The year 2018 has been a landmark year for Vadose Zone Journal for several reasons.First of all, from 1 Jan. 2018, VZJ flipped from a subscription journal to a golden open access (OA) journal.This now makes the research published in VZJ accessible to a global readership, and it expands our visibility and impact beyond the vadose and critical zone research community.This flip went smoothly, and it was prepared and implemented in an excellent manner by our editorial office and the Tri-Societies.It could not have succeeded without the relentless support and engagement of Pamm Kasper, VZJ managing editor, and our publication system managers Lauren Coleman and Abby Morrison.We are also grateful for the support that we received from the board of the Tri-Societies and the Soil Science Society of America in making this change.Secondly, the international visibility and attractiveness of VZJ has continued to improve.The impact factor (IF) of VZJ for 2017 reached an all-time high of 2.7 since its beginning, and it increased by 0.7 compared with 2016.We are now again a Q1 journal in water research, and we are confident that we will become Q1 again in soil and environmental research in the next years.The reasons for the increased IF are several-fold, but key to this success is the high quality of papers that we have received in the last years, the establishment of update papers, as well as the publication of reviews that were very well received.Several review and update papers showed very high download rates for several months.
The capacitance (CAP) method and time domain reflectometry (TDR) are two popular electromagnetic techniques used to estimate soil water content. However, the frequency dependence of the real and imaginary part of the permittivity complicates sensor calibration. The frequency dependence can be particularly significant in fine-textured soils containing clay minerals. In this work, we applied both the CAP method and TDR to a nondispersive medium (fine sand) and a strongly dispersive medium (bentonite). The measurements were conducted for a range of water contents. Results using a network analyzer showed that the frequency dependence of the real permittivity of the bentonite was particularly strong below 500 MHz. Above this frequency, the real permittivity of the bentonite was mainly a function of the water content. The TDR predicted apparent permittivity in the bentonite was below the CAP predicted real permittivity at low water contents. This was attributed to the dispersive nature of the bentonite combined with the high frequency of operation of TDR (up to 3 GHz in dry soil). The CAP sensor (frequency of 100–150 MHz) overestimated the real permittivity of the bentonite at high water contents. An electric circuit model proved partially successful in correcting the CAP data by taking the dielectric losses into account. The TDR signal became attenuated at higher water contents. It seems worthwhile to raise the effective frequency of dielectric sensors above 500 MHz to benefit from the relatively stable permittivity region at this frequency.
Nuclear magnetic resonance relaxation measurements were used to identify different characteristic porosity domains in soil and aquifer materials. The porosity distribution can be inferred from these measurements by a regularization method applicable to any nuclear magnetic resonance (NMR) relaxation, or by an analytic method applicable only to multiexponential relaxations (D. Orazio et al., 1989). The porosity distribution obtained from NMR relaxation measurements strongly depends on the pore shape factor. For the Borden aquifer material, both the regularized and the analytic pore size distribution obtained from NMR relaxation measurements are consistent with those obtained by Ball et al. (1990) using Hg porosimetry and N 2 adsorption. For the Eustis and the Webster soils, the measured porosity domains are qualitatively consistent with those expected based on their respective composition. Our findings suggest that due to the long time required to saturate fine pores, NMR measurements of porosity distribution that are collected at short saturation times are biased toward larger pore sizes.
Different factors contribute to soil moisture variability at different space scales and timescales, including soil properties, topography, vegetation, land management, and atmospheric forcings, such as precipitation and temperature. Field experiments supported by adaptive geostatistical and exploratory analysis, including categorical elimination of different governing factors, are needed to bring new insight to this important hydrologic problem. During the Southern Great Plains 1997 (SGP97) Hydrology Experiment in Oklahoma, we investigated the within‐season (intraseasonal) spatiotemporal variability of surface (0–6 cm depth) soil moisture in a quarter section (800 m×800 m) possessing relatively uniform topography and soil texture but variable land cover. Daily soil moisture measurements were made between June 22 and July 16 using portable impedance probes in a regular 7×7 square grid with 100‐m spacings. Initially, the land cover was split between grass and wheat stubble; row tilling on June 27 converted the wheat stubble to bare ground. Geostatistical and median polishing schemes were used to analyze the within‐season evolution of the spatial structure of soil moisture. The effects of daily precipitation, variable land cover, land management, vegetation growth, and microheterogeneity including subgrid‐scale variability were all visible in the analysis. Isotropic spatial correlation range for soil moisture varied between <100 m (for nugget and subgrid‐scale variability) and >428 m (for spherical and Gaussian models) within the 4‐week‐long SGP97 experiment. The findings will be useful for assessing remotely sensed soil moisture data collected during the SGP97 Hydrology Experiment in mixed vegetation pixels.
A traditional method of reclaiming salt‐affected soils involves ponding water on a field and leaching salts from the soil through a subsurface tile drainage system. Because water and salts move more slowly in areas midway between drain lines than in areas near the drains, achieving a desired level of desalinization across the entire field requires that ponding continue long after areas close to the drains are already free of salts, thus causing an inefficient leaching process that wastes water. A partial ponding method of leaching was recently suggested to improve the leaching efficiency by up to 85%. In this study, we tested the partial ponding method for its potential to save water and time by simulating the leaching of salts from salt‐affected profiles with various soil textures, tile‐drain depths, and soil depths. Simulations for laboratory sand tanks and field conditions both showed that transport velocities midway between drains are greater under partial ponding than under total ponding because the local hydraulic head gradient is larger under partial ponding conditions. As the ponded area increases toward the drain, water originating from areas near the drain moves faster than water from midway between the drains. By adopting partial ponding, water and time savings of 95 and 91%, respectively, were found possible for a sandy soil. The method also showed water savings of 84% when applied to a loam soil and 99% for a layered sand over loam soil but only 13% when applied to a layered loam over sand soil.
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