Soil inorganic carbon (SIC), a potential carbon sink especially in arid and semi-arid environments, contributes to soil development, landscape stability, carbon (C) sequestration, and global C dynamics but due to the lack of SIC scientific reporting in most C sequestration research, its importance is unclear. A detailed overview of primary and secondary carbonate occurrence, formation, and importance is much needed to understand the role of pedogenic (PC)/secondary carbonate (a common biogeochemically derived soil mineral over time) in the SIC. The mechanisms involved in the formation of PC including carbon dioxide (CO₂) from microbial respiration and precipitation, silicate mineral weathering, dissolution, and reprecipitation are highlighted. The isotopic composition of carbonates related to biological C₃ or C₄ carbon fixation pathways and other paleoecologic and/or climactic factors responsible for new soil carbonate formation are discussed in detail. To address the lack of knowledge associated with SIC, this review attempts to highlight the currently known aspects of the literature, and briefly describe the formation and methodologies that can aid in addressing the research gaps surrounding SIC sequestration. The authors also suggest that greater focus needs to be provided on the actual measurement of SIC to develop a more comprehensive SIC inventory to provide sound data for future research direction, and modeling efforts and to predict C terrestrial storage and change efficiently.

Increased adoption of no‐till systems in the Northern Plains has led to an increased volume of post‐harvest crop residue. A cool climate coupled with short growing seasons benefits from a conservation tillage approach by increasing water storage in semi‐arid areas where weather conditions are variable each year. The short frost‐free period presents challenges for residue decomposition and the subsequent nutrient uptake period is reduced in heavy accumulated crop fields. A combination of soil management practices can be used to optimize nutrient utilization, particularly for nitrogen (N), including the use of cover crops, crop rotation and diversification, and variances in fertilizer form, method, and timing. Despite many management practices being effective in conserving N in the soil, they still may not meet nutrient demands for succeeding crops in short season and water‐ and N‐limited environments. Decomposition of crop residue is dependent on soil moisture, soil temperature, and the carbon/nitrogen (C/N) ratio of crop residue. Generally, post‐harvest crop residues have a wider C/N ratio than aged residue that accumulates on the soil surface over time. Adding fertilizer N may reduce the immobilization of nutrients near the soil surface of a post‐harvest residue in heavily accumulated crop fields, making it more available for utilization by plants. Recommendations for fertilizer N rates are inconsistent throughout the northern US for long‐term no‐till systems. This review highlights several decades of known research yet points to the continued gaps needed for producers to fully support fertilizer N recommendations for no‐till systems in temperate climates.

Core Ideas: Production‐scale conservation tillage systems had few effects on crop yields. Strip till had the least costs per hectare and may be more economical for farmers. Tillage affected only fungi/bacteria ratios out of 19 soil properties. Farmers’ presumed yield losses among tillage systems did not reflect actual yields. In the US upper Midwest, the narrow growing season causes many farmers to presume yield losses when reducing tillage. The purpose of this study was to determine how four production‐scale tillage systems affected residue cover, stand populations, crop yields, and soil chemical, biological, and physical properties. Tillage systems (chisel plow, fall strip‐till with shanks, spring strip‐till with coulters, and shallow vertical till) were continued for 4 yr. Tillage effects within a site were few and mixed (0.17–0.36 Mg ha⁻¹ difference), whereas site effects were common (0.50–3.00 Mg ha⁻¹ difference). Among 19 soil properties, only fungal/bacteria ratios differed among strip‐till with shanks (0.078) and strip‐till with coulters (0.066) at one site. Our results suggest that many farmers’ concerns about using conservation tillage practices do not necessarily translate into yield losses when compared to standard chisel plow practices. Economics and the level of erosion control among the tillage practices compared here, rather than yield alone, should guide farmer preferences.

Long winters in the Red River Valley (RRV) of eastern North Dakota and western Minnesota result in short growing seasons for corn (Zea mays L.)–soybean (Glycine max L. Merr.) systems. Historically, producers implement aggressive tillage to warm the soil, which has caused hesitation when considering reduced tillage systems. The association between soil warming–drying and crop yields via research at farmer-operated, production-scale systems practicing reduced tillage is lacking. A two-year study was conducted at three producer-operated, corn–soybean fields in the RRV with five soil series ranging from sandy loams to silty clays. Soil temperature (T), soil volumetric water content (θ), and crop yields were measured to evaluate the effects of soil warming and drying and crop performance under reduced tillage practices of vertical tillage (VT), strip tillage with shanks (STS), strip tillage with coulters (STC), and chisel plow (CP). Results showed that daytime soil T and θ in the tilled strips for STC and STS (i.e., in the plant rows) were similar to CP and significantly different from VT. The ST treatments demonstrated added benefits of higher soil θ between the tilled strips (i.e., between the plant rows) during the mid-growing season when plant water needs are at their highest. However, daily averaged soil T and θ demonstrated little to no significant differences among the tillage treatments. Moreover, crop yields were inconsistent with soil T and θ, indicating weak to no practical association in these on-farm settings.

North Dakota producers have adopted conservation tillage practices to conserve soil moisture and reduce wind and water erosion. As a result, an accumulation of crop residue has been observed but current recommendations encourage a fertilizer N credit in fields under no‐till for more than 6 yr. Producers are concerned that post‐harvest crop residues are not contributing to N needs of subsequent crops during the growing season. This study was established to assess N mineralization from common crop residue in conventional tillage systems using long‐term incubation studies in order to establish a baseline for future studies on no‐till systems. Three commonly cultivated North Dakota soil series were selected for study with seven residue treatments (varying C/N ratios) including corn (Zea mays L.), soybean [Glycine max (L.) Merr.], flax (Linum usitatissimum L.), forage radish (Raphanus sativus L.), winter pea (Pisum sativum L.), spring and winter wheat (Triticum aestivum L.), and a soil‐only control. Biweekly leachings were collected for nine incubation periods and analyzed for nitrate‐nitrogen (NO₃–N). Soils with higher organic matter (OM) resulted in increased soil N mineralization (Fargo [1.63 mg kg^–1 N] > Forman [0.65 mg kg^–1 N] > Heimdal–Emrick [0.38 mg kg^–1 N]). Radish and pea residues (narrow C/N ratios) were the only treatments showing N mineralization potential compared with the soil only controls. However, post‐harvest residues with wide C/N ratios (>25:1) promote N immobilization when compared with mineralization by the soil alone. These findings raise the question of whether the N credits for >6 yr of no‐till management are appropriate in the northern Great Plains.

The adoption of no-till management practices has increased in the United States over the last decade. In the state of North Dakota, approximately 5.7 million hectares of cropland is managed under no-till or conservation tillage management practices. Even though conservation tillage is known for building soil health, increasing soil organic matter, capturing soil moisture, and reducing wind and water erosion, it also presents a unique best management practice since an increased mass of crop residue remains on the soil surface. Producers are concerned about whether plant needs are being met by nitrogen fertilizer that is currently being applied based on current North Dakota recommendations for long-term no-till systems. A Forman clay loam soil (fine-loamy, mixed, superactive, frigid Calcic Argiudolls) was used in this study, as it represented glacial till soils of the region. We examined whether N mineralization from surface-applied crop residue would result in similar or different results when compared to crop residue mixed into the soil. Soil freeze-thaw contribution to soil N mineralization was also evaluated. Six residue treatments with different C/N ratios including corn (Zea mays L.), soybean (Glycine max L.), forage radish (Raphanus sativus L.), winter pea (Pisum sativum L.), spring wheat (Triticum aestivum L.), and winter wheat (Triticum aestivum L.) were used. Five 10–14-week cycles with a three-week freeze period between each cycle at 0 ºC were evaluated for NO₃-N production. Crop residues with a narrow C/N ratio contributed to greater instances of N mineralization during each incubation cycle, and the accumulation of crop residues with a wide C/N ratio over each incubation cycle following the first incubation did not offset the immobilization trends observed in the first incubation. A change in N mineralized in the untreated control soil during the last two incubation cycles may have been caused by freeze-thaw effects or a shift in microbial population due to a lack of fresh C inputs.