The impact of biochar on soil nutrient pool has been well‐studied in degraded and acidic soils, yet its effects in fertile soils such as Luvisols remain underexplored. To address this, two laboratory incubation experiments were conducted using biochar derived from wheat straw (Triticum aestivum)—Experiment 1 evaluated biochar produced at three pyrolysis temperatures (350°C, 500°C, and 650°C) with two residence times (1 and 2 h), whilst Experiment 2 examined the feasibility of different application rates (5 or 10 Mg ha−1) and placements (thorough mixing or surface broadcast). Biochar significantly increased exchangeable Ca, K, Mg, and Na concentrations compared to both control and straw‐amended soils, particularly with the higher temperature biochar. Soil available P and K were enhanced two‐ and fivefold, respectively, compared to control and straw‐amended soils. The effects on soil available N were inconsistent, with no significant improvement observed and some treatments indicating possible immobilization. Soil cation exchange capacity (CEC) significantly increased with certain biochar compared to the control but did not differ from straw‐amended soil, with occasional instances where biochar led to lower CEC. Soil available N was higher with biochar application than straw. However, these did not significantly differ from the control, except for biochar produced at 500°C with a 1‐h residence time. Soil available N was notably higher when biochar was surface broadcasted than when thoroughly mixed into the soil. Consequently, this study highlights the influence of biochar pyrolysis conditions on soil nutrient pool, with outcomes also linked to some extent by the application rates and placements, suggesting careful consideration of these management factors for optimal biochar benefit in Luvisols.

Understanding phosphorus (P) dynamics in soils under conservation agriculture remains challenging because the long‐term effects of fertilization rates and soil texture on P accumulation, availability, and environmental risk are not being fully understood. This study evaluated P fraction accumulation and saturation indices across soil layers in response to increasing phosphate fertilizer rates in two long‐term experiments in North Carolina. The trials were conducted on Portsmouth soil (fine‐loamy over sandy or sandy‐skeletal, mixed, semiactive, thermic Typic Umbraquults) at Tidewater, managed under minimum tillage, and Lloyd soil (fine, kaolinitic, thermic Rhodic Kanhapludults) at Piedmont, under no‐tillage. Soil samples from 0‐ to 5‐cm, 5‐ to 10‐cm, 10‐ to 20‐cm, and 20‐ to 30‐cm depths were analyzed in 2022 using sequential chemical fractionation and P‐related indices, including P sorption and degree of P saturation (DPS). Most P fractions were significantly influenced by P rates and depth. In clayey Piedmont soil, occluded P reached 58% of total P and increased linearly with rates (up to 30 cm). Sandy Tidewater soil showed higher soluble P (up to 4 mg kg−1 at 0–5 cm) and DPS values reaching 40%, signaling environmental risk. The DPS index proved sensitive to increasing P fertilization, outperforming the P sorption index. Mehlich‐3 P exceeding 169 mg kg−1 in sandy soil indicates a contamination risk threshold due to elevated soluble P. Different behaviors of P fractions, especially occluded P, highlighted the importance of soil‐specific fertilization strategies and considering P saturation as essential for optimizing P use and mitigating environmental impacts. The DPS index emerges as a valuable tool for assessing fertilization history and guiding P management strategies.

Switchgrass (Panicum virgatum L.) has been identified as a “model” herbaceous species for bioenergy production by the United States Department of Energy. Switchgrass can provide several ecosystem services, including biodiversity support, soil erosion control, runoff filtering, and reclamation of marginal land. In addition to the reduction in greenhouse gas emissions from switchgrass‐derived biofuel, soil carbon sequestration is of particular importance. The objective of this study was to evaluate the variability in soil carbon sequestration, particularly in response to water limitation, and to investigate the relationship between soil carbon sequestration and switchgrass yield. For this purpose, dry aboveground biomass yield and soil reactive carbon—specifically, permanganate oxidizable carbon (POXC)—content at three depths (0–15, 15–30, and 30–60 cm) were measured for 150 different switchgrass genotypes for three consecutive years. We found that drought significantly reduced yield compared to control plots, reduced the amount of soil POXC, and that POXC decreased with soil depth. A positive correlation (r = 0.27, p < 0.05) between POXC and yield was observed in the drought‐stressed plots. This study provides insight into the impact of switchgrass on soil POXC over time and at different depths, offering a framework for future evaluation of root‐related traits in switchgrass, particularly in relation to drought stress.

