By John Boyum
In 2015 and 2016, the Minnesota Department of Agriculture (MDA) partnered with Fillmore SWCD, Wabasha SWCD, University of Minnesota, and University of Minnesota Extension to implement 103 on-farm nitrogen trials. Participating farmers and crop advisers were able to compare nitrogen rate, timing, source, stabilizer, rate after manure, and rate with first year corn following alfalfa.
2015 and 2016 proved to be excellent growing conditions that supported the natural processes for obtaining nitrogen from the soil (mineralization). This can be a very important source of nitrogen for your soil. In both years there was not a statistical difference between replicated nitrogen comparisons on most on-farm trials. In many cases, higher nitrogen (N) rates did not support a significantly higher yield.
2015 and 2016 corn on corn trials averaged 212-214 bu/ac with an average rate of 178-182 lbs N/ac. The corn following soybean trials averaged 215-217 bu/ac with an average rate of 151-153 lbs N/ac. The University of Minnesota guidelines maximum return to nitrogen (MRTN) at the 0.10 ratio for C-C is 155 lbs N/ac, acceptable range 145-170 lbs N/ac. For C-SB the MRTN at the 0.10 ratio is 120 lbs N/ac, acceptable range 105-130 lbs N/ac.
Of the 103 sites, eight of them had in-season soil nitrate tests, chlorophyll readings, grain and stover samples, stalk nitrate and residual soil nitrate tests. With these tests we are able to look at total corn N uptake, percent N supplied by the soil, percent N fertilizer recovery, bushels produced per unit of N, and amount of residual soil nitrate left in the soil after harvest. Stalk nitrate tests were variable, but on average higher N fertilizer rates resulted in residual stalk nitrate in the excessive range, indicating the crop had access to more N than it needed.
The University of Minnesota took the lead on five full N rate response trials. In 2016, the results from the three advanced scientific plots showed the maximum return to N rate ranged from 100-142 lb N/ac for both corn following soybean and corn following corn with average yields of 233 bu/ac. Lower than expected N fertilizer response for the corn following corn plots and no response to the split applied rates were the result of ideal growing conditions and precipitation during the first half of the 2016 growing season.
These on-farm trials were part of the Southeast Minnesota Nitrogen Best Management Practice Outreach Program and the Nutrient Management Initiative. They would not be possible without the excellent cooperation of the farmers, crop advisors and project partners. Thank you to all the participants in these programs. If you are interested in participating or would like more information, please contact John Boyum at the Fillmore SWCD (507) 765-3878, ext. 3 or Dawn Bernau, Minnesota Department of Agriculture (507) 206-2881. For additional information on the Nutrient Management Initiative, please visit www.mda.state.mn.us/nmi. Funding provided by the State of Minnesota’s Clean Water Fund (from the Clean Water Land and Legacy Amendment).