Evaluation of the Soil Health Nutrient Tool for Corn Nitrogen Recommendations across the Midwest.

Use and development of soil biological tests for estimating soil N availability and subsequently corn (Zea mays L.) fertilizer N recommendations is garnering considerable interest. The objective of this research was to evaluate relationships between the Soil Health Nutrient Tool (SHNT), also known as the Soil Health Tool or Haney test, and the economically optimum N rate (EONR) for corn grain yield at 17 sites in eight Midwest states in 2016. Trials were conducted with a standard set of protocols that included a nonfertilized control plus six N rates applied at planting or as a split between planting and sidedress, soil samples for the SHNT prior to planting, and grain harvest at physiological maturity, and determination of EONR for the two N application timings. Results indicated that SHNT recommendations with expected yield accounted for ≤30% of the variation in EONR. Two components of the SHNT not directly used in the SHNT N recommendation for corn, the soil health calculation and the 24 hr flush of CO₂ following rewetting of soil (Solvita), accounted for the most variation in EONR. The soil health calculation and Solvita were highly correlated (R² = 0.98) and subsequently both accounted for about one-half (R² = 0.48) of the variation in EONR for N applied at planting and nearly two-thirds (R² = 0.61) of the variation for N applied as a split. Thus, these two components, but especially Solvita because it costs less to determine than and is highly correlated to the soil health calculation, may help improve N recommendations for corn in the Midwest.