Soil‐test biological activity with the flush of CO₂: VI. Economics of optimized nitrogen inputs for corn

Abstract Standard N fertilizer rates for corn ( Zea mays L.) production are often based on yield goal and a simplified N factor. Unfortunately, simplified systems generally ignore management history that affects soil health condition. We analyzed economic return to N fertilizer investment using a soil‐test biological activity (STBA)‐based approach compared with current approaches in the United States, and specifically in North Carolina (NC) and Virginia (VA). The STBA‐based approach addressed management history on 99 fields through cumulative effects on biological activity as an indicator of soil health. Economically optimum N fertilizer rate was determined for each field from replicated, small‐plot trials with four N rates applied to corn at sidedress and using four levels of cost‐to‐value threshold (CVT; i.e., 5, 10, 15, and 20 kg grain kg −1 N). Economic return was often greater using the STBA‐based method compared with current recommendation systems (US$4.10 ± 4.96 ha −1 , $23.63 ± 5.30 ha −1 , $49.36 ± 5.63 ha −1 , and $83.22 ± 6.81 ha −1 with low, medium, high, and very high CVTs, respectively; mean ± standard error). Greater STBA led to greater economic return (i.e., $0.03 ha −1 [ p = .58], $0.23 ha −1 [ p < .001], $0.28 ha −1 [ p < .001], and $0.33 ha −1 [ p < .001] for every unit increase in STBA [mg kg −1 ] at low, medium, high, and very high CVTs, respectively). Farmers can increase profit by adopting soil‐health building practices and adjusting N fertilizer inputs in their nutrient management plan in response to conserved nutrient cycling in the biologically active organic fraction.