Abstract Temperature and precipitation change can increase crop water stress leading to declines in crop yield. In the US Corn Belt, previous studies have found that the topsoil is drying. But crops, even in systems with restrictive soil layers, access water from beneath the topsoil and it is poorly understood how weather variability will affect water availability throughout the entire root zone. To investigate these impacts, I built an integrated surface water–groundwater model of a field in the Central Mississippi River Basin. Using stochastically downscaled precipitation forcings, I found that in the topsoil (top 30 cm), less frequent precipitation leads to soil water more frequently dropping below the stress point. Increased precipitation during the spring did not impact the simulated soil moisture because soil was already near saturation at that time, meaning that additional precipitation primarily increased runoff. The shallow groundwater and soil layers beneath the topsoil did not experience drying, though unquantified recharge pathways limit the interpretation of groundwater results. Overall, this study showed that less frequent, more intense precipitation increases topsoil moisture stress. But the moisture in the critical zone below the topsoil is not likely to be affected, meaning it can be an important water source to sustain crop yields in places with unreliable precipitation. Thus, improvements to genetics and management that facilitate deep root growth should be investigated to sustain agricultural production in the future.

Abstract Crop production on fragipan soils can be severely limited due to restrictive root growth and perched water table. We hypothesized that roots of multispecies cover crop mixtures containing annual ryegrass (ARG, Lolium multiflorum L .), hairy vetch ( Vicia villosa ), and crimson clover ( Trifolium incarnatum ) can improve soil physical conditions for main crop root growth, and roots of ARG can penetrate through the fragipan layer to remove excess moisture. Two on‐farm sites, Marion and Springerton, in southern Illinois were established in 2019 and 2013, respectively. Depth from surface to fragipan layer was 70 cm and 50 cm for Marion and Springerton, respectively. Both sites had replicated trials in a corn ( Zea mays L.)–soybean ( Glycine max L. Merr.) rotation with two treatments: with cover crop (CC) and without cover crop (NCC) mixes having ARG as the dominant species. In spring of 2023, intact soil cores were collected and analyzed for soil water retention characteristics and particle size distributions. Volumetric water contents (VWCs; cm 3 cm −3 ) of the soil through 90‐cm depth were monitored during corn phase and during cover crop growth of 2023–2024. At Marion, NCC had higher VWC at 25‐ and 55‐cm depths than CC most of the time during summer. At Springerton, CC soils within 15‐ to 35‐cm depths had higher VWC than NCC during cover crop growth in winter. Inclusion of cover crop mixtures can improve soil water movement, but the magnitude depends on the length of adoption and depth to the fragipan layer.

Abstract The chemical compounds that plant roots release into the soil, referred to as rhizodeposits, affect soil hydraulic properties like the surface tension and viscosity of soil water, and the contact angle between menisci and the pore surface. What remains less clear is how these effects manifest when considering soil water infiltration and retention, and the consequent impact on the availability of water for uptake by roots. A novel model for soil water transport was developed that incorporates the influences of rhizodeposits on soil hydraulics and root water uptake. The finite element method was used to generate model simulations and investigate how the presence of rhizodeposits of wheat ( Triticum aestivum L.) affected water uptake of three differently aged root systems under precipitation regimes that varied in total precipitation and delivery pattern. The overriding effect on soil hydraulics of wheat rhizodeposits was to facilitate infiltration. A trade‐off was identified in how this could improve water availability to the root system by reducing evaporation but also worsen it by increasing deep percolation. When total precipitation was shared over several rainfall events, the effect of rhizodeposits on root water uptake was positive. However, when higher levels of total precipitation were delivered in a single event, the presence of rhizodeposits reduced the water uptake of shallower root systems. This suggests that the influence of rhizodeposits on soil hydraulics and root water uptake is nuanced and will require careful consideration when developing crops for improved water use efficiency and stress resilience.

Abstract Peat thickness mapping is crucial for supporting soil conservation practices at the field‐scale, but the presence of limnic layers complicates accurate estimates, including through manual probing. At this scale, proximal sensors could provide extensive data on soil stratigraphy. However, this approach relies on a solid understanding of the variability associated with depth and soil materials, including limnic and mineral layers. In Eastern Canada, reference characterization data for all three layers in an agricultural context are limited. Therefore, the objectives of this study were (1) to characterize and compare geophysical properties of peaty, limnic, and mineral layers from drained and cultivated Histosols in Eastern Canada as a function of depth (0–1 m); and (2) to evaluate probes or geophysical sensors that are responsive to properties which may aid in identifying soil layers in situ, minimizing the necessity for manual probing. Ninety sites were sampled across nine fields. At each site, the upper meter of soil was divided into discrete 10 cm layers. The impacts of soil material and depth on six soil properties were assessed using linear mixed‐effects models. Both effects were significant ( p < 0.0001) for all soil properties. Volumetric soil water content, electrical conductivity, and soil penetration resistance were promising candidates for identifying soil materials. In future studies, a time‐domain reflectometry probe could be automated and combined with a soil penetrometer to reduce manual sampling efforts by leveraging regional reference data. Bulk density and organic matter content quantification from this project will support future carbon stock mapping projects.

