Knowledge of how biochar impacts soil denitrification kinetics as well as the mechanisms of interactions is essential in order to better predict the nitrous oxide (N2O) mitigation capacity of biochar additions. This study had multiple experiments in which the effect of three biochar materials produced from corn stover (Zea mays L.), ponderosa pine wood residue (Pinus ponderosa Douglas ex Lawson and C. Lawson), switchgrass (Panicum virgatum L.), and their corresponding biomass materials (corn stover, ponderosa pine wood residue, and switchgrass) on cumulative N2O emissions and total denitrification in soils from two different landscape positions (crest and footslope) were studied under varying water-filled pore space (40, 70, and 90% WFPS). Cumulative N2O emissions were reduced by 30 to 70% in both crest and footslope soils. The effect of biochars and biomass treatments on cumulative N2O emissions and total denitrification were only observed at ≥40% WFPS. The denitrification enzyme activity (DEA) kinetic parameters, K s (half-saturation constant), and V max (maximum DEA rate) were both significantly reduced by biochar treatments, with reductions of 70-80% in footslope soil and 80-90 % in the crest soil. The activation energy (E a) and enthalpy of activation of DEA (ΔH) were both increased with biochar application. The trends in DEA rate constants (K s and V max) were correlated by the trends of thermodynamic parameters (activation energy E a and enthalpy of activation ΔH) for denitrifying enzyme activity (DEA). The rate constant V max/K s evaluated the capacity of biochars to mitigate the denitrification process. Denitrifying enzyme kinetic parameters can be useful in evaluating the ability of biochars to mitigate N2O gas losses from soil.

A common restoration treatment for saline-sodic soils involves improving soil drainage, applying soil amendments (e.g., CaSO 4 , CaCl 2 , or elemental S), and leaching with water that has a relatively low electrical conductivity. However, due to high subsoil bulk densities and low drainable porosities, these treatments many not be effective in glaciated dryland systems. A 3-yr field study conducted in three model systems determined the impact of chemical amendments (none, CaCl 2 , CaSO 4 , and elemental S) on plant growth, microbial composition, temporal changes in electrical conductivity (EC e ), and the relative sodium content (%Na). Chemical amendments (i) either reduced or did not increase maize (Zea mays), soybean (Glycine max), and sorghum (Sorghum bicolor) yields; (ii) did not increase water infiltration or microbial biomass as determined using the phospholipid-derived fatty acid (PLFA) technique; and (iii) did not reduce EC e or %Na. These results were attributed to high bulk densities and low drainable porosities that reducing the drainage effectiveness in the model backslope and footslope soils, the presence of subsurface marine sediments that provided a source for sodium and other salts that could be transported through capillary action to the surface soil, high sulfate and gypsum contents in the surface soil, and relatively low microbial biomass values. The results suggests that an alternative multistep saline sodic soil restoration approach that involves increasing exchangeable Ca +2 through enhanced microbial and root respiration and increasing transpiration and soil drainage by seeding full season deep rooted perennial vegetation should be tested.

CORE IDEAS (85 characters max)• Remote soil judging contests are a viable alternative to in-person contests.• Students gain more mastery of soil science concepts with hands-on practice.• Soil judging participation results in more favorable attitudes toward soil science.• Soil judging, regardless of contest format, is a precursor to a soil science career.

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