United States Midwest Soil and Weather Conditions Influence Anaerobic Potentially Mineralizable Nitrogen

Nitrogen provided to crops through mineralization is an important factor in N management guidelines. Understanding of the interactive effects of soil and weather conditions on N mineralization needs to be improved. Relationships between anaerobic potentially mineralizable N (PMNₐₙ) and soil and weather conditions were evaluated under the contrasting climates of eight US Midwestern states. Soil was sampled (0–30 cm) for PMNₐₙ analysis before pre-plant N application (PP₀N) and at the V5 development stage from the pre-plant 0 (V5₀N) and 180 kg N ha⁻¹ (V5₁₈₀N) rates and incubated for 7, 14, and 28 d. Even distribution of precipitation and warmer temperatures before soil sampling and greater soil organic matter (SOM) increased PMNₐₙ. Soil properties, including total C, SOM, and total N, had the strongest relationships with PMNₐₙ (R² ≤ 0.40), followed by temperature (R² ≤ 0.20) and precipitation (R² ≤ 0.18) variables. The strength of the relationships between soil properties and PMNₐₙ from PP₀N, V5₀N, and V5₁₈₀N varied by ≤10%. Including soil and weather in the model greatly increased PMNₐₙ predictability (R² ≤ 0.69), demonstrating the interactive effect of soil and weather on N mineralization at different times during the growing season regardless of N fertilization. Delayed soil sampling (V5₀N) and sampling after fertilization (V5₁₈₀N) reduced PMNₐₙ predictability. However, longer PMNₐₙ incubations improved PMNₐₙ predictability from both V5 soil samplings closer to the PMNₐₙ predictability from PP₀N, indicating the potential of PMNₐₙ from longer incubations to provide improved estimates of N mineralization when N fertilizer is applied.