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Fragipans are dense subsurface soil layers that severely restrict root penetration and water movement. The presence of shallow fragipan horizons limits row crop production. We hypothesized that the roots of cover crop might improve soil physiochemical properties and biological activity, facilitating drainage and increasing effective soil depth for greater long-term soil water storage. To evaluate annual ryegrass as one component of a cover crop (CC) mix for promoting the characteristics and distribution of soil water, on-farm studies were conducted at Marion and Springerton in southern Illinois, USA. Soil samples were collected at 15 cm increments to 60 cm (Marion) and 90 cm (Springerton) depths during the fall of 2022. Both sites had low total soil carbon and nitrogen contents and acidic soil pH (≤6.4). A soil water retention curve was fitted using the van Genuchten equation. At Springerton, the CC treatment increased saturated (thetaS) and residual (thetaR) soil water contents above those of the no cover crop (NCC) at the 60–75 cm and 75–90 cm depths. Changes in volumetric soil water content were measured using a multi-depth soil water sensor for the Springerton site during late July to early August of the soybean growing phase of 2022; NCC had higher soil water than CC within the 0–15 cm depth, but CC had higher soil water than NCC at the 30–45 cm depth. These findings indicate that cover crop mix has the potential to improve soil water movement for soils with restrictive subsoil horizon, possibly through reducing the soil hydraulic gradient between the surface and restrictive subsurface soil layers. [ABSTRACT FROM AUTHOR]

Management practices such as relay cropping, cover crops, and no-tillage may promote soil health in the North Central United States. However, soil health indicators in corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] systems involving multiple management practices are not well documented. The objective of this study was to determine the sensitivity of soil health metrics and the Soil Management Assessment Framework (SMAF) to contrasting management systems with different tillage, crops, and fertilization in a North Central US Mollisol. Different management systems, including conservation tillage and nitrogen fertilization strategies, cover cropping, and camelina [Camelina sativa (L.) Crantz] relay intercropping, were compared to a conventional corn–soybean system. Different systems did not affect most soil health indicators compared to the conventional system. Aggregate stability was the only indicator to change due to management, where no-till with cover crops increased aggregate stability by 38% compared with camelina relay cropping. The SMAF scores for all the soil quality indices were unaffected by treatments but displayed high values of over 90%. Overall, crop yields were more closely related to weather conditions and management systems than to soil health indicators. Soybean yields were decreased (between 1 and 2 Mg ha−1 ) in the camelina relay cropping system, while corn yields were lower (up to 70%) in the treatment that received no N fertilization. Ultimately, these findings suggest that soil health indicators are resilient to change due to management in these highly productive Mollisols and may not be closely associated with crop yields. [ABSTRACT FROM AUTHOR]

Farmland within the Williston Basin of North Dakota was the site of the largest terrestrial oil spill to date in the United States in 2013. Over 3200 m3 of oil was released into the topsoil and subsoil, creating a risk to soil, water, and air resources. The purpose of this document is to provide a summary of results from a 7‐year project investigating the impacts of how thermal desorption (TD), the method used to remediate topsoil and subsoil, impacted contaminant reduction, soil function, and plant productivity simultaneously with site remediation. Soil disturbance and TD decreased soil organic matter and microbial communities, resulting in decreased soil function and plant production. However, TD did not reduce soil microbial recovery 4 years after treatment. Blending TD‐treated soil with uncontaminated topsoil appeared to minimize these negative effects and promote recovery of soil function. These findings provided critical information to stakeholders in the understanding of soil remediation and reclamation in this region. Core Ideas: We synthesize research conducted at a terrestrial oil spill site concurrently with site remediation.Thermal desorption reduces contaminant concentration after oil spill but harms soil function and plant production.We thoroughly document the results of thermal remediation, but we cannot compare results to other techniques.This information can be used by stakeholders to make more informed decisions after future incidents. [ABSTRACT FROM AUTHOR]