Groundwater nitrate contamination is largely attributed to fertilizer and intensive livestock manure inputs in agricultural systems. California's Salinas Valley is an area where regional policy is aimed at reducing nitrate leaching. Nonlegume winter cover crops can help decrease nitrate leaching by scavenging residual soil nitrogen (N) during winter fallow periods following the cropping season. However, the ability of fall-incorporated cover crops to decrease nitrate leaching and recycle N to subsequent cash crops is unknown. We conducted a 112-day laboratory soil incubation experiment using Merced rye (Secale cereale) cover crop shoot biomass, with four carbon-to-nitrogen (C/N) ratios (10, 14, 19, and 30), at three temperatures (10°C, 15°C, and 20°C). Destructive soil sampling was done at six intervals during the incubation to measure plant-available nitrogen. Rye biomass with the lowest C/N ratio (10) had the highest average nitrogen mineralization (Nmin) rate (56%) at the warmest temperature (20°C). Conversely, biomass with the highest C/N (30) showed net nitrogen immobilization at 10°C and 15°C during the incubation, transitioning to net mineralization only at 20°C. We found a linear correlation between soil temperature and nitrogen mineralization (at Day 112) for higher C/N ratios. Furthermore, doubling the soil mineral nitrogen content had a negligible impact on the percent mineralization of the C/N 30 residue. These results provide useful information to help farmers and policymakers understand mineralization dynamics from fall-, winter-, or spring-terminated cereal cover crops.

Miscible displacement experiments traditionally rely on measured effluent concentrations of a given chemical with time to characterize its transport through soils. Time-dependent distributions of heavy metals within a soil column are difficult to obtain and are typically ignored. We developed a methodology for measuring time-dependent distributions of zinc (Zn) and nickel (Ni) within soil using a Kapton film (KF) column and portable X-ray fluorescence (pXRF) device. Matrix-matched calibrations were developed for each matrix/solute combination based on linear regressions between known and pXRF-measured Zn and Ni concentrations within the KF column. We assessed the accuracy of pXRF measurements using mass balance calculations; our matrix-matched calibration significantly reduced cumulative mass balance errors for three of the four experimental datasets. We compared pXRF-measured Zn or Ni concentrations at various column lengths to those predicted by a single-site, nonlinear kinetic model. The model accurately predicted the timing of peak Zn or Ni concentrations at each column length in reference sand and Wolfpen soil; however, overall model performance was element- and matrix-dependent. Our results demonstrate that use of a KF column and pXRF device enables the acquisition of time-dependent distributions of Zn or Ni distributions in soil columns. We expect that this approach will be appropriate for other heavy metals, particularly those with higher energy fluorescent X-rays (atomic number>30) where less X-ray attenuation by the KF column and soil matrix is expected. Accurate descriptions of heavy metal distributions with column length and time will provide an additional metric to validate reactive transport models.

Phosphorus (P) management remains a challenge in agricultural watersheds. The Choptank River Conservation Effects Assessment Project watershed, located in Maryland and Delaware and draining to the Chesapeake Bay, contains legacy soil P from historical dairy and poultry manure applications. These practices elevated soil P beyond crop needs, contributing to persistent P export to aquatic ecosystems. We assessed spatial P distribution and analyzed GIS (Geographic Information Systems)‐derived landscape features driving legacy P movement on a farm (47 ha). We hypothesized that P accumulates in drained lowlands and depressional areas due to gravity‐driven processes that accelerate P‐enriched water to receiving waters via overland flow. In collaboration with the US Department of Agriculture Legacy P project, we collected 105 soil samples (0‐ to 5‐cm and 5‐ to 15‐cm depths) and 14 ditch sediment samples across five topographic openness classes from a farm with >100 years of dairy manure application. Average Mehlich‐III P concentrations were 218 and 179 mg kg−1 at 0‐ to 5‐cm and 5‐ to 15‐cm depths, respectively, with legacy areas defined by P content > 100 mg kg−1. Soil P and clay particle size were positively correlated (r = 0.42, p < 0.05), increased as landscape openness decreased, and were negatively correlated with topographic openness (ranging from −0.2 to −0.4, p < 0.05), indicating accumulation of P and clay in low‐lying areas. These patterns suggest that historical field‐level managements have primarily shaped P distribution, while hydrologic and landscape properties further influence its redistribution via transport pathways and drainage. These findings support the development of landscape models to map critical source areas in low‐relief watersheds and guide targeted mitigation in high‐risk P export zones.

