Abstract Soil health assessments evaluate and monitor the effects of conservation management on soil properties. A popular measurement, permanganate oxidizable carbon (POXC), is routinely included in these assessments. The standard POXC protocol calls for air‐dried soil samples, but commercial laboratories typically dry samples in a forced‐air oven before routine analysis. In order to evaluate if heat would change POXC measurements, we treated soil (52 silty clay loam and 51 sandy loam samples) with oven drying at 45 and 65 °C and compared their POXC values with those from air‐dried samples. We also examined relationships between POXC values and soil organic matter, pH, and electrical conductivity across drying treatments. Drying soil did not substantially change POXC values for either soil texture and did not change the relationships between POXC and other measured soil properties. This work suggests that commercial laboratories could perform POXC analysis on soil samples dried using heat.

Microbial carbon-use efficiency (CUE) is defined as the portion of carbon (C) incorporated into biomass relative to the total carbon consumed and plays a pivotal role in regulating microbially-mediated C and nutrient transformations in soil. However, little is understood about how CUE is impacted by edaphic properties, like soil moisture. Soil moisture physically regulates microbial activity through its effects on both water potential and water content. Low water potential can result in high, compensatory intracellular solute concentrations that may inhibit biochemical functions through cytoplasmic desiccation, whereas low soil water content results in thin water films that can limit substrate diffusion, reducing microbial access to dissolved substrates. Because these two aspects of soil moisture may affect microbial respiration differently than C assimilation, they may have different effects on CUE. The purpose of this research was to evaluate the relative importance of water potential and water content in regulating CUE of soil microbial communities. Moist soil incubations of a sandy loam soil were used to determine the impact of both aspects of soil moisture on CUE, and soil slurries were used to determine the impact of water potential alone. Both C-13-acetate and N-15-ammonium were added to moist soils and slurries to quantify gross rates of C and N transformations. In moist soils, acetate assimilation and respiration rates and gross N mineralization and immobilization rates increased exponentially with increasing soil moisture (3.0 to 0.03 MPa). In contrast, acetate assimilation and respiration and gross N transformation rates remained constant in soil slurries across a similar water potential gradient, created by modifying solute concentrations. Similarly, values of CUE in moist soils increased exponentially with increasing soil moisture, whereas slurry values of CUE remained constant across the soil water potential gradient. Because no changes in rates and CUE were observed in slurries, changes observed in moist soils were attributed to limited substrate diffusion associated with low water contents rather than to adverse physiological effects associated with low water potentials. Results of this study demonstrate that limited substrate diffusion is the primary physical mechanism through which soil moisture regulates microbially-mediated C and N transformation rates and CUE in this sandy loam soil.

Soil salinization is a global issue affecting 831 million ha of arable land and resulting in approximately US$27.3 billion in crop losses annually. The purpose of our research was to determine the effects of natural gradients in soil salinity on field-grown corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in silty clay loam and sandy loam soils in southeastern North Dakota. Both corn and soybean yield were hand-harvested at the ends of the 2014 and 2015 growing seasons and related to the electrical conductivity (ECe) of the root zone using the modified discount response function (MDRF). Neither corn nor soybean yields demonstrated significant declines when grown in finer-textured soil. Contrarily, when corn and soybean were grown in sandy loam soils, significant declines occurred. Calculated values at which 50% yield reductions occurred (EC50) in sandy loam soil resulted in salinity tolerance indices (STI) of 9.68 for corn and 7.04 for soybean. The lack of yield declines for both crops in silty clay loam soil may indicate a reduced effect of salinity stress in finer textures. Additionally, the composition of ions in the soil solution may also play a role in crop response to salinity.

Soil salinization may negatively affect microbial processes related to carbon dioxide (CO2) and nitrous oxide (N2O) emissions. A short-term laboratory incubation experiment was conducted to investigate the effects of soil electrical conductivity (EC) and moisture content on CO2 and N2O emissions from sulfate-based natural saline soils. Three separate 100-m long transects were established along the salinity gradient on a salt-affected agricultural field at Mooreton, North Dakota, USA. Surface soils were collected from four equally spaced sampling positions within each transect, at the depths of 0-15 and 15-30 cm. In the laboratory, artificial soil cores were formed combining soils from both the depths in each transect, and incubated at 60% and 90% water-filled pore space (WFPS) at 25 degrees C. The measured depth-weighted EC of the saturated paste extract (ECe). across the sampling positions ranged from 0.43 to 4.65 dS m(-1). Potential nitrogen (N) mineralization rate and CO2 emissions decreased with increasing soil ECe, but the relative decline in soil CO2 emissions with increasing ECe was smaller at 60% WFPS than at 90% WFPS. At 60% WFPS, soil N2O emissions decreased from 133 mu g N2O-N kg(-1) soil at ECe < 0.50 dS m(-1) to 72 ug N2O-N kg(-1) soil at ECe = 4.65 dS m(-1). In contrast, at 90% WFPS, soil N2O emissions increased from 262 mu g N2O-N kg(-1) soil at ECe = 0.81 dS m(-1) to 849 sg N2O-N kg(-1) soil at ECe = 4.65 dS m(-1), suggesting that N2O emissions were linked to both soil ECe and moisture content. Therefore, spatial variability in soil ECe and pattern of rainfall over the season need to be considered when up-scaling N2O and CO2 emissions from field to landscape scales.

Soil salinity is a global issue threatening land productivity, and estimates predict that 50% of all arable land will become impacted by salinity by 2050. Consequently, it is important to have a fundamental understanding of crop response to salinity to minimize economic loss and improve food security. While an immense amount of research has been performed assessing corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] response to salinity, there are few, if any, comprehensive reviews compiling previously published literature. This review provides a detailed description of our current knowledge on the impacts of salinity on corn and soybean growth and development. Both osmotic stress and specific ion toxicities with respect to corn and soybean are addressed. Additionally, potential areas of future research are recommended.Core Ideas Review of salinity's effects on corn and soybean growth and development. Impacts of osmotic stress and specific ion toxicities discussed. Potential areas of future research addressed.