Research performed in 2016-17 by the NRCS in cooperation with Cronin Farms was designed to evaluate the impacts of nitrogen rates and application methods on corn yields seeded into full-season cover-crop residue.
Corn (DK 45-64) was no-till planted on May 4, 2017. Seeding rate was 23,800 pls per acre. The field had been planted to a 12 species cover crop on July 10, 2016 and grazed in December 2016 and January 2017. Soil samples were taken from the area on April 17, 2017. Results indicated 30 lbs. of Nitrate-N/acre in the top two feet. There were five nitrogen fertilizer treatments (Table 1). The treatments varied in nitrogen fertilization rate and application method. Treatments were replicated three times. Nine pounds of nitrogen was applied with pop-up fertilizer at planting (banded on the seed row) to all plots. Three treatments received no side-band nitrogen with the planter. Three treatments received 51 lbs. of N/acre as urea applied in a side band 2.5 inches to the side of the corn row and at the same depth as the seed. This produced a total of 60 lbs. of fertilizer N/acre (all planter placed) on one treatment A field sprayer was used to apply urea-ammonium nitrate liquid fertilizer at various rates on the remaining plots to achieve treatments 69 lbs. of N/a (9 pop-up and 60 UAN); 120 lbs. of N/acre (9 pop-up, 51 side-band, and 60 UAN stream); 129 lbs. of N/acre (9 pop-up, 120 UAN stream); and 180 lbs. of N/acre (9 pop-up, 51 side-band, and 120 UAN stream). Total N available to the crop was 30 lbs. of N/acre greater than the fertilizer applied.
Yield and lbs. of N/bushel results followed by the same letter were not different at 0.01 probability. All plots received 9 lbs. of N/acre in a pop-up fertilizer banded in proximity to the seed. Net return was calculated using $0.40/lb. of N for the nitrogen fertilizer applied and $2.80/bu. for the corn. All treatments also had 30 lbs. of nitrate-N/acre in the soil.
The N fertilizer-yield response curves experienced in this trial are typical of yield response curves experienced in this area when yield levels are above yield goals. It shows the N efficiency falls below 1 lb. of N/bushel of corn. This is higher efficiency than is assumed when making nitrogen recommendations. Differing weather and soil characteristics lead to differences in N efficiency. The fact that protein content of the grain did not increase at the highest N rate as compared to the other high yielding rates indicates that N was adequate to maximize yield. Mineralization probably played a role in supplying fertility to the corn during the grain filling period.
The most interesting (and predictable) aspect of these data is the consistent response to fertilizer placement. This difference was eight bushels where all the N was placed vs where it all was broadcast (except the pop-up). The difference was smaller where only part of the total N was placed. The original design was intended to provide the same N rate over the placement variables. The reality was that the broadcast only treatments had 9 more lbs. of N/acre than the associated treatments with side-band nitrogen. What happened is that the treatments with at least part of the N in a side-band at seeding produced higher yields, greater N fertilizer efficiency, and better return to fertilizer expense. These differences were not significantly different at the 0.01 level. Yield response to side-band fertilizer placement in no-till systems is common especially when residue levels are high. Other reasons for side-banding include reduced weed competition, less potential for N loss, and one less trip. This experiment was not designed to determine the reason for the placement response.
|Table 1. Corn yield, protein, nitrogen efficiency, and return to fertilizer (soil test nitrate-N of 30 lbs./a)|
|Treatment no.||Fertilizer N treatment (lbs./a)||Sideband N
|Total N Fertilizer + Soil
|Return over Fertilizer N Costs $/ac||lbs. of Mineral N/bu.
(Soil N + Fertilizer)
|Check||9||0||0||39||133 a||369||0.29 a||7.7|
|1||60||51||0||90||157 b||416||0.57 b||8.6|
|2||69||0||60||99||149 b||390||0.66 b||8.3|
|3||120||51||60||150||185 c||470||0.81 c||9.1|
|4||129||0||120||159||181 c||455||0.88 c||9.1|
|5||180||51||120||210||176 c||421||1.09 d||9.2|