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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. [ABSTRACT FROM AUTHOR]

Corn (Zea mays L.) is an important cereal grain in many states and typically receives large N fertilizer inputs, irrespective of historical management. Tailoring N inputs to soil-specific conditions would help to increase efficiency of N use and avoid environmental contamination. A total of 47 trials were conducted on research stations and private farms in four different regions of North Carolina and Virginia from 2014 to 2016 to associate soil N availability with yield response to sidedress N application. Corn grain yield was 10.6 ± 3.4 Mg ha–1 on 36 sites and silage yield was 44.6 ± 8.2 Mg ha–1 on 11 sites. There was positive association between relative yield (i.e., yield without sidedress N application divided by yield with full fertilization) and levels of both plant available N (residual inorganic N + net N mineralization during 24 d) and the flush of CO2 following rewetting of dried soil during 3 d. Economically optimum N fertilizer requirement (EONR) at sidedress declined with increasing level of plant available N and soil-test biological activity (i.e., the flush of CO2). The scalable N factor for production at EONR declined from 20 kg N Mg–1 of grain (i.e., 1.1 lb N bu–1) with no soil biological activity to no N required with soil-test biological activity of 600 mg CO2–C kg–1 in a 3-d period (depth of 0–10 cm). The flush of CO2 when determined in spring at or prior to planting corn was considered an ideal soil-test indicator of soil biological activity due to its simple, rapid, and reliable characteristics related to potential soil N mineralization and corn yield responses to applied N fertilizer [ABSTRACT FROM AUTHOR]