This study aimed to investigate the occurrence and concentration patterns of three groups of trace contaminants-potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons (PAHs), and per- and polyfluoroalkyl substances (PFASs)-in river catchments with contrasting land use and landscape characteristics. A second objective was to relate the concentrations in suspended particulate matter (SPM) to those in soils and to catchment attributes in order to identify dominant transport processes and contaminant sources. A spatially explicit monitoring campaign was conducted in three river catchments of the central Danube River Basin: Zagyva and Koppány in Hungary and Wulka in Austria. Composite soil samples (∼10 per catchment, totaling ∼200 subsamples) were collected from forest, pasture, and cropland areas. SPM was collected using both passive and active samplers under base-flow and high-flow conditions. The results revealed strong spatial variability in concentrations for five of seven PTEs, all PAHs, and eight of 10 PFASs. Substances predominantly deposited atmospherically-such as PAHs and several PFASs-were more concentrated in forest soils compared to pasture and cropland. Base-flow SPM samples were often more contaminated than high-flow samples, especially for PAHs and some PTEs. Concentrations in SPM were generally correlated with soil concentrations, suggesting that erosion-related transport of these chemicals may be significant in rural catchments. However, enrichment patterns and correlation strength varied by substance group and land use type. These findings support the use of parallel SPM and soil sampling for improving empirical emission modeling and source identification in catchments with mixed land use.

Excessive loading of phosphorus (P) in coastal systems has been a growing concern for watershed managers due to the link with harmful algal blooms. In particular, legacy P creates a persistent challenge for eutrophication management in a range of aquatic systems, including wetlands, lakes, and estuaries, as a source of indirect, internal P loading. Following reductions in external P loads, internal sediment sources have been known to release bioavailable P back into the water column, undermining nutrient restoration goals. This study investigates the flux dynamics and longevity of sediment legacy P in three subtropical rivers-Amite, Tangipahoa, and Tickfaw-draining into the Lake Pontchartrain estuary. We employed a controlled laboratory incubation using intact and dredged sediment cores subjected to both aerobic and anaerobic treatments to quantify the flux of soluble reactive P over an 8-week period with regular surface water replacements. The soluble reactive phosphorus (SRP) flux under anaerobic water column conditions was three to five times higher than under aerobic conditions, with the most significant release occurring during the first 4 weeks. Following the fourth week, cores across all treatments observed a significant decrease in the rate of SRP released. Dredged cores showed consistently lower SRP flux across both aerobic and anaerobic treatments. These findings underscore the salient role of redox conditions and recent sediments in the mobilization of legacy P in river networks. Our work provides new evidence of the temporal limitation of internal P loading and the potential for strategic sediment management to complement external nutrient load reduction efforts to improve surface water quality.

Soil moisture, carbon, and nitrogen are vital factors affecting greenhouse gas (GHG) emissions in agricultural soils. However, research on GHG dynamics across different soil moisture regimes, ranging from simultaneous flooding-to-upland conversion, transition phases, to continuous flooding, and their interaction with crop straw and nitrogen (N) fertilizer amendments remains limited. To address this research problem, we conducted a laboratory study to investigate the impact of water regimes, rice straw (Oryza sativa L.), and N fertilizer on GHGs. The addition of rice straw and fertilizer significantly increased GHG emissions. N2O and CO2 emissions increased as soil moisture levels were converted from flooded conditions to 60% water-filled pore space (WFPS), while CH4 emissions decreased. The highest cumulative N2O and CH4 emissions were 0.85mg N2O-N kg-1 and 65.21mg CH4-C kg-1, respectively, in rice straw treatment, while cumulative CO2 emissions were highest (2003.69mg CO2-C kg-1) in rice straw + N fertilizer treatment. The NH4 + and NO3 - levels were highest with values of 202.43 and 63.72mg kg-1, respectively, in the rice straw + N fertilizer treatment during the transition phase. The highest levels of dissolved organic carbon (201.31mg kg-1) and microbial biomass carbon (425.92mg kg-1) were recorded in the rice straw treatments during the flooding and 60% WFPS phases, respectively. Our findings emphasize the critical role of soil moisture and organic amendments in regulating soil GHG emissions. Sustainable agricultural practices should focus on balancing soil management techniques to reduce GHG emissions while promoting long-term soil health.