Late-split application of nitrogen on corn

The practice of applying a portion of N fertilizer during late vegetative growth of corn using high-clearance equipment has grown rapidly in the last few years, despite the absence of evidence supporting the profitability of this practice. We conducted trials at fifteen Illinois sites – six in which corn followed corn and nine in corn following soybean in 2016-2017. In each trial, six N rates ranging from 0 to 280 kg N ha-1 in increments of 56 kg N ha-1 were assigned to main plots. Two subplot treatments were 1) each rate applied as UAN solution injected at or near the time of planting, and 2) late-split N application with a portion applied at or near planting and the remaining 56 kg N ha-1 hand-applied near the base of the plants at tasseling. Grain protein content, grain N content, and chlorophyll concentration measurements were collected in the trials conducted at Urbana. Grain protein and N content were found to be very similar between application timings. Chlorophyll concentrations in late-split plots were found to be lower prior to application at VT compared to plots receiving all N early, however, readings taken after application indicated plants were capable of increasing chlorophyll concentration during reproductive growth stages. Appropriate curves were fitted to the data, and economically optimum N rates (EONR), the yields at those rates (EOY), and return to nitrogen (RTN) values were calculated. EONR values ranged from 125 to 214 kg N ha-1 in S-C trials conducted during 2016 with EOY values ranging from 14.6 to 15.0 Mg ha-1. EONR values in C-C trials conducted in 2016 ranged from 144 to 196 kg N ha-1 with yields at the EONR ranging from 14.3 to 14.7 Mg ha-1. EONR values in the S-C trials conducted during the 2017 growing season ranged from 135 to 233 kg N ha-1 with EOY values ranging from 9.2 to 16.6 Mg ha-1. EONR values ranged from 143 to 181 kg N ha-1 in the 2017 C-C trials with yields at these rates ranging from 12.9 to 14.5 Mg ha-1. RTN values ranged from $489 to $687 ha-1 in S-C 2016 trials, $690 to $1,1129 ha-1 in C-C 2016 trials, $387 to $730 ha-1 in S-C 2017 trials, and $180 to $933 ha-1 in C-C 2017 trials. The average RTN over the four S-C trials conducted in 2016 was $556 ha-1 when all N was applied early compared to $560 ha-1 when N was late split. The average RTN over the three C-C trials conducted in 2016 was $978 ha-1 when all N was applied at planting while the average RTN when N was late-split was found to be $983 ha-1. The average RTN for 2017 S-C trials when all N was applied early was $496 ha-1 compared to $476 ha-1 when N was late-split. The average RTN for 2017 C-C trials was $488 ha-1 when all N was applied early versus $463 ha-1 when N was late-split. While the 56 kg N ha-1 applied late was utilized to increase yields in some cases (at the lower N rates), it did not increase the return to N; with higher application costs, late-split N was less profitable than application of all of the N at planting. It appears that late-split application of the last increment of N is unlikely to be profitable in comparison to early application of all of the N, at least in productive soils.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste