural and engineering hazards because of their relatively poor water retention properties. Knowledge of the unsaturated soil hydraulic properties of purple soils is crucial for their optimal management and various assessment studies. In this work, the hydraulic properties of purple soils from southern China were measured in the laboratory over the full moisture range using a combination of evaporation (HYPROP) and psychrometer (WP4C) approaches. Measured data were analyzed in terms of four different unimodal and bimodal soil hydraulic models. The measurements and analyses showed that bimodality was not overly significant for most samples. The good fit of the Peters–Durner–Iden models furthermore suggested that corner and film flows were important under relative dry conditions. Existing soil pedotransfer functions were found to provide a fairly close match for the slope of water retention curves with the exception of near saturated water contents and the saturated conductivity. To the best of our knowledge, this is the first time that unsaturated hydraulic data of purple soils are provided over the full moisture range.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140578313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jan Vanderborght, Valentin Couvreur, Mathieu Javaux, Daniel Leitner, Andrea Schnepf, Harry Vereecken
Water uptake by plant roots is an important component of the soil water balance. Predicting to what extent potential transpiration from the canopy, that is, transpiration demand, can be met by supply of water from the soil through the root system is crucial to simulate the actual transpiration and assess vegetation water stress. In models that simulate the dynamics of vertical soil water content profiles as a function of water fluxes and soil water potential gradients, the root water uptake (RWU) distribution is represented by macroscopic sink terms. We present RWU functions that calculate sink terms based on a mechanistic model of water flow in the soil–root system. Based on soil–root hydraulics, we define α‐supply functions representing the maximal uptake by the root system from a certain soil depth when the root collar water potential equals the wilting point, ω‐supply factors representing the maximal supply from the entire root system, and a critical ωc factor representing the potential transpiration demand. These functions and factors are subsequently used to calculate RWU distributions directly from potential transpiration or demand and the soil water potentials. Unlike currently used approaches, which define α‐stress functions and ω factors representing ratios of actual uptake to uptake demand, the supply‐based formulations can be derived directly from soil and root hydraulic properties and can represent processes like root hydraulic redistribution and hydraulic lift.
{"title":"Mechanistically derived macroscopic root water uptake functions: The α and ω of root water uptake functions","authors":"Jan Vanderborght, Valentin Couvreur, Mathieu Javaux, Daniel Leitner, Andrea Schnepf, Harry Vereecken","doi":"10.1002/vzj2.20333","DOIUrl":"https://doi.org/10.1002/vzj2.20333","url":null,"abstract":"Water uptake by plant roots is an important component of the soil water balance. Predicting to what extent potential transpiration from the canopy, that is, transpiration demand, can be met by supply of water from the soil through the root system is crucial to simulate the actual transpiration and assess vegetation water stress. In models that simulate the dynamics of vertical soil water content profiles as a function of water fluxes and soil water potential gradients, the root water uptake (RWU) distribution is represented by macroscopic sink terms. We present RWU functions that calculate sink terms based on a mechanistic model of water flow in the soil–root system. Based on soil–root hydraulics, we define <jats:italic>α</jats:italic>‐supply functions representing the maximal uptake by the root system from a certain soil depth when the root collar water potential equals the wilting point, <jats:italic>ω</jats:italic>‐supply factors representing the maximal supply from the entire root system, and a critical <jats:italic>ω<jats:sub>c</jats:sub></jats:italic> factor representing the potential transpiration demand. These functions and factors are subsequently used to calculate RWU distributions directly from potential transpiration or demand and the soil water potentials. Unlike currently used approaches, which define <jats:italic>α</jats:italic>‐stress functions and <jats:italic>ω</jats:italic> factors representing ratios of actual uptake to uptake demand, the supply‐based formulations can be derived directly from soil and root hydraulic properties and can represent processes like root hydraulic redistribution and hydraulic lift.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140578455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Julie N. Weitzman, J. Renée Brooks, Jana E. Compton, Barton R. Faulkner, R. Edward Peachey, William D. Rugh, Robert A. Coulombe, Blake Hatteberg, Stephen R. Hutchins