Abstract Capillary barrier is an engineered structure composed of a fine‐grained layer overlying a coarse‐grained layer. However, traditional two‐layer configurations of fine and coarse grains exhibit suboptimal water storage performance in semi‐humid to humid regions. Thus, we investigated the enhancement of water storage capacity in the fine‐grained layer by incorporating diatomite, wheat straw ( Triticum aestivuml ), and peanut shells ( Arachis hypogaea L). The results demonstrate that (1) modified capillary barriers exhibit significantly enhanced water storage capacity (admixture ratio > 1:0.3 at least 10% increased), diatomite outperforms 20% better than peanut shells and wheat straw as a modifying material. (2) Both modified and unmodified capillary barriers show stable water storage capacity under continuous rainfall. (3) All modified fine‐grained layers show improved evaporation characteristics. The residual moisture content increases as the volume admixture ratio increases. (4) Modified fine‐grained layers exhibit pseudo‐cohesive force. The shear strength of the fine‐grained layer modified by diatomite increases as the volume admixture ratio increases.

Abstract Grouping topographic indices (TIs) values, a topographic metric incorporating upslope contributing area and slope gradient, into topographic index classes (TIC) to estimate soil moisture variability has been shown to improve hydrologic model characterization of complex landscapes. However, the performance of TIC may be enhanced by understanding the inputs in its derivation. In this study, in situ soil moisture measurements across 25 locations in a 4.2 ha field and the k‐means clustering machine learning algorithm were used to identify the optimum number of classes for characterizing field soil moisture. The effect of using equal‐interval, equal‐area, k‐means, and Fisher classification approaches; U.S. Geological Survey (USGS) (1 and 9 m); and drone‐captured light detecting and ranging (LiDAR) digital elevation models (DEMs) re‐gridded to 0.25, 0.5, 1, 2, 3, 4, 5, and 10 m resolution was evaluated. The k‐means clustering, along with elbow analysis and Gap* statistics, identified the spatial pattern of the soil moisture in the field into three groups. Spearman's correlation between a three‐class TIC and the identified soil moisture patterns showed wide variability due to DEM resolution for TIC from drone‐captured LiDAR DEMs—from r = −0.41 to −0.17 for high resolution (0.25–4 m) to r = 0.52 to 0.58 for low resolution (10 m), compared to TIC derived from 1 and ∼9 m resolution USGS DEMs (r = 0.53–0.64). TIC generated using the equal‐interval approach best correlated with identified soil moisture patterns. Selecting the right classification approach, DEM type, and resolution are important considerations when using TI to estimate soil moisture patterns.

Abstract It has long been suggested that soil compaction indices should be monitored as part of a routine soil management program. Moreover, in addition to properties related to storage of gases and fluid within a bulk volume (i.e., bulk density [BD] and air porosity [θa]), some authors have suggested that properties linked to fluid and gas exchanges such as gas diffusion and hydraulic conductivity should be used to assess the physical health of soils. Given the risk of severe compaction due to the increasing size of farm equipment and the lack of long rotation in cash crop production, data on soil storage and exchange properties need to be collected. The objective of this study was to assess the physical soil health of the top 30 cm of 18 southern Quebec corn fields using a set of indicators. The data were also used to determine crop response to nitrogen fertilization. The results showed that over 93% of the corn fields had a relative gas diffusivity (Ds/Do) below the 0.03 threshold at both 15‐ and 30‐cm depth, suggesting substantial crop growth limitations. They also showed that around 40% of the soils had subsurface drainage problems linked to a low saturated hydraulic conductivity (49% at 15 cm and 47% at 30 cm lower than 0.001 cm s−1). The levels of relative gas diffusivity were low, not only limiting crop growth but also likely reducing nitrogen efficiency through increasing risk of denitrification. Moreover, the results suggest that in some fields, high yields can be achieved with as little as 60 and up to 215 kg of nitrogen per hectare, and that slow‐draining soils will have a very poor response to N fertilization, leading to lower net revenues and nitrogen losses. Overall, the findings suggest that appropriate soil conservation and water management practices based on soil physical health criteria like relative gas diffusivity and hydraulic conductivity must be implemented to maintain or improve soil productivity and health in the face of climate change.

Abstract This study investigates the interplay between shallow groundwater and on‐surface drip irrigation in facilitating water uptake of agricultural crops. Lysimeter experiments utilizing ceramic cups mimicking plant roots provide insights into wetting patterns within the root zone and water balance components. Results reveal that while plants can effectively utilize shallow groundwater even with limited root systems, higher irrigation rates diminish groundwater contribution to water uptake. Conversely, shallow groundwater enhances water uptake from on‐surface irrigation, reducing drainage at low irrigation rates. The findings underscore the potential of groundwater as a supplementary water source for crops, offering practical implications for optimizing supplemental irrigation strategies and sustainable water management in agriculture. When the vertical distance between active roots and the water table exceeds a characteristic length of the soil, it disrupts the continuity of the liquid water phase. As a result, intensive capillary upward water flow, against gravity, cannot be reliably described by Darcy's law. It becomes imperative to formulate a practical continuum theory to more accurately depict capillary rise in such scenarios.