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We present a new open-source and modular instrumentation package composed of up to ten automatic infiltrometers connected to data acquisition systems for automatic recording of multiple infiltration experiments. The infiltrometers are equipped with differential transducers to monitor water level changes in a Mariotte reservoir, and, in turn, to quantify water infiltration rates. The data acquisition systems consist of low-cost components and operate on the open-source microcontroller platform Arduino. The devices were tested both in the laboratory and on different urban and agricultural soils in France and India. More specifically, we tested three procedures to treat the transducers readings, including a filtering algorithm that substantially improved the ability to determine cumulative infiltration from raw data. We combined these three procedures with four methods for estimating the soil parameters from infiltrometer data, showing pros and cons of each scenario. We also demonstrated advantages in using the automatic infiltrometers when infiltration measurements were hindered by: i) linearity in cumulative infiltration curves owing to gravity-driven flow, ii) an imprecise description of the transient state of infiltration, and iii) the occurrence of soil water repellency. The use of the automatic infiltrometers allows the user to obtain more accurate estimates of soil hydraulic parameters, while also reducing the amount of effort needed to run multiple experiments.

The objective of this paper was to evaluate a recently proposed comprehensive model for three-dimensional single-ring infiltration and its suitability for estimating soil hydraulic properties. Infiltration data from four different soils with contrasting characteristics were inverted to estimate field-saturated soil hydraulic conductivity, Kfs, values using a total of fourteen different scenarios. Those scenarios differed by: i) the way they constrained the macroscopic capillary length, λ, and the initial and saturated soil water contents, θi and θs, ii) the use of transient or steady-state data, and iii) the fitting methods applied to transient data. For comparative purposes, the SSBI method (Steady version of the Simplified method based on a Beerkan Infiltration run) was also applied. For validation purposes Kfs data estimated from the different scenarios were compared with those values obtained by numerical inverse modeling with HYDRUS-2D/3D. This comparison identified Approaches 1 and 3, which respectively estimate Kfs via optimization and using analytical expressions, as the most accurate methods. The steady-state scenario of Approach 4 and the SSBI method, both of which use a λ value of first approximation, appeared preferable for field campaigns aimed to sample remote or large areas, given that they do not need additional data and still provide acceptable estimates. The reliability of Kfs data was also checked through a comparison with unsaturated hydraulic conductivity, Kh, values measured in laboratory on extracted soil cores, in order to discriminate between theoretically possible (Kfs > Kh) and impossible (Kfs ≤ Kh) situations. Physically possible Kfs values were always obtained with the exception of the crusted soil, where Kfs < Kh situations suggested that the crust layer reduced water flow during ponding experiments in the field. The new comprehensive model tested in this study represents a valuable tool for analyzing both transient and steady-state infiltration data, as well as experiments carried out with different depths of ponded water, ring sizes and ring insertion depths.

Dual-permeability models simulate flow and transport within soils characterized by preferential (macro) and matrix (micro) pore domains, with each exhibiting distinct hydraulic properties. The lack of suitable methods for determining appropriate and physically based model parameters remains a major challenge to applying these models. Here, we present a method that characterizes dual-permeability model parameters using experimental results of saturated flows from water and a non-Newtonian fluid. We present two sub-models that solve for the effective pore sizes of micropores and macropores, with macropores represented either with cylindrical (for biological pores) or planar (for shrinkage cracks and fissures) pore geometries. The model also determines the percentage contribution (wi) of the representative macro-and micropores to water flow. We applied the model to experimental soil samples complemented with capillary tubes simulating the macropores and showed its ability to derive the bimodal pore size distributions in dual-domain soils using only two fluids. As such, we present this method of characterization of dual structures for improved modeling of nonuniform preferential flow and transport in macroporous soils.

This introduction to the special section Nonuniform Flow across Vadose Zone Scales is a brief summary of this special section’s diverse contributions covering nonuniform flow across a wide range of scales, processes, and applications. We summarize the 17 articles constituting this special section and hope that those contributions are positive steps toward a new, generalizable, and comprehensive paradigm to modeling flow and transport in porous media.

In this essay, we provide a brief overview of the chapter titled “Field Measurements of Soil Cracks”, recently published in the Methods of Soil Analysis series.

Many clayey soils shrink as they dry, causing a shift of porosity from inside to outside the soil aggregates and leading to the formation of shrinkage cracks and/or surface subsidence. During swelling, shrinkage cracks begin to seal and/or the soil surface rises. Previous models have focused on describing shrinkage at the aggregate level, with little success in predicting soil cracking and subsidence. To remedy this shortcoming, we provide a unified, physically based set of governing equations for these three pore domains (aggregates, cracks, and subsidence) and predict the porosity distribution among domains as a function of soil water content and minimal (up to six) additional parameters. Examples collected from a variety of soils show how these functions describe shrinkage of soil samples in the laboratory; quantify the relationships among soil suction, soil shrinkage, and water content using the same set of parameters; and predict sealing of soil cracks in the field. This approach provides the framework for accurate and unified hydromechanical modeling of swelling soils.

