Isotopic evaluation of in‐season Y Drop applications for corn production

Abstract

A common strategy for improving fertilizer N uptake efficiency by corn (Zea mays L.) is to synchronize application with crop N demand during the growing season, which can be done using the Y Drop system recently developed for surface dribble placement. A 2‐yr field study was conducted using dual‐labeled urea‐ammonium nitrate (UAN) solution to compare fertilizer 15N uptake efficiency (F15NUE) for surface and subsurface sidedress applications to soils of contrasting fertility under either second‐year corn or a corn–soybean [Glycine max (L.) Merr.] rotation. Besides placement, treatments were designed to allow comparison of 15N uptake from UAN applications made at planting vs. at the V9 growth stage. The importance of soil N supply was demonstrated by estimates of N derived from fertilizer that ranged from 17 to 47% in total aboveground biomass and never exceeded N derived from soil. Of the fertilizer N recovered in the crop at harvest, the majority originated from the 15N applied at sidedressing rather than at planting. The range in F15NUE was from 12 to 42% (26% on average) for grain and from 14 to 51% (31% on average) for total aboveground biomass, the only significant difference occurring when the subsurface treatment outperformed Y Drop placement under conditions conducive to urea N loss through NH3 volatilization. Both methods of application offer the same fundamental advantage, in that fertilizer N is supplied during the period of maximal crop uptake.

Nitrogen‐15 evaluation of fertilizer placement at planting for corn production

“…For both growing seasons studied, dry matter production without fertilization was consistent with what was observed for overlapping site‐years in other 15 N studies aimed at evaluating fall applications of anhydrous NH 3 (Griesheim et al., 2019) or in‐season placement of UAN (Griesheim et al., 2022). Consistencies were also observed when comparing grain yields from fertilized plots with county‐level data, which averaged slightly lower in 2017 (11.3 Mg ha −1 ) than in 2021 (11.5 Mg ha −1 ) when expressed on a dry‐weight basis (https://www.nass.usda.gov).…”

“…In this analysis, a KMnO 4 ‐Fe pretreatment was modified as described by Griesheim et al. (2022) to control frothing during a series of heating steps ramping from 90°C to 350°C in a block digester (Seal Analytical Model BD50). The digest was alkalized for diffusion with 10 M NaOH, and the NH 4 + ‐N liberated was quantified by acidimetric titration and then analyzed for 15 N content using an automated mass spectrometer (Mulvaney et al., 1990).…”

“…Linear mixed models were constructed and a two-way ANOVA with a type 3 test of fixed effects was performed, and the Tukey method was utilized to separate treatment means at p < 0.05. As previously done for overlapping site-years in other 15 N studies (Griesheim et al, 2019(Griesheim et al, , 2022, data were analyzed in R (R Core Team, 2014) using lme4 (Bates et al, 2015) with treatments and sites as fixed effects and replications as a random effect.…”

Isotopic comparison of ammonium and nitrate sources applied in‐season to corn

“…Considering the dominance of soil N uptake that has been documented in numerous 15 N field studies with corn (Cerrato & Blackmer, 1990; Griesheim et al., 2023; Power et al., 1986; Schindler & Knighton, 1999; Stevens et al., 2005) and the 112 kg ha −1 application of unlabeled N that was supplied at planting, NDFSU was expected to exceed NDF 15 F at R6. This was indeed observed for every plant part analyzed in our work, as Tables 6 and 7 show a range of 63% to 89% for NDFSU and 11% to 37% for NDF 15 F.…”

“…Considering the dominance of soil N uptake that has been documented in numerous 15 N field studies with corn (Cerrato & Blackmer, 1990;Griesheim et al, 2023;Power et al, 1986;Schindler & Knighton, 1999;Stevens et al, 2005) and the f Data reported as a mean from triplicate plots. Means within a column followed by the same letter do not differsignificantly (p < 0.05).…”