A substantial fraction of nitrogen (N) fertilizer applied in agricultural systems is not incorporated into crops and moves below the rooting zone as nitrate (NO3−). Understanding mechanisms for soil N retention below the rooting zone and leaching to groundwater is essential for our ability to track the fate of added N. We used dual stable isotopes of nitrate (δ15N–NO3− and δ18O–NO3−) and water (δ18O–H2O and δ2H–H2O) to understand the mechanisms driving nitrate leaching at three depths (0.8, 1.5, and 3.0 m) of an irrigated corn field sampled every 2 weeks from 2016 to 2020 in the southern Willamette Valley, Oregon, USA. Distinct periods of high nitrate concentrations with lower δ15N–NO3− values indicated that a portion of that nitrate was from recent fertilizer applications. We used a mixing model to quantify nitrate fluxes associated with recently added fertilizer N versus older, legacy soil N during these “fertilizer signal periods.” Nitrate leached below 3.0 m in these periods made up a larger proportion of the total N leached at that depth (∼52%) versus the two shallower depths (∼13%–16%), indicating preferential movement of recently applied fertilizer N through the deep soil into groundwater. Further, N associated with recent fertilizer additions leached more easily when compared to remobilized legacy N. A high volume of fall and winter precipitation may push residual fertilizer N to depth, potentially posing a larger threat to groundwater than legacy N. Optimizing fertilizer N additions could minimize fertilizer losses and reduce nitrate leaching to groundwater.
{"title":"Vadose zone flushing of fertilizer tracked by isotopes of water and nitrate","authors":"Julie N. Weitzman, J. Renée Brooks, Jana E. Compton, Barton R. Faulkner, R. Edward Peachey, William D. Rugh, Robert A. Coulombe, Blake Hatteberg, Stephen R. Hutchins","doi":"10.1002/vzj2.20324","DOIUrl":"https://doi.org/10.1002/vzj2.20324","url":null,"abstract":"A substantial fraction of nitrogen (N) fertilizer applied in agricultural systems is not incorporated into crops and moves below the rooting zone as nitrate (NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>). Understanding mechanisms for soil N retention below the rooting zone and leaching to groundwater is essential for our ability to track the fate of added N. We used dual stable isotopes of nitrate (δ<jats:sup>15</jats:sup>N–NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> and δ<jats:sup>18</jats:sup>O–NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>) and water (δ<jats:sup>18</jats:sup>O–H<jats:sub>2</jats:sub>O and δ<jats:sup>2</jats:sup>H–H<jats:sub>2</jats:sub>O) to understand the mechanisms driving nitrate leaching at three depths (0.8, 1.5, and 3.0 m) of an irrigated corn field sampled every 2 weeks from 2016 to 2020 in the southern Willamette Valley, Oregon, USA. Distinct periods of high nitrate concentrations with lower δ<jats:sup>15</jats:sup>N–NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> values indicated that a portion of that nitrate was from recent fertilizer applications. We used a mixing model to quantify nitrate fluxes associated with recently added fertilizer N versus older, legacy soil N during these “fertilizer signal periods.” Nitrate leached below 3.0 m in these periods made up a larger proportion of the total N leached at that depth (∼52%) versus the two shallower depths (∼13%–16%), indicating preferential movement of recently applied fertilizer N through the deep soil into groundwater. Further, N associated with recent fertilizer additions leached more easily when compared to remobilized legacy N. A high volume of fall and winter precipitation may push residual fertilizer N to depth, potentially posing a larger threat to groundwater than legacy N. Optimizing fertilizer N additions could minimize fertilizer losses and reduce nitrate leaching to groundwater.","PeriodicalId":23594,"journal":{"name":"Vadose Zone Journal","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140578356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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