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

Authors: Franzluebbers, Alan; SHOEMAKER, ROBERT - Virginia Department Of Conservation And Recreation

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2020
Publication Date: 4/25/2020
Citation: Franzluebbers, A.J., Shoemaker, R. 2020. Soil-test biological activity with the flush of CO2: VI. Economics of optimized N inputs for corn. Agronomy Journal. 112:2848-2865.

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 collaborated with a nutrient management specialist from Virginia Department of Conservation and Recreation to evaluate the economic outcomes of using a soil-based nitrogen prediction system compared with current nitrogen recommendation systems in North Carolina and Virginia. Dollar savings were calculated from 99 field trials that had four nitrogen fertilizer rates applied to determine the actual cost-effective rate of nitrogen application for corn grain production. On average, the soil-based system performed as good, and often better, than current recommendation systems. This positive result was because the change in how soil supplies nitrogen with recent management could be better assessed with knowledge of soil-test biological activity than with broad categorical adjustments or without any consideration of management in some systems. Savings up to $50/acre could be achieved with more precise nitrogen application using this soil test. This study demonstrated that 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.

Technical 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 biological soil testing approach compared with current approaches in the USA, and specifically in North Carolina and Virginia. The soil-based approach addressed management history through cumulative effects on soil-test biological activity as an indicator of soil health. Evaluation was from a survey of 99 fields North Carolina, South Carolina, and Virginia. 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 three levels of cost-to-value threshold (i.e. 5, 10, and 20 kg grain kg-1 N). Economic return was often greater using the soil-based method compared with current recommendation systems ($8.77 + 4.01 ha-1, $19.21 + 3.30 ha-1, and $73.44 + 3.27 ha-1 with low, medium, and high cost-to-value thresholds, respectively; mean + standard error). Greater economic return on fields with higher versus lower soil-test biological activity [$0.03 ha-1 (p=0.52), $0.25 ha-1 (p<0.001), and $0.36 ha-1 (p<0.001) for every unit increase in soil-test biological activity (mg kg-1) at low, medium, and high cost-to-value thresholds, respectively] confirmed the validity of the approach. 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.