Producers utilizing fall manure injection have reported increased growth and greenness in small grains growing on the injection band compared to small grains growing between injection bands. To determine how producers utilizing fall manure injection in small grains should manage potential differential growth, 24 sites under fall manure injection were established. Soil samples were taken in‐band and between‐band 1 month after manure application and at silage harvest for soil NO3‐N. Small grain growth stage was assessed 1 month after planting and at silage harvest, while dry matter (DM) yield and forage nutritive value parameters were assessed at silage harvest. Soil NO3‐N was elevated in‐band compared to between‐band 1 month after manure application (p < 0.05); however, this did not persist until silage harvest. No differences in growth stage were observed 1 month after planting in 2021; however, growth stage means were consistently elevated in‐band in 2022, likely due to earlier planting dates in 2022 compared to 2021. Growth stage at harvest was the same in‐band and between‐band at each site. Small grain DM yield was only increased in‐band compared to between‐band in three of 24 sites. Two of the three sites planted with wheat (Triticum aestivum L.) showed significantly increased DM yield in‐band, suggesting DM yield response could be species dependent. No consistent differences in forage nutritive value parameters were observed. As no consistent differences in small grain DM yield and forage nutritive value were found at harvest, we recommend no changes to management practices for producers utilizing fall manure injection in small grains. Core Ideas: Manure injection consistently elevated soil nitrate in the manure injection band across sites.Some increased small grain tillering observed in the manure injection band 1 month after planting.Soil nitrate concentrations were the same in‐band and between‐band at silage harvest.No differences in small grain maturity, silage yield, and forage quality occurred in‐band versus between‐band.Producers using fall manure injection in small grains do not need to adjust management practices due to banding. [ABSTRACT FROM AUTHOR]

Manure injection alters the spatial distribution of manure by concentrating it in a subsurface band which can lead to differential soil nutrient distribution and growth in small grains. This study assessed the effects of fall manure applications on soil NO3‐N, active carbon, and small grain growth compared to broadcasting and a no manure control. Soil samples were taken to represent whole plot soil means for all treatments, while in‐band (IB) and between‐band (BB) soil samples were taken in injected plots to assess nutrient spatial distribution after injection. Small grain forage samples were also taken IB and BB to assess the effects of manure injection on small grain growth. Soil samples were analyzed for NO3‐N, permanganate oxidizable carbon (POXC), and carbon mineralization (C‐min), while small grain dry matter (DM) yield and forage quality parameters were measured from plant samples. Manure injection did not result in any differences between whole plot injection and broadcast soil NO3‐N concentrations. However, injection resulted in initially elevated soil NO3‐N concentrations IB compared to BB. There were no differences in soil POXC or C‐min under manured versus unmanured soils, nor between IB and BB samples. Manure injection did not increase small grain DM yield or forage quality compared to broadcasting, nor were these measurements altered IB and BB. Even though manure injection altered the spatial distribution of soil NO3‐N, it did not affect soil C‐min, POXC, or small grain growth under the conditions seen in this study. Therefore, differential small grain growth and quality is likely not a concern under injection. Core Ideas: Manure injection increased soil NO3‐N in the injection band.There were no differences in soil permanganate oxidizable carbon and carbon mineralization between manured and unmanured treatments.Manure application, independent of method, increased small grain dry matter yield compared to no manure control.Small grain dry matter yield was not increased on the injection band compared to between injection bands. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) and soil respiration (SR) are essential in carbon cycling and storage. Consequently, proper soil management requires knowledge of factors influencing DOC and SR in soil. The main objective is to identify the most critical indicators that control DOC and SR in the major climatic regions of Iran. The carbon cycling of sixteen pedons from six study sites with different soil moisture and temperature regimes was measured. Soil samples were collected from various genetic horizons to assess their physicochemical properties. Stepwise multiple linear regression (MLR) models were conducted on all horizons and B horizon properties (representing the subsoil) to identify the strongest correlation with DOC and SR. The MLR model revealed that organic carbon (OC) was negatively affected by pH, electrical conductivity (EC), amorphous and crystalline iron oxide contents in all horizons (R2 = 0.69), EC, and cation exchange capacity (CEC) in B horizons (R2 = 0.62). On the other hand, SR was negatively affected by pH, EC, soil water content, and clay contents in all horizons (R2 = 0.67), and calcium carbonate equivalent (CCE), pH, and sodium adsorption ratio in B horizons (R2 = 0.67). The most important indicators associated with carbon cycling included EC and pH in the different soil types of Iran. This study contributes to improving crop yield and mitigating soil degradation, mainly by controlling and managing salinity and pH threats for soil fertility to increase carbon storage in such climatic regions. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) gas diffusion is an important component of carbon cycling in soils. This process is particularly relevant in karst landscapes, which contain easily weathered rock, subsurface fractures, and cave networks. We instrumented three soil profiles--the shoulder, back slope, and toe slope of a sinkhole--above a karst cave in Virginia. Each profile had solidstate CO2 sensors and soil water content/temperature sensors at 20 and 60 cm depth that collected hourly measurements from 2017 to 2019. We calculated CO2 fluxes using Fick's first law along with measured soil and assumed atmospheric CO2 concentrations. With this approach, we identified occasional near-surface zero-flux planes, in which CO2 likely diffused both upward and downward. All profiles had upward CO2 fluxes during warm-season months, with maximum fluxes of 1.2 lmol CO2 m22 s21 in the shoulder and back slope versus 2.0 lmol CO2 m22 s21 in the toe slope. During cool-season months, upward CO2 fluxes were smaller (0-0.3 lmol CO2 m22 s21) and were often counteracted by downward fluxes in the toe slope, possibly driven by ventilation into the underlying cave. The toe slope had a cumulative annual efflux of 14.5 mol CO2 m22, which was .3 times greater than the other profiles. Fluxes were sensitive to soil porosity, with an order-of-magnitude difference when porosity was assumed to be 0.40 versus 0.56 cm3 cm23. The results of this study offer new insight into short-term and seasonal variations in diffusive CO2 gas transport in karst soils, and they may inform other investigations of non-uniform diffusion processes. [ABSTRACT FROM AUTHOR]