Maximizing cover crop biomass production is key to agroecosystem service delivery. Cover crop biomass accumulation is particularly important in corn (Zea mays L.) silage cropping systems due to the high rate of crop biomass removal that leaves the soil surface mostly bare from early fall until planting the following spring. We evaluated how weather factors affect rye (Secale cereale L.) cover crop shoot biomass in different rotations including corn silage and soybean [ Glycine max (L.) Merr.] and their influence on soybean and corn silage yields. In a 13-year field study in a corn silage-soybean rotation, we assessed rye biomass and main crop yields when rye was planted after one or both main crops every year. Rye after silage produced 1.98 Mg ha−1 more shoot biomass than rye after soybean. Thermal time (expressed as growing degree days) had a greater impact than precipitation on the shoot biomass of rye cover crop. A threshold of 800 growing degree days (0°C base) in the fall was determined, above which final biomass was not limited by fall thermal time (R2=0.58). Rye biomass was most strongly affected by fall thermal time (below 800 growing degree days) after soybean and by spring growing degree days and precipitation after corn silage. Rye cover crop inclusion did not decrease corn silage and soybean yields in 12 out of 13 years. Fall growing degree days below a threshold may limit the maximum potential for spring rye cover crop growth, but spring growing degree days or precipitation may prevent maximum growth from occurring when exceeding 800 growing degree days. Planting rye cover crops in both phases of the rotation did not affect cover crop biomass or main crop yields and may hold a greater potential to protect the soil than planting after only one crop in the rotation. Cropping systems that allow a rye cover crop to be planted early enough to accumulate 800 growing degree days in the fall have the best potential for high cover crop biomass production. • We studied GDD and precipitation effects on cereal rye cover crop biomass planted after corn silage and soybean harvest. • Rye after corn silage produced on average 1.98 Mg ha−1 more shoot biomass than rye after soybean. • Final biomass was not limited by fall GDD when more than 800 GDD were accumulated in the fall. • Rye biomass was most strongly affected by fall GDD after soybean and by spring GDD after corn silage. • Rye cover crop inclusion decreased corn silage and soybean yields in only one of 13 years. [ABSTRACT FROM AUTHOR]

Harvesting corn (Zea mays L.) stover for use as bioenergy feedstock may provide short‐term economic benefits and perhaps improve grain yield in continuous corn systems, but excessive stover removal may lead to long‐term depletion of soil C stocks. To better quantify the impacts of stover harvest on the soil C balance, we investigated CO2 fluxes under three harvest treatments (none, moderate, and high) in three continuous corn systems: (a) no tillage and no biochar applications, (b) chisel plowing with biochar amendments, and (c) chisel plowing without biochar amendments were quantified. We sampled static chambers 14, 13, and 15 times in 2010, 2011, and 2012, respectively, and the measurements were used to calibrate the Agricultural Production Systems sIMulator model. Although CO2‐C emissions did not differ among the three systems, both moderate (approximately 30%) and high (approximately 60%) stover removal rates reduced simulated CO2‐C emissions by nearly 10% and more than 22%, respectively. Despite these reductions in CO2 flux, the sum of CO2‐C and stover C exceeded CO2‐C losses in those plots without stover removal. This finding suggested soil C depletion was occurring for the soil and crop management practices used, even though depletion was not evident after 3 years. Application of biochar increased soil C levels, suggesting it may be able to offset some C losses. We conclude that for sustainable, highly productive agroecosystems that include stover harvest, all agronomic practices must be optimized to minimize C losses and maintain soil quality. [ABSTRACT FROM AUTHOR]

Alley-cropping systems that pair economically important tree species with crop production in alleyways have the potential to diversify outputs and improve resource use efficiency. However, management practices are more complex because trees and crops have different nutrient requirements and access different depths in the soil profile. Foliar nutrient concentrations are often used to determine fertility plans for fruit and nut production orchards, but these recommendations may not be appropriate in integrated tree and crop production systems. This research describes foliar nutrient concentrations in three different tree species, red oak (Quercus rubra L.), pecan [Carya illinoinensis (Wangenh.) K. Koch], and black walnut (Juglans nigra L.), at an alley-cropping site in northwest Arkansas, USA from 2004 to 2012. Foliar nutrient concentrations did not differ in trees fertilized by poultry litter when compared to those receiving synthetic N fertilizer. Concentrations of nutrients changed over time in all three species, with Mg and Ca increasing and N, K, S, Fe, and Na decreasing as trees aged. A principal components analysis indicated that leaf nutrient levels in oak and pecan were much more similar to each other than to black walnut. Some of the foliar nutrient concentrations identified in this study were inconsistent with sufficiency ranges reported in fruit and nut production orchards. However, given the multiple aims of an alley-cropping system, these inconsistencies may not represent deficiencies in available nutrients for these tree species. [ABSTRACT FROM AUTHOR]

Purpose: Natural degradation of petroleum hydrocarbons (PHC) is a crucial process to consider when managing contaminated soils. However, the degradation rate is dictated by site-specific environmental factors and contaminant characteristics, so it is highly variable. Thus, region-specific research is required to determine the capacity of natural degradation processes to reach cleanup goals. This study describes the natural degradation of low levels of Bakken crude oil contamination in the Northern Great Plains, USA.Materials and methods: Soils contaminated by PHC from an accidental release of Bakken crude oil in western North Dakota, USA, were used to construct research plots adjacent to an active remediation site. The plots had four different initial PHC concentrations, 1400, 700, 220, and 100 mg kg−1, and they were monitored over two growing seasons under crop production. The wheat (Triticum aestivum L.) and field pea (Pisum sativum L.) grown in the plots were assessed for uptake of polycyclic aromatic hydrocarbons (PAH).Results and discussion: After two growing seasons under crop management, PHC concentrations were reduced between 46 and 53%. Neither the incorporation of composted manure nor the depth of sampling had any effect of PHC reduction, indicating that initial concentration is the driving factor in determining how long it will take to meet a given threshold. Half-life values ranged from 455 to 573 days, which is critical information for land managers determining the best remediation approach. Notably, crops grown in these contaminated soils did not show increased risk of plant uptake of PAHs.Conclusions: Overall, these findings indicate that soil PHC concentrations decrease while producing common agricultural crops in this region, and the crops grown in these contaminated soils show no increased risk to crop safety. Thus, depending on specific project goals, continuing a normal crop rotation may be a viable management strategy for low-level soil contamination in this region. [ABSTRACT FROM AUTHOR]

Core Ideas: Surface energy balance was quantified with micro‐Bowen ratio instrumentation.Surface energy balance was similar over native topsoil and soils treated with thermal desorption.Thermal desorption did not alter soil temperature dynamics or evaporation.A mix of topsoil and thermal desorption–treated soil matched surface energy balance of topsoil best. Remediation efforts to reduce contaminant concentrations in soils often alter soil properties. Since these alterations can affect the capacity of soil to function, their extent and magnitude may dictate future land use. This study addresses the suitability of soils for agricultural production after remediation of petroleum hydrocarbons using ex situ thermal desorption by quantifying the daytime surface energy balance prior to the growing season. The energy balance was quantified using micro‐Bowen ratio instrumentation to compare non‐contaminated topsoil (A) to both subsoil materials treated by thermal desorption (TD) and a 1:1 mixture (v/v) of TD and A (TDA). Despite differences in soil characteristics, the net radiation, soil heat flux, latent heat flux, and sensible heat flux were each similar among the three reclamation conditions over a period of 18 d. The fluctuations in these fluxes between the three conditions were attributed to natural variability, and they were not large enough to induce apparent inconsistencies in soil temperature dynamics or evaporative losses. Overall, these findings suggest the surface energy balance in thermal desorption–treated soils is similar to that of the native topsoil and that using a mixture of treated soils with native topsoil may even be a better representation of pre‐disturbance conditions. [ABSTRACT FROM AUTHOR]

• The surface energy balance is a useful way to assess the effects of tillage. • Few studies describe the relationship between tillage and surface energy balance. • Tillage practices typically increase available energy at the soil surface. • Partitioning of increased energy due to tillage is dictated by soil water content. Tillage is commonly implemented worldwide to improve crop productivity by optimizing soil temperature and moisture, reducing penetration resistance of the seedbed, and suppressing weeds. However, these benefits are accompanied by drawbacks, including increased erosion and loss of soil organic matter. Research continues on how to maximize benefits and minimize drawbacks of tillage in a range of agricultural systems. The surface energy balance (SEB) may be a promising avenue for future tillage research because it describes the partitioning of energy into compartments crucial to crop productivity, especially heating the soil and evaporating water. Despite this relevance, very little research addresses the effects of tillage on the SEB, and the existing literature does not adequately describe the relationship between these two topics. The aims of this review are to identify research that has been completed on the subject, synthesize current knowledge, and propose topics for continuing research. This review suggests that alterations to soil surface cover, surface roughness, and near-surface porosity caused by tillage are reflected in changes in the SEB, with the greatest effects evident during wetting-drying cycles. The total available energy is increased following tillage, but the magnitude of change and partitioning of that energy is not understood, which directly relates to the energy available for heating the soil and evaporating water. Future research should focus on quantifying the magnitude of effects of tillage on the SEB, how those effects change over time, and identifying any other indirect effects that may inform better management decisions. [ABSTRACT FROM AUTHOR]