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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]

Vineyard soils often contain mineralogy that can confound predictions of plant‐available potassium (K). Too little or too much K uptake into wine‐grape (Vitis varieties) tissues can negatively affect fruit chemistry, making it important to have soil tests that accurately quantify plant‐available K. Our goal was to determine the best soil sampling, processing, and extraction methods for predicting K availability in vineyard soils. We sampled soil and grapevine tissue in 39 vineyard blocks from 22 vineyards in Virginia, Maryland, and New Jersey. Plant tissue sampling included petioles at bloom and both petioles and leaf blades at veraison. Soil samples were collected from 0 to 10‐ and 0 to 38‐cm depths. We tested three soil extraction methods—Mehlich 1, Mehlich 3, and sodium tetraphenylboron (NaTPB)—on both oven‐dried and field‐moist samples. The different sampling, processing, and extracting procedures produced distinct K concentrations, with shallow 0–10 cm samples and NaTPB extraction resulting in higher K concentrations than their counterparts. Upon drying, three soils fixed K and 24 samples released K. Whole leaf (petiole plus leaf blade) samples collected at veraison had the best relationships with most soil K concentrations. The best soil testing method for predicting tissue K concentration in whole leaves at veraison was Mehlich 1 extractions of field‐moist soils from 0 to 38‐cm depth. This sampling combination appears to be best suited for growers to use when assessing K concentrations in vineyard soils. Core Ideas: Extractions from field‐moist soils had best correlation with grapevine tissue potassium (K) concentration.Soil samples collected from 0 to 38‐cm depths best predicted grapevine tissue K concentration.Soil K extracted via Mehlich 1 had better correlation with vine tissue K concentration than Mehlich 3 or sodium tetraphenylboron. [ABSTRACT FROM AUTHOR]

Peatland functions (e.g., carbon sequestration and flora diversity) are largely driven by soil moisture dynamics and thus dependent on interactions between hydrologic regimes and organic soil properties. Understanding these interactions is particularly important in drained peatlands, where drier conditions may alter soil properties with feedbacks to soil water retention and associated ecosystem functions. In this work, we focused on the Great Dismal Swamp (GDS) in Virginia, USA, a historically drained, temperate peatland with ongoing hydrologic restoration efforts. Two distinct soil layers varying in thickness exist at GDS: an upper layer with subangular blocky structure thought to be a result of past drainage, and a sapric lower layer with a massive structure more representative of an undisturbed state. To understand the occurrence and consequences of these distinct layers, we used continuous water table data and analysed soil physical and hydraulic properties to characterize soil profiles at 16 locations. We found significant differences between layer properties, where upper layers had lower fibre and organic matter contents and higher bulk densities. Further, moisture release curves demonstrated lower water retention in upper layers compared with lower layers and key differences in pore structure, with upper layers having higher macroporosity. Upper layers varied in thickness across sampling locations (~0.30 to 1.0 m) with a transition to lower soil layers typically occurring at depths below contemporary water level observations, suggesting that the upper layer may be a result of historical drainage and deeper water table conditions. Yet, upper layers with more frequent saturation exhibited higher water retention and lower macroporosity compared with drier upper layers, thus indicating potential recovery following re‐wetting efforts. These findings highlight how past drainage influences soil properties and water retention, with important implications for current management objectives at GDS and other drained peatland systems. [ABSTRACT FROM AUTHOR]

Neonicotinoid insecticides provide crop protection via water solubility and systemicity, yet these chemical characteristics, combined with high toxicity to non-target invertebrates (e.g., honeybees), elicit concern of environmental transport. Neonicotinoids have been detected in soil and surface water throughout North America; however, no investigation has defined a direct connection to planted seed dressings. We quantified the physical transport of thiamethoxam (TMX), a neonicotinoid, under field conditions. We planted TMX-coated corn seeds and maintained plots with and without viable crops (n = 3 plots per treatment) to determine plant influence on pesticide transport. TMX concentrations were measured in soil and drainage throughout the growing season. Storm-generated runoff was the dominant transport mechanism (maximum TMX concentration 1.72 ± 0.605 μg L -1 ; no viable plants), followed by shallow (<72 cm) lateral drainage (0.570 ± 0.170 μg L -1 ; no viable plants), and deep (110 cm) drainage (0.170 ± 0.265 μg L -1 ; viable plants). Soil samples confirmed vertical and lateral movement within 23 and 36 days of planting, respectively. Plants facilitated downward migration of TMX in soil but restricted TMX drainage. Altogether, these study results revealed that neonicotinoids can be transported from seed coatings both above and through the soil profile, which may enable migration into surrounding ecosystems., (Published by Elsevier Ltd.)

Drainage is a globally common disturbance in forested peatlands that impacts peat soils, forest communities, and associated ecosystem functions, calling for informed hydrologic restoration strategies. The Great Dismal Swamp (GDS), located in Virginia and North Carolina, U.S.A., has been altered since colonial times, particularly by extensive ditch networks installed to lower water levels and facilitate timber harvests. Consequently, peat decomposition rates have accelerated, and red maple has become the dominant tree species, reducing the historical mosaic of bald cypress, Atlantic white-cedar, and pocosin stands. Recent repair and installation of water control structures aim to control drainage and, in doing so, enhance forest community composition and preserve peat depths. To help inform these actions, we established five transects of 15 plots each (75 plots total) along a hydrologic gradient where we measured continuous water levels and ecosystem attributes, including peat depths, microtopography, and forest composition and structure. We found significant differences among transects, with wetter sites having thicker peat, lower red maple importance, greater tree density, and higher overall stand richness. Plot-level analyses comported with these trends, clearly grouping plots by transects (via nonmetric multidimensional scaling) and resulting in significant correlations between specific hydrologic metrics and ecosystem attributes. Our findings highlight hydrologic controls on soil carbon storage, forest structure, and maple dominance, with implications for large-scale hydrologic restoration at GDS and in other degraded forested peatlands more broadly., (Copyright © 2018 Elsevier Ltd. All rights reserved.)