Soil-test biological activity with the flush of CO2: V. Validation of predicted nitrogen for corn production

Authors: Franzluebbers, Alan

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2019
Publication Date: 3/13/2020
Citation: Franzluebbers, A.J. 2020. Soil-test biological activity with the flush of CO2: V. Validation of predicted nitrogen for corn production. Agronomy Journal. 112:2188-2204.

Interpretive Summary: Soil testing for nitrogen availability is now possible with a rapid and reliable indicator that assesses soil biological activity. A scientist from USDA-Agricultural Research Service in Raleigh NC evaluated corn grain yield response to sidedress nitrogen application in a series of 111 field trials throughout North Carolina, South Carolina, and Virginia. Yield response to sidedress nitrogen application validated an earlier finding that supports determination of soil-test biological activity as an indicator to modify nitrogen fertilizer requirements on a site-specific basis. Strong association occurred between soil-test biological activity and net nitrogen mineralization. Management systems that promote soil health with greater soil-test biological activity are able to provide a greater supply of nitrogen that can be used to lower nitrogen fertilizer costs and overcome potential nitrogen deficits during adverse weather conditions. Adjustment of nitrogen fertilizer rates based on cost-to-value threshold (i.e. fertilizer cost to grain value) should be an important component of any fertilizer recommendation system. This study validated the concept of nitrogen fertilizer adjustment on a site-specific basis with knowledge of soil-test biological activity. These results will be valuable for farmers wanting to make efficient applications of nitrogen to enhance profit and steward natural resources.

Technical Abstract: Production of corn (Zea mays L.) requires significant N availability to reach maximum yield potential. Nitrogen fertilizer recommendations generally have ignored site-specific conditions and have focused more on total N demand for representative soils across a region. Recent evidence suggested that site-specific conditions of the soil surface (0-10-cm depth) could inform the magnitude of yield response to applied N fertilizer. This approach was tested further on 111 fields in Coastal Plain, Piedmont, and Blue Ridge regions (states of NC, SC, and VA). Plant-available N (sum of residual inorganic N and net N mineralization during a 24-d aerobic incubation) was negatively associated with economically optimum N rate scaled to grain production level. Soil-test biological activity as a simple, rapid, and reliable indicator of net N mineralization was also predictive of economically optimum N rate. Relationships between the N factor for economically optimum production and soil-test biological activity validated an earlier assessment. Whether evaluation was on private farm or research station made little difference in this relationship, but greater soil-test biological activity was obtained from private farms, as well as from fields with minimum tillage, multi-species cover cropping, and amendment with animal manures. Results imply that farmers are making choices to improve soil health condition of surface soil and these choices can lead to lower requirement for N fertilizer inputs. A paradigm shift towards site-specific N management should focus on soil biological activity and its association with N mineralization as indicators of soil health to increase profit and reduce environmental impacts.