Soil Test Biological Activity with the Flush of CO2: III. Corn Yield Responses to Applied Nitrogen

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.