For nitrate-nitrogen reduction, the strategy presents a scenario in which MRTN adoption for applied nitrogen could reduce losses by 10% per acre. IFCA’s program is focused on identifying farmers to place nitrogen rate trials in their fields and ensuring proper implementation of the trials using University of Illinois protocols to ensure quality data for analysis. IFCA and Illinois receive funding from NREC to manage the trials. Nitrogen rates of 0, 50, 100, 150, 200, and 250 pounds per acre are replicated three times in each field, and data collect-ed at harvest determines the corn response to different applied nitrogen rates, timing, and sources.
The University of Illinois Department of Crop Sciences analyzes harvest data, which is uploaded each year to the MRTN Calculator (cnrc.agron.iastate.edu). These ongoing nitrogen rate trials ensure that the MRTN for corn in Illinois are updated each year, thus ensuring actual on-farm yield response to nitrogen, from all regions of the state, is factoring into the recommendation system. Individual field trial results from 2014–20 are available at ifca.com/4R/Trials. Figure 4.27 illustrates one example of an ongoing nitrogen rate trial.
The nitrogen rate trial in Figure 4.27 illustrates how this approach to nitrogen management incorporates the variability that is a universal feature of nitrogen response trials. These trials alternate between two similar fields with corn following soybean each time. While the average optimum nitrogen rate over the seven years was only 162 lb N, the MRTN approach, which maximizes the dollar return using a set of results shows a best nitrogen rate (for 2021) of 195 lb N per acre.
The map in Figure 4.28 shows the locations of on-farm nitrogen rate trials performed in 2019 and 2020, in all regions of the state. The map also illustrates the north, central, and south climate and soil regions in the land grant university nitrogen rate calculator. The central region includes a rate recommendation for the Lake Springfield watershed. Farmers can access the nitrogen rate calculator online, or as a free app to determine optimum economic and agronomic nitrogen